Medford
Everett
Chelsea
Somerville
Cambridge
Circumferential
Transportation
Improvements
in the
Urban Ring Corridor
Boston
Urban Ring
Phase 2
Brookline
TECHNICAL TUNNEL ALTERNATIVES
SUMMARY REPORT
November 2008
U.S. Department of Transportation
Federal Transit Administration
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Executive Summary
This document provides a summary of the tunnel alternatives developed as part of the combined Revised
Draft Environmental Impact Report (RDEIR) and Draft Environmental Impact Statement (DEIS) process
for the Urban Ring Phase 2.
The physical context and key constraints that influence the planning of a tunnel alignment within the
project corridor are presented, including: geology; water courses; utilities; historic structures; and land
use. A range of alignment alternatives have been developed including short tunnel and long tunnel
options. The tunnel alignments have been further refined and developed on the basis of preliminary
ridership and cost-benefit analyses, and in coordination with public consultation. The full range of
alignment alternatives presented in this document are considered to be feasible from an engineering
perspective, although costs, benefits, and impacts vary widely among the alternatives.
The principal tunnel elements comprise the portals, the running tunnels, and the stations. Typical cross
sections have been developed based on the criteria presented in this document. The cross sections take into
account potential Urban Ring Phase 3 rail transit requirements. It was shown that the current Phase 2 BRT
requirements were the controlling factor in determining the cross section, and therefore there is no cost
premium associated with the basic Phase 2 tunnel cross section. Further refinement to the BRT vehicle
envelope in subsequent engineering studies may afford a reduction in the tunnel cross sectional area, and
therefore cost.
There are a number of different tunneling techniques that can be used to construct the running tunnels.
The primary ones to be considered are: cut and cover tunnel; sequential excavation method (SEM) mined
tunnel; and tunnel boring machine (TBM) bored tunnel. Each of these techniques offers the possibility to
construct a single tunnel carrying two lanes or two tunnels each carrying one lane. While each of these
techniques has been considered, either exclusively or in combinations, in the development of the tunneled
alignment alternatives, the initial assumption is that the running tunnels would be constructed using a
TBM in a single bore configuration. It is considered that, at this stage in the planning process, this has not
precluded the development of a viable alignment option, and that alternative construction methods and
configurations (e.g. twin bored tunnels, cut and cover tunnels, or SEM mined tunnels) would be reassessed during subsequent engineering studies and as more information on geology, hydrogeology,
settlement and building response, electromagnetic field impacts, and noise and vibration becomes
available. Similar to the running tunnels, there are a variety of construction techniques that can be used to
build the underground stations. The use of an over-size TBM is not considered practicable at this stage,
principally due to physical constraints of major segments of the corridor. SEM mined platform tunnels
have been considered where required by site constraints, but for overall planning purposes, the conceptual
design of a typical underground station is a cut and cover construction.
Compatibility of the alternative alignment options with Phase 3 rail alignments has been presented and all
alignments will allow at least some portion of the Phase 2 BRT tunnel to be converted to Phase 3 rail use.
The alignment alternative development stages are presented and discussed, culminating in the
recommendation of a Locally Preferred Alternative (LPA) for the busway tunnel. Recommendations for
further work relating to the busway tunnel are also presented.
S-1
232551/01/G - November, 2008/S-1 of S-1
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
List of Contents
Page
Abbreviations
iv
Glossary
v
Chapters and Appendices
1
2
3
Introduction
1-1
1.1
Project Background
1-1
1.2
Need for Urban Ring Phase 2 Tunnel Analysis
1-2
Physical Context and Constraints
2-1
2.1
Location
2-1
2.2
Geology
2-3
2.3
Charles River
2-4
2.4
Muddy River
2-4
2.5
Stony Brook Culvert
2-4
2.6
Utilities
2-5
2.7
Historic Structures
2-7
2.8
Land Use
2.8.1 Parcel 18 West Property
2.8.2 Air Rights Parcel 7 Development
2.8.3 Longwood Medical and Academic Area
2.8.4 Boston University
2.8.5 Children’s Hospital Boston
2.8.6 Green Line “D” Branch and CSX Right-of-way Proposals
Tunnel Specifications and Characteristics
2-8
2-8
2-9
2-10
2-10
2-11
2-12
3-1
3.1
Tunnel Design Criteria
3.1.1 Spatial Requirements
3.1.2 Alignment
3.1.3 Underground Stations
3.1.4 Tunnel Systems and Operation
3.1.5 Fire Life Safety
3.1.6 Security
3-1
3-1
3-5
3-6
3-7
3-11
3-12
3.2
Construction Methodology
3.2.1 Cut and Cover Tunnel
3.2.2 SEM Mined Tunnel
3.2.3 TBM Bored Tunnel
3.2.4 Initial Recommendations
3-14
3-14
3-16
3-18
3-20
i
232551/01/G - November, 2008/i of v
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
3.3
4
Hatch Mott MacDonald
Earth Tech, Inc.
Typical Tunnel Cross Sections
3.3.1 Tunnel Portals
3.3.2 Running Tunnels
3.3.3 Underground Stations
3-23
3-23
3-25
3-31
Alternatives Considered
4-1
4.1
Tunneled Alignment Alternatives – Development Stage 1
4.1.1 Alternative 3
4.1.2 Alternative 3A
4.1.3 Alternative 3B
4.1.4 Alternative 3C
4.1.5 Alternative 4
4.1.6 Alternative 4A
4-2
4-3
4-8
4-8
4-10
4-11
4-13
4.2
Tunneled Alignment Alternatives – Development Stage 2
4.2.1 Alternative 3A-1
4.2.2 Alternative 3A-2
4.2.3 Alternative 3A-3
4-15
4-15
4-16
4-16
4.3
Tunneled Alignment Alternatives – Development Stage 3
4.3.1 Alternative H2(T) – “Tight Turn”
4.3.2 Alternative H2(T) – “Wide Turn”
4.3.3 Alternative H2(T) – Sub-options
4-17
4-17
4-18
4-19
4.4
Tunneled Alignment Alternatives – Summary
4.4.1 Noise and Vibration
4.4.2 Electromagnetic Fields
4.4.3 Phase 3 Compatibility
4.4.4 Preliminary Capital Cost Estimate of Options
4-23
4-23
4-24
4-25
4-27
5
Current Locally Preferred Alternative for Busway Tunnel
5-1
6
Conclusions and Recommendations for Further Work
6-1
Attachment A
Typical Station Layout
A-1
Attachment B
Tunneled Alignment Alternatives
B-1
B.1
Alternatives Development Stage 1
B-2
B.2
Alternatives Development Stage 2
B-3
B.3
Alternatives Development Stage 3
B-4
Attachment C
Alternative H2(T) Sub-options Memorandum
C-1
Attachment D
Current LPA Busway Tunnel
D-1
D.1
Preliminary Plan and Profile Drawings
D-2
D.2
Estimate of Truck and Rail Car Numbers During Construction
D-3
ii
232551/01/G - November, 2008/ii of v
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Figures and Tables
Figure 2.1: Study Corridor ......................................................................................................................... 2-2
Figure 2.2: Stony Brook Culvert ................................................................................................................ 2-5
Figure 2.3: MWRA Pumping Station Shaft ............................................................................................... 2-6
Figure 2.4: 440 Park Drive ......................................................................................................................... 2-7
Figure 2.5: Northeastern University Parcel 18 West Development ........................................................... 2-8
Figure 2.6: Air Rights Parcel 7 Development ............................................................................................ 2-9
Figure 2.7: Children’s Hospital Boston 819 Beacon Street Development ............................................... 2-11
Figure 2.8: Green Line Storage Track Adjacent to Fenway Station (looking northeast) ......................... 2-12
Figure 2.9: Mixed Use Path Proposals ..................................................................................................... 2-13
Figure 3.1: BRT Clearance Envelope (Two-way busway tunnel).............................................................. 3-2
Figure 3.2: BRT Clearance Envelope (One-way busway tunnel) .............................................................. 3-3
Figure 3.3: Phase 3 Clearance Envelope (rail) ........................................................................................... 3-4
Figure 3.4: Typical Slurry Wall Equipment for Cut and Cover Construction.......................................... 3-15
Figure 3.5: SEM Mined Tunnels Using Multiple Drifts .......................................................................... 3-16
Figure 3.6: SMART Project Tunnel Boring Machine (43’-4” diameter) ................................................. 3-19
Figure 3.7: Typical Cross Section – Tunnel Portal Approach Ramp ....................................................... 3-24
Figure 3.8: Typical Cross Section – Cut and Cover Section .................................................................... 3-24
Figure 3.9: Typical Cross Section – Twin Bored Tunnels ....................................................................... 3-25
Figure 3.10: Typical Cross Section – Single Bored Tunnel ..................................................................... 3-28
Figure 3.11: Examples of Constrained Tunneling Worksites................................................................... 3-30
Figure 4.12: Leon Street Portal Worksites ................................................................................................. 4-4
Figure 4.13: Longwood Avenue (Avenue Louis Pasteur) Station Worksites ............................................ 4-5
Figure 4.14: Abandoned Rail Freight Spur / Landmark Center Portal..................................................... 4-10
Figure 4.15: Underground Stations on the Green Line ............................................................................ 4-21
Figure 4.16: Longwood Avenue Alignment............................................................................................. 4-22
Figure 5.1: LPA Busway Tunnel................................................................................................................ 5-2
Table 3.1: Summary of Alignment Criteria................................................................................................ 3-5
Table 3.2: Platform Lengths ....................................................................................................................... 3-6
Table 4.3: Phase 3 Compatibility Matrix ................................................................................................. 4-26
Table 4.4: Preliminary Estimate of Capital Cost for Tunnel Alternatives ............................................... 4-27
Table 5.1: Summary of LPA Tunnel Lengths ............................................................................................ 5-1
iii
232551/01/G - November, 2008/iii of v
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Abbreviations
BRT
Bus Rapid Transit
BU
Boston University
CAC
Citizens Advisory Committee
CNG
Compressed Natural Gas
DEIS
Draft Environmental Impact Statement
ECD
Emission Controlled Diesel
EMF
Electromagnetic Field
EMI
Electromagnetic Interference
GJRR
Grand Junction Railroad
LMA
Longwood Medical and Academic Area
MBTA
Massachusetts Bay Transportation Authority
MIS
Major Investment Study
MTA
Massachusetts Turnpike Authority
MWRA
Massachusetts Water Resources Authority
NAVD
North American Vertical Datum
NFPA
National Fire Protection Association
NGVD
National Geodetic Vertical Datum
RDEIR
Revised Draft Environmental Impact Statement
ROW
right-of-way
SEM
Sequential Excavation Method
TBM
Tunnel Boring Machine
iv
232551/01/G - November, 2008/iv of v
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Glossary
Busway – dedicated right-of-way provided for exclusive use of the Bus Rapid Transit service.
Cut and cover tunnel – a method of tunnel construction involving the installation of earth support systems
(e.g. slurry walls) followed by the main excavation, placing of the base slab, roof slab and subsequent
backfilling to the final ground level.
Sequential Excavation Method – a method of tunnel construction that involves the use of standard
construction equipment for excavation. The tunnel is usually lined in two steps: An initial lining of
sprayed concrete provides immediate support and a subsequent secondary or permanent lining is then
placed using either sprayed concrete or cast insitu concrete. A waterproof membrane is usually installed
between the primary and secondary linings.
Slurry wall – a form of earth support system whereby a continuous trench is excavated in the ground to the
required depth, using slurry to provide temporary support during excavation of the trench. Reinforcement
(which may be reinforcing cages or steel H sections) is lowered into the trench and concrete is
subsequently placed by tremie pipe, displacing the slurry from the trench.
Tunnel Boring Machine – a method of tunnel construction that involves the procurement of a custommade piece of construction equipment. The TBM is equipped with a cutterhead that is used to mine the
ground. The excavation is continuously supported by installing precast concrete segments within the TBM
and grouting them in place as the machine advances.
Tunnel eye – the interface point of cut and cover tunnel and the bored or mined tunnel.
Tunnel portal – the interface point of the open cut and the cut and cover tunnel.
Tunnel portal approach ramp – open retained cut that takes the alignment from ground level down to the
tunnel portal.
Tunnel portal structure – all structural elements associated with the transition from a grade level alignment
to a bored or mined tunnel alignment.
v
232551/01/G - November, 2008/v of v
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
1
Hatch Mott MacDonald
Earth Tech, Inc.
Introduction
This document provides a summary of the tunnel alternatives developed as part of the combined Revised
Draft Environmental Impact Report (RDEIR) and Draft Environmental Impact Statement (DEIS) process
for the Urban Ring Phase 2. The document presents the key design criteria used in developing the tunnel
alternatives, provide a brief narrative of the alternatives developed, and outlines some of the main issues
in relation to constructability, operation, and potential conversion to Phase 3 (rail). It is intended that the
text from this report will be used in preparing the RDEIR/DEIS, and therefore the project introduction will
be kept very brief in this report, as it is anticipated to be covered by others in the environmental document.
1.1
Project Background
The idea of transportation improvements in the Urban Ring Corridor has been the subject of considerable
public debate and analysis dating back to the era when a system of circumferential highways were
proposed and later abandoned. The 1970’s marked a period of fundamental change in state policy away
from highways and in favor of transit based solutions to mobility problems. Starting with the
Circumferential Transit Feasibility Study in 1989, potential ridership in the Corridor began to be
quantified and the cost and feasibility of various alternatives was examined in greater detail. The Urban
Ring Major Investment Study (MIS) completed in 2001 presented the approach of three additive phases to
transit improvements in the Corridor:
Phase 1
New and improved cross-town bus routes on existing streets;
Phase 2
Addition of Bus Rapid Transit (BRT) routes with new and improved inter-modal
connections; and
Phase 3
Addition of rail rapid transit.
The MIS evaluated various tunneled alternatives for Phase 3 rail transit. As part of the Phase 2
RDEIR/DEIS process the possibility of providing a portion of the Phase 3 tunnel alignment earlier in the
project, during Phase 2, is to be investigated. Under this scenario, the tunnel alignment would be used by
the BRT service during Phase 2, and subsequently converted to rail usage in Phase 3. This report presents
the tunnel alignment alternatives developed for operation with BRT in Phase 2, and also addresses issues
related to the potential conversion of the tunnel from Phase 2 BRT to Phase 3 rail transit.
1-1
232551/01/G - November, 2008/1-1 of 2
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
1.2
Hatch Mott MacDonald
Earth Tech, Inc.
Need for Urban Ring Phase 2 Tunnel Analysis
The Urban Ring Phase 2 is the subject of the current planning and environmental review process. The
proposed Urban Ring Phase 2 project would be bus rapid transit (BRT), a form of transit that uses rubbertired bus vehicles with a comprehensive system of improvements that are designed to enable service
quality that is more like that of rapid transit. These improvements include provision of dedicated right-ofway (i.e. special bus roadways referred to as “busways,” or bus lanes on general traffic roadways); widelyspaced stops with substantial transit stations that have a distinct transit identity; high-capacity vehicles
with low floors and low emissions; high-frequency service; and advanced communications and traffic
control technologies.
The provision of dedicated right-of-way (ROW), in the form of busways and bus lanes, is central to
effective and efficient operation of the Urban Ring Phase 2. Wherever possible, surface busways or bus
lanes have been proposed for the Urban Ring Phase 2 BRT service. In areas where busways or bus lanes
are not feasible, the Urban Ring Phase 2 BRT service may need to operate in mixed traffic.
There are, however, some areas in the Urban Ring Phase 2 corridor where significant segments of
dedicated ROW are not available and heavy traffic congestion limits the speeds that are possible for BRT
vehicles operating in mixed traffic. In order to address these challenges, the Urban Ring Phase 2 project
team investigated the potential travel time improvements, ridership benefits, construction impacts, and
cost implications of tunnels in certain segments of the Urban Ring Phase 2 corridor.
This technical memorandum summarizes the analysis of potential tunnel alternatives and options for the
Urban Ring Phase 2, including the issues and constraints, design criteria and specifications, potential
tunnel alignments, and key findings of the analysis. The tunnel analysis encompasses a range of different
tunnel lengths and connections, but all of the tunnel alternatives include a segment beneath the Longwood
Medical and Academic Area (LMA). The LMA has a very high density of travel demand, making it an
important hub for Urban Ring Phase 2 service, but also very high levels of traffic congestion and limited
opportunities for dedicated ROW at the surface.
1-2
232551/01/G - November, 2008/1-2 of 2
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
2
Physical Context and Constraints
2.1
Location
The Urban Ring Phase 2 RDEIR/DEIS Study Corridor is shown in Figure 2.1. The MIS identified two
Phase 3 tunnel alignments that connect the Orange Line at Assembly Square with the former Orange Line
terminus at Dudley Square. At a general level, points north and south of the Charles River and west into
Allston formed the broad limits of the tunnel alternatives considered, all of which included a tunnel and
one or more underground stations in the Fenway/Longwood Medical and Academic Area (LMA). The
general extent of the corridor for which tunnel alternatives have been assessed as part of the Urban Ring
Phase 2 RDEIR/DEIS process, is shown in Figure 2.1.
2-1
232551/01/G - November, 2008/2-1 of 13
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Urban Ring
Phase 2 Corridor
Section of Corridor
Assessed for Tunneled
Alignments
Figure 2.1: Study Corridor
2-2
232551/01/G - November, 2008/2-2 of 13
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
2.2
Hatch Mott MacDonald
Earth Tech, Inc.
Geology
At present there is a lack of site-specific geological or geotechnical information along the potential Urban
Ring tunnel alignments. Presented below is a general summary of the regional geology interpreted from
secondary sources. Geotechnical investigations should be performed during subsequent planning phases of
the project to better determine the geotechnical characteristics along the proposed tunnel alignments.
In general, the area through which the Urban Ring tunnels would be constructed is the site of an ancient
estuary. As a result, the area is typically characterized by marine and glacial deposits and extensive layers
of organic silts and clays. Upland areas are generally overlain by glacial till (a typically hard and compact
mixture of clay, silt, sand, pebbles, cobbles and boulders); and lowland areas typically have stratified
deposits near the surface, which may include both sands and gravels, and fine-grained silts and clays. In
the lowest lying areas, near the Charles River and the Muddy River, an extensive, fine-grained deposit
known as the Boston blue clay was deposited under shallow marine conditions. This is overlain by recent
estuarine deposits, which in turn are overlain by artificial fill in some areas.
At the northern end of the tunnel alignments in the vicinity of Boston University (BU) Bridge and
Commonwealth Avenue, the soil conditions are variable, but typically include fills, organic silts,
sand/gravels and clay. Along the shores of the Charles River and along Commonwealth Avenue, depths
of up to 15 feet of miscellaneous fill was found to overlie pockets of organic silts. The organic silts are
typically thicker towards the river. Beneath the organics is a deep deposit of granular soil, a stratum that
ranges from fine to coarse sands with occasional pockets of clay within the stratum. The top of the Boston
Blue Clay formation in this area was found to be greater than 100 feet below ground surface.
At the west end of Ruggles Street, the upper soils include about 10 feet of fill underlain by up to 20 feet of
organic silts underlain by a thin layer of sand and then Boston Blue Clay. However, as the profile moves
easterly, the organics taper out and the fill is underlain by sand and sand with gravels which in turn is
underlain by clay. The clay deposit is quite thick in the Ruggles Street area, extending to depths in excess
of 150 feet.
The bedrock of the lower Charles River watershed comprises a sequence of sedimentary and volcanic
rocks that were deposited about 600 million years ago. The rock layers vary from relatively soft siltstones
and slates (known as Cambridge Argillite), to harder conglomerates consisting of pebbles and cobbles in a
sand matrix (for example the Roxbury Conglomerate). Uplands in Newton, Brookline, and the southern
portion of Boston are underlain by the hard conglomerate and volcanic rocks; lowlands in Cambridge and
the northern portion of Boston are underlain by the argillite.
The bedrock elevations in the project area vary and are expected to have a high point in the vicinity of
Harvard Medical School on Longwood Avenue at around 70 to 95-ft below ground level.
2-3
232551/01/G - November, 2008/2-3 of 13
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
2.3
Hatch Mott MacDonald
Earth Tech, Inc.
Charles River
Water depths in the Lower Charles River range from 6-ft to 12-ft in the basin upstream of the Boston
University Bridge and 9-ft to 36-ft in the lower basin 1 .
2.4
Muddy River
Preliminary information received from the United States Army Corps of Engineers for the Muddy River
Flood Damage Reduction and Environmental Restoration Project (Phase I) indicates that the Muddy River
will be day-lighted through the Sears Rotary area to an invert elevation of approximately -4.0-ft to -5.0-ft
based on North American Vertical Datum 1988 (NAVD 88). NAVD 88 is 0.65-ft below National
Geodetic Vertical Datum 1929 (NGVD 29).
As part of the Muddy River project two new pile-supported bridge structures will be built, one under the
Riverway (at the western end of the Sears Rotary) and one under Brookline Avenue (at the eastern end of
the Sears Rotary). The current design for the Muddy River restoration project will eliminate the jughandle
turn east of Brookline Avenue, so this road will not require a bridge structure. The toe elevations of the
drilled shaft foundations for the new bridge structures range from -38.5 to -57.5-ft, NAVD 88. Any Urban
Ring Phase 2 tunnel alternatives passing beneath these planned bridge structures would need to either
provide sufficient ground cover beneath the drilled shaft foundations, or underpin and support the bridge
structures during construction of the Urban Ring tunnels.
2.5
Stony Brook Culvert
The Stony Brook tributary of the Lower Charles River was culverted in the late 19th and early 20th
centuries. The culvert runs north-south along Parker Street and crosses perpendicular to Ruggles Street, as
shown in Figure 2.2. The combined width of the twin culvert structure is approximately 32-ft and the
crown of the culvert is located immediately below street level. Where the culvert crosses Ruggles Street it
does not appear to be supported on piled foundations and the bottom of the construction is approximately
17-ft below ground level.
As a result of these conditions, an Urban Ring Phase 2 tunnel that follows the alignment of Ruggles Street
would need to pass beneath the Stony Brook Culvert. This would require either an increase in the tunnel
depth at this point to provide sufficient ground cover below the culvert, or underpinning and support of the
Stony Brook Culvert during construction.
1
According to the draft publication for the USEPA “A Hydrodynamic and Water Quality Model for the Lower Charles River Basin,
Massachusetts”, dated November 2005.
2-4
232551/01/G - November, 2008/2-4 of 13
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Source: MASCO
Figure 2.2: Stony Brook Culvert
2.6
Utilities
Utility diversions are costly and disruptive in their own right and therefore any alternative should seek to
minimize the impact on existing utilities where possible. At this stage in the project there is little
information on existing utilities along the Urban Ring corridor. As more utility information has become
available during the development of the alignment alternatives it has been included in the consideration of
alignment alternatives.
The Stony Brook Culvert, as discussed above, is located beneath Parker Street. Located to the east of
Huntington Avenue and in the grounds of the Wentworth Institute of Technology, the Massachusetts
Water Resources Authority (MWRA) operates a pumping station (see Figure 2.3) that connects four major
sewer lines:
•
South Charles Relief Sewer (108” internal diameter) that crosses under Huntington Avenue;
•
Boston Main Drainage Relief Sewer (78” internal diameter) that runs under Ruggles and
Huntington Avenue;
2-5
232551/01/G - November, 2008/2-5 of 13
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
•
Charles River Valley Sewer (78” × 84”) that crosses under Huntington Avenue from Vancouver
Street; and
•
Mission Hill Relief Sewer (78” × 84”) under Vancouver Street.
Urban Ring Phase 2 tunnel construction would seek to avoid or minimize impacts to utilities wherever
practicable, particularly to strategic infrastructure such as the MWRA pump station and these four sewer
lines.
The type and extent of mitigation required for utilities will depend on the utility and the owner or agency
requirements, the age of the structure, the sensitivity to ground movements, the risks associated with
potential damage, the method of construction proposed for the Urban Ring, the proximity of the proposed
Urban Ring infrastructure to the utility, and safety and security considerations with respect to existing and
proposed infrastructure.
MWRA Shaft
Huntington Avenue
Ruggles Street
Source: MASCO
Figure 2.3: MWRA Pumping Station Shaft
2-6
232551/01/G - November, 2008/2-6 of 13
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
2.7
Hatch Mott MacDonald
Earth Tech, Inc.
Historic Structures
Listed structures have been investigated during later stages of option development. One particular
structure of note is the building at 440 Park Drive, currently used by the Boston Youth Fund, owing to the
possible location of a tunnel portal in this area. The building at 440 Park Drive is identified as the
Riverway Administration Building (BOS.7536) in the MACRIS database. The building was designed by
Shepley, Rutan and Coolidge and construct circa 1898. The building is within the Back Bay Fens section
of Olmstead Park System (BOSIO) and Emerald Necklace Parks (BOSJE) National Register Historic
Districts (listed December 8, 1971) and furthermore is listed as a local landmark (December 18, 1989). On
June 5, 1998 a preservation restriction was enacted for the Emerald Necklace Parks. The building facilities
also include a yard and a refueling station, as shown in Figure 2.4.
Emerald Necklace
Park Drive
Refueling Station
Figure 2.4: 440 Park Drive
2-7
232551/01/G - November, 2008/2-7 of 13
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
2.8
Hatch Mott MacDonald
Earth Tech, Inc.
Land Use
There are a number of ongoing and incipient development projects on or near the proposed Urban Ring
Phase 2 project alignment. The Urban Ring Phase 2 project team have coordinated with appropriate
institutions and developers to ensure consistency between the land use proposals and the Urban Ring
Phase 2 recommendations.
Some key land parcels along the Urban Ring corridor that are either under development, have
development proposals, or have some other significant are highlighted below.
2.8.1
Parcel 18 West Property
Northeastern University is currently developing the Parcel 18 West property into the Parcel 18 West
Development, an approximately 1,200-bed, 22-story student residence building and a six-story mixed-use
building. Parcel 18 West was previously occupied with a 162-space surface parking lot, and is located at
the intersection of Tremont Street and Ruggles Street (see Figure 2.5).
Source: Institutional Master Plan Notification Form, Northeastern University, July 10, 2006
Figure 2.5: Northeastern University Parcel 18 West Development
2-8
232551/01/G - November, 2008/2-8 of 13
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
2.8.2
Hatch Mott MacDonald
Earth Tech, Inc.
Air Rights Parcel 7 Development
Meredith Management’s proposed development is sited on the Massachusetts Turnpike Authority’s
Parcel 7 land and air rights, bounded by Beacon and Maitland Streets to the west, and Brookline Avenue
to the east. The Parcel is within a block of Fenway Park, the Lansdowne Entertainment District and
Kenmore Square. The Beacon Street level plan for the development of Air Rights Parcel 7 is shown in
Figure 2.6.
Beacon Street
Brookline Ave
Source: Project Notification Form, Massachusetts Turnpike Parcel 7 Air Rights, Kenmore/Fenway Area, January 16, 2008
Figure 2.6: Air Rights Parcel 7 Development
2-9
232551/01/G - November, 2008/2-9 of 13
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
2.8.3
Hatch Mott MacDonald
Earth Tech, Inc.
Longwood Medical and Academic Area
The Longwood Medical and Academic Area (LMA) is an important regional employment center along the
Urban Ring corridor with various medical, academic and research institutions, comprising many distinct
facilities. Most of these institutions have active, pending, or proposed construction projects that will affect
both travel demand and physical constraints for Urban Ring Phase 2 surface and tunnel options. Each of
these institutions has a master plan describing its future development proposals. The Urban Ring Phase 2
project team has reviewed these master plans and met with LMA institutions to better understand future
demands and constraints. The tunnel alternatives reflect the project team’s best understanding of
development proposals in the LMA.
2.8.4
Boston University
Boston University has developed a long-term vision for the land around the south end of Boston
University Bridge. This vision includes MTA air rights parcels, reconfiguration of Mountfort Street, and a
potential new transportation hub. BU’s 2007 Strategic Plan 1 discusses some of these proposals:
“Our current master planning, which looks out over the next quarter-century, calls for the
creation of a major regional transportation hub roughly at our end of the BU Bridge, including
the rationalization of the various roads, light rails, and railroads that traverse this very busy
intersection. It also calls for a reinforcement of the “short axis” of our campus, with the
thoughtful use of air rights over the Mass Pike giving us more room for concentrated growth
and—just as important—physical cohesion.”
1
“Choosing to be Great, A Vision of Boston University – Past, Present, and Future – The University’s 2007 Strategic Plan”,
Draft, dated October 19th 2007. Source: http://www.bu.edu/strategicreport/
2-10
232551/01/G - November, 2008/2-10 of 13
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
2.8.5
Hatch Mott MacDonald
Earth Tech, Inc.
Children’s Hospital Boston
Children’s Hospital Boston are planning to develop the parcel at 819 Beacon Street to include a residential
building fronting onto Beacon Street with a multi-story parking garage to the rear. The project is located
on the south side of Beacon Street between Munson Street and Maitland Street and will be located
adjacent to the proposed Parcel 7 Air Rights development. The lobby level plan for the development is
shown in Figure 2.7.
Source: Children’s Hospital Boston, 819 Beacon Street Project (Lobby Level), Elkus Manfredi Architects, August 3, 2006
Figure 2.7: Children’s Hospital Boston 819 Beacon Street Development
2-11
232551/01/G - November, 2008/2-11 of 13
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
2.8.6
Hatch Mott MacDonald
Earth Tech, Inc.
Green Line “D” Branch and CSX Right-of-way Proposals
During the development of the RDEIR/DEIS alignment alternatives the MBTA constructed a storage track
for the Green Line “D” Branch to the east of Fenway station and beneath Park Drive within the CSX rightof-way, as shown in Figure 2.8.
Fenway Station
Park Drive
CSX Right-of-way
Storage track
440 Park Drive
Figure 2.8: Green Line Storage Track Adjacent to Fenway Station (looking northeast)
There are proposals for a pedestrian and bicycle path utilizing the abandoned rail freight spur adjacent to
the Green Line “D” Branch between Park Drive and Miner Street, sharing the strip of land that now
contains the Green Line storage track. Draft proposals to accommodate both the storage track and the
multi-use path are shown in Figure 2.9.
2-12
232551/01/G - November, 2008/2-12 of 13
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Figure 2.9: Mixed Use Path Proposals
2-13
232551/01/G - November, 2008/2-13 of 13
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
3
Hatch Mott MacDonald
Earth Tech, Inc.
Tunnel Specifications and Characteristics
To provide a framework for development of alignments and conceptual designs for the Urban Ring
Phase 2 busway tunnel, it was necessary for the project team to set certain technical parameters and
assumptions. These include a wide range of design criteria, including appropriate tunnel dimensions and
other specifications. The project team also reviewed the available tunnel construction methods and
evaluated them relative to the project’s needs and constraints.
In the course of developing technical parameters and tunnel alignment options for Urban Ring Phase 2, the
project team has also given significant consideration to the potential for converting the tunnel for use in
Urban Ring Phase 3, which would use either light rail or heavy rail as the mode of transport. In analyzing
the various Urban Ring Phase 2 tunnel options, the project team has taken care to ensure that the Urban
Ring Phase 2 proposals accomplish the following, where possible:
•
Do not preclude the development of Urban Ring Phase 3 in any form that may reasonably be
expected (e.g. light rail or heavy rail, in a range of potential alignments); and
•
Where possible, include some minor alterations to Urban Ring Phase 2 that would facilitate the
transition to Urban Ring Phase 3.
3.1
Tunnel Design Criteria
This section provides a summary of the design criteria used in the development of tunnel alternatives for
Urban Ring Phase 2. These design criteria will help to inform choices and assumptions about tunnel
geometry, design, alignment, and construction assumptions for the tunnel alternatives. The tunnel design
criteria include the following:
•
Spatial Requirements;
•
Alignment;
•
Underground Stations;
•
Fire Life Safety; and
•
Tunnel Systems and Operation.
3.1.1
Spatial Requirements
The vehicular clearance envelope required for a two lane bi-directional busway tunnel is shown in Figure
3.1. Within covered tunnel sections there is likely to be a central dividing wall required for ventilation
purposes. A central median may also be required to ensure that a head-on collision between two buses
traveling in opposite directions is avoided. If a central dividing wall is provided then each lane is treated
as a separate single lane busway tunnel and the clearances shown in Figure 3.2 are adopted. The section
shown in Figure 3.1 is used primarily in open cut approach ramps.
3-1
232551/01/G - November, 2008/3-1 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
The preferred lane width is 12.0-ft and the minimum vertical clearance is 14.5-ft minimum to any
structure. The clear vertical distance to any tunnel services or signage suspended above the roadway is
taken to be 15.0-ft, allowing an additional 0.5-ft vertical clearance. In addition to these dimensions
walkways would be provided on each side of the roadway.
15'-0"
14'-0"
1'-0"
MINIMUM WITHOUT NICHE
MINIMUM WITH NICHE
12'-0"
6'-0"
CL LANE
CL LANE
14'-6"
STRUCTURE
GAGE
7'-6"
NICHE
(1'-0" DEEP)
ROADWAY
SURFACE
Figure 3.1: BRT Clearance Envelope (Two-way busway tunnel)
The requirements for a single lane uni-directional busway tunnel are shown in Figure 3.2. A walkway
would be provided on one side of the roadway.
3-2
232551/01/G - November, 2008/3-2 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
16'-0"
15'-0"
1'-0"
12'-0"
MINIMUM WITHOUT NICHE
MINIMUM WITH NICHE
1'-0"
6'-0"
CL LANE
7'-6"
14'-6"
STRUCTURE
GAGE
NICHE
(1'-0" DEEP)
ROADWAY SURFACE
Figure 3.2: BRT Clearance Envelope (One-way busway tunnel)
In all of the alternatives examined below, walkways are provided throughout the tunnel to allow for safe
access during routine maintenance operations, without the need to close the tunnel. It is recommended that
a minimum walkway width of 3.0-ft be provided for maintenance purposes. If it is not practicable to
provide a 3.0-ft walkway, then it is recommended that a 2.0-ft walkway is provided with refuge niches,
sized at 7.5-ft high by 2.0-ft wide and 1.0-ft deep, spaced at 20.0-ft centers. The refuge niches should be
protected from errant vehicles.
Additional elements that need to be incorporated in the tunnel cross section but are not defined at this
stage may include: signaling and signage; lighting; fire-life safety systems; and drainage. Some of these
items can be incorporated within the required tunnel cross section. Other elements would require special
design and construction accommodation.
Phase 3 would involve conversion of the BRT tunnels for use by either light rail or heavy rail. The
clearance envelopes for Phase 3 have been based on those for the MBTA Green Line and Orange Line for
light rail and heavy rail, respectively. The rail clearances are shown in Figure 3.3.
3-3
232551/01/G - November, 2008/3-3 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
8'-6"
PREFERRED
8'-0"
MINIMUM WITHOUT NICHE
6'-6"
3'-9"
MINIMUM WITH NICHE
STRUCTURE
GAGE
NICHE
(1'-0" DEEP)
7'-6"
10'-3"
14'-6" (GREEN LINE)
15'-0" (ORANGE LINE)
CL TRACK
TOP OF RAIL
Figure 3.3: Phase 3 Clearance Envelope (rail)
The development of tunnel cross sections that meet the busway spatial requirements provide sufficient
space to accommodate either light rail or heavy rail transit clearance requirements, as shown in Figure 3.3.
Therefore, designs that allow for the BRT clearance requirements above would also be consistent with any
Urban Ring Phase 3 options. Further discussion on the typical tunnel cross sections that accommodate
these spatial requirements is given in Section 3.3.
3-4
232551/01/G - November, 2008/3-4 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
3.1.2
Hatch Mott MacDonald
Earth Tech, Inc.
Alignment
The design speed for BRT in tunnels is 30-mph, while the posted speed limit and assumed maximum
operating speed would be 25-mph (to provide for a more conservative design for vehicle envelope). The
25-mph speed limit may be reduced at specific locations where warranted by special conditions, for
example on approach to stations and at sharp turns.
The horizontal and vertical alignment criteria used to set out the alternative tunnel alignments are
summarized in Table 3.1. The criteria are presented with respect to Phase 2 BRT and Phase 3 light
rail/heavy rail. The tunnel alignments have been developed, as far as practicable, to be in conformance
with the requirements of Phase 3. However there are certain locations where compliance with Phase 3
criteria has not been achieved for reasons relating to constructability, Phase 2 operability, or for other
technical reasons. Where Phase 3 compatibility has not been achieved for a specific tunnel alignment, this
fact has been noted, along with remedial actions that would need to be taken to enable Phase 3
implementation.
BRT
Light Rail
Heavy Rail
-
75 ft
-
75 ft
65 ft
250 ft
100 ft
-
250 ft
150 ft
-
1800 ft
700 ft
700 ft
75 ft
-
75 ft
-
5.0%
8.0%
-
5.0%
7.0%
200 ft
75 ft
3.0%
4.0%
200 ft
75 ft
-
1.0%
0.0%
0.5%
L = 32.8 D *
L = 39.4 D *
-
L = 0.034 DV
2
L = 0.034 DV
70 ft
Horizontal Alignment
Minimum tangent length
General
Beyond station platform
Minimum radius
General
Approaching station
Absolute minimum
Minimum length of curve
Reverse curves
Minimum tangent length between curves
Vertical Alignment
Gradients - general
Minimum grade
Preferred maximum grade
Absolute maximum grade
Preferred minimum length
Absolute minimum length
Gradients - stations
Preferred grade
Maximum grade
Vertical curve
Minimum length - crest
Minimum length - sag
Absolute minimum length
L = length of curve in feet
D = algebraic difference in grade (%)
V = train speed in miles per hour
* Based on 30 mph design speed
Table 3.1: Summary of Alignment Criteria
3-5
232551/01/G - November, 2008/3-5 of 31
2
2
L = 0.0344 DV
2×L
100 ft
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
It is acknowledged that allowing for future conversion to heavy rail imposes certain restrictions on
horizontal radii and on gradients. For current planning purposes, a minimum horizontal radius of 700-ft
has been assumed to allow for Phase 3 rail conversion. Sharper radii (less than 700-ft) can be achieved,
and some options that have been developed with tighter radii are only compatible with light rail vehicles
as a result. However, in general, options are being developed to be heavy rail compatible to keep open all
potential Phase 3 recommendations from the Major Investment Study (MIS).
3.1.3
Underground Stations
The controlling factors for the overall length of the station construction will be the platform length
required, the vertical circulation elements (passenger access and egress), and the ventilation equipment to
be located at each end of the station. An underground platform length of 220-ft has been assumed for
Phase 2, which is comparable to the MBTA Silver Line platform length. The platform lengths for Phase 2
and Phase 3 underground stations are shown in Table 3.2. Additional factors affecting the final station
dimensions will include the requirements for plant and equipment rooms, substations, communications
equipment, machine rooms, fare collection facilities, vertical circulation elements, and site constraints.
Platform Length
Phase 2 – BRT
220-ft
Phase 3 – Light Rail
300-ft
Phase 3 – Heavy Rail
410-ft
Table 3.2: Platform Lengths
The project team has reviewed different options for accessing the underground station platforms, either
from a central location along the platform (center-loaded) or from the end of the platform (end-loaded). In
general, spatial constraints in relation to buildings, foundations, and other existing infrastructure would be
a governing factor in the arrangement of access to the platforms.
Alternatives for station construction using cut and cover tunnel methods and sequential excavation
methods (mined tunnels) have been investigated. The selected method would depend on a number of
factors, including: the location of the station; the site constraints; and the geology and groundwater
conditions. Construction methodology is discussed in more detail later in this report.
Depending on the alignment alternative developed, potential underground stations were investigated at the
following locations:
•
Ruggles Station;
•
Huntington Ave (Green Line “E” Branch);
•
Longwood Ave – at Avenue Louis Pasteur/Tugo Circle or at Brookline Avenue;
3-6
232551/01/G - November, 2008/3-6 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
•
Yawkey Commuter Rail;
•
Kenmore Square;
•
Boston University Bridge (west, central, and east);
•
Longwood (Green Line “D” Branch);
•
Hawes Street (Green Line “C” Branch);
•
Park Drive (Green Line “C” and “D” Branches); and
•
West Station (Allston).
The following assumptions have been made in relation to platform layouts:
1. 12.0-ft nominal platform width;
2. 8.0-ft minimum platform width at objects/stairs/escalators etc.;
3. 10.0-ft vertical clearance above platform to any overhead signage, lighting etc.;
4. 0.75-ft platform height;
5. 4,000-ft minimum horizontal radius for convex platforms; and
6. 5,000-ft minimum horizontal radius for concave platforms.
The major items to be considered for conversion of the stations from Phase 2 to Phase 3 will be:
•
Extension of the station and platforms;
•
Installation of track;
•
Installation of rail systems and signaling;
•
Modifications to the tunnel ventilation and fire life safety systems;
•
The elevation of the station platform; and
•
The potential requirement for crossovers.
3.1.4
Tunnel Systems and Operation
There will be a number of systems required within the tunnel and associated structures to enable the safe
operation of BRT services. The systems are discussed below.
3-7
232551/01/G - November, 2008/3-7 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
(i)
Hatch Mott MacDonald
Earth Tech, Inc.
Tunnel Ventilation
The general objective of a tunnel ventilation system is to ensure a safe and tenable environment under
reasonably anticipated operating conditions for passengers and employees, covering normal, congested,
and emergency scenarios.
The tunnel ventilation system will need to address the implications of vehicle engine choice for the BRT
vehicles. The four main options considered are:
(a) Emission Controlled Diesel (ECD);
(b) Compressed Natural Gas (CNG);
(c) Dual Mode (electrified trolley bus in the tunnels); and
(d) Hybrid Electric (battery powered in the tunnels).
Ventilation of the tunnels may be broadly classified as natural, vehicle-induced, and mechanical. Natural
ventilation relies on the pressure difference between the tunnel portals and shafts created by changes in
elevation, air temperature, and wind. Vehicle-induced ventilation is due to the piston effect of vehicles
moving through the tunnels.
For the case of BRT tunnels and stations the specific objectives of tunnel ventilation systems are to:
•
Dilute vehicle exhaust emissions such as CO, NOx and particulate matter to acceptable levels
during all operating conditions (ECD and CNG only).
•
Remove heat generated by the vehicles (mainly radiators, engines and air conditioning units) and
other heat sources within the tunnels and stations.
•
Provide air exchange with the atmosphere.
•
Control and purge smoke and hot gases generated during a tunnel or station fire.
It is assumed that both dual-mode and hybrid vehicles will be 100% electrically operated within the tunnel
(the diesel engines will be completely shut-off), and as such underground emissions are not applicable to
these choices of vehicle.
The emissions associated with CNG and ECD vehicles are not considered to be significantly different.
This statement will require substantiation during design, but it is estimated that the particulate matter and
CO2 released into the system will be similar for both vehicles, the NOx emissions will be less for CNG,
but that the CO and toxic emissions will be significantly higher. For both these vehicle choices some
ventilation is considered likely while the buses are idle in the stations. This may represent a separate
discrete system, or could consist of the emergency tunnel ventilation fans operating at a lower capacity to
induce draft through the facilities. Without further analysis it is not possible to determine whether the
movement of the vehicles through the tunnels will be enough to generate sufficient air exchange to
adequately dilute the vehicle exhaust and to provide air exchange for the passengers while the vehicles are
passing through the tunnels. It is possible that ventilation will also be required during normal operation in
the tunnels as well as the stations.
3-8
232551/01/G - November, 2008/3-8 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Fire heat release rates are an important criterion used to design tunnel emergency ventilation systems and
to test the appropriateness of the system response (ensuring safe evacuation of patrons from the facilities).
It is considered a valid assumption that fire will be the governing criterion for the size of the primary
ventilation infrastructure for a BRT tunnel. In this regard, and on the basis of a preliminary assessment of
the vehicle engine types, all of the vehicle choices are similar and significant change in the size of the
emergency ventilation plant is not anticipated based on vehicle engine choice alone. Note:
•
The CNG vehicle has a slightly higher estimated fire size due to the larger quantity of
combustible material. The difference is +15% in the fire heat release rate. It is recognized though
that compressed gas represents a complexity requiring further study, due to the potential
explosive nature of the gas tanks, and the unknown rate of the vehicle fire growth.
•
Hybrid vehicles will be more efficient, and for the same range there exists the potential to reduce
the onboard fuel. Considering however that the diesel itself represents only 25% of the assumed
design fire size, this will not result in a large reduction in the ventilation plant requirement.
A summary of the ventilation implications (both operational and emergency) associated with BRT vehicle
engine choice are given below:
•
The size of the emergency ventilation plant will likely be similar for all four vehicle engine
options. Further investigation will be necessary to more accurately estimate the peak fire heat
release rate and fire growth associated with the selected vehicle.
•
The presence of combustion engines, for ECD and CNG, introduces pollutants in the tunnels and
stations. It is considered likely that mechanical ventilation will be required during normal and/or
congested bus operations to provide sufficient control and removal of contaminants. This may
consist of operating the emergency/primary ventilation systems at a reduced mode, or may
require that discrete ventilation be available in the stations. Normal mode operation will result in
higher costs due to power and maintenance.
•
Mechanical ventilation may be required for normal/congested operation to ensure adequate
removal of heat from all vehicle choices (such as engines and air conditioning) and to provide
sufficient air exchange for passengers and employees. For ECD and CNG this would be
combined with the pollutant control requirement. For electrically driven vehicles this may mean
some operation of system fans, however the requirement will certainly be less than that for buses
equipped with ICEs.
•
The ventilation system will need to be designed for the ultimate peak fire size considering both
the BRT and the Phase 3 rail vehicle technology.
Preliminary assessments of the tunnel ventilation system requirements have been performed by Earth
Tech. Assuming a single bored tunnel with a central dividing wall, jet fans would not be required in the
running tunnels (such a single bored tunnel is the assumed tunnel configuration, as discussed below). If
twin bored tunnels were implemented, ventilation requirements may be different.
The conceptual tunnel ventilation system would require fan plants to be located at each end of
underground stations and at tunnel portals. For longer sections of tunnel, ventilation shafts may be
required at intermediate locations. Based on the design criteria and assumptions, none of the alignment
alternatives identified below would require ventilation ducting within the running tunnels.
3-9
232551/01/G - November, 2008/3-9 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Initial assessment of vehicle technologies for the Urban Ring Phase 2 Project, based on the tunnel
ventilation requirements and capital and operational and maintenance costs, indicate that the currently
preferred technology is hybrid electric. If MBTA buses other than hybrid electric vehicles are to use the
tunnel then this could impact the tunnel ventilation design.
(ii)
Tunnel Lighting
Road tunnel lighting designs should be prepared as required to meet the latest edition of “Recommended
Practice for Tunnel Lighting” (RP-22). This standard identifies the minimum levels of lighting to be
achieved at the tunnel entrance through zones referred to as threshold, transition and interior zones,
located from the portal to the inside of the tunnel. The object of the road tunnel lighting is to enable
traffic to travel safely through the tunnel. This is best achieved by providing the tunnel user with
sufficient lighting to be aware of the road and to see any vehicles and obstructions ahead. Tunnel lighting
is not expected to be a controlling factor in the layout of the tunnel cross section or tunnel alignments.
(iii)
Electrical and Safety Equipment
The various tunnel systems will require a supply of power. Depending on the power requirements and the
length of the tunnel sections, there may be a need for high voltage distribution within the tunnel with sub
stations to step-down to low voltage supply over each section of the tunnel.
Safety equipment within the tunnel may include:
(iv)
•
Monitoring and supervision – Supervisory Control And Data Acquisition (SCADA);
•
Communications;
•
Closed Circuit Television;
•
Traffic control; and
•
Fire detection, fire suppression and fire fighting systems and equipment.
Drainage
The drainage system would consist of longitudinal drains feeding sumps which are discharged by pumps
to the stormwater drainage system via an interceptor to separate pollutants from spillages. The drainage
system would be located under the roadway surface. Cross-drains and sumps would likely be located at
the tunnel portals to intercept water running down the tunnel portal approach ramps. Sumps would be
required at low points in the tunnel alignment. The roadway surface would be designed to accommodate
the drainage system requirements and the drainage system would be specified to deal with inflow of
rainfall at the portals, groundwater seepage, accidental spillage and cleaning up, routine wall washing and
fire fighting.
3-10
232551/01/G - November, 2008/3-10 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
(v)
Hatch Mott MacDonald
Earth Tech, Inc.
Operation
A tunnel control center will likely be required to ensure the safe operation of the bus tunnels. This facility
could be incorporated within the station architecture or within some other part of the Urban Ring Phase 2
operational facilities.
An additional consideration during the operation of the tunnels is the scenario of a disabled vehicle within
the tunnel. The method of recovery of the vehicle would ideally be timely and would minimize potential
disruption to BRT services within the tunnels.
The current assumption is that the Urban Ring Phase 2 BRT service will adopt the use of 60-ft articulated
buses. The nature of these vehicles is such that they must be towed from the front in the normal direction
of travel; they cannot be pushed from behind. The method of recovering a disabled vehicle would
normally require the recovery vehicle to reverse into position to tow the disable vehicle out of the tunnel.
The distance over which the vehicle must reverse greatly increases the time taken to remove the disabled
vehicle from the tunnel. Therefore, reducing the distance over which a recovery vehicle must reverse is
one way to improve the efficiency of vehicle recovery. The ability to cross from one lane (or tunnel bore)
to another either continuously or at regular intervals along the alignment can reduce the reversing
distance.
3.1.5
Fire Life Safety
The fire life safety and fire protection of the tunnel require assessment of and planning for the following
features:
•
Emergency egress;
•
Emergency ventilation;
•
Fire protection of structures;
•
Fire detection, fire suppression, and fire fighting equipment and systems;
•
Communication systems;
•
Traffic control;
•
Drainage; and
•
Emergency response plans.
3-11
232551/01/G - November, 2008/3-11 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
The key criteria at this stage are the emergency egress requirements for road tunnels1, which state that the
spacing between emergency exits should not be more than 1000-ft. Where tunnels are divided by a
minimum of 2-hour fire-rated construction or where the tunnels are in twin bores, cross passageways can
be used instead of emergency exits. Cross passageways should have a maximum spacing of 656-ft. The
impacts of these requirements on different tunnel configurations is discussed in Section 3.3.2. The
emergency ventilation requirements are also an important element in the development of options and this
is discussed in Section 3.1.4.
Fire protection of the tunnel structures is important to minimize fire damage, thereby reducing the risk of
structural failures or collapse, and minimizing the duration and cost of tunnel closures while necessary
repairs are carried out after an incident. The tunnel structures and the tunnel systems should be protected
against fire damage. In concrete structures, adequate concrete cover over steel reinforcement members
should be provided, and polypropylene monofilament fibers or fire protection boards should be considered
to minimize damage by concrete spalling. Fire resistant ducting for tunnel systems should also be
evaluated.
Fire detection systems and communication systems can typically be accommodated within the tunnel
structures without impacting upon the required tunnel cross section. The project team has determined that
there is potential for this accommodation at a conceptual design level; more specific details of these
systems would be developed at a later stage in design.
Safety management planning would assess a range of possible incidents in the tunnel (including
breakdowns, collisions, and fires) and determine the most efficient range of recovery and rescue measures
and procedures for emergency evacuation and intervention. It is likely that a control center would be
required to ensure the safe operation of the tunnel and to initiate and coordinate any rescue efforts.
The fire life safety provisions, tunnel systems, and operation of the tunnel asset should be considered for
both BRT and rail operation during future design development once a preferred alternative has been
identified. The analysis will include an evaluation of costs for providing Phase 2 compatible systems
versus Phase 2 and Phase 3 compatible systems for: structural elements; loading; utility accommodation;
ventilation; lighting; electrical and safety equipment; drainage; utilities; stray current protection; and
roadway construction details to accommodate future installation of rail.
3.1.6
Security
The approach to security of an Urban Ring Phase 2 tunnel would start early in the preliminary engineering
phase and would be borne out through detailed vulnerability assessments and risk management methods.
The key steps toward securing such a transportation asset would be to:
1
•
Identify the threats;
•
Assess damage potential and consequences of threats;
•
Assess a range of countermeasures;
•
Cost estimation; and
Standard for Road Tunnels, Bridges, and Other Limited Access Highways, NFPA 502, 2004
3-12
232551/01/G - November, 2008/3-12 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
•
Hatch Mott MacDonald
Earth Tech, Inc.
Implementation.
There exist a number of means and methods to deter, detect, and defend against potential threats, such that
the security of this asset could be protected. The MBTA Silver Line has already shown that such measures
are necessary and effective in preventing unauthorized vehicles from entering transit tunnels: In April
2007 a Jeep Cherokee broke through a gate at the entrance to the Silver Line tunnel portal in South Boston
but was subsequently stopped from proceeding through the tunnel when a metal barricade was raised from
the roadway 1 .
Security design criteria for the Urban Ring Phase 2 busway tunnel should be developed during the
preliminary engineering phase.
1
Massachusetts Bay Transportation Authority website:
http://www.mbta.com/about_the_mbta/news_events/?id=11463&month=4&year=07
3-13
232551/01/G - November, 2008/3-13 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
3.2
Hatch Mott MacDonald
Earth Tech, Inc.
Construction Methodology
There are a number of potentially feasible construction methodologies that could be used to construct the
Urban Ring tunnels. The methodologies can be grouped into three main types: cut and cover tunnels
(including the top-down method); sequential excavation method (SEM) mined tunnels with a sprayed
concrete lining; and tunnel boring machine (TBM) bored tunnels. Each method has advantages and
disadvantages and some are more suited to particular ground types and environments than others.
Any tunneling method will cause ground movements and the ground movements will be affected by
tunnel depth, tunnel diameter, geology, and the quality of construction. Some methods produce larger
ground movements than others, but in all cases building settlement assessments should be carried out as
necessary to determine the potential for unacceptable movements. The outcome of the building settlement
assessments should assist in determining the need for underpinning, ground treatment or other protective
measures. The cost and disruption of such measures should be balanced with the cost and disruption of
alternative construction methods.
3.2.1
Cut and Cover Tunnel
The cut and cover technique has traditionally been used for transportation links in Boston dating back to
the 1890’s when the Green Line was constructed. Cut and cover construction will require earth support
systems to be installed prior to the commencement of the main excavation. There are different methods
that can be used to provide earth support, including: slurry walls; bored pile walls; and sheet pile walls.
The selection of a suitable method will be made during final design, and will depend upon local conditions
and the performance criteria that will be developed for each location. A typical clamshell grab for
excavating slurry walls is shown in Figure 3.4.
Depending on the design of the earth support system either it will require a cast-in-place concrete
permanent structure or the earth support system itself will provide the permanent structure. The majority
of the structures would be located in areas where the use of groundwater lowering techniques during
construction should be minimized or very carefully controlled. Ground treatment is likely to be required at
the base of such excavations to reduce the insitu permeability and minimize groundwater flows. The
tunnel structure is subsequently backfilled to restore the ground surface.
The traditional cut and cover method requires the ground to be open for the duration of construction and
the main excavation takes place with full surface access. Typically, temporary propping is installed as
excavation proceeds following by construction of the base slab, intermediate slabs, and finally the roof
slab. The structure is subsequently backfilled to restore the ground surface. In urban environments, the use
of the top-down method (i.e. installing the perimeter walls and roof prior to main excavation beneath) of
cut and cover tunneling is advantageous over other cut and cover techniques in relation to minimizing
impacts to the general public during construction. The top-down method requires installation of the
perimeter walls and a roof deck prior to commencement of the main excavation. The roof deck allows
traffic flows to be restored while construction takes place beneath.
3-14
232551/01/G - November, 2008/3-14 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Cut and cover construction in close proximity to existing buildings is achievable with good control of
ground movements. The main disadvantage is that the operation is potentially very disruptive, even when
the top-down method is employed, as many of the operations will have to occur on the surface. Lane
closures, utility diversions, temporary relocation of building access points, and diversion of traffic will be
inevitable in most cases.
Clamshell
Trench Cutter/Hydromill
Figure 3.4: Typical Slurry Wall Equipment for Cut and Cover Construction
The major advantages and disadvantages of the cut and cover tunnel construction method with respect to
planning a tunnel within the Urban Ring Phase 2 corridor are:
(i)
Advantages
•
Generally less expensive than underground tunneling methods for shorter lengths and relatively
shallow depths because of simpler excavation methods;
•
Generally shorter overall construction duration for shorter lengths of tunnel;
•
Underground obstructions can usually be handled without excessive increases in cost and schedule;
•
Flexibility in terms of horizontal alignments if other constraints allow (e.g. building foundations)
and in tunnel cross section; and
•
Construction in close proximity to existing buildings is achievable with good control of ground
movements.
(ii)
Disadvantages
•
Major construction phase impacts and disruption due to open excavation, including lane closures,
temporary relocation of building access points, and diversion of traffic.
•
Impacts will be experienced along the full length of the tunnel due to open excavation;
3-15
232551/01/G - November, 2008/3-15 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
•
Less economical for longer lengths of tunnel;
•
Major right-of-way and property requirements for excavation; and
•
Major utility diversions likely to be required.
3.2.2
SEM Mined Tunnel
The second construction method is mining the Urban Ring Phase 2 tunnels using SEM mined tunnels. The
SEM method involves excavation of the tunnel using standard construction equipment. The tunnel is
usually lined in two steps: An initial lining of sprayed concrete provides immediate support and a
subsequent secondary or permanent lining is then placed using either sprayed concrete or cast-in-place
concrete. A waterproof membrane is usually installed between the primary and secondary linings.
Figure 3.5: SEM Mined Tunnels Using Multiple Drifts
The SEM relies on the insitu ground having suitable properties to remain stable following excavation and
until such time as the initial support can be placed – known as stand-up time. Where the stand-up time is
insufficient, then additional ground pre-support methods or ground treatment methods are required to
stabilize the excavation. In addition, the tunnel heading can be sub-divided into a number of smaller
excavation headings to minimize the size of the exposed face, as illustrated in Figure 3.5. Timely closure
of the tunnel lining ring is important in controlling ground movements and ensuring stability of the
excavation.
3-16
232551/01/G - November, 2008/3-16 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
This option has the significant advantage that the cross section for the tunnel is not restricted to a circular
shape as it is with a TBM tunnel. Use of non-circular geometry can lead to a more efficient section and
therefore lower costs. Use of the SEM also allows more flexibility with the alignment. The main
disadvantage of the SEM is that significant ground treatment may be required since the tunnel is not
sealed off from the ground water pressure during construction as it is with a TBM driven tunnel.
On the recent Silver Line Phase 2 Russia Wharf project in Boston, the SEM was successfully used in
conjunction with ground freezing. However, the length of tunnels was comparatively short (approximately
400-ft) and the approach used for Russia Wharf would not be practical for extended lengths of tunnel for
the Urban Ring. Other forms of ground treatment are available that could be feasible, however detailed
geotechnical investigation along the alignment would need to be carried out to determine their viability. If
it is not possible to perform the ground treatment from the tunnel face, then significant surface disruption
may be caused by the ground treatment process. Although use of the SEM may allow optimized tunnel
cross section and reduced potential for ground movements, SEM tunnels can result in greater ground
movements than for a TBM driven tunnel of similar cross sectional area.
The major advantages and disadvantages of the SEM mined tunnel construction method with respect to
planning a tunnel within the Urban Ring Phase 2 corridor are:
(i)
Advantages
•
Flexibility in terms of horizontal alignments if other constraints allow (e.g. building foundations
etc) and in tunnel cross section. The tunnel cross section does not need to be circular as for a TBM
bored tunnel and this can lead to optimization of the tunnel cross section and reduced costs;
•
Generally shorter overall construction duration for shorter lengths of tunnel;
•
Underground obstructions can usually be handled without excessive increases in cost and schedule;
•
Minimizes surface disruption as the majority of the construction work takes place below ground
(with the exception of portal and station locations);
•
Potential to limit the material handling (supply and removal) to discrete locations rather than the
entire length of the tunnel if suitable shaft access sites can be found;
•
Minimizes the need for utility diversions.
(ii)
Disadvantages
•
Significant ground treatment may be required to stabilize the excavation during tunneling, as the
tunnel is not sealed off from the ground water pressure as it is with a pressurized face TBM driven
tunnel;
•
Less economical for longer lengths of tunnel; and
3-17
232551/01/G - November, 2008/3-17 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
•
3.2.3
Hatch Mott MacDonald
Earth Tech, Inc.
Shallow vertical tunnel alignments may result in ground movements that pose potential for
structural damage to nearby buildings, thereby requiring protective works (e.g. compensation
grouting).
TBM Bored Tunnel
The third construction method is TBM bored tunnels. This method entails the procurement of a custommade TBM – a specialized and expensive piece of construction equipment. The TBM is then assembled
within a cut and cover launch chamber at one end of the tunnel alignment from which it is launched to
bore through the ground. The front of the TBM is equipped with a cutterhead on which a number of
cutting tools are mounted. The cutting tools are designed to suit the geological conditions anticipated to be
encountered during the tunnel drive. The cutting tools excavate the ground and the resulting excavated
material is then removed from behind the cutterhead. The excavated material is transported back through
the tunnel to the launch point where it can be raised to the surface and removed from the site by rail or by
truck. As the tunnel is bored, reinforced precast concrete segments are installed behind the TBM to form
the tunnel lining. The annular void between the outside of the segmental lining and the ground is filled
with grout to ensure full contact between the ground and the lining and to minimize ground surface
settlements.
The likely choice of TBM for the Urban Ring Phase 2 tunnels would be a pressurized face machine owing
to the anticipated geology and the urban environment. There are two general categories of pressurized face
machine: an earth pressure balance machine or a slurry machine. Both types of machine have the ability to
maintain a positive face pressure to ensure stability of the ground during tunneling with the primary
difference being the method used to achieve this face pressure.
The state of the art in TBM technology has advanced considerably over the last 10 years. Pressurized face
TBMs can safely construct tunnels in soft ground conditions, while minimizing impacts on surrounding
structures. Developments in cutterhead design mean that TBMs can be equipped to deal with variable
ground conditions, from soft ground to hard rock. Machine diameters in the region of 50-ft have been
manufactured to build urban tunnels in Spain (Madrid Calle M30) and in China (Shanghai Yangtze River
tunnel).
A TBM tunnel also offers good ground movement control owing to the continuous grout injection process
that fills the annular void between the back of the tunnel lining and the ground during the subsequent
excavation cycle. Grouting operations would occur concurrently with advance of the TBM. Ground
movements can be minimized through careful control of the tunnel face pressures and grouting pressures.
Some disadvantages of a TBM are the large capital cost of the machine itself, which require a minimum
length of tunnel to be constructed to be cost effective, and the restriction on turning radius.
3-18
232551/01/G - November, 2008/3-18 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Figure 3.6: SMART Project Tunnel Boring Machine (43’-4” diameter)
The major advantages and disadvantages of the TBM bored tunnel construction method with respect to
planning a tunnel within the Urban Ring Phase 2 corridor are:
(i)
Advantages
•
Efficient for longer tunnels – in terms of both cost and schedule – as economies of scale are
realized for the capital investment in the TBM and precast concrete lining assembly;
•
Good control of ground movements through the use of pressurized face TBMs with gasketted
precast conrete linings and continuous grouting operations;
•
Minimizes surface disruption as the majority of the construction work takes place below ground
(with the exception of portal and station locations);
•
Limits the material handling (supply and removal) to discrete locations rather than the entire length
of the tunnel;
•
Minimizes the need for utility diversions.
(ii)
Disadvantages
•
More expensive for shorter lengths of tunnel owing to the capital investment in the TBM and the
precast concrete lining assembly;
•
Dealing with underground obstructions can potentially be costly and time-consuming;
3-19
232551/01/G - November, 2008/3-19 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
•
Shallow vertical tunnel alignments may result in ground movements that pose potential for
structural damage to nearby buildings, thereby requiring protective works (e.g. compensation
grouting);
•
Horizontal tunnel alignments are potentially limited by the capability of the TBM (this can be
mitigated through the use of short cut and cover sections to negotiate tighter horizontal radii);
•
Tunnel material handling (supply and removal) will be concentrated in discrete locations. Although
it is a benefit to avoid disturbance along the entire alignment, as would be the case for cut and
cover tunneling, focusing the work in discrete locations will intensify the impacts as these points;
and
•
Changes in tunnel diameter are not achievable without other construction methods.
3.2.4
Initial Recommendations
The three tunneling methods were evaluated to determine which method or methods would be appropriate
for the Urban Ring Phase 2 busway tunnel structures, given the requirements and constraints of the project
and the corridor. The intent of this evaluation process was to make an initial recommendation of viable
construction methods to be used for alignment alternatives analysis. The primary purpose of making this
initial recommendation was to allow a more transparent comparison of the numerous alignment
alternatives. This initial selection of construction methodology has not precluded the development of a
viable alignment alternative. Indeed, some alternatives have required different construction methods to be
employed and this is noted in the description of alternatives considered in Chapter 4.
Recommendation of a tunnel construction method should not be considered to preclude other methods
from being considered during subsequent stages of the planning and design process. The decision on
which construction methods to be used to build the preferred busway tunnel, including portals, running
tunnels, and stations, remains open.
The final choice of running tunnel construction method and configuration will depend on the final busway
tunnel alignment chosen; the geology and hydrogeology; the vertical alignment; the anticipated ground
movements and building settlement assessments; and noise and vibration impacts on sensitive hospital and
research operations. These issues will need to be addressed during subsequent engineering studies as more
information becomes available.
(i)
Tunnel Portal Structures
The tunnel portal structures will comprise an open cut approach ramp (“boat” section) and a covered
tunnel section. The construction will most likely require temporary earth support systems to be installed to
enable the construction of a cast in-situ concrete structure that provides permanent support.
The intrinsic nature of tunnel portals providing a transition from surface level into bored/mined tunnel
requires the use of open cut and cut and cover tunnel techniques.
3-20
232551/01/G - November, 2008/3-20 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
(ii)
Hatch Mott MacDonald
Earth Tech, Inc.
Running Tunnels
The three construction methods described above were considered for the construction of the running
tunnels. The evaluation of each technique and the selection of a viable method for current planning
purposes is described below. Single bore or twin bore configurations can be achieved with any
construction method and discussion of these configurations is presented later in this document.
The cut and cover method was not recommended for use in planning the Urban Ring Phase 2 running
tunnels for the following reasons:
•
Physical constraints and heavy traffic demand make it impossible to allow extended roadway
closure on the principal Huntington Avenue – Longwood Avenue – Brookline Avenue tunnel
alignment. Even if the open excavation period were minimized through phasing and expedited
roadway restoration (which would increase costs), traffic on these roadways, and access to
buildings, would still be severely affected for extended periods.
•
Cut and cover construction would have major impacts on sensitive environmental and open space
resources (in particular the Emerald Necklace parkway system) on and near the proposed tunnel
alignment. Outside of the more environmentally sensitive zones, environmental impacts would still
be significant (e.g. noise, dust etc.).
•
Lack of available public right-of-way corridors for key components of the corridor would require
significant land takings to allow cut and cover construction, resulting in additional cost and
disruption.
•
The cut and cover method could be appropriate for discrete lengths of some tunnel options where
surface impacts would be more tolerable or where site constraints, alignment geometry, project
requirements or other factors favor this method of construction.
The SEM mined tunnel method was not recommended for use in planning the Urban Ring Phase 2 running
tunnels for the following reasons:
•
The potential need for a significant amount of costly and time-consuming ground treatment could
reduce potential benefits of shorter construction duration and minimized surface disruption. The
very limited amount of geotechnical information currently available results in the SEM mined
tunnel being at greater risk of significant cost increases at this stage in the project than does a TBM
bored tunnel. This was a primary reason for choosing the TBM method at this stage in the planning
process. Once further geotechnical information is available and the tunnel alignment is finalized,
this decision should be reviewed.
•
The significant lengths of some tunnel alignment alternatives do not favor construction using SEM
for the entire length.
•
SEM mined tunnel could be appropriate for discrete lengths of some tunnel options where
changing cross sections are required or where site constraints, alignment geometry, project
requirements or other factors favor this method of construction.
The TBM bored tunnel method was recommended for use in planning the Urban Ring Phase 2 running
tunnels for the following reasons:
3-21
232551/01/G - November, 2008/3-21 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
•
The TBM bored tunnel option offers the potential to minimize surface disruption and reduce
environmental impacts. These are considerable benefits for any alignment alternative, but are of
particular importance in the more densely developed sections of the corridor with heavy traffic
demand. While this may be true also of the SEM mined tunnel, it will be heavily dependent on the
extent and nature of ground treatment required.
•
Pressurized face TBMs can safely construct tunnels in soft ground conditions, while minimizing
impacts on surrounding structures. Developments in cutterhead design mean that TBMs can be
equipped to deal with variable ground conditions, from soft ground to hard rock, and boulders.
Machine diameters in the region of 50-ft have been manufactured to build urban tunnels in Spain
(Madrid Calle M30) and in China (Shanghai Yangtze River tunnel).
•
The majority of the tunnel alternatives are of sufficient length to enable a TBM drive to be an
economically viable method.
•
Consideration of environmentally sensitive zones (e.g. Emerald Necklace, Muddy River, and
Charles River) would favor methods that do not require excavation from the surface or ground
treatment methods.
Noise and vibration impacts relative to the SEM and TBM methods will required further assessment once
geotechnical information is available and the extent and type of ground treatment has been better
established. It is considered that the SEM will have noise and vibration impacts that would be either equal
to or less than those created by TBM construction, however the major factors will be the geology and the
method of removing excavated material from the tunnel (e.g. truck, rail, or conveyor).
As a result of this review, it was determined that TBM construction was an environmentally acceptable
solution offering the potential to minimize disruption and provide the most cost-effective approach for the
planning of the Urban Ring Phase 2 running tunnels.
(iii)
Underground Stations
Alternatives for station construction using cut and cover, the SEM, and TBM methods were investigated.
The selected method would depend on a number of factors, including the location of the station, the site
constraints, and the geology and groundwater conditions.
The use of an over-sized TBM which would accommodate station platforms was rejected owing to spatial
constraints, right-of-way issues, impacts on portal structures and difficulties converting to Phase 3 rail use,
as discussed later in this report. The SEM method is a viable solution, and can reduce surface impacts.
However, the SEM method will still require two large shafts at each end of the station to accommodate
ventilation equipment and vertical circulation elements. Given the lack of geotechnical information, the
desire to keep the stations relatively shallow, and the relatively short length of the stations, it was
considered prudent at this stage in the planning process to adopt cut and cover for the full length of the
station.
3-22
232551/01/G - November, 2008/3-22 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Traditional cut and cover or the top-down method, where the main excavation occurs below a temporary
roof deck, are both viable methods for the station construction. The current thinking is that in the densely
developed and heavily trafficked areas such as the LMA, the top-down method would help to minimize
disruption to the surrounding communities. The increase in cost and construction duration associated with
this method need to be balanced with the perceived minimization of disruption.
3.3
Typical Tunnel Cross Sections
The principal tunnel elements comprise the portals, the running tunnels, and the stations. Typical cross
sections for the principal tunnel elements have been developed taking into account the design criteria
outlined in Section 3.1.
The tunnel cross sections have been developed for the Phase 2 BRT requirements and subsequently
checked to confirm whether or not Phase 3 light rail and heavy rail requirements can be accommodated
within the bus tunnel cross section. Excepting the rail, traction power, and other systems, the primary
structural differences in cross-sectional requirements between Phase 3 light rail and Phase 3 heavy rail are
the vertical clearances required (see Figure 3.3), and the walkway requirements (the light rail walkway is
low-level, whereas heavy rail may require an elevated walkway).
It was shown that the BRT clearance envelope requirements were the controlling factor in determining the
tunnel cross sections, and that the clearances for rail can be easily accommodated by any tunnel
construction method. Therefore there is no cost premium associated with protecting future conversion to
rail with respect to tunnel cross section. Further refinement to the BRT vehicle envelope in subsequent
engineering studies may afford a reduction in the tunnel cross section.
3.3.1
Tunnel Portals
The tunnel portals will comprise a tunnel portal approach ramp (open cut “boat” section) and a cut and
cover tunnel section down to the tunnel eye. Typical cross sections through a tunnel portal approach ramp
(with walkway niches) and a cut and cover tunnel section (without walkway niches) are presented in
Figure 3.7 and Figure 3.8.
3-23
232551/01/G - November, 2008/3-23 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
CL STRUCTURE
2'-0"
12'-0"
PARAPET
WALL
15'-0"
CL LANE
2'-0"
CL LANE
WALKWAY
NICHE
(1'-0" DEEP)
7'-6"
VARIES
14'-6"
EXISTING
GROUND LEVEL
4'-0"
ROADWAY
SURFACE
CAST-IN-PLACE
CONCRETE
SYMMETRICAL ABOUT CL
TEMPORARY EXCAVATION
SUPPORT SYSTEM
Figure 3.7: Typical Cross Section – Tunnel Portal Approach Ramp
C
L TUNNEL
12'-0"
EXISTING
GROUND LEVEL
1'-0"
3'-0"
3'-0"
CL LANE
VARIES
C
L LANE
14'-6"
17'-6"
1'-6"
WALKWAY
4'-0"
ROADWAY
SURFACE
CAST-IN-PLACE
CONCRETE
SYMMETRICAL ABOUT CL
3'-0"
(TYP.)
Figure 3.8: Typical Cross Section – Cut and Cover Section
At the tunnel eye, where the running tunnels are to connect into the portal, there may be a need for
additional ground treatment as the ground cover is usually relatively shallow at this location.
3-24
232551/01/G - November, 2008/3-24 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
3.3.2
Hatch Mott MacDonald
Earth Tech, Inc.
Running Tunnels
As discussed in Section 3.2, there are a number of different tunneling techniques that can be used to
construct the running tunnels and of these methods, the TBM bored tunnel method was recommended for
use in planning the Urban Ring Phase 2 running tunnels. TBM construction can be configured to provide
either a single tunnel carrying two lanes separated by an internal dividing wall or two tunnels each
carrying one lane. Cross sections for twin bored tunnels (Figure 3.9) and a single bored tunnel (Figure
3.10) were developed.
(i)
Twin Bored Tunnels
Some potential benefits of the twin bored tunnel solution compared with the single bored tunnel may
include:
•
Reduced ground surface settlements;
•
Reduced cost for bored tunnels (although the savings may be offset to a degree by the stations
being deeper where the twin bored tunnels are vertically separated and provisions of egress shafts
or cross passages or both);
•
Reduced volume of excavated material;
•
Shorter portal structures as the tunnel diameter is less than for single bore and the resulting
amount of ground cover above the tunnel at the tunnel eye is therefore less; and
•
Higher utilization of the space formed within the tunnel.
CL TUNNEL
C
L TUNNEL
14'-0"
6'-1"
Ø
CL LANE
1"
'-1
25
PRECAST CONCRETE
TUNNEL LINING
12'-0"
CROSS PASSAGE
CL LANE
14'-6"
1'-3"
WALKWAY
ROADWAY
SURFACE
77'-9"
Figure 3.9: Typical Cross Section – Twin Bored Tunnels
3-25
232551/01/G - November, 2008/3-25 of 31
3'-0"
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Twin bored tunnels with connecting cross passages, as shown in Figure 3.9, require the two tunnels to be
positioned at a similar elevation. The available horizontal corridor width is heavily constrained along key
portions of the alignment such that twin bored tunnels would need to be vertically separated and may
require vertical shafts to provide emergency escape facilities.
(ii)
Single Bored Tunnel
The potential benefits of a twin bore approach are outweighed by the benefits of the single bore tunnel and
the challenges facing the twin bore approach in the Urban Ring Phase 2 corridor. The principal reasons for
this are presented below.
•
The public right-of-way corridors are narrow along key parts of the alignment, particularly
Longwood Avenue and Brookline Avenue where the minimum width between buildings is
approximately 50-ft and 60-ft, respectively. A single bored tunnel would have a smaller plan
footprint width (approximately 42-ft) than twin bored tunnels positioned side by side
(approximately 78-ft for twin 26-ft diameter tunnels and one diameter of ground between tunnels).
Even if ground cover between the twin bored tunnels could potentially be reduced to 10-ft, the
resulting plan footprint width would be approximately 62-ft;
•
Although twin bored tunnels could be vertically separated to reduce the plan footprint (to
approximately 26-ft), this would potentially limit the flexibility to use cross passages for a means
of egress, and may require escape shafts to be constructed to ensure that the distance between
egress points is no greater than 1000-ft (as per the requirements of NFPA 502, Standard for Road
Tunnels, Bridges, and Other Limited Access Highways, 2004). Where cross passageways are
provided, these should have a maximum spacing of 656-ft. Vertical separation of the twin bored
tunnels would place additional constraints on the tunnel alignments to enable the transition from a
horizontally separated position to a vertically separated position;
•
Twin bored tunnels have the potential for greater construction phase impacts both spatially
because they would create a wider plan footprint and escape shafts may be required, and
temporally because the bores would be made either sequentially using one TBM or concurrently
using two TBMs with a lag between the drives;
•
The use of a single bored tunnel with a dividing wall potentially allows more flexibility in BRT
operations in the case of a disabled bus in the tunnel. The articulated buses cannot be pushed from
behind, they have to be towed from the front. In the single bored tunnel, access doors could be
located within the central wall that would allow a rescue vehicle to cross from one roadway to the
other to rescue a disabled vehicle. These access doors would limit the length of tunnel through
which the rescue vehicle must reverse, and may reduce the time taken to clear the tunnel of the
disabled vehicle and restore normal service. Provision of such access doors would require careful
consideration of NFPA requirements, fire life safety issues, and protection from errant vehicles.
One way of effecting the recovery is outlined below:
o
The closest central access doors located both in front of and behind the disabled vehicle
would be opened.
3-26
232551/01/G - November, 2008/3-26 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
o
The recovery vehicle would enter the tunnel using the blocked lane, while BRT service
can remain in operation in the opposite lane.
o
When the recovery vehicle reaches the central access door behind the disabled bus, the
BRT service in the opposite lane would be temporarily suspended for a short period of
time to allow the recovery vehicle to pull out into the opposite lane, pass the disabled
vehicle, and then return to the blocked lane in front of the disabled vehicle through the
next central access door.
o
Once the recovery vehicle has returned to the blocked lane, the BRT service in the
opposite lane would resume and the recovery vehicle can tow the disabled bus out of the
tunnel.
o
Depending on the spacing of the central access doors, the length of tunnel through which
the recovery vehicle would need to reverse will be relatively short, thereby reducing the
length of time taken to restore normal service.
•
The single bored tunnel could potentially provide increased flexibility in Phase 3 with regard to
providing track crossovers. A length of the central dividing wall would be removed to install the
necessary switches and crossings to allow trains to cross from one track to the other, although this
would need to be verified in relation to the ventilation strategy for the particular section of tunnel.
This could reduce the extension of station excavations. It should be noted that vertically stacked
twin bored tunnels would preclude the installation of crossovers;
•
There is the possibility to include drainage sump structures within the main tunnel rather than
creating separate enlargements, as would likely be required for a twin bored tunnel solution with
low points in between stations;
•
There is an opportunity to include revenue generating utilities within a service corridor below the
road deck; and
•
Narrower and deeper TBM launch and reception points compared with twin bored tunnels side by
side.
Given the large number of tunnel options being investigated, it is most efficient and understandable to
evaluate them based on a single tunnel construction method for the purposes of comparison.
For the reasons described above, a single bore TBM tunnel is expected to be the most suitable and costeffective tunneling method for the Urban Ring Phase 2. At the same time, the project team has taken care
that the proposals remain somewhat flexible with respect to alternative alignments, tunnel configuration,
and methodologies. As a result, the alignment alternatives were primarily developed on the basis of a
single bored tunnel.
3-27
232551/01/G - November, 2008/3-27 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
CL TUNNEL
14'-0"
DIVIDING WALL
12'-0"
11'-2"
1'Ø4
14'-6"
CL LANE
"
10
CL LANE
WALKWAY
3'-0"
ROADWAY
SURFACE
BACKFILL CONCRETE
TUNNEL DRAINAGE & SYSTEMS
(POTENTIAL UTILITY CORRIDOR)
PRECAST CONCRETE TUNNEL LINING
Figure 3.10: Typical Cross Section – Single Bored Tunnel
Over-Sized Single Bored Tunnel. Consideration has been given to the possibility of constructing the
running tunnels using an over-sized TBM (approximately 50-ft excavated diameter), such that an upper
deck and a lower deck could be built within the bored tunnel. This would allow the construction of station
platforms within the single bore and would provide flexibility in the location of station platforms (i.e.
anywhere that the tunnel alignment meets the horizontal and vertical curvature requirements for a station).
Off-line vertical circulation and ventilation shaft structures can then connect to the bored tunnel through
mined tunnels.
It is acknowledged that this solution has potential benefits with relation to reducing surface construction
works and providing the flexibility to locate – and extend, for Phase 3 – station platforms. However, such
a solution has not been adopted at this stage, for the following reasons:
•
Increasing the size of the TBM will require longer and deeper portal structures. The diameter of
the single bored tunnel solution has been kept to the minimum required dimension for this
reason;
•
The public right-of-way corridors are narrow along key parts of the alignment, particularly
Longwood Avenue and Brookline Avenue where the minimum width between buildings is
approximately 50-ft and 60-ft, respectively. The diameter of the single bored tunnel solution has
been kept to the minimum required dimension for this reason but will likely require
underpinning and ground treatment works. Enlarging the tunnel diameter will potentially
significantly increase building foundation conflicts and underpinning and ground treatment
works depending on the final alignment selected;
3-28
232551/01/G - November, 2008/3-28 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
•
Providing the grade separation required for the two-deck approach would either require further
extension of the tunnel portals, or more complex construction within the bored tunnel itself.
Where underground stations are located in close proximity to portals, this grade separation may
not be achievable over the distance available; and
•
Potential future conversion to Phase 3 rail would be more complicated and costly at the locations
where the future Phase 3 tunnel would connect into the Phase 2 tunnel than for a smaller
diameter single bored tunnel (without the two-deck approach) or for twin bored tunnels.
It is considered that the use of a large diameter running tunnel that can accommodate station platforms
would be more suited to the initial construction of a rail transit system rather than for a BRT system that
can accommodate potential future conversion to rail. The option to provide a larger diameter single bored
tunnel with two decks – an upper deck for BRT, fitted out during Phase 2, and a lower deck provided
during Phase 2 and fitted out for rail during Phase 3 – was also assessed, but rejected for similar reasons.
Therefore the tunneled alternatives have, in general, been developed on the basis of a single bored tunnel
of approximately 42-ft diameter. The minimum horizontal turning radius for the TBM has been assumed
to be 700-ft (the Stormwater Management and Road Tunnel in Malaysia used a 43-ft diameter TBM
which was designed to negotiate a 660-ft radius). Although this could potentially be reduced depending
upon, among other factors, the diameter of the machine and the design of the backup gantries, it is
unlikely to be reduced to the extent that the alignment options developed would change significantly i.e. a
smaller diameter TBM that can accommodate single lane traffic is unlikely to be able to negotiate a 150-ft
radius curve. At present, the vertical curves in the bored tunnel are compatible with heavy rail criteria and
are generally in excess of 6000-ft – this is considered to be well within the limits of the TBM
maneuverability.
(iii)
Tunnel Boring Machine Launch and Reception Areas
At the launch point for the TBM, there would need to be sufficient space for the following main tunneling
operations and facilities:
•
TBM assembly;
•
Storage of tunnel segments;
•
Grout batching plant;
•
Storage of TBM consumables and supplies;
•
Logistics to enable supply of tunnel segments to the advancing tunnel face;
•
Removal, storage and handling of excavated material (may require slurry separation plant if a
slurry TBM is selected for tunnel construction); and
•
Site offices and support facilities.
The reception point for a TBM will require a suitably sized reception shaft or chamber into which the
TBM can be driven, for subsequent disassembly and removal.
3-29
232551/01/G - November, 2008/3-29 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Several of the alignment alternatives that have been developed have limited space for launching and
servicing a TBM to drive the running tunnels. Potential construction staging areas have been identified for
the various alignment alternatives that are considered to provide the minimum required space for this
function. Although the staging areas may not be ideal in terms of their size and layout, it is not uncommon
in the tunneling industry to have to work from confined construction sites, as urban areas are increasingly
seeking to exploit underground space while minimizing the impacts on the existing environment.
Examples of constrained tunneling worksites can be seen in Figure 3.11.
Project:
Weintal Collector
Country:
Austria
Use:
Wastewater
TBM Type:
Earth Pressure Balance
Geology:
Clay, silts and sand
Diameter:
28’-3”
Project:
Lake Thun Flood Relief
Country:
Switzerland
Use:
Flood Relief
TBM Type:
Mixshield
Geology:
Gravel, sand and silt
Diameter:
20’-7”
Figure 3.11: Examples of Constrained Tunneling Worksites
3-30
232551/01/G - November, 2008/3-30 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
3.3.3
Hatch Mott MacDonald
Earth Tech, Inc.
Underground Stations
For current planning purposes, the conceptual design of the typical station is a cut and cover construction
and requires a plan footprint of approximately 550-ft by 60-ft, with some local enlargements for vertical
circulation elements. This structure includes allowance for the tunnel ventilation fans and damper layouts.
However, a detailed assessment of associated mechanical and electrical equipment rooms, substations,
communications, machine rooms, etc. has not been performed at this stage.
This typical station has been developed based on the most constrained site locations along Longwood
Avenue that would require the station platforms to be end-loaded, thereby limiting the width of the station
while increasing the length. Further refinements to station design on a location by location basis would be
required in subsequent engineering studies to determine whether a more economical and efficient structure
could be accommodated. The typical station layout is shown in Attachment A.
3-31
232551/01/G - November, 2008/3-31 of 31
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
4
Hatch Mott MacDonald
Earth Tech, Inc.
Alternatives Considered
A central consideration in planning for the proposed Urban Ring Phase 2 project is the provision of as
much dedicated right-of-way (ROW), in the form of busways and bus lanes, as possible. Dedicated ROW
is essential to providing high-speed and reliable service, especially in areas of heavy traffic congestion.
Federal guidelines for BRT projects call for a minimum 50% of the project route to be in dedicated ROW.
Maximizing the amount of dedicated ROW, and optimizing its efficiency and effectiveness, have been
among the central focuses of the Urban Ring Phase 2 project team and the Citizens Advisory Committee
(CAC).
The project team has tried to identify opportunities for dedicated ROW on surface busways and bus lanes
wherever possible. However, there are some locations in the corridor where high levels of traffic
congestion and physical constraints on available ROW have limited the opportunities for surface busways
and bus lanes. In response to these constraints, the project team has reviewed the anticipated ridership
benefits, costs, and impacts of a range of tunnel alternatives.
The primary objectives of the tunnel alignments are to:
•
Reduce transit trip times;
•
Increase quality and reliability of service; and
•
Minimize impacts of surface transit operations in sensitive locations, especially on the pleasurevehicle-only segments of the Emerald Necklace parkways.
The tunnel alternatives that have been analyzed encompass a significant range of lengths, number of
underground stations, connections, and costs. However, all of the options include tunnel segments beneath
the Longwood Medical and Academic Area (LMA). This is because the LMA is a critical activity center
with a combination of characteristics that create the greatest challenges for surface BRT connections: it
has a very high density of travel demand, a limited roadway network, significant traffic congestion, and
limited opportunities for roadway expansion or new roadway connections. In addition, it is bounded on the
north by the Fenway, a pleasure-vehicle-only parkway that is a component of the Emerald Necklace park
system.
The proposed tunnel options all follow the general Urban Ring Corridor alignment, and all include a
segment beneath the LMA that would enable the Urban Ring Phase 2 BRT vehicles to avoid the most
congested and space-constrained segments of the corridor while still serving the transit demand of the
LMA. This results in a minimum tunnel segment extending from the vicinity of Ruggles Station in the
southeast to beyond the Sears Rotary in the northwest. Beyond this segment, the tunnel options encompass
a range of lengths, alignments, and connections.
The tunnel alignment alternatives have been developed and evaluated in three stages:
•
Development Stage 1. This corresponds to the “Build Alternatives” that were developed in winter
2007 and evaluated in spring 2007. This includes a broad range of tunnel alignments, lengths, and
connections.
4-1
232551/01/G - November, 2008/4-1 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
•
Development Stage 2. This corresponds to a closer analysis of several of the Build Alternatives as
they pass through the LMA. This analysis included a more detailed engineering analysis of several
different tunnel alignments, tunnel portal locations, and cut and cover work areas.
•
Development Stage 3. This corresponds to the “Hybrid Alternatives,” the stage of the alternatives
analysis process which generated a narrowed-down set of options that include the most promising
segments and elements from the Build Alternatives. These include Alternative H2(T), which
entails a tunnel connection from the vicinity of Ruggles Station through the LMA to the vicinity
of Yawkey Station/Kenmore Station. This stage of tunnel analysis also included a more detailed
engineering analysis of several different tunnel alignments, tunnel portal locations, and cut and
cover work areas.
The description below summarizes the basic design and engineering features of the various tunnel options
that have been analyzed. These include alignment, horizontal and vertical curvature, physical constraints,
capital costs of the tunnels and underground stations, and anticipated impacts, both temporary construction
phase impacts as well permanent impacts from the proposed alignment. The discussion of these
alternatives includes the full range of tunnel options. As the development stages described below
illustrate, further efforts have been invested in the more promising alignment alternatives.
4.1
Tunneled Alignment Alternatives – Development Stage 1
The tunnel alignments that were developed in the “Build Alternatives” stage of the alternatives analysis
included a very wide range of options. These were developed based on the project goals and technical
constraints, in addition to significant consultation and input from the project CAC and other stakeholders.
There were many suggestions and desired tunnel alignments articulated by various stakeholders. In order
to be as responsive as possible to stakeholder aspirations and concerns, the project team added several new
tunnel options to the alternatives analysis in this development stage. In the first stage, a total of six
different tunnel alternatives were developed and evaluated.
These options captured a broad range of tunnel approaches, encompassing various tunnel lengths,
alignments, and connections. These different options can be broadly classified into two categories – short
tunnel options and long tunnel options. The short tunnel alternatives, which are included in the Build
Alternative 3 “family,” begin immediately west of Ruggles Station (avoiding the cost of an underground
connection with Ruggles Station), pass beneath the LMA, and extend to either Yawkey Station, the
vicinity of the BU Bridge, or Allston Landing (depending on the option). However, all of the tunneled
sections in the “short tunnel” family stay to the south of the Charles River. The reason for investigating
short tunnel options is to try to maximize the benefits of a tunneled alignment by enabling the Urban Ring
Phase 2 to avoid the worst of the congestion and physical constraints while minimizing the costs
associated with tunnels and underground stations. The short tunnel options include Alternative 3,
Alternative 3A, Alternative 3B, and Alternative 3C, described below.
4-2
232551/01/G - November, 2008/4-2 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
The longer tunnel alternatives, which are included in the Build Alternative 4 “family,” provide connection
from the Melnea Cass Boulevard corridor, with an underground connection to Ruggles Station, beneath
the LMA, to Allston and Cambridge, requiring bifurcations in the tunnel alignment and passing beneath
the Charles River. The longer tunnel options would entail many more underground stations and greater
overall complexity compared with the short tunnel options, resulting in significantly increased cost. The
reason for investigating the long tunnel options is to explore whether or not the increase in benefits of
longer tunnels (e.g. reduced travel times, increased ridership etc) would offset the additional cost
compared with the short tunnel options. The longer tunnel options include Alternative 4 and Alternative
4A, described below and presented in Attachment B.
4.1.1
Alternative 3
Alternative 3 comprises two separate lengths of tunneled alignment: the LMA tunnel which would
connect Ruggles to Yawkey, through the LMA; and the Mountfort Street tunnel which would link
Mountfort Street with either the Boston University Bridge area or with Allston.
LMA Tunnel
The LMA tunnel would be located to the west of the existing Ruggles Station. The portal approach ramp
would commence at Leon Street and descend in a westerly direction, parallel to Ruggles Street and along
the existing Massachusetts Bay Transportation Authority (MBTA) right of way, in front of the
Northeastern University residence halls. The tunnel portal – the transition between the open cut approach
ramp and the cut and cover section – would be located to the east of Field Street to enable reinstatement of
Field Street. The cut and cover tunnel would extend form the tunnel portal to a point immediately west of
Parker Street, from which the bored tunnel would commence.
Construction of the Leon Street portal will be in a very constrained site, adjacent to Northeastern
University residence halls and Ruggles Street. Preliminary worksite locations have been identified, as
shown in Figure 4.12. It should be noted that not all of these sites would necessarily be required for
construction of a portal in this location. The parking lot adjacent to the Sweeney Field would be required
to construct the TBM reception chamber end of the portal. The Sweeney Field itself would not be used
during construction.
The Leon Street portal would pass beneath the Stony Brook conduits, and a construction methodology
would need to be developed to ensure the continuity of this utility during construction.
A section of tangent, level track would be provided along Huntington Avenue to accommodate a cut and
cover station in this location, in the vicinity of the Green Line “E” Branch station. Immediately after the
underground station the bored tunnel would make a turn to align with Longwood Avenue, passing
underneath the Mass Art building on the northern corner of the intersection of Huntington and Longwood
Avenues.
4-3
232551/01/G - November, 2008/4-3 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
The preferred location for the Huntington Avenue station is assumed to be as close as possible to the
intersection between Huntington and Longwood Avenues. Therefore the station would be located at the
southern end of the length of tangent track beneath Huntington Avenue, placing the southern end of the
platform approximately 450-ft from the intersection. Headhouse locations would be configured to
facilitate convenient connections with the Green Line “E” Branch station located at street level.
A construction access shaft for top-down construction could be located in the Wentworth Institute of
Technology parking lot off Vancouver Street, with the parking lot providing space for the construction
worksite for Huntington Avenue station. Any construction works in this area will need to consider the
MWRA pumping station and shaft, as shown in Section 2.6. [Note: Wentworth Institute has since
indicated plans to develop the parking lot site with a new campus building.]
Parker Street
Leon Street
Ruggles Station
Potential worksite
location
Northeastern University
Tavern Road
Field Street
Ruggles Street
Potential worksite
locations
Potential worksites shown are preliminary indications of sites that could serve as construction staging and
laydown areas . Further work will be required to define these sites during preliminary engineering studies.
Figure 4.12: Leon Street Portal Worksites
The bored tunnel would generally follow the existing alignment of Longwood Avenue from Huntington
Avenue until a point near Binney Street towards the west. A section of tangent, level track would be
provided through Longwood Avenue in the vicinity of Avenue Louis Pasteur to accommodate an
underground station.
Foundation constraints limit the length of tangent track that can be provided through Longwood Avenue,
and building constraints limit the location of a cut and cover station. Therefore the Longwood Station
under this alternative would commence in the vicinity of Avenue Louis Pasteur and extend west beneath
Longwood Avenue.
4-4
232551/01/G - November, 2008/4-4 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
For the Longwood station a construction access shaft would be located in Tugo Circle. The front lawn of
Harvard Medical School would be required for construction worksite space, supported by additional
worksite space at another location in the general area. Construction works in this area will need to account
for the underground parking garage beneath the Harvard lawn.
Longwood Ave
Potential worksite
locations
Potential worksites shown are preliminary indications of sites that could serve as construction staging and
laydown areas . Further work will be required to define these sites during preliminary engineering studies.
Figure 4.13: Longwood Avenue (Avenue Louis Pasteur) Station Worksites
At Binney Street, the alignment would curve in a northerly direction to pass underneath the south-west
corner of the Shapiro Center and Brookline Avenue and connect with an alignment that follows the
existing path of Pilgrim Road. The turn from Longwood Avenue would likely require some underpinning
and foundation modification works to the south-west corner of the Shapiro Center building.
From Pilgrim Road the tunnel would pass underneath the Muddy River and follow Brookline Avenue. The
bored tunnel would terminate beneath Brookline Avenue, immediately to the north of Fullerton Street, and
cut and cover tunnel would extend north along Brookline Avenue from this point to the intersection with
Yawkey Way. From this intersection, the cut and cover tunnel would curve west into the Air Rights
Parcel 7 development site, through an approach ramp structure and up to a station that would be at
approximately the same elevation as the existing Yawkey Commuter Rail station. The BRT station would
be aligned with the Commuter Rail station at Yawkey. A widened section of the Beacon Street overbridge
would accommodate the BRT approximately parallel with the Commuter Rail, emerging to the west of
Beacon Street.
4-5
232551/01/G - November, 2008/4-5 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
The approach to Yawkey station would be constructed using top-down construction methods to minimize
disruption to traffic flows. The TBM would need to be disassembled and removed from the reception
chamber at Fullerton Street. The cut and cover tunnel and approach ramp through the Parcel 7 site would
require close coordination with the developers of the site to ensure that an envelope is preserved through
the foundations and sufficient space is maintained through the Air Rights Parcel 7 structure to enable
construction and installation of the necessary structural support and operational equipment at this location.
The portal structure would require the use of an 8% gradient which is not preferred, but is within the
maximum allowable limits. The depth of the potential future Phase 3 station beneath the Mass Turnpike is
not controlled by the maximum operational gradient of the selected Phase 3 rail service, rather it is the
consideration of providing sufficient ground cover to: the Mass Turnpike; the existing station structures at
Kenmore Square; and the Muddy River conduit. The maximum operational gradient of the selected
Phase 3 rail service will affect the gradient and length of the tunnel portal structure in Phase 2.
The combination of a steep grade with a tight turn through the portal is not preferable, however this
alignment geometry is located close to a station where the BRT speeds should be low. The BRT route will
be below ground in a cut and cover structure over this length, creating the opportunity to increase the line
of sight by widening the cut and cover structure. The roadway will also be protected from the adverse
effects of weather, helping to improve operational safety.
It is considered that although this solution is not ideal from an operational perspective it is achievable and
would not preclude the development of a Phase 3 alignment underneath the Mass Turnpike with a
Yawkey/Kenmore station. The assumed platform elevation for this Phase 3 station is EL -81.5, as per the
MIS preliminary drawings.
Although much of the section of alignment between Brookline Avenue and Beacon Street would be at
existing grade, the site is likely to be built up as part of the Air Rights Parcel 7 development proposals (by
others) and, therefore, would be effectively underground.
The Beacon Street bridge would need to be temporarily propped and re-constructed in stages to lengthen
the bridge span while maintaining a reduced traffic flow during construction. Particular attention would
need to be paid to the Green Line tunnel, which runs parallel to and underneath Beacon Street in this
location. The widening of the cut section immediately to the west of Beacon Street would require the
closure of Mountfort Street during construction. Works adjacent to the railway with regard to lengthening
the span of the Beacon Street bridge and widening the cut section will need to be carefully planned and
executed to ensure the safety of the operational railway.
Assuming that the LMA tunnel terminates in the southeast near Leon Street and in the northwest at
Brookline Avenue/Yawkey Station/Parcel 7, there is not adequate space for a TBM assembly chamber at
either end of the tunnel. Therefore space for TBM assembly would need to found in an intermediate
location, where a cut and cover TBM assembly chamber would be built. The TBM would be assembled
and launched from this shaft to drive toward the Leon Street portal, where it would be disassembled,
transported along the surface to the access shaft for re-assembly and launch, and subsequently driven to
the Yawkey portal. The only feasible intermediate spot that could accommodate a cut and cover TBM
assembly chamber in or near the alignment is Winsor School playing fields. This would have major
impacts on Winsor School operations.
4-6
232551/01/G - November, 2008/4-6 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Mountfort Street Tunnel – Boston University Bridge option
Build Alternative 3 entails a second tunnel segment intended to avoid the congestion in the vicinity of the
Boston University Bridge. The portal structure for the tunnel would be built in Mountfort Street, and it
would descend from existing grade level in a westerly direction down through an open approach ramp to a
cut and cover tunnel that would extend to a portal located within the surface parking lot of the BU owned
former Cadillac Building located on Commonwealth Avenue. The alignment would meet perpendicular to
Commonwealth Avenue, and such that an at-grade intersection would allow the BRT to cross
Commonwealth Avenue and continue over the Mass Turnpike to cross the Grand Junction Railroad
(GJRR) bridge, thereby allowing surface routing across the Charles River.
The Mountfort Street to Boston University Bridge tunnel would likely be constructed entirely using cut
and cover tunnel owing to its short length. This will require several staged closures of roads in the area to
allow the tunnel to be built. The use of top-down construction could be maximized to reduce disruption to
traffic. Works in close proximity to the railway will need to be carefully planned and executed to ensure
the safety of the operational railway. The car park area at the back of the Cadillac Building would be used
as the main construction worksite.
Mountfort Street Tunnel – Allston option
The portal structure in Mountfort Street would descend from existing grade level in a westerly direction
down through an open approach ramp to a cut and cover tunnel, with the bored tunnel commencing to the
east of St Mary’s Street. The bored tunnel would pass underneath the Mass Turnpike and roughly follow
the alignment of Storrow Drive before crossing underneath the Mass Turnpike viaduct to connect with a
portal structure in the CSX rail yard.
The Mountfort Street to Allston tunnel would require closure of Mountfort Street during construction of
the portal in this area, and this would also serve as the construction worksite for the portal. At the Allston
portal an area of the CSX rail yard would be required for the construction worksite to build the portal and
to provide space for the tunneling facilities and operations. To the east of the Allston portal, the Mass
Turnpike viaduct would need to be temporarily propped and the existing piled foundations would need to
be modified to accommodate passage of the TBM through this area.
The following are some of the major findings of the engineering analysis and evaluation of Alternative 3:
•
Neither tunnel terminus (Leon Street or Yawkey Station/Parcel 7) has optimal space or
configuration for a TBM launch chamber. This may require an intermediate location for a TBM
launch chamber, which would potentially require additional cut and cover construction, and the
efficiency of the tunnel boring operations would be reduced by requiring the TBM to be
assembled, launched, received, and disassembled twice instead of once.
•
The Mountfort Street tunnel options would be expensive and disruptive, and would not provide
major travel time, ridership, or abutter benefits.
4-7
232551/01/G - November, 2008/4-7 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
•
The Brookline Avenue/Yawkey Station/Parcel 7 tunnel portal would be difficult to build, would
cause major construction phase traffic disruption on Brookline Avenue, and would have
permanent impacts on the Parcel 7 development and the future development potential of the
parking lot site on the west side of Brookline Avenue opposite Yawkey Way.
•
The proposed connection beneath Beacon Street between Yawkey Station/Parcel 7 would have
impacts on the design and construction of the Yawkey Station improvements and the Parcel 7
development.
4.1.2
Alternative 3A
Alternative 3A would eliminate the Mountfort Street tunnel options in Alternative 3 and replace them with
surface routing. The LMA tunnel, extending from Leon Street to Yawkey, would be the complete extent
of tunneling under Alternative 3A, and would follow the same alignment as the LMA tunnel described in
Alternative 3.
Alternative 3A has been developed to eliminate the cost and disruption caused by constructing either of
the Mountfort Street tunnel options in Alternative 3, and minimize the length of tunnel while still
achieving the bulk of the tunnel benefits.
The construction issues for Alternative 3A are the same as for the LMA tunnel of Alternative 3.
4.1.3
Alternative 3B
Alternative 3B is intended to address many of the challenges and issues of Alternative 3. Like Alternative
3A, Alternative 3B eliminates the Mountfort Street tunnel options and their associated cost and disruption.
Additionally, Alternative 3B is intended to:
•
Minimize the impacts upon the air rights Parcel 7 development and Brookline Avenue by
relocating the position of the northern portal; and
•
Minimize the impact to Beacon Street traffic flow by avoiding reconstruction of the Beacon Street
bridge.
The Mountfort Street tunnel options of Alternative 3 are instead replaced with surface routing for these
sections. The tunnel alignment from Leon Street through Longwood Avenue to Binney Street would be
common with the LMA tunnel described in Alternative 3. At Binney Street the alignment would depart
from the Alternative 3 route and curve to the north underneath the playing fields of the Winsor School, the
Riverway and the Muddy River before rising up to a portal structure located parallel with the Green Line
“D” Branch at Fenway Station (no station would be provided here), in the vicinity of Park Drive. The
alignment would surface at Miner Street and allow surface BRT routing through the proposed Air Rights
Parcel 7 development and to connect with Yawkey Commuter Rail.
4-8
232551/01/G - November, 2008/4-8 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
The construction issues for Alternative 3B are similar to those for the LMA tunnel of Alternative 3, with
the following exceptions:
•
The bored tunnel would pass beneath the Winsor School and the Emerald Necklace. However,
the TBM would be able to remain underground for the length of its alignment, and would have
no surface impacts to the Winsor School or the Emerald Necklace. The alignment would extend
to a portal located in the abandoned rail freight spur adjacent to the Green Line “D” Branch and
the Landmark Center;
•
The abandoned rail freight spur/Landmark Center portal location affords adequate space for a
TBM assembly chamber. This would eliminate the need for an intermediate cut and cover TBM
assembly chamber at a location such as the Winsor School;
•
The portal structure will require working in close proximity to the Green Line “D” Branch, a
retaining wall for the Green Line portal and the side of the Landmark Center. Construction will
need to take place beneath the Park Drive bridge, utilizing low-headroom construction
equipment, and ensure that the foundations of the bridge structure are not compromised (see
Figure 4.14); and
•
Future Phase 3 construction would require establishment of a cut and cover structure to create an
underground chamber to receive and disassemble the future Phase 3 TBM. This construction
could be done during Phase 2, or at a later time, including during Phase 3 construction.
However, it is important to ensure that there is adequate space in a suitable location. The most
suitable location would be beneath the Winsor School playing fields. However, this surface
impact would only be required if and when Urban Ring Phase 3 were built.
The construction of the abandoned rail freight spur/Landmark Center portal will have temporary impacts
on the Landmark Center car park (and possibly access to the units on the western side of the shopping
center), the Parks and Recreation buildings located adjacent to the Green Line “D” Branch Fenway
Station, and the Children’s Hospital parcel between Munson Street and Maitland Street (currently used as
a parking lot).
4-9
232551/01/G - November, 2008/4-9 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Green Line “D”
Branch tracks
Green Line “D”
Branch portal
Park
Drive
Beacon Street
Potential worksite locations
Emerald
Necklace
Landmark Center
Sears Rotary
Potential worksites shown are preliminary indications of sites that could serve as construction staging and
laydown areas . Further work will be required to define these sites during preliminary engineering studies.
Figure 4.14: Abandoned Rail Freight Spur / Landmark Center Portal
4.1.4
Alternative 3C
Alternative 3C takes the two-tunnel concept of Alternative 3 and effectively connects the tunnels into one
slightly longer overall tunnel. The objectives of this alternative are to:
•
Eliminate the need for additional tunnel portals by extending the length of bored tunnel; and
•
Minimize the impacts upon the air rights Parcel 7 development by reconfiguring the proposed
location of the station at Yawkey.
The tunnel alignment from Leon Street through Longwood and up Brookline Avenue to Yawkey Way
would be common with the LMA tunnel described in Alternative 3. From Brookline Avenue and partially
beneath the Mass Turnpike, there would be provision for a deep underground station. Towards
Commonwealth Avenue the alignment would make a sharp turn to the west to align with Commonwealth
Avenue and would head toward to the Boston University Bridge. There would be a split portal
arrangement: one leg of the tunnel would create a portal starting beneath the BU Academy, passing
beneath the BU Bridge to the roughly triangular plot of land in order to accommodate a surface route
across the Grand Junction Railroad bridge; the second leg of the tunnel would continue underground out
to Allston. It should be noted that such a split portal arrangement is challenging in terms of both
construction and operations, given the rapidly changing grades, lane separation, and horizontal curves.
4-10
232551/01/G - November, 2008/4-10 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
The construction issues for Alternative 3C are similar to those for the LMA and Mountfort-Allston tunnels
of Alternative 3, with the following exceptions:
•
The interface with Parcel 7 is almost completely removed as the tunnel now passes beside the
development, rather than through it.
•
No reconstruction of Beacon Street bridge is required.
•
A mined station tunnel underneath the Mass Turnpike would be built. This would be an
expensive and more risky undertaking than the station in the Parcel 7 site.
•
Construction of the split portal at the Boston University Bridge site would be challenging given
the very small worksite, although access to the CSX rail yard beneath the Mass Turnpike would
provide a laydown and support area during construction. Disruption to the BU Academy would
be inevitable.
•
The TBM would be launched and serviced from the Allston portal. An additional section of cut
and cover tunnel would be built at the sharp curve in the alignment on Commonwealth Avenue
to allow the TBM to negotiate the tight radius at this location.
4.1.5
Alternative 4
Alternative 4, the first of the long tunnel options, comprises a bored tunnel that commences from Melnea
Cass Boulevard and bifurcates to the south of Commonwealth Avenue to provide two routes, one to
Allston and one to Cambridge.
The tunnel portal to the east of Ruggles Station would be located to pick up the proposed center median
surface BRT route along Melnea Cass Boulevard. The tunnel would then pass beneath the existing boat
section of Ruggles Station in an alignment approximately parallel to and to the north of Ruggles Street. A
mined station would be constructed beneath the existing Ruggles Station. The proposed station would
require shafts at each end for tunnel ventilation, mechanical and electrical equipment, and passenger
access and egress.
The alignment then continues in bored tunnel to Huntington Avenue, where a section of tangent, level
track would be provided to accommodate a cut and cover station in this location, in the vicinity of the
Green Line “E” Branch station. Immediately to the south of the underground station the bored tunnel
would make a turn to align with Longwood Avenue, passing underneath the Mass Art building on the
northern corner of the intersection of Huntington and Longwood Avenues.
The preferred location for the Huntington Avenue station is the same as in Alternative 3.
The bored tunnel would generally follow the existing alignment of Longwood Avenue with a section of
tangent, level track located at the intersection of Longwood and Brookline Avenues to accommodate an
underground station. The alignment would continue in a westerly direction, passing beneath the Emerald
Necklace and the Muddy River. A section of tangent, level track would be provided beneath the Muddy
River to allow construction of a mined station beneath the river in the vicinity of the Green Line “D”
Branch Longwood Station. The proposed mined station would require shafts at each end for tunnel
ventilation, mechanical and electrical equipment, and passenger access and egress.
4-11
232551/01/G - November, 2008/4-11 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
The tunnel would follow approximately the alignment of Borland Street and cross beneath Beacon Street.
A section of tangent, level track across Beacon Street would accommodate an underground station in the
vicinity of the existing Green Line “C” Branch Hawes Street station. At the northern end of the proposed
station, a bifurcation would be constructed to allow routing west to Allston and north to Cambridge.
Allston Route
From the bifurcation point, the tunnel would follow the alignment of Cottage Farm Road to
Commonwealth Avenue. An underground station would be constructed within Commonwealth Avenue,
between St Paul Street station and Boston University West station on the Green Line “B” Branch. The
alignment would continue west beneath Commonwealth Avenue before turning north to pass beneath
Alcom Street and the Commuter Rail and CSX rail yard. An underground station could be provided
beneath a possible future commuter rail station in the existing storage area to the north of the rail tracks
and south of the I-90 toll plaza. The tunnel would pass beneath the toll plaza to emerge from a portal that
runs parallel and to the east of the houses along Windom Street to meet bus lanes along a future Stadium
Way.
Cambridge Route
From the bifurcation point, the tunnel would follow the alignment of Essex Street. An underground station
would be provided beneath Essex Street to the south of Commonwealth Avenue, before the tunnel
alignment heads beneath the Charles River to Cambridge. The portal in Cambridge would be located
relatively close to the river, immediately to the north of the Grand Junction Railroad west of Fort
Washington Park.
Key issues associated with the construction of Alternative 4 include:
•
Construction of the Melnea Cass Boulevard portal would require temporary land take on either
side of the boulevard to provide a construction worksite.
•
Northeastern University are currently constructing a new hall of residence on the corner of
Ruggles St and Tremont St. The tunnel would need to avoid the foundations of this building.
•
Construction of the mined station beneath the existing Ruggles station boat section, with
relatively shallow cover to the underside of the boat section, will require extensive ground
treatment and support. The invert levels of the boat section will also require confirmation.
•
Construction of Huntington Ave and Longwood Ave stations would be similar to Alternative 3.
•
The construction of the Longwood Green Line “D” Branch station would be mined to attempt to
minimize impacts on the Emerald Necklace and Muddy River. The shafts at either end and the
mined tunnel would still have an impact on the Emerald Necklace and Muddy River. There is
also very limited space for a construction worksite and adverse topography. Extension of the
station to accommodate Phase 3 is likely to require land acquisition and possible building
demolition.
•
Construction of the station at Hawes Street will include the construction of a turnout. There will
be a large temporary impact to the Amory Playground during open cut construction works as the
area would be used for a worksite.
4-12
232551/01/G - November, 2008/4-12 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
•
Construction of the Boston University west station would be similar to Huntington Avenue
station.
•
Construction of West Station would require some of the storage tracks in the CSX rail yard to be
temporarily closed or diverted to enable construction. Part of the rail yard would be used during
construction as a worksite.
•
The Allston portal would likely be a TBM launch point and so a relatively large area would be
required to provide space for the tunneling facilities and operations.
•
The new Boston University central station would be constructed in a very constrained residential
area. The worksite would likely be located in the Cadillac Building car park and in the disused
gas station at Essex Street. Impacts to the residences around this station would be inevitable.
•
Construction of the Cambridge portal would be relatively simple given the availability of land on
this side of the Charles River in the area of the portal. This would be a TBM launch site for the
tunnel drive to the turnout location at Hawes Street station.
4.1.6
Alternative 4A
The second long tunnel option has been developed to explore the possibility of maintaining connectivity
with the Green Line branches, as in Alternative 4, but with a reduced number of stations. Additionally, a
longer length of tunnel in Cambridge would pass beneath the Red Line and portal onto or near Binney
Street.
The alignment follows the same route as for Alternative 4 from Melnea Cass Boulevard through to
Longwood Avenue. However at the western end of Longwood Avenue the tunnel follows Brookline
Avenue. The location of the station on Longwood Avenue would therefore need to be near Avenue Louis
Pasteur, as in the Alternative 3 alignment. From Brookline Avenue the tunnel would turn beneath Park
Drive and an underground station would be provided beneath Park Drive to the south of Beacon Street.
This station would allow connection with the Green Line “C” Branch St Mary’s Street station and “D”
Branch Fenway station.
The tunnel would continue along Park Drive with a bifurcation at Mountfort Street to allow routing to
both Allston and Cambridge.
Allston Route
From the bifurcation point, the tunnel would pass beneath the Mass Turnpike and follow the alignment of
Commonwealth Avenue. An underground station would be provided in the vicinity of the Green Line “B”
Branch Boston University West station. The tunnel would then follow the same alignment as the
Alternative 4 alignment, with a potential station in the CSX rail yard and a portal in Allston.
4-13
232551/01/G - November, 2008/4-13 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Cambridge Route
From the bifurcation point, the tunnel would pass beneath the Mass Turnpike and follow the alignment of
St Mary’s Street. An underground station would be provided in the vicinity of the Green Line “B” Branch
Boston University Central station. The tunnel would then pass beneath the Charles River to Cambridge
where it would generally follow the GJRR, with underground stations in the vicinity of Fort Washington
Park in Cambridgeport and Massachusetts Avenue/MIT. The tunnel would then pass underneath the Red
Line at Kendall Square and surface through a portal onto or near Binney Street.
Construction of Alternative 4A would be similar to Alternative 4 with the following main differences:
•
Construction of Park Drive station would require use of the Landmark Center parking lot as a
construction worksite. The station would be located between the bridge abutment of the Park
Drive bridge over the Green Line “D” Branch and the cut and cover box section of the Green
Line “C” Branch – this will be a challenging construction. For Phase 3 compatibility, the station
would likely need to be deep enough that the extension to accommodate longer platforms would
occur to the north as a mined tunnel beneath the Green Line cut and cover section.
•
Construction of the turnout at Mountfort Street will require extensive ground treatment and will
require close coordination with the Commuter Rail, with some work undertaken from within the
railway property. The construction site would need to be located within the street, requiring
closure of Mountfort Street or the end of Park Drive for a considerable period of time.
•
Details of the foundations of the buildings to the north of the Mass Turnpike are not known, and
the alignment has been developed to avoid the buildings on plan, where possible. This has
required the use of tighter than desirable gradients from a tunneling perspective and from the
perspective of conversion to heavy rail in Phase 3.
•
The construction of the tunnel and portal by Kendall Square/Binney Street will need to be below
the Red Line and avoid the building foundations in this area.
4-14
232551/01/G - November, 2008/4-14 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
4.2
Hatch Mott MacDonald
Earth Tech, Inc.
Tunneled Alignment Alternatives – Development Stage 2
Preliminary ridership analysis and evaluation of cost and benefit indicated that the increase in ridership for
the long tunnel options (Alternative 4-series) compared with the short tunnel options (Alternative 3-series)
was marginal, but came at a greatly increased cost as a result of the considerable additional length of
tunnel and increased number of underground stations. This, in combination with feedback from various
public meetings, suggested that further development of the Alternative 3-series alignments was warranted,
particularly in the LMA. The Alternative 4-series alignments remain viable options.
Sub-variants of Alternative 3A were developed and referred to as: Alternative 3A-1; Alternative 3A-2;
and Alternative 3A-3, as discussed below and presented in Attachment B.
4.2.1
Alternative 3A-1
Alternative 3A-1 shares the same alignment as Alternative 3A from Leon Street/Ruggles Street, along
Huntington Avenue, with an underground station on Huntington Avenue, and along Longwood Avenue
until the intersection of Longwood Avenue and Binney Street. At this location, the 3A-1 alignment
continues along Longwood Avenue before making a relatively tight turn (250-ft radius) at the intersection
of Brookline Avenue and Longwood Avenue. A length of tangent track beneath the Winsor School
playing fields allows a station to be accommodated in this location, before the alignment makes a second
tight turn (250-ft radius) to connect with a Pilgrim Road alignment, and from this point follows the
Alternative 3A routing along Brookline Avenue to a portal at Yawkey/Air Rights Parcel 7. The tight turns
could not be constructed using a TBM and would require use of other construction methods. The tight
turns in this option would limit Phase 3 flexibility.
The construction issues for Alternative 3A-1 are similar to those for Alternative 3A, with the following
exceptions:
•
As in Build Alternative 3, the portal locations at Leon Street and Yawkey Station/Air Rights
Parcel 7 would not have adequate space for a TBM launch chamber. This would require an
intermediate TBM launch chamber, assumed to be at the Winsor School playing fields, with the
associated impacts and disruption as in Alternative 3. The TBM launch point beneath the Winsor
School would be incorporated within the cut and cover station at this location;
•
Locating the Longwood Avenue station beneath the Winsor School rather than by Tugo Circle
would reduce disruption to Longwood Ave and minimize building access conflicts. However,
this would cause serious disruption to the Winsor School; and
•
The two tight turns required for this alignment would need to be constructed using either SEM
mined tunnels or by extending the cut and cover tunnel for the adjacent station.
4-15
232551/01/G - November, 2008/4-15 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
4.2.2
Hatch Mott MacDonald
Earth Tech, Inc.
Alternative 3A-2
Alternative 3A-2 shares the same alignment as Alternative 3A from Leon Street/Ruggles Street, along
Huntington Avenue, with an underground station on Huntington Avenue, and along Longwood Avenue
until the intersection of Longwood Avenue and Avenue Louis Pasteur (Tugo Circle). An underground
station would be provided at this location, before the 3A-2 alignment follows the alignment corridor
identified in the MIS by making an 800-ft radius curve beneath the Children’s Hospital Garage, Children’s
Research Center, 333 Longwood Ave, and the Shapiro Center. A length of tangent track and a second
800-ft radius curve connects with a Brookline Avenue alignment. The alignment continues along
Brookline Avenue and surfaces at the Yawkey Station/Air Rights Parcel 7 portal, as for Alternative 3A.
The construction issues for Alternative 3A-2 are similar to those for Alternative 3A, with the following
exceptions:
•
4.2.3
The major issue with Alternative 3A-2 is in relation to building foundations and right-of-way.
Passing beneath several buildings in the LMA is going to increase the chance of a conflict with
foundations (details unknown at present) and increase potential for settlement-related problems.
Alternative 3A-3
Alternative 3A-3 shares same alignment as Alternative 3A from Leon Street/Ruggles Street, along
Huntington Avenue, with an underground station on Huntington Avenue, and along Longwood Avenue
until the intersection of Longwood Avenue and Binney Street. At this location, the 3A-3 alignment
continues along Longwood Avenue before making a turn beneath the Emerald Necklace. A reverse curve
brings the alignment into line with Brookline Avenue and surfaces at the Brookline Avenue/Air Rights
Parcel 7 portal, as for Alternative 3A.
Extending the alignment along Longwood Avenue allows the Longwood Avenue station to be located at
the intersection of Brookline Avenue. This provides increased spacing between this station and the station
at Huntington Avenue.
The construction issues for Alternative 3A-3 are similar to those for Alternative 3A, with the following
exceptions:
•
The Longwood Avenue station is located at the intersection of Brookline Ave rather than by
Tugo Circle. This will likely increase disruption by constructing the station across the
intersection but will eliminate potential complications of interfacing with the underground
parking garage beneath the Harvard lawn.
4-16
232551/01/G - November, 2008/4-16 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
4.3
Hatch Mott MacDonald
Earth Tech, Inc.
Tunneled Alignment Alternatives – Development Stage 3
During further discussion of the Alternative 3-series alignments, it became clear that there were several
significant advantages to locating the north-westerly tunnel portal between the Green Line “D” branch and
the Landmark Center in the abandoned rail freight spur rather than in Yawkey Station/Air Rights Parcel 7:
•
The abandoned rail freight spur/Landmark Center portal location affords adequate space for a
TBM assembly chamber. Therefore, the TBM could be assembled at the northwest end of the
tunnel and driven the full length of the tunnel alignment (horizontal radius permitting). This
avoids the need for an intermediate cut and cover TBM assembly chamber at a location such as
the Winsor School playing fields;
•
The extensive length of cut and cover tunnel along Brookline Avenue and the associated traffic
disruption would be avoided by eliminating the Brookline Avenue portal;
•
The impacts and uncertainties regarding the interface with the Air Rights Parcel 7 development
would be avoided; and
•
Phase 3 routing option flexibility would be maximized (since the Brookline Avenue tunnel portal
section would have major negative impacts on Phase 3 tunnel interface).
The need for two underground stations at either end of Longwood Avenue, in close proximity, was also
questioned. Therefore the idea of providing a single underground station more centrally located along
Longwood Avenue was explored as this could potentially provide a similar level of service but with
reduced cost and reduced disruption during construction. The underground station at Huntington Avenue
was therefore eliminated.
Finally, it was decided to further investigate the possibility of increasing the use of public right-of-way to
minimize potential land takings and impacts on key institutions along the alignment.
Following further analysis and consultation with stakeholders, two further alignment variants emerged,
referred to as Alternative H2(T) – “Tight Turn” and Alternative H2(T) – “Wide Turn”, presented in
Attachment B. Additional sub-options were investigated including further variants in the alignment
between Longwood Avenue and the Landmark Center portal.
4.3.1
Alternative H2(T) – “Tight Turn”
The objectives of Alternative H2(T) – “Tight Turn” are to:
•
Maximize the use of public right-of-way;
•
Reduce cost and disruption by providing only one underground station, centrally located along
Longwood Avenue at Tugo Circle; and
•
Minimize the length of abandoned tunnel structures for a potential Phase 3 conversion.
4-17
232551/01/G - November, 2008/4-17 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Alternative H2(T) – “Tight Turn” is based on Alternative 3B and shares the same alignment from Leon
Street/Ruggles Street, along Huntington Avenue and Longwood Avenue until the intersection of
Longwood Avenue and Binney Street. At this location, the H2(T) alignment continues further along
Longwood Avenue before making a tight turn (150-ft radius) from Longwood Avenue onto Brookline
Avenue. The alignment continues along Brookline Avenue until a point just south of the Emerald
Necklace, where a second tight turn (150-ft radius) would bring the alignment beneath the Emerald
Necklace and the Muddy River to the abandoned rail freight spur/Landmark Center portal. The tight turns
are approaching the absolute minimum horizontal radius for the BRT vehicles (100-ft) and may require a
reduction in operating speed.
A single underground station would be provided in this alternative, centrally located along Longwood
Avenue at Tugo Circle.
The tight turns could not be constructed using a TBM and would require use of other construction
methods. The tight turns in this option would provide a connection point for a potential future Phase 3
alignment, however the choice of rail technology may be restricted depending on the final Phase 3
alignment.
The benefit of minimizing the length of abandoned tunnel in Phase 3 could only be realized if Phase 3
were to be light rail. This would require abandonment of the length of tunnel from the tight turn
immediately south of the Emerald Necklace to the abandoned rail freight spur/Landmark Center portal. If
heavy rail services were implemented in Phase 3, then the length of abandoned tunnel would extend to the
tight turn at the intersection of Brookline Avenue and Longwood Avenue.
Construction of Alternative H2(T) – “Tight Turn” would be similar to Alternative 3B with the following
main differences:
•
Two underground structures will need to be built to enable the tight turns in the alignment to be
made. These would most likely need to be built using cut and cover methods to allow sufficient
space for the TBM to be turned and re-launched;
•
The underground station at Huntington Avenue would be eliminated.
•
Construction of the running tunnels using the SEM would eliminate the need for special
structures at the tight turn locations.
4.3.2
Alternative H2(T) – “Wide Turn”
The objectives of Alternative H2(T) – “Wide Turn” are to:
•
Minimize disruption to Brookline Avenue;
•
Minimize surface disruption along the length of the tunnel alignment;
•
Maximize the uninterrupted use of the TBM during the tunnel drive; and
•
Reduce cost and disruption by providing only one underground station, centrally located along
Longwood Avenue at Tugo Circle.
4-18
232551/01/G - November, 2008/4-18 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Alternative H2(T) – “Wide Turn” is based on Alternative 3B and shares the same alignment from Leon
Street/Ruggles Street, along Huntington Avenue and Longwood Avenue until the intersection of
Longwood Avenue and Binney Street. At this location, the H2(T) – “Wide Turn” alignment would
commence a wider horizontal curve to head beneath the Winsor School playing fields and the Emerald
Necklace, before surfacing at the abandoned rail freight spur/Landmark Center portal. In this option, the
TBM would pass beneath the Winsor School playing fields and the Emerald Necklace, but would create
no surface disruption at these locations.
A single underground station would be provided in this alternative, centrally located along Longwood
Avenue at Tugo Circle.
The structures required to perform the tight turns in H2(T) – “Tight Turn” are eliminated in this alternative
and therefore the potential disruption to Brookline Avenue is also eliminated. In addition, the TBM drive
would be in two discrete sections rather than four sections, simplifying the TBM drive and maximizing
use of the TBM.
During development of this option the layout of the Leon Street portal was modified to include the
protective works that would be required to the Stony Brook conduits. The portal structure was extended
across Parker Street to the car park of the Sweeney Field. This results in the portal being tangent for the
complete length and minimizes encroachment on Ruggles Street. The number of utility diversions
required within Ruggles Street is potentially reduced by this configuration. It is proposed that this portal
layout be adopted for any of the alternatives that include a portal in the vicinity of Leon Street.
Construction of Alternative H2(T) – “Wide Turn” would be similar to Alternative 3B with the following
main differences:
•
The turnout structure for Phase 3 would not be built during Phase 2, but an agreement would
need to be reached between the Urban Ring Project and the Winsor School that any future
development on the site would either incorporate the construction of the turnout, or would not
prevent its construction at some date in the future;
•
The underground station at Huntington Avenue would be eliminated.
4.3.3
Alternative H2(T) – Sub-options
Sub-options have also been evaluated for the busway tunnel section in the LMA to improve connectivity
with the Green Line and to mitigate potential impacts to the Winsor School.
(i)
Underground Stations on the Green Line
The possibility of constructing new underground stations on the Green Line “C” and “D” Branches to the
west of Kenmore Station and in the vicinity of the Air Rights Parcel 7 development was considered to
provide a more direct connection between the Urban Ring and the Green Line in this location. A summary
of the key issues is presented below.
4-19
232551/01/G - November, 2008/4-19 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
•
A single underground station capturing both Green Line “C” and “D” Branches, to the south of the
Mass Turnpike, is not possible owing to the track configuration in this location. To the west of
Kenmore Square the switch to branch the “C” and “D” lines starts approximately beneath the
commuter rail line and the bifurcation is complete in the region of Maitland Street. A station could
not be constructed along this length of track owing to the location of the switch. To have a station
immediately south of the switch would require two separate stations on each branch of the Green
Line.
•
If a single station were to be constructed immediately to the north of the switch, then it would need
to be located beneath the Mass Turnpike. The station platform length for a Green Line Station is
300-ft and this would place the northern end of the station platforms approximately 1000-ft from
Kenmore Square station. The station would need to be mined beneath the Mass Turnpike. The
station may interfere with the Beacon Street bridge piers and the Air Rights Parcel 7 development
foundations.
•
On the “D” Branch, there is a section of approximately 170-ft of straight track that would allow a
two-car platform (74-ft long cars) to be constructed beneath 819 Beacon Street, as shown in Figure
4.15. A three-car platform would encroach on the 400-ft radius curves which may be acceptable to
MBTA with a special waiver. The gradient through this area is approximately 0.3% which is
within the limits specified for a station.
•
On the “C” Branch, there is ample straight track to the south of the Mass Turnpike to locate a
station, as shown in Figure 4.15. It would appear that the gradient in this area is less than 1.0%
which is the maximum permissible for a Green Line station, although this requires confirmation. A
three-car platform could easily be accommodated in this location.
•
For a station in either location, construction would need to be carried out while keeping trains
operational.
•
Traffic would need to be maintained on Beacon Street during construction of the “C” Branch
station.
•
The Green Line stations would not provide an integrated interchange with the Urban Ring as there
would be two additional underground stations for the Green Line and a separate surface station for
the Urban Ring.
•
There are operational considerations of adding a station to the Green Line and this may have an
impact upon Green Line capacity and add to journey times.
Consideration of the above issues and the additional cost and complexity of construction in building two
new underground stations on both branches of the Green Line without providing an integrated interchange
with the Urban Ring resulted in these options not being pursued any further.
4-20
232551/01/G - November, 2008/4-20 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Figure 4.15: Underground Stations on the Green Line
(ii)
Alternative Locations and Configurations for the Landmark Center Portal
Three alternatives relating to the Landmark Center portal have been identified:
•
Extend the Landmark Center portal further to the north and include an underground BRT station
within the portal infrastructure;
•
Revise the tunnel alignment to follow Park Drive with a split portal arrangement on Mountfort
Street and an underground station beneath Park Drive to connect with the Green Line “C” and “D”
Branches; and
•
Revise the tunnel alignment to follow Park Drive with a portal located near the BU Bridge and
underground stations beneath Park Drive and to the north of the Mass Turnpike.
These sub-options are described and discussed in a memorandum dated October 7, 2008 and included in
Attachment C. The additional cost and the limitations imposed on Phase 3 rail conversion associated with
the split portal option or the BU Bridge option have resulted in these alternatives not being considered any
further. The improved connection with the Green Line and the increased ridership associated with the
underground station at the Landmark Center portal is considered to be worth the additional cost and is
therefore recommended for inclusion in the LPA.
4-21
232551/01/G - November, 2008/4-21 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
(iii)
Hatch Mott MacDonald
Earth Tech, Inc.
Longwood Avenue Alignment
In an effort to mitigate potential impacts to the Winsor School and increase the use of public ROW,
further variants to the tunnel alignment for Alternative H2(T) were investigated. A preliminary evaluation
indicates that extending the busway tunnel alignment to continue along Longwood Avenue prior to
making the turn to the north to connect with the Landmark Center portal may afford an opportunity to
alleviate the impact to the Winsor School and increase usage of public ROW. The location of the Phase 3
turnout structure and possible building foundation conflicts (375 Longwood Avenue) remain to be
investigated. This alternative alignment is shown in Figure 4.16. The Alternative H2(T) – “Tight Turn”
alignment also offers similar benefits in terms of alleviating impacts to the Winsor School and increasing
usage of public ROW but places more restrictions on construction methodologies and on Phase 3
compatibility as discussed earlier in this report.
Figure 4.16: Longwood Avenue Alignment
4-22
232551/01/G - November, 2008/4-22 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
4.4
Hatch Mott MacDonald
Earth Tech, Inc.
Tunneled Alignment Alternatives – Summary
A range of alignment alternatives have been developed for both the short tunnel and long tunnel options.
These alignments have been further refined and developed on the basis of preliminary ridership and costbenefit analyses, and in coordination with public consultation. The full range of alignment alternatives
presented in this document are considered to be viable.
A summary table comparing the stations provided by each alternative, the approximate tunnel lengths and
costs is given in Table 4.4.
The following sections present a general discussion on noise and vibration, electromagnetic fields, Phase 3
compatibility, and capital costs.
4.4.1
Noise and Vibration
Noise and vibration analyses have been undertaken by Harris Miller Miller & Hanson Inc. and address
both construction phase and operations phase impacts for Urban Ring Phase 2. Some general issues
related to Phase 3 impacts are also discussed. The noise and vibration analyses are detailed in a separate
report and will be summarized in the RDEIR/DEIS document. A brief summary of the findings is
presented below.
(i)
Construction
The primary locations for assessing construction noise impact will be at the tunnel portals and the
underground stations. Potential construction noise impacts and mitigations will be evaluated during
engineering and design of the project, as more details of the construction scenarios are known.
Construction vibration levels were predicted for tunnel construction operations in the LMA. The LMA
has a range of sensitive locations including residential locations and research facilities with vibrationsensitive equipment. Since many of the details regarding the specific equipment that is present and their
locations at the research facilities is not known, potential vibration impact was assessed by determining
the distance to impact for each criterion and each vibration source.
The vibration impact analysis indicates that vibration impact may occur for nighttime residential human
use at distances up to 36 feet from the tunnel when tunneling in rock with efficient propagation conditions.
For common vibration-sensitive equipment such as electron microscopes (classified as VC-A or VC-B
equipment), ground-borne vibration impact may occur up to 57 feet from the tunnel depending on soil
conditions. In consideration of the most highly-sensitive equipment (classified as VC-E equipment),
ground-borne vibration impact may occur at distances up to 359 feet from the centerline of the tunnel.
As more detailed information regarding construction methodology, tunnel alignment, geotechnical
conditions, specific equipment locations and building coupling losses becomes available during final
design, more accurate assessments for each piece of equipment can be made and mitigations can be
developed if required.
4-23
232551/01/G - November, 2008/4-23 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
(ii)
Hatch Mott MacDonald
Earth Tech, Inc.
Operations
The noise impact assessment indicates that there are no locations along the tunnel alignments, including
stations, projected to have noise impacts during operation of the BRT service.
The vibration impact analysis indicates that the bus operations are not projected to generate vibration
levels higher than existing vibration generated by current bus operations, trucks, and deliveries to
buildings. In addition, because the primary source of vibration from rubber-tired vehicles is from roadway
irregularities such as potholes, it is expected that buses operating on purpose-built, dedicated use busways
or in the proposed tunnel would generate lower vibration levels than are currently experienced from buses
and trucks on existing streets.
In Phase 3 of the project there is the potential for the tunnel to be converted to rail transit. While the noise
and vibration impact assessment for that future phase of the project will be conducted separately from this
Phase 2 analysis and does not have an effect on the analysis of Phase 2 impacts, the potential for rail
transit vibration impacts through the LMA tunnel alternatives is addressed here. Unlike bus operations,
there is significant potential for vibration impacts from rail transit through a tunnel in the LMA.
The extent of any potential impacts would need to be evaluated based on specific project factors, including
vehicle type, speeds, and ground conditions in the LMA. However, a conservative estimate is that there is
the potential for vibration impact on sensitive equipment at 400 feet or more without mitigation,
depending on project-specific factors. There are a number of mitigation methods for rail transit available,
including specially-designed fasteners and floating slab trackwork, which would have the potential to
significantly reduce vibration levels through the LMA. Any Urban Ring Phase 2 tunnel recommendations
would include a general assessment of vibration impacts (in accordance with Federal Transit
Administration guidance) from Phase 3 rail operations. The general assessment would result in an upper
bound for the potential for vibration impact from Phase 3 operations. This assessment would be based on
available data in the literature, and assumptions regarding soil conditions and buildings foundations and
Phase 3 rail operations. The assessment will include a discussion of the potential for reducing those
impacts through a range of mitigation measures, at both the track and the receiver.
4.4.2
Electromagnetic Fields
An analysis of Electromagnetic Field (EMF)/Electromagnetic Interference (EMI) impacts has been
undertaken by Gradient Corporation for Urban Ring Phase 2. Some general issues related to Phase 3
impacts have also been addressed. The EMF/EMI analysis is detailed in a separate report and will be
summarized in the RDEIR/DEIS document. A brief summary of the findings is presented below.
Wherever electric propulsion is used, the key determinants of EMF/EMI potential are: magnitude of
electric currents and voltages utilized by the vehicles, mass and size of the ferromagnetic material in the
vehicle (for “moving metal” fields), proximity of sensitive receptors to the transit corridor, pattern of
current and voltage time variations, spatial configuration of the conductors supplying electric power, the
quantity of traffic, and the degree of EMF/EMI isolation required by sensitive receptors.
4-24
232551/01/G - November, 2008/4-24 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
The magnetic-field excursions from electric-propulsion currents are expected to have a frequency
spectrum of 0 to 10 Hertz, and to occur at intervals (e.g., every two minutes) determined by the
intermittency of bi-directional transit traffic. It is expected that the magnetic component of EMF/EMI
produced by the transit system is likely to be the most problematic in terms of interference with sensitive
research measurements. The highest magnetic fields are expected at grade, at the edge of the right of way
(~15 feet from the route centerline). For the various technologies, this maximum is ~65 milli Gauss (mG)
for hybrid electric/emission-controlled diesel/compressed natural gas BRT, ~210 mG for dual-mode BRT,
~1,010 mG for light rail technology, and ~1,610 mG for heavy rail technology. These values should be
compared to the earth’s (steady) magnetic field, which is ~550 mG in Boston. However, these EMF/EMI
fields drop rapidly with distance.
The analysis illustrates peak fields in the vicinity of the various alignment alternatives and also lists some
potential mitigation measures that can be employed.
4.4.3
Phase 3 Compatibility
In assessing the conversion of Phase 2 tunnel alternatives to Phase 3, the rail alignment from Assembly
Square to Dudley Square previously identified in the MIS and presented in the DEIR as Figure 2-1.3 is
used as the base case for comparison. In addition, the analysis of Phase 3 compatibility also recognizes the
potential for Phase 3 rail service connections to Allston, which was not included in the Urban Ring
corridor in the MIS.
A summary matrix presenting Phase 3 compatibility is presented in Table 4.3. This shows three
categories: basic compatibility (i.e. tunnel cross section and alignment criteria); basic features (i.e. portal
elements, station elements, turnouts etc.); and advanced features (i.e. detailed elements of rail
functionality). Also included is a section on non-compatible tunnel that would not be converted in
Phase 3.
Major structural works required for Phase 3 that could be built during Phase 2 may include:
•
Dedicated underground turnout structures to suit Phase 3 rail alignments;
•
Longitudinal extension of underground stations to allow for Phase 3 platform lengths;
•
Vertical extension of underground stations to allow Phase 3 station platforms to be built beneath
the Phase 2 station (such that both BRT and rail could operate simultaneously); and
•
Construction of a larger diameter tunnel to incorporate two decks - an upper deck for BRT, fitted
out during Phase 2, and a lower deck provided during Phase 2 and fitted out for rail during
Phase 3.
In general, where cut and cover structures are required for tight turns in Phase 2, these would be built to
incorporate Phase 3 turnouts. In addition, where portals are required to be re-graded during Phase 3
conversion, the portals would be designed and constructed to accommodate these requirements in Phase 2.
4-25
232551/01/G - November, 2008/4-25 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Phase 3 Com patible (basic)
Tunnel Cross Section
Phase 3 Feat ur es
(adv anced)
Phase 3 Feat ures (basic)
Alignment
Non-com pat ible t unnel
HR
LRT
HR
LRT
HR
LRT
HR
Description
LMA Tunnel (Ruggles - Yawkey)
Note 1, Note 2
Note 1, Note 2
None
None
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
Yawkey (Parcel 7) Station would be abandoned
Mountfort street tunnel would not be used in Phase 3, but could
remain a BRT tunnel.
550
Mountfort Street Tunnel (BU Bridge)
LMA Tunnel (Ruggles - Yawkey)
Note 1, Note 2
Note 1, Note 2
None
None
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
Yawkey (Parcel 7) Station would be abandoned
Mountfort street tunnel would not be used in Phase 3, but could
remain a BRT tunnel.
550
Mountfort Street Tunnel (Allston)
Approximate
Abandoned Length
(feet)
LRT
Note 1, Note 2
Note 1, Note 2
None
None
Yawkey (Parcel 7) Station would be abandoned
550
Note 1, Note 2
Heavy rail precluded by tight turns adjacent to the station at Brookline Avenue
None
None
Yawkey (Parcel 7) Station would be abandoned
550
Note 1, Note 2
None
None
Yawkey (Parcel 7) Station would be abandoned
550
Note 1, Note 2
None
None
Yawkey (Parcel 7) Station would be abandoned
550
Note 1
None
None
The tunnel from the turnout to the Park Drive portal (including the
portal) would be abandoned
2500
None
None
The tunnel along Commonwealth Ave to Allston, including the
portals at Allston and BU Bridge, would be abandoned.
8000
Note 4
Note 4
The spur to Cambridge could be converted to HR
0
Alt ernat iv e 3 (Opt ion 1 )
0
Alt ernat iv e 3 (Opt ion 2 )
0
Alt ernat iv e 3 A
-
Note 1, Note 2
Note 1, Note 2
LMA Tunnel (Ruggles - Yawkey)
Note 1
Alt ernat iv e 3 A-1
LMA Tunnel (Ruggles - Yawkey)
Alt ernat iv e 3 A-2
LMA Tunnel (Ruggles - Yawkey)
Alt ernat iv e 3 A-3
LMA Tunnel (Ruggles - Yawkey)
Alt ernat iv e 3 B
LMA Tunnel (Ruggles - Park Drive)
A turnout would be included during Phase 2 (beneath the Winsor School playing fields) to allow a Pilgrim Road tunnel alignment compatible with Phase 3 LR/HR to Park Drive or
Alt ernat iv e 3 C
LMA Tunnel (Ruggles - Allston)
Note 1
Note 1
The platform tunnel for Yawkey/Kenmore station would be built and stub created for launch the The platform tunnel for Yawkey/Kenmore station would be built and stub created for launch the
TBM toward Cambridge
TBM toward Cambridge
Alt ernat iv e 4
Ruggles to Cambridge
Melnea Cass Blvd portal can be regraded to extend tunnel to Dudley Square.
Melnea Cass Blvd portal can be regraded to extend tunnel to Dudley Square.
Cambridge portal would need to be regraded to extend the tunnel to Sullivan Square
Cambridge portal would need to be regraded to extend the tunnel to Sullivan Square
Melnea Cass Blvd portal could be used for LRT to come to surface and run on surface route to
Dudley Square.
n/a
n/a
n/a
n/a
Allston Branch
Note 3
n/a
n/a
n/a
n/a
Conversion of the Allston branch is not part of the MIS identified
route, but could be achieved.
0 or 7700 + 2 stations
Melnea Cass Blvd portal can be regraded to extend tunnel to Dudley Square.
Melnea Cass Blvd portal can be regraded to extend tunnel to Dudley Square.
None
None
The spur to Cambridge could only be used for LRT
0
Melnea Cass Blvd portal could be used for LRT to come to surface and run on surface route to
Dudley Square.
Note 3
n/a
n/a
The spur to Allston would be abandoned (it could not be
converted to rail due to horizontal alignment radii)
8200
Alt ernat iv e 4 A
Ruggles to Cambridge (& Kendall Sq)
Vertical alignment through Park Drive would need to be deep to allow mined extension of station Vertical alignment through Park Drive would need to be deep to allow mined extension of station
tunnel beneath Green Line cut and cover box.
tunnel beneath Green Line cut and cover box.
Allston Branch
n/a
n/a
n/a
n/a
n/a
n/a
Note 1
Note 1
If LR, tunnel abandoned from the Fenway tight turn up to and
inclduing the Park Drive portal.
1500
A turnout structure immediately south of the Fenway allows Park Drive or Yawkey/Kenmore
alignments in Phase 3
A turnout structure at the intersection of Longwood/Brookline Aves allows Yawkey/Kenmore or
Cottage Farm alignments in Phase 3.
If HR, tunnel abandoned from the Longwood Ave tight turn up to
and including the Park Drive portal.
3000
Note 1
Note 1
The tunnel from the turnout to the Park Drive portal (including the
portal) would be abandoned
2500
Hy brid 2 (T ) - "T ight T ur n"
LMA Tunnel (Ruggles - Park Drive)
Hy brid 2 (T ) - "Wide T ur n"
LMA Tunnel (Ruggles - Park Drive)
Passive provision for future construction of a turnout beneath the Winsor School allows either LR or HR to Park Drive or Yawkey/Kenmore.
All Alt er nat iv es
n/a
n/a
n/a
n/a
Passive provision is made in the alignment for the extension of stations (tangent, level track).
Where portals are to be regraded, the portal should be designed and constructed during Phase 2 to accommodate the regrade during Phase 3.
NOTES
1 Leon Street portal can be regraded to extend beneath Ruggles Station and extend to Dudley Square. The Phase 2 portal should be built with Phase 3 in mind to minimize future disruption and construction complexities.
2 Yawkey portal can be regraded to suit Yawkey/Kenmore Station and extension to Sullivan Square. The Phase 2 portal should be built with Phase 3 in mind to minimize future disruption and construction complexities.
3 The horizontal alignment is compatible with LRT but not Heavy Rail. The alignment to Cambridge could potentially be amended to be Heavy Rail compatible once further information is available on foundation constraints.
4 Hawes St station (Green Line "C" Branch) would be extended to meet the turnout, thereby creating the full station box for Phase 3.
5 Special tunnel lining rings would used where future station extension walls to be built.
6 Advanced items that could be considered during detailed design include: accommodation of rail systems within the tunnel (utility ducting, supports etc), stray current protection, roadway construction details that facilitate later removal and replacement with rail, platform dimensions for LRT conversion.
7 Consider the diversion of existing utilities (e.g. sewers, water mains, etc) during Phase 2 that will accommodate the works associated with Phase 3 to minimize cost, disruption, and schedule.
Table 4.3: Phase 3 Compatibility Matrix
4-26
232551/01/G - November, 2008/4-26 of 28
Note 5
Note 6
Note 7
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
4.4.4
Hatch Mott MacDonald
Earth Tech, Inc.
Preliminary Capital Cost Estimate of Options
$
1.7 billion
4
4
17,700
17,700
$
3.5 billion
8
6
2
23,300
15,500
7,800
$
5.2 billion
7
5
2
30,500
22,200
8,300
$
6.3 billion
3
3
9,800
9,800
$
2.2 billion
3
3
9,100
9,100
$
2.1 billion
3
3
11,000
11,000
$
2.4 billion
1
1
8,000
8,000
$
1.5 billion
1
1
7,900
7,900
$
1.5 billion
West Station
TOTAL NUMBER OF
UNDERGROUND
STATIONS
Boston University Central
(Green Line “B” Branch)
7,900
7,900
z
Boston University Central
(south of BU Bridge)
2
2
z
Boston University West
(Green Line “B” Branch)
2.2 billion
z
Park Drive (Green Line "B" &
"C" Branches)
$
z
Hawes Street
(Green Line "C" Branch)
9,800
9,800
z
Longwood
(Green Line "D" Branch)
3
3
Yawkey/Kenmore
3.6 billion
Yawkey
(Parcel 7)
17,100
9,800
7,300
$
z
3
3
0
Longwood Avenue
(Brookline Ave)
2.8 billion
Longwood Avenue
(Ave Louis Pasteur)
12,500
9,800
2,700
$
z
3
3
0
z
Huntington Ave
(Green Line "E" Branch)
Total
Length of
Tunnel *
(feet)
z
Ruggles
A preliminary capital cost estimate for each of the tunneled options has been prepared by Keville
Enterprises Inc., and is presented in Table 4.4. The estimate provides a comparison between each of the
tunnel alternatives, but does not indicate the change in cost for the remainder of the Urban Ring (e.g.
change to surface routing options required to connect to the tunnels).
Alternative 3 (Option 1)
z
z
LMA Tunnel (Ruggles - Yawkey)
Mountfort Street Tunnel (BU Bridge)
Alternative 3 (Option 2)
z
z
LMA Tunnel (Ruggles - Yawkey)
Mountfort Street Tunnel (Allston)
Alternative 3A
Alternative 3B
LMA Tunnel (Ruggles - Park Drive)
z
z
Stage 1
z
z
z
LMA Tunnel (Ruggles - Yawkey)
Alternative 3C
z
z
z
z
LMA Tunnel (Ruggles - Allston)
Alternative 4
z
z
z
z
z
z
z
Ruggles to Cambridge
Allston Branch
Alternative 4A
z
Alternative 3A-1
Alternative 3A-2
z
LMA Tunnel (Ruggles - Yawkey)
z
Stage 2
z
z
LMA Tunnel (Ruggles - Yawkey)
Alternative 3A-3
z
z
LMA Tunnel (Ruggles - Yawkey)
Stage 3
Hybrid 2(T) - "Tight Turn"
LMA Tunnel (Ruggles - Park Drive)
Hybrid 2(T) - "Wide Turn"
LMA Tunnel (Ruggles - Park Drive)
z
z
z
z
z
Ruggles to Cambridge (& Kendall Sq)
Allston Branch
Total Estimated
Cost
* length of tunnel is approximate and includes portal structures and underground stations
Note 1 – Columns in the above table refer to the underground stations associated with each alternative.
Note 2 – Total costs are preliminary in 2007 dollars including contingency and soft costs.
Table 4.4: Preliminary Estimate of Capital Cost for Tunnel Alternatives
The costs Presented here are for comparison purposes only. Further cost estimates have been prepared in
more detail for the LPA and reflect a more detailed level of engineering analysis. These cost estimates are
presented in the RDEIR/DEIS.
4-27
232551/01/G - November, 2008/4-27 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
The station costs in Table 4.4 are for Urban Ring Phase 2 BRT stations only. If the stations were to be
built to accommodate Phase 3 rail transit during construction of Phase 2, then each station cost for each
alternative would need to increase by approximately $22 million for light rail or $51 million for heavy
rail. Additional construction of underground works that would enable connection of a future Phase 3
tunnel into the proposed Phase 2 tunnel would add between $20 to $96 million, depending on the
alternative and the final configuration of the Phase 3 alignment.
The number of rail-ready facilities (e.g. embedded rail, stray current protection, utilities, etc.) that are
provided within the bus tunnel has not be established. These items, if included, will add cost during
Phase 2 for a potential future rail conversion.
4-28
232551/01/G - November, 2008/4-28 of 28
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
5
Hatch Mott MacDonald
Earth Tech, Inc.
Current Locally Preferred Alternative for Busway Tunnel
The current Locally Preferred Alternative (LPA) for the busway tunnel is based on the Alternative H2(T)
alignment options. The following features from the Alternative H2(T) alignment options form part of the
LPA busway tunnel:
•
The east portal location and configuration at Leon Street within the MBTA ROW;
•
The alignment of the tunnel from the east portal at Leon Street to the proposed underground
station beneath Longwood Avenue (following the alignment of Huntington Avenue);
•
The location of the proposed underground station beneath Longwood Avenue in the vicinity of
Avenue Louis Pasteur;
•
The location of the west portal adjacent to the Landmark Center and the Green Line “D” Branch
within the abandoned CSX ROW; and
•
The inclusion of an underground BRT station as part of the west portal structure adjacent to the
Green Line “D” Branch to provide better connectivity with existing Green Line stations.
There are currently three different options for the section of busway tunnel alignment between Longwood
Avenue and the west portal, presented earlier in this report as Alternative H2(T) – “Tight Turn”,
Alternative H2(T) – “Wide Turn”, and the Longwood Avenue Alignment, herein these options are
referred to as eastern, central and western, respectively.
A summary of the lengths of running tunnel for each alignment alternative and the length of tunnel that
would need to be abandoned on conversion to Phase 3 rail transit is presented in Table 5.1. The LPA
busway tunnel including the western, central, and eastern alignment options is presented in Figure 5.1.
Length of Running Tunnel (feet)
Alignment
Alternative
Constructed in Phase 2
Minimum Horizontal
Radius of Running Tunnel
Abandoned on Conversion
to Phase 3 Rail
(feet)
Western
6,293
2,710
700
Central
5,710
1,630
700
Eastern
5,895
765 (light rail)
150
2,545 (heavy rail)
Table 5.1: Summary of LPA Tunnel Lengths
5-1
232551/01/G - November, 2008/5-1 of 4
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Eastern
Alignment
Central
Alignment
Western
Alignment
Figure 5.1: LPA Busway Tunnel
Advantages and disadvantages of the three alignment alternatives are summarized below.
Western Alignment
Advantages:
•
Maintains full flexibility in Phase 3 alignments;
•
Increases use of Public ROW and minimizes impacts to private properties;
•
Avoids interface with Shapiro Center building foundations at the corner of Longwood Avenue
and Brookline Avenue; and
•
The minimum radius horizontal curve is 700-ft allowing flexibility in the choice of construction
method, ensuring compatibility with Phase 3 heavy rail, and potentially eliminating speed
restrictions for BRT operation.
Disadvantages:
•
The Phase 3 turnout structure will impact utilities and disrupt traffic as it will be located in the
street;
•
Potential foundation conflict with 375 Longwood Avenue for construction of Phase 3;
•
Increased length of tunnel to be constructed during Phase 2; and
5-2
232551/01/G - November, 2008/5-2 of 4
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
•
Hatch Mott MacDonald
Earth Tech, Inc.
Increased length of abandoned tunnel on conversion to Phase 3.
Central Alignment
Advantages:
•
Maintains full flexibility in Phase 3 alignments with minimized length of tunnel constructed
during Phase 2 and minimized length of tunnel abandoned during Phase 3 conversion;
•
The turnout is not located within the street therefore minimizing disruption to traffic and
reducing potential for utility diversions; and
•
The minimum radius horizontal curve is 700-ft allowing flexibility in the choice of construction
method, ensuring compatibility with Phase 3 heavy rail, and potentially eliminating speed
restrictions for BRT operation.
Disadvantages:
•
Passes directly beneath the Winsor School and will require close coordination with any
development proposals that the Winsor School may propose; and
•
Interfaces with Shapiro Center building foundations at intersection of Longwood Avenue and
Brookline Avenue.
Eastern Alignment
Advantages:
•
Increases use of Public ROW and minimizes impacts to private properties; and
•
Minimizes length of abandoned tunnel on conversion to Phase 3 heavy rail, but only if Phase 3 is
to be light rail.
Disadvantages:
•
The minimum radius horizontal curve is 150-ft, placing more restrictions on the choice of
construction methods, potentially reducing flexibility in terms of Phase 3 conversion, and
potentially requiring speed restrictions to allow safe operation of the BRT service;
•
Interface with Muddy River Restoration project structures;
•
Interface with Shapiro Center building foundations at intersection of Longwood Avenue and
Brookline Avenue;
•
Construction of a turnout structure at the intersection of Brookline Avenue and the Fenway will
be challenging regardless of the construction method employed. Cut and cover methods will
cause major surface disruption in close proximity, and possibly within, the environmentally
sensitive Fenway and Emerald Necklace. Use of the SEM would require major ground
improvement given the size and geometry of the structure. Such ground improvement methods
would almost certainly require surface disruption; and
•
Shallow ground cover to the Muddy River at the portal approach may require additional ground
improvement.
5-3
232551/01/G - November, 2008/5-3 of 4
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
Preliminary plan and profile drawings of the LPA busway tunnel are presented in Attachment D. The final
selection of an alignment (western, central, or eastern) for the LPA busway tunnel will depend on more
detailed geotechnical information and site investigations, assessment of construction methodologies, costs,
environmental impacts and more detailed engineering analyses that will be undertaken during preliminary
engineering.
Estimates of the number of trucks required to deliver and remove bulk materials to and from site during
construction of the LPA busway tunnel are presented as histograms in Attachment D, with the option to
use rail during construction at the Landmark Center portal resulting in an additional set of histograms. The
histograms are intended to provide an order of magnitude estimate commensurate with the current stage of
the planning process, and are therefore calculated relative to the central alignment only. These estimates
will need to be refined once the alignment is fully defined and preliminary engineering studies have been
progressed. The use of rail transport and the identification of potential truck haul routes will require
further study and coordination with the relevant authorities and agencies during subsequent stages of the
planning process.
5-4
232551/01/G - November, 2008/5-4 of 4
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
6
Hatch Mott MacDonald
Earth Tech, Inc.
Conclusions and Recommendations for Further Work
A broad range of busway tunnel alignment alternatives have been developed. Consultation with key
stakeholders, in combination with assessment of key issues including: costs; ridership; and environmental
impacts, has resulted in additional development of more promising alignment alternatives and ultimately,
a recommendation for a LPA for the busway tunnel. The LPA for the busway tunnel still includes some
flexibility in terms of the alignment of the tunnel, but provides a well defined extent of the tunnel, location
of tunnel portal structures and location of underground stations. The following list provides a basis for
further work on the busway tunnel:
•
Continue to pursue relevant organizations for existing geotechnical data;
•
Continue to pursue relevant organizations for foundation information;
•
Conduct project specific geotechnical investigations;
•
Gather additional information on major and strategic public and private utilities along the
corridor and develop utility relocation plans;
•
Once further geotechnical and utility information is available, perform a detailed evaluation of
construction methodologies for the entire length of the LPA busway tunnel with respect to:
-
Costs;
-
Environmental impacts;
-
Geotechnical conditions;
-
Noise and vibration;
-
Schedule;
-
Settlements;
-
Structure function;
-
Surface disruption; and
-
Utilities.
•
Perform detailed site survey of critical locations (e.g. corridor between Landmark Center and
Green Line “D” Branch) to confirm site geometry and clearances;
•
Advance engineering study of portal adjacent to Landmark Center to confirm impacts on
abutters and extent of protective measures required (e.g. Landmark Center, Green Line
infrastructure, Park Drive bridge, 440 Park Drive, etc);
•
Assess impacts on Green Line operations and measures required to ensure continuing operation
during construction in coordination with MBTA;
•
Perform preliminary settlement and building response assessments for preferred route options
and refine construction methodology as required;
•
Obtain latest guidance from MBTA to confirm assumptions regarding Phase 3 rail criteria (e.g.
platform lengths etc);
•
Obtain information from MBTA on the Silver Line Phase 2 project (constructed) and the
proposed Silver Line Phase 3 project (in planning);
6-1
232551/01/G - November, 2008/6-1 of 2
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Hatch Mott MacDonald
Earth Tech, Inc.
•
Perform more detailed and site-specific station planning to verify the accommodation and layout
of mechanical and electrical equipment rooms, access, egress, etc.;
•
Re-assess the BRT vehicle envelope requirements and examine the possibility of reducing the
tunnel size;
•
Assess output from noise and vibration studies to determine whether mitigation is required or if
alternative alignments should be investigated;
•
Finalize ridership projections and calculate cost-effectiveness measures for all alternatives.
6-2
232551/01/G - November, 2008/6-2 of 2
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Attachment A
Hatch Mott MacDonald
Earth Tech, Inc.
Typical Station Layout
A-1
232551/01/G - November, 2008/A-1 of 1
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Attachment B
Hatch Mott MacDonald
Earth Tech, Inc.
Tunneled Alignment Alternatives
B-1
232551/01/G - November, 2008/B-1 of 4
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
B.1
Hatch Mott MacDonald
Earth Tech, Inc.
Alternatives Development Stage 1
Alternatives:
3, 3A, 3B, 3C, 4, and 4A
B-2
232551/01/G - November, 2008/B-2 of 4
Urban Ring Phase 2
Me df or d
RDEIR/DEIS
Ev e re tt
So merv i lle
Chel sea
Ea st
Bo st o n
Ca mbri dg e
Br o ok lin e
So uth B o sto n
Ro xb ury
Proposed Alignment
Do rch est er
Mixed Traffic
Buslane
Busway (Surface)
Busway (Tunnel)
Proposed Stop
Tunnel Portal
Alternative 3
May 14, 2007
Urban Ring Phase 2
Me df or d
RDEIR/DEIS
Ev e re tt
So merv i lle
Chel sea
Ea st
Bo st o n
Ca mbri dg e
Br o ok lin e
So uth B o sto n
Ro xb ury
Proposed Alignment
Do rch est er
Mixed Traffic
Buslane
Busway (Surface)
Busway (Tunnel)
Proposed Stop
Tunnel Portal
Alternative 3A
May 14, 2007
Urban Ring Phase 2
Me df or d
RDEIR/DEIS
Ev e re tt
So merv i lle
Chel sea
Ea st
Bo st o n
Ca mbri dg e
Br o ok lin e
So uth B o sto n
Ro xb ury
Proposed Alignment
Do rch est er
Mixed Traffic
Buslane
Busway (Surface)
Busway (Tunnel)
Proposed Stop
Tunnel Portal
Alternative 3B
May 14, 2007
Urban Ring Phase 2
Me df or d
RDEIR/DEIS
Ev e re tt
So merv i lle
Chel sea
Ea st
Bo st o n
Ca mbri dg e
Br o ok lin e
So uth B o sto n
Ro xb ury
Proposed Alignment
Do rch est er
Mixed Traffic
Buslane
Busway (Surface)
Busway (Tunnel)
Proposed Stop
Tunnel Portal
Alternative 3C
May 14, 2007
Urban Ring Phase 2
Me df or d
RDEIR/DEIS
Ev e re tt
So merv i lle
Chel sea
Ea st
Bo st o n
Ca mbri dg e
Br o ok lin e
So uth B o sto n
Ro xb ury
Proposed Alignment
Do rch est er
Mixed Traffic
Buslane
Busway (Surface)
Busway (Tunnel)
Proposed Stop
Tunnel Portal
Alternative 4
May 14, 2007
Urban Ring Phase 2
Me df or d
RDEIR/DEIS
Ev e re tt
So merv i lle
Chel sea
Ea st
Bo st o n
Ca mbri dg e
Br o ok lin e
So uth B o sto n
Ro xb ury
Proposed Alignment
Do rch est er
Mixed Traffic
Buslane
Busway (Surface)
Busway (Tunnel)
Proposed Stop
Tunnel Portal
Alternative 4A
May 14, 2007
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
B.2
Hatch Mott MacDonald
Earth Tech, Inc.
Alternatives Development Stage 2
Alternatives:
3A-1, 3A-2, 3A-3
B-3
232551/01/G - November, 2008/B-3 of 4
SY
ST
AR
UN
DE
MU
N
ST
M
IN
L
ER
SO
N
ST
BURLINGT
YA
W
ST
KE
Y
LIC A
L LE Y
HE
EP
YT
WA
ER
OP
E
ON AVE
PL
NA
VE
RA
ING
TO
CK
H
ON
HU
AV
E
PL
YT
H
GT
IN
NT
WA
Y
O
N
WA
Y
y
dd
BU
Mu
GRE ENLEAF ST
CO
L UM
ER
RY
ST
Bay
QU
E
EN
SB
Fens
Ruggles
Station
KD
R
N
NW
AY
H
UT
O
MUSEUM RD
3A & 3A-1
ST
NM
DR
ON
M
O
RK
LE
O
CT
PA
BILLS CT
NE
TO
ST
N
FENW AY C O
R
LD
ST
FIE
ST
ST
ST
3B
O
AC
BE
H
TAVER N RD
RL
TO
N
H
RS
CT
FE
CA
YT
YL
BO
RWA
Y
PA
R
ST
UT
Back
RIVE
R
ED
AM
N
N
O
FO
YT
PARKER ST
U
NM
RS
FENCT ST
RS
ST
B
R O
O S
O TO
K
L N
IN
E
M
O
R
ST
FO
D
B
FO
SA
VE
ST
D
IC
K
NO
M
ED
SA
IN
T
SW
AR
FI
EL
AR
KE
ST
CT
YS
ST
M
IVY
ST
PE
BE
D
EY
HU
DR
RS
Ri
TE
O
ME
JE
EA
TO N ST
SP
FULLER
ver
ST
NT
ST
H
UG
EN
RO
DE
O
ER
N
ST
ST
KI
LM
RUGGL ES ST
Existing MBTA Stops
Tugo Station
DRAFT
T
TS
ON
EM
TR
Urban Ring Phase 2
225
450
Feet
Data supplied by MassGIS and LMA.
TS
ON
EM
RDEIR/DEIS
Fenway - LMA
1:5,400
0
TR
MCG REE VEY WAY
T
PRENTI SS ST
LONGWOOD AVE
Tunnel Alignment
Surface Alignment
Proposed Station
WARD ST
Huntington Ave.
Station
O ST
LE
CIRC
KFAN
BINNEY
ST
IN E AVE
BROO KL
PILG RIM RD
ST
AUTUMN
Brookline Ave. Station
BLAC
CO
LC
ST
ST
ER ST
NT
L PHONSU S ST
KE
Common
to All
SAINT A
3A-2
3A
HALLECK ST
HE
ST
ER
BE
ST
EC
VANCOUV
3A-1
MI NDOR
C H AP
TETLOW ST
H
RD
ST
I ER
EDGAR ST
ANNUNCIATIO N RD
EL ST
ST
AM
AT
H
CH
SHORT
PUBLIC ALLEY 1001
RD
PILGRIM
ST
EVA NS WAY
HA
W
ES
ES
ST
EVA NS WAY
D
PAL ACE RD
Map Document: (M:\work\UrbanRing\maps\Tunnels_June26.mxd)
11/6/2007 -- 10:56:57 AM
AN
TT
ST
RL
AVE LOUI S PASTEUR
3A-3
HA
W
WH
I
VANCOUVER
PL
LOUIS PRANG ST
BO
8 22
ST
ST
AC
NA
H
OUG
ST
EN
H EM
W
AY
ST
UN
R
SBO
PU B
N
SS
Yawkey/
Kenmore
Station
8 10
EY
D
AB
N
S TO
ST
GA IN
HEME NWAY
EU
DR
D
RB
ME
AN
OV ERLAND
L
SW
EL
NA
TL
NE
M
AI
ST
E
RD
AL L
ST
T ST
FO R
NPIK
Z
SI
VA
N
TU R
ST
T
TTS
BU
UN
11
EY 8
A LL
N
MO U
U SE
AS
LIC
8 07
ST
C
AC H
PU B
EY
YS
SA
MAS
HUS
R
S TU
E TT
S
MAS
E
NPIK
RD
AL L
ST
AG
LIC
ITT
NY
PU B
ST
AR
TM
BB
HO
ON
SAIN
BA
MP
LP H ST
H
OT O
IC
TB
W
SA
IN
IP
S
IN
T
AVE
L IC
N
LTH
GT
O
MM
CO
A
WE
SA
AVE
P UB
TH
EAL
IN
MM
NW
CU
O
MM
CO
Tunnel Alternatives
June 27, 2007
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
B.3
Hatch Mott MacDonald
Earth Tech, Inc.
Alternatives Development Stage 3
Alternatives:
H2(T) – “Tight Turn” and H2(T) – “Wide Turn”
B-4
232551/01/G - November, 2008/B-4 of 4
SY
ST
UN
DE
MU
N
ST
ER
SO
N
ST
BURLINGT
YA
W
ST
KE
Y
RK
N
HE
EP
ING
NT
HU
GT
IN
SA
VE
BU
CO
L UM
WH
I
ST
ER
ST
ST
CO
LC
T
TS
ON
EM
ER ST
HE
I ER
TR
TETLOW ST
H
TT
EDGAR ST
ANNUNCIATIO N RD
EVA NS WAY
RD
PILGRIM
PUBLIC ALLEY 1001
PL
ES
EL ST
NT
RUGGL ES ST
LOUIS PRANG ST
HA
W
C H AP
HU
MUSEUM RD
Tugo Station
DRAFT
Proposed Station
Hybrid 2(T) Tunnel Alignment October 4, 2007
Existing MBTA Stops
Phase 3 Potential Alignments
1:5,400
0
225
450
Feet
Data supplied by MassGIS and LMA.
TS
ON
EM
TR
O ST
MI NDOR
MCG REE VEY WAY
LONGWOOD AVE
T
PRENTI SS ST
HALLECK ST
LE
CIRC
KFAN
BLAC
BINNEY
ST
BROO KL
PILG RIM RD
ST
WARD ST
L PHONSU S ST
AUTUMN
Hybrid 2(T) Tunnel
Alignment
SAINT A
IN E AVE
PAL ACE RD
ST
ON
R
EA
y
dd
DR
ST
Potential Future
Turnout for Phase 3
NT
AV
E
PL
ST
RY
ER
SB
H
UT
O
NM
M
O
PA
ST
O
CT
TO
ON
NE
R
LE
RD
GRE ENLEAF ST
BILLS CT
EC
WA
Y
VANCOUV
BE
H
ST
ST
WA
Y
LD
AM
YT
ST
AT
H
H
RS
VANCOUVER
SHORT
ST
Ruggles
Station
EVA NS WAY
ST
CH
FO
YT
NW
AY
ST
ST
H
Fens
Hybrid 2(T) Tight Turn
Tunnel Alignment
ES
YT
KD
R
AVE LOUI S PASTEUR
Map Document: (M:\work\UrbanRing\maps\Tunnel_H2T_Oct07.mxd)
10/29/2007 -- 5:18:51 PM
8 22
PL
FIE
ST
Bay
EN
N
O
AC
BE
Back
N
FENW AY C O
HA
W
RS
TAVER N RD
RL
TO
N
RS
CT
FE
CA
KE
L LE Y
FENCT ST
QU
E
RIVE
H
ST
Potential Future
Turnout for Phase 3
ST
UT
Ri
TE
ST
N
O
ST
YL
BO
RWA
Y
D
R
ED
AM
N
N
O
CK
Phase 3
via Kenmore
PA
R
FO
PARKER ST
U
NM
NO
FO
B
R O
O S
O TO
K
L N
IN
E
M
O
AR
D
ST
M
ED
SA
IC
K
ST
FI
EL
SW
IN
T
M
AR
KE
ST
CT
YS
ST
EY
PE
BE
D
RS
Mu
DR
JE
SP
TO N ST
ver
FULLER
Hybrid 2(T) Wide Turn
Tunnel Alignment
D
RA
ST
H
UG
ST
RO
EN
O
DE
O
ME
B
AN
ER
OP
E
RB
ER
N
ST
ST
IVY
RL
YT
WA
ON AVE
KI
LM
BO
LIC A
ST
ST
AC
NA
H
OUG
ST
EN
H EM
W
AY
ST
UN
R
SBO
PU B
ST
Yawkey/
Kenmore
Station
SS
ST
ST
NE
D
OV ERLAND
L
AB
N
S TO
AN
GA IN
8 10
EY
TO
D
TL
VA
N
M
AI
RD
HEME NWAY
EU
DR
AR
E
M
IN
L
ME
NPIK
Phase 3
via Park Dr.
SW
EL
NA
TU R
Z
SI
AL L
NA
VE
ST
T
TTS
T ST
FO R
BU
UN
11
EY 8
A LL
N
MO U
U SE
AS
LIC
8 07
ST
C
AC H
PU B
EY
YS
SA
MAS
HUS
R
S TU
E TT
S
MAS
E
NPIK
RD
AL L
ST
AG
LIC
ITT
NY
PU B
ST
AR
TM
BB
HO
ON
SAIN
BA
MP
LP H ST
H
OT O
IC
TB
W
SA
IN
IP
S
IN
T
AVE
L IC
N
LTH
GT
O
MM
CO
A
WE
SA
AVE
P UB
TH
EAL
IN
MM
NW
CU
O
MM
CO
Urban Ring Phase 2
RDEIR/DEIS
Fenway - LMA
October 4, 2007 Hybrid 2(T) Tunnel
Alignment Developed by
Hatch, Mott, MacDonald
November 6, 2007
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Attachment C
Hatch Mott MacDonald
Earth Tech, Inc.
Alternative H2(T) Sub-options Memorandum
C-1
232551/01/G - November, 2008/C-1 of 1
M E M O
Date:
October 7, 2008
To:
Ned Codd, P.E. Project Manager, EOTPW
From:
James A. Doyle, AICP, Project Manager
Earth Tech AECOM
CC:
Jeff Maxtutis, AICP
David Watson, HMM
File
Subject:
Urban Ring Phase 2 RDEIR/DEIS
Review and Comparison of LPA Tunnel Options
Introduction
The Urban Ring Phase 2 RDEIR/DEIS planning process developed a Locally Preferred Alternative (LPA)
established in early 2008. The planning process has recommended a tunnel segment as part of the LPA,
and that tunnel is included in the current review draft of the environmental document. The current LPA
tunnel comprises a busway tunnel approximately 1.5 miles in length extending from a portal on the east
adjacent to Ruggles Station and a portal on the west adjacent to the Landmark Center, with one
underground station in the Longwood Medical Area. Connections with the Green Line occur at Kenmore
Square where the Green Line B, C, and D Lines can be reached at a single station directly served by at
least one of the three Urban Ring BRT routes planned in this area. The Landmark Portal Option has the
BRT7 route serving Kenmore Square directly, while the other two routes (BRT5 and BRT6) would rely
on walk connection from Yawkey to reach Kenmore Square. All three routes serve Yawkey station
directly.
Most CAC members, stakeholders, and members of the public have been generally supportive of the
proposed LPA tunnel, though some parties have raised concerns about its connections with the Green
Line via Yawkey and Kenmore Square due to walk distances, routing complexity, and congestion in the
Kenmore Square roadway network and bus terminal. In response to these concerns, the project team has
explored a number of options for modifying or extending the west end of the LPA tunnel and moving or
adding stations to improve Green Line connectivity and overall service. This memorandum reviews the
engineering feasibility for different tunnel options, and evaluates three new options relative to key
measures of engineering feasibility, Green Line connectivity, commuter rail connectivity, ridership, cost,
and compatibility with Phase 3.
Summary Descriptions
The following is a summary of the three new tunnel options that have been evaluated in detail. These are
the “Landmark Portal with Fenway Station Option,” the “Mountfort Street Split Portal Option,” and “BU
Bridge Portal Option,” each of which has different portal and station characteristics at its northwestern
end.
Memo – October 7, 2008
Evaluation of Tunnel Options
Page 2
The Landmark Portal with Fenway Station Option is a modified version of the current LPA that would
retain the same tunnel alignment as the LPA and would provide an underground additional station. The
new underground station would be located near the western portal, at the Landmark Center adjacent to the
Green Line D Fenway Station. This would require extending the portal slightly northward beneath Miner
Street. In this option service at Yawkey would be the same as in the current LPA with all three routes
serving Yawkey station directly for connection with commuter rail. Direct connection with the Green
Line D Branch would occur at the Fenway Station, and connection with the Green Line C Branch would
be via walk connection to St. Mary’s Station. Green Line B Branch connection would be at the BU
Central Station on Commonwealth Avenue as in the current LPA. The BRT7 in this option would
terminate at Yawkey rather than at Kenmore Square.
The Mountfort Street Split Portal Option would realign the tunnel beneath Park Drive and extend it to the
Mountfort Street corridor. This option would have one additional underground station, which would be
located beneath Park Drive, roughly between Beacon Street and the Green Line D Branch. This station
would have headhouse access from the C Branch at Beacon Street (near St. Mary’s Station) and the D
Branch at Fenway Station. It would surface in Mountfort Street in a split portal configuration, with a
westbound portal surfacing just west of St. Mary’s Street and the eastbound portal surfacing just west of
Carlton Street.
The BU Bridge Portal Option would significantly extend the tunnel alignment and would add two new
underground stations. It would extend the tunnel beneath Park Drive and the Massachusetts Turnpike,
and portal near the BU Bridge. One new underground station would be located beneath Park Drive
between the Fenway D Branch station and Beacon Street (a short walk to the St. Mary’s C Branch
station); the other new underground station would be beneath Commonwealth Avenue near the BU
Central B Branch Station. This option would bypass Kenmore Station (providing a more direct
alignment); it would also bypass Yawkey Station (eliminating the direct connection to the
Framingham/Worcester commuter rail, which would become a walk connection from the new
underground Park Drive Station).
Engineering Feasibility
Over the course of the RDEIR/DEIS planning process, the project team has reviewed a wide range of
different tunnel alignments, station locations, and portal configurations, including six of the nine Build
Alternatives. A key element of the tunnel alternatives evaluation has been a review of engineering
feasibility, from the perspective of constructability as well as basic physical configuration. The following
is a summary of the engineering feasibility of the three options under study.
Landmark Portal with Fenway Station Option
This option would modify the LPA by extending the proposed portal structure at the Landmark Center to
include a shallow underground BRT station parallel to the Green Line “D” Branch. The portal structure
would be extended to meet with the re-alignment of Maitland Street proposed by Meredith Management
as part of the Parcel 7 Air Rights development proposals. This option is shown in Figure 1.
The following are principal issues with this option:
•
The available corridor width adjacent to the Landmark Center is relatively narrow, constrained by
the Landmark Center to the south and the Green Line “D” Branch incline to the north.
Construction of a station in this area would require the station walls to be located very close to
both abutting structures. As a result, additional ground treatment and support measures may be
required to enable construction.
Memo – October 7, 2008
Evaluation of Tunnel Options
•
•
•
•
•
Page 3
This option would entail construction impacts, ventilation structures, and station access at the D
Branch Fenway Station.
The relatively narrow corridor between the Landmark Center and the Green Line “D” Branch
requires that the station platforms be staggered through this area to minimize the width of the
station structure.
A pump house associated with the Green Line portal in the vicinity of Miner Street would need to
be relocated. This may have temporary impacts on the parking lot at this site.
The gradient through the portal structure will be less than the maximum allowable gradient and
would tie in with the surface grading plans proposed by Meredith Management as part of the
Parcel 7 Air Rights development.
The BRT route in this option would avoid the need to cross Miner Street at grade. The portal
structure would prevent future surface roadway connection between existing Munson Street and
Burlington Street.
Recommendation: With appropriate planning and construction staging, the engineering and construction
issues of this option could be managed. Retain for further analysis and comparison to LPA.
Mountfort Street Split Portal
This option is based on a proposals submitted to EOT by Harvard University. This option would require a
realignment of the LPA tunnel to align with Pilgrim Road. The tunnel would follow the alignment of
Pilgrim Road, making a turn to the west to pass beneath Park Drive and the Green Line D and C
Branches. An underground BRT station would be constructed beneath Park Drive between the C Branch
at Beacon Street and the Green Line D Branch with headhouses located to the north end (south side of
Audubon Circle) and south end (immediately south of Fenway Station). The tunnel alignment would then
continue north beneath Park Drive, making a turn to the west beneath Mountfort Street where a split
portal arrangement would bring the northbound and southbound tunnel lanes up to existing grade in
separate structures. This option is shown in Figure 2.
The routing of the BRT service would be modified from the LPA to include the additional length of
tunnel and underground station. In addition, further surface routing modifications would be required to
incorporate northbound BRT service over Carlton Street with a surface station over the Mass Turnpike,
and southbound BRT service along Mountfort Street with a surface station to the south of Commonwealth
Avenue.
Construction of the portal structures and connecting tunnels would take place within Mountfort Street.
The crossing beneath St Mary's Street would be relatively shallow as the alignment is just inside the
portal at this location. This may conflict with the foundations of the St Mary's Street bridge, requiring
protective works to the bridge or possibly re-construction. Construction work would also need to
accommodate the topography to the north of Mountfort Street, including a steep drop to the Commuter
Rail line, and maintenance and protection of traffic along Mountfort Street, Carlton Street, and St Mary’s
Street.
If an additional station were to be constructed on the “C” Branch to allow a direct vertical connection
with the Urban Ring, the construction would likely cause major disruption to Audubon Circle. In any
case, Proximity of the proposed tunnel portals in this option to the existing Commuter Rail line may offer
opportunities for the removal of excavated material and supply of materials during construction.
However, the narrow, constrained alignment of Mountfort Street and the adjacent historic residential
neighborhood of Cottage Farm would pose challenges to a tunnel servicing operation.
Memo – October 7, 2008
Evaluation of Tunnel Options
Page 4
The following are principal issues with this option:
•
•
•
•
•
•
•
•
•
•
The southbound portal would be inaccessible from the future southbound BRT route that uses the
BU Academy and University Road alignment; this would necessitate Urban Ring use of the BU
Bridge for crossing the Charles River, or the so-called “slip ramp” option to connect from the
Grand Junction Railroad up to Commonwealth Avenue west of the BU Bridge.
The proposed portal structures would occupy a significant portion of Mountfort Street’s width.
Mountfort Street currently accommodates four narrow lanes in approximately 40-45 feet; each of
the two proposed portal structures would occupy at least 20 feet, which would reduce Mountfort
Street to 20-25 feet. This means that if Mountfort Street were to remain in its current alignment, it
would be reduced to one lane in each direction between St. Mary’s Street and Essex Street.
Furthermore, these lanes would be offset from each other by approximately 20 feet in the vicinity
of Carlton Street (due to the fact that the eastbound portal is along the south side of the street and
the westbound portal is along the north side of the street). This would either result in significant
roadway design and traffic operations impacts or else it would require a major reconstruction and
widening of Mountfort Street.
Construction of the Urban Ring tunnel in this option between the Green Line C Branch tunnel and
the D Branch would likely require additional ground treatment and protective works.
This option would entail construction impacts, ventilation structures, and station access at
Audubon Circle, as well as at the D Branch Fenway Station.
The proximity of the proposed tunnel portals in this option to the existing Commuter Rail line
may offer opportunities for the removal of excavated material and supply of materials during
construction. However, the narrow, constrained alignment of Mountfort Street and the adjacent
historic residential neighborhood of Cottage Farm would pose challenges to locating and
operating construction laydown and removal of tunnel excavate.
The portal structures are inconsistent with any future re-alignment of Mountfort Street, such as
the one proposed by Boston University.
The portal structures would have permanent impacts and construction phase impacts on the
historic Cottage Farm neighborhood.
The proposed tunnel alignment would eliminate the direct BRT connection with the Framingham/
Worcester commuter rail line at Yawkey Station.
The station platform shown on Mountfort Street is very close to the intersection and is also on a
curve. The location of this station platform is limited by the gradient required to enter the tunnel.
This option reduces the utility of tunnel alignments for Urban Ring Phase 3. A large portion of
the tunnel would be inconsistent with a Phase 3 alignment through Kenmore Square because it
passes beneath Park Drive toward the BU Bridge/Allston. In addition, a large portion of the
tunnel would be inconsistent with a Phase 3 alignment toward the BU Bridge/Allston because it
ascends to portal in Mountfort Street, while a Phase 3 tunnel would need to descend to pass
beneath the Mass Turnpike.
In summary, the engineering, construction, and compatibility issues with municipal and institutional plans
seriously impact the feasibility of this option. For this reason, this option should not be pursued in its
current configuration. Instead, this option was modified to achieve the objectives of the proposal in a
feasible configuration that would extend the tunnel to the BU Bridge; this is described below as the BU
Bridge Portal Option.
Recommendation: Design challenges, construction issues, traffic impacts, and abutter impacts of this
option are very high. Do not pursue, reconfigure to pass beneath the Mass Turnpike and portal at the BU
Bridge.
Memo – October 7, 2008
Evaluation of Tunnel Options
Page 5
BU Bridge Portal Option
This option is a reconfiguration of the Mountfort Street Split Portal Option. Instead of the tunnel
surfacing along Mountfort Street, it would stay at depth, pass beneath the Mass Turnpike and head toward
the BU Bridge where the alignment would connect with the Grand Junction Railroad (GJRR) through a
portal structure emerging from beneath the Boston University Bridge approach road. Two underground
stations would be provided, one beneath Park Drive (as in the option to extend the tunnel to Mountfort
Street) and one adjacent and to the north of the Mass Turnpike between St Mary’s Street and Carlton
Street. This option is shown in Figure 3.
The routing of the BRT service would be modified from the LPA to include the additional length of
tunnel and underground stations.
Construction of the underground station between Carlton Street and St Mary’s Street would be relatively
straightforward, but it relies on the BU buildings within the footprint being demolished as part of BU’s
institutional masterplanning. Construction of the portal beneath the BU Bridge approach road would
require careful phasing to ensure maintenance of traffic. The short length of tunnel between the portal and
the underground station between Carlton Street and St. Mary’s Street would like be constructed using the
sequential excavation method or by extending the cut and cover structures for the portal and station. The
following are some of the key issues related to the BU Bridge Portal Option:
•
•
•
•
•
•
As with the Mountfort Street Split Portal option, construction of the Urban Ring tunnel between
the Green Line C Branch tunnel and the D Branch would likely require additional ground
treatment and protective works.
This option would entail construction impacts, ventilation structures, and station access at
Audubon Circle, as well as at the D Branch Fenway Station.
As with the Mountfort Street Split Portal, this option also reduces the flexibility of tunnel
alignments for Urban Ring Phase 3.
The proximity of the proposed tunnel portal in this option to the Commuter Rail line and the
Grand Junction Rail Line and Beacon Park Rail Yard may offer opportunities for the removal of
excavated material and supply of materials during construction.
As with the Mountfort Street Split Portal option, the proposed tunnel alignment would eliminate
the direct BRT connection with the Framingham/ Worcester commuter rail line at Yawkey
Station.
Operationally, this route offers a direct connection with the GJRR busway bridge without
entering mixed traffic.
Recommendation: With appropriate planning and construction staging, the engineering and
construction issues of this option could be managed. Retain for further comparison to LPA and the
Landmark Portal with Fenway Station Option.
Performance
The benefits of the Landmark Portal with Fenway Station Option include a direct connection with the
Green Line D Branch and an improved walk distance to the Green Line C Branch St Mary’s Street Station
(500’ shorter than walking to the C Line at Kenmore). The Landmark Portal with Fenway Station Option
provides somewhat higher ridership than the Landmark Portal Option because of improved Green Line D
Branch and C Branch connections. It also eliminates the need for a connection into the congested
Kenmore Square bus terminal.
Memo – October 7, 2008
Evaluation of Tunnel Options
Page 6
The BU Bridge Portal Option also provides a direct connection with the Green Line D Branch, and does
so by providing a headhouse from the south end of its Park Drive underground station. The north end of
the same station can provide a headhouse at Audubon Circle with walk access to St. Mary’s station on the
C Branch. The BU Bridge Portal Option provides no station stop at Yawkey. It achieves a faster travel
time due to a combination of more direct routing and the higher speed of extending the busway tunnel.
Ridership is higher than the Landmark Portal with Fenway Station Option due primarily to the higher
travel speed. While the BU Bridge Portal Option provides better Green Line connectivity, it provides no
direct connection with commuter rail and requires a longer walk distance to reach Yawkey Station from
Audubon Circle.
Costs
The added capital cost of the different options compared to the current LPA is shown in the table below.
The BU Bridge Portal Option is significantly higher cost than the Landmark Portal Option or the
Landmark Portal with Fenway Station Option due to additional length of tunnel and underground stations.
Phase 3 Compatibility
The Landmark Portal with Fenway Station Option is same as the Landmark Portal Option: both could
accommodate either Kenmore or Park Drive Phase 3 alignment. The BU Bridge Portal Option would
only be consistent a Park Drive alignment for Phase 3, but would provide a longer tunnel for future
conversion to Phase 3 operation.
Table 1
Summary Comparison of LPA Tunnel Options with LPA
LPA
Landmark
Portal with
Fenway
Station Option
BU Bridge
Portal Option
Base
1
Same
2
2,080
3
1010’/3.8 min
1,640’/6.2 min
1,640’/6.2 min
1010’/3.8 min
1,150’/4.4 min
220’/0.8 min
790’/2.9 min
840’/3.2 min
220’/0.8 min
direct
direct
1270 ft/5 min
13 min
18 min
14 min
19 min
11 min
16 min
135,320
+5% (approx.)
+12% (approx.)
Capital Cost above LPA ($2007)
Base
$160 million
$683 million
Phase 3 Alignment Choices
Kenmore or
Park Drive
Kenmore or
Park Drive
Park Drive
Infrastructure
Added Tunnel Length (feet)
Underground Stations
Green Line Connectivity
B Branch (walk distance/time)
C Branch (walk distance/time)
D Branch (walk distance/time)
Commuter Rail Connectivity
Yawkey (walk distance/time)
Travel Time
LMA Station to Kendall Station
LMA Station to Harvard Square
Ridership 2030
BRT5, BRT6, BRT7 daily riders
Cost
Conclusions
The Landmark Portal with Fenway Station Option provides a significantly improved Green Line
connection, particularly for the D Branch, and provides increased ridership for a much lower incremental
Memo – October 7, 2008
Evaluation of Tunnel Options
Page 7
cost than the BU Bridge Portal Option. It preserves the options of either a Kenmore or Park Drive
alignment for Urban Ring Phase 3. However, the additional station stop does add to the travel time for
some trips.
By comparison, the BU Bridge Portal Option provides a further improvement to the Green Line
connectivity for the C Branch, while being essentially the same as the Landmark Portal Option and the
Landmark Portal with Fenway Station Option for Green Line D and B. It requires a longer walk distance
to the commuter rail at Yawkey Station compared to either the Landmark Portal Option or the Landmark
Portal with Fenway Station Option. The routing beneath Park Drive provides for more direct and faster
travel times for key O/D pairs compared to the Landmark Portal Option or the Landmark Portal with
Fenway Station Option, which route further east to reach Yawkey. However, the BU Bridge Portal Option
limits the Phase 3 alignment to Park Drive and presents a significant engineering and construction
challenge for tying in the relatively shallow profile of the Phase 2 west portal with a future Phase 3 tunnel
alignment under the Charles River.
Memo –October 7, 2008
Evaluation of LPA Tunnel Options
Figure 1
Landmark Portal with Fenway Station Option
Page 8
Memo – October 7, 2008
Evaluation of LPA Tunnel Options
Figure 2
Mountfort Street Split Portal Option
Page 9
Memo – October 7, 2008
Evaluation of LPA Tunnel Options
Figure 3
BU Bridge Portal Option
Page 10
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
Attachment D
Hatch Mott MacDonald
Earth Tech, Inc.
Current LPA Busway Tunnel
D-1
232551/01/G - November, 2008/D-1 of 3
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
D.1
Hatch Mott MacDonald
Earth Tech, Inc.
Preliminary Plan and Profile Drawings
Drawing Title
Sheet No.
Urban Ring Phase 2, Plan & Profile – Fenway, Boston
LMA Tunnel (Western), STA W-0+00 – STA W-16+50
Urban Ring Phase 2, Plan & Profile – Fenway, Boston
LMA Tunnel (Western), STA W-16+50 – STA W-31+36.5
Urban Ring Phase 2, Plan & Profile – Fenway, Boston
LMA Tunnel (Western), STA W-31+36.5 – STA W-45+17.8
Urban Ring Phase 2, Plan & Profile – Fenway, Boston
LMA Tunnel (Central), STA C-0+00 – STA C-16+50
Urban Ring Phase 2, Plan & Profile – Fenway, Boston
LMA Tunnel (Central), STA C-16+50 – STA C-26+50
Urban Ring Phase 2, Plan & Profile – Fenway, Boston
LMA Tunnel (Central), STA C-26+50 – STA C-39+30.9
Urban Ring Phase 2, Plan & Profile – Fenway, Boston
LMA Tunnel (Eastern), STA E-0+00 – STA E-15+34.2
Urban Ring Phase 2, Plan & Profile – Fenway, Boston
LMA Tunnel (Eastern), STA E-15+34.2 – STA E-23+84.8
Urban Ring Phase 2, Plan & Profile – Fenway, Boston
LMA Tunnel (Eastern), STA E-23+84.8 – STA E-41+15.8
Urban Ring Phase 2, Plan & Profile – Fenway, Boston
LMA Tunnel, STA 39+30.9 – STA 56+36.5
Urban Ring Phase 2, Plan & Profile – Fenway, Boston
LMA Tunnel, STA 56+36.5 – STA 72+01
Urban Ring Phase 2, Plan & Profile – Fenway, Boston
LMA Tunnel, STA 72+01 – STA 86+27
1T-W
D-2
232551/01/G - November, 2008/D-2 of 3
2T-W
3T-W
1T-C
2T-C
3T-C
1T-E
2T-E
3T-E
4T
5T
6T
Urban Ring Phase 2
Tunnel Alternatives
Summary Report for RDEIR/DEIS
D.2
Hatch Mott MacDonald
Earth Tech, Inc.
Estimate of Truck and Rail Car Numbers During Construction
The histograms that follow illustrate an order of magnitude estimate of the number of trucks and or rail
cars that would be required during construction. Individual histograms are presented for each construction
site, followed by histograms that present the total numbers of trucks and rail cars arising as a result of the
entire project.
The histograms are intended to provide an order of magnitude estimate commensurate with the current
stage of the planning process, and are therefore calculated relative to the central alignment only. These
estimates will need to be refined once the alignment is fully defined and preliminary engineering studies
have been progressed. The use of rail transport and the identification of potential truck haul routes will
require further study and coordination with the relevant authorities and agencies during subsequent stages
of the planning process.
D-3
232551/01/G - November, 2008/D-3 of 3
100
Rail car capacity - net weight (maximum)
tons per car
equiv. yd per car
3
rings per car
yd per car
3
yd per truck
3
tons per truck
rings per truck
3
equiv. yd per
truck
yd per truck
3
Unit
Theoretical insitu excavation volumes are multiplied by an assumed
bulking factor to give a bulked volume of excavated material for
removal from site.
Assumed working time is ten hour shifts, five days per week for
portal and station construction activities.
For tunneling works, the following is assumed:
o The tunnel will be constructed by a 42’-8” excavated
diameter earth pressure balance tunnel boring machine
(TBM).
o The tunnel lining is assumed to have an internal diameter of
39’-11”, a thickness of 1’-9” and a ring length of 6’-0”.
o Productivity assumed to be 30’ per day with two shifts per
day, five days per week. Weekends used for TBM
maintenance, extending TBM utilities etc.
Quantities are based on the portals being constructed using
permanent slurry walls. An additional 10% (insitu) volume of
overbreak has been assumed for the slurry wall excavation and
concreting works.
60.0
Rail car capacity - tunnel grout
Ready-mix Concrete Truck
70
8
Truck capacity - net weight (maximum)
1.0
34
Truck capacity - tunnel grout
Rail car capacity - segment rings
16
Truck capacity - segment rings
Rail car capacity - bulk materials
30
0.33
Truck capacity - bulk materials
1.3
Assumed
Quantity
Bulking factor
Item
ab
Values are based on average outputs over activity duration. Peak
values resulting from intense activities (e.g. concrete pours) or from
increased tunneling advance rates, which may be in excess of 100’
per day, are not reflected in this chart.
Values shown indicate the total number of trucks per day. Truck
movements (i.e. to and from site) would be twice the value shown.
The number of trucks is estimated and will vary depending on the
Contractor's means and methods.
Utility relocations and other associated works are not included in the
estimates of durations and quantities.
Excavated diameter of bored tunnel will depend on design of tunnel
boring machine and is subject to further refinements of the clearance
envelopes.
Notes:
A general allowance of four trucks per day, per construction site, has
been made to account for general site deliveries, including soil
conditioning, grease, and other supplies for TBM tunneling. It is
assumed that tunnel
The FHWA maximum gross weight limit on the Interstate system is
80,000 pounds. Tractor/trailer weight has been assumed to be
12,000 pounds resulting in a maximum useable load of 68,000
pounds (34 tons).
Urban Ring Phase 2 – LPA Tunnel
Estimated Number of Trucks/Rail Cars per Day
Assumptions and Notes
The following table lists some of the principal values and
assumptions made in preparing the truck/rail car histograms:
Assumptions:
July 28, 2008
0
20
40
60
80
100
120
M
th
on
3
M
th
on
6
M
th
on
9
M
th
on
12
M
th
on
15
M
th
on
18
M
th
on
21
M
th
on
24
M
th
on
27
M
th
on
M
th
on
Month
30
33
M
th
on
36
M
th
on
39
M
th
on
42
M
th
on
45
M
Urban Ring Phase 2 - LPA Tunnel
Estimated Number of Trucks per Day - Landmark Center Portal
Truck Only Option
See cover sheet for assumptions and notes
July 28, 2008
Number of Trucks per Day
th
on
48
M
th
on
51
M
th
on
54
M
th
on
57
M
th
on
60
ab
Number of Trucks per Day
M
M
M
th
on
9
M
th
on
12
M
th
on
15
M
th
on
18
M
th
on
21
M
th
on
24
M
th
on
27
M
th
on
30
M
th
on
33
M
th
on
36
M
th
on
39
M
th
on
42
M
th
on
45
M
th
on
48
M
th
on
51
M
th
on
54
Month
M
th
on
57
M
th
on
60
0
0
6
10
20
th
on
20
40
3
30
60
th
on
40
80
Rail Cars
Trucks
60
ab
50
See cover sheet for assumptions and notes
Urban Ring Phase 2 - LPA Tunnel
Estimated Number of Trucks and Rail Cars per Day - Landmark Center Portal
Truck and Rail Option
100
120
July 28, 2008
Number of Rail Cars per Day
0
20
40
60
80
100
120
M
th
on
3
M
th
on
6
M
th
on
9
M
th
on
12
M
th
on
15
M
th
on
18
M
th
on
21
M
th
on
24
M
th
on
27
M
th
on
M
th
on
Month
30
33
M
th
on
36
M
th
on
39
M
th
on
42
M
Urban Ring Phase 2 - LPA Tunnel
Estimated Number of Trucks per Day - LMA Station
See cover sheet for assumptions and notes
July 28, 2008
Number of Trucks per Day
th
on
45
M
th
on
48
M
th
on
51
M
th
on
54
M
th
on
57
M
th
on
60
ab
0
20
40
60
80
100
120
M
th
on
3
M
th
on
6
M
th
on
9
M
th
on
12
M
th
on
15
M
th
on
18
M
th
on
21
M
th
on
24
M
th
on
27
M
th
on
M
th
on
Month
30
33
M
th
on
36
M
th
on
39
M
th
on
42
M
th
on
45
Urban Ring Phase 2 - LPA Tunnel
Estimated Number of Trucks per Day - Leon Street Portal
See cover sheet for assumptions and notes
July 28, 2008
Number of Trucks per Day
M
th
on
48
M
th
on
51
M
th
on
54
M
th
on
57
M
th
on
60
ab
0
20
40
60
80
100
120
140
160
180
200
M
th
on
3
M
th
on
6
M
th
on
9
M
th
on
12
M
th
on
15
M
th
on
18
M
th
on
21
M
th
on
24
M
th
on
27
M
th
on
M
th
on
Month
30
33
M
th
on
36
M
th
on
39
M
th
on
42
Urban Ring Phase 2 - LPA Tunnel
Estimated Number of Trucks per Day - All Sites
Truck Only Option
See cover sheet for assumptions and notes
July 28, 2008
Number of Trucks per Day
M
th
on
45
M
th
on
48
M
th
on
51
M
th
on
54
M
th
on
57
M
th
on
60
Landmark Center Portal Site
LMA Station Site
Ruggles/Leon St Portal Site
ab
Number of Trucks per Day
M
th
on
M
th
on
6
M
th
on
9
M
th
on
12
M
th
on
15
M
th
on
18
M
th
on
21
M
th
on
24
M
th
on
27
M
th
on
30
M
th
on
33
M
th
on
36
M
th
on
39
M
th
on
42
M
th
on
45
th
on
M
th
on
M
th
on
M
th
on
M
th
on
Month
0
0
M
10
20
60
20
40
57
30
60
54
40
80
51
50
100
48
60
120
70
90
140
Rail Cars - Landmark Center Portal Site
Trucks - Landmark Center Portal Site
Trucks - LMA Station Site
Trucks - Ruggles/Leon St Portal Site
100
ab
80
3
See cover sheet for assumptions and notes
Urban Ring Phase 2 - LPA Tunnel
Estimated Number of Trucks and Rail Cars per Day - All Sites
Truck and Rail Option
160
180
200
July 28, 2008
Number of Rail Cars per Day