CITY OF COLUMBIA
INTER-OFFICE MEMORANDUM
TO:
Steven A. Gantt, Interim City Manager
FROM:
John David Spade, Director of Parking Services
DATE:
November 17, 2009
SUBJECT:
COUNCIL AGENDA ITEM:
Geotechnical Engineering Services for the New Downtown Garage
The site for the proposed New Downtown Parking Garage is at the northwest corner of
Taylor and Sumter Streets. Funding for this project will come from the 2005 Parking
Facilities Revenue Bond Issue (PG001101/PG001102). Attached is a Task Order to the
Master Service Agreement in the amount of $15,200.00 with Terracon, a geotechnical
firm located in the City of Columbia, to provide geotechnical engineering services for the
proposed parking deck. Construction Management has reviewed the attached Task Order
and we are recommending it be placed on City Council’s Agenda for approval.
This project is located in City Council District 2.
Recommend the City award the task order to Terracon in the amount not to exceed
$15,200.00.
Upon your approval, please forward for inclusion on the next available Council Agenda
Meeting.
October 7, 2009
Mr. John Spade
City of Columbia Parking Services
820 Washington St.
Columbia, SC 29201
Re:
Proposal for Geotechnical Engineering Services
Sumter Street Parking Garage
Sumter and Taylor Streets
Columbia, South Carolina
Terracon Proposal No. P73090279
Dear Mr. Spade:
Terracon Consultants Inc. (Terracon) appreciates the opportunity to submit this proposal for
geotechnical engineering services for the proposed parking garage project to be located at
Sumter and Taylor Streets in Columbia, South Carolina. The following sections of this
proposal outline our understanding of the project information, our recommended scope of
services, and a time and cost estimate for providing those services.
A. PROJECT INFORMATION
We understand from our conversation with and the information provided by Mr. Schutte of
LS3P that the City of Columbia is planning the construction of a parking garage on the
northwest corner of the Sumter Street/Taylor Street intersection in downtown Columbia,
South Carolina. The Scheme A approximate site dimensions are 213 feet by 150 feet,
covering about one-sixth of the City block. There is a potential that the site area will be
expanded to north by about 40 feet (Scheme B).
According to the provided information, the parking garage will be 5 to 7 levels high. It will be
a pre-cast concrete structure with a concrete slab-on-grade. The structure will be built atgrade with no below grade levels. The following loading estimates were provided by the
structural engineer.
Exterior Column Loads:
• 5 Elevated Levels = 800-900 kips
• 7 Elevated Levels = 1200-1300 kips
Interior Column Loads:
• 5 Elevated Levels = 1600-1800 kips
• 7 Elevated Levels = 2400-2600 kips
Terracon Consultants, Inc.
521 Clemson Rd.
Columbia, South Carolina 29229
P [803] 741 9000
F [803] 741 9900
terracon.com
Sumter Street Parking Garage
Terracon Proposal No. P73090279
October 7, 2009
TERRACON
The proposed site is currently a surface parking area. The surface topography is relatively
flat with elevations ranging from 307 feet to 308 feet.
From our review of the available data, we understand that there were buildings previously at
the site. The data indicates these typically smaller structures, a gas station, a house and the
like.
B. SCOPE OF SERVICES
General Discussion
From our experience with the area structures including the Palmetto Health Baptist campus
just to the east and southeast, the Meridian Building and Parking Garage, the First Citizens
Bank Corporate Headquarters Building, and the 17-story Main & Gervais Street Office Tower
to the south, the general soil conditions in the area include a deep deposit of loose to
medium dense Coastal Plain sands with varying fines contents to depths ranging from about
85 to 95 feet. These deposits are underlain by a thin divide of granite-based residual soils
and rock between the Coastal Plain horizon and the basement parent bedrock. Liquefaction
is typically not an issue due to soil composition and deep groundwater level.
The surrounding heavy buildings and parking decks are supported by a variety of foundation
systems ranging from shallow foundations or mats to auger-cast piles and drilled shafts.
Drilled shafts are more likely to be associated with buildings with deep basements as rock is
relatively deep. From our experience, moderate diameter auger cast piles have been
successfully tested to allowable compressive loads of 100 to 150 tons in purely frictional
applications (i.e., terminated in the Coastal Plain sands at depths of 70 to 80 feet) with
limited deflections.
The Coastal Plain sands in the downtown area also lend themselves well to ground
improvement techniques as they generally have a low to moderate fines (silt and clay)
content and groundwater is typically deep (40 to 60 feet below the surface). As such, stone
column systems such as Vibrapiers® and Geopiers® can be considered as a means of
densifying and reinforcing the existing soils at the site. Such methods can increase the
allowable bearing pressures of the soils by a factor of 2 or more, depending on the stone
column spacing and depth.
With such considerations in mind, we believe that the field exploration should be tailored to
provide information to allow the consideration of several foundation types to identify the most
cost efficient method available. This would include first considering shallow foundations as
they require the most common equipment and trades to construct. We note that the
referenced column loads may rule out their sole use; but if bolstered by stone columns, their
use may be practical. Other alternates which should be considered and compared to stone
columns would be both displacement and non-displacement auger-cast piles. Both
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Sumter Street Parking Garage
Terracon Proposal No. P73090279
October 7, 2009
TERRACON
considered generally appropriate to the downtown setting. To that end and in considerations
of requirements of this RFP, we recommend the following scope of work.
Field Exploration
Terracon proposes to perform five (5) Standard Penetration Test (SPT) borings at the
corners and center of the site to about 90 feet below the existing ground surface
(approximate depth of partially weathered rock) to provide information regarding the possible
foundation systems. The borings would be laid out by Terracon personnel or our field
representative based on the provided drawings.
The borings will be sampled at regular intervals of 2-½ to 5 feet in general accordance with
industry standards. In addition, we will observe and record the groundwater levels at the time
of drilling. Upon completion of drilling the borings and observation of groundwater levels
(obtained during drilling), the boreholes will be backfilled with the soil cuttings to within 1 foot
of the existing ground surface. The final 1 foot will be filled with cold patch asphalt mix. The
patching of the asphalt at the boring locations should be considered temporary.
In addition to the soil test borings, we recommend performing four cone penetration tests
(CPT) at intermediate locations between the soil test borings. They would be extended to a
similar depth as the SPT testing or to refusal, whichever is first encountered. The data
generated by the CPT testing is very helpful in evaluating the capacity of pile foundations as
well as shallow foundations, although it does not provide the direct sample collection of SPT
testing needed for other evaluations (such as densification potential associated with stone
columns and displacement auger cast piles). Therefore, the two methods are very
complementary for the foundation evaluation for this site.
Subsurface conditions may be encountered which merit alterations of the field boring and/or
sampling program described above. If such conditions are encountered, we will notify you,
discuss the nature of the conditions, and obtain your authorization for any additional field
work in advance, prior to demobilization of the drill rig and crew.
Site Access
The client shall provide the right-of-entry to conduct the exploration at the subject property.
Terracon understands that the borings will be conducted within an existing City leased
parking lot. We will coordinate our services with the City’s designated personnel including
providing drill schedule and coning of parking spaces in advance of drilling.
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Sumter Street Parking Garage
Terracon Proposal No. P73090279
October 7, 2009
TERRACON
Boring Location
The following services will be performed to locate and access the borings at the project site:
•
Terracon will contact Palmetto Utilities Protection Service regarding location of public
utility lines at the project site to prevent conflict between boring locations and existing
utilities. The utility locator service generally requires 72 hours to locate utilities.
•
If our client requests, Terracon can provide the services of a utility location firm to
check the boring locations prior to drilling at the site. A fee for this work can be
provided upon request.
•
Terracon personnel will layout the borings by measuring distances and estimating
right angles from available site features. Boring layout will be approximate.
•
The boring elevations can be estimated from topographic survey mapping, if
provided. If more accurate elevations are required, it will be necessary to survey the
borings. Surveying the borings is not included in the scope of services of this
proposal, but can be performed for an additional cost.
If there are additional restrictions or special requirements regarding boring locations and site
conditions, they should be brought to our attention prior to commencing the subsurface
exploration.
Field Shear Wave Velocity Testing for Seismic Site Classification
It is our experience that the seismic site class of the downtown area is typically
underestimated when soil test boring data is used in its determination. Therefore, we more
often use geophysical testing (SeisOpt® ReMi™ method) to develop the full depth shear
wave profile at the site as the basis of determining this design parameter. We have
successfully used this approach in several major downtown buildings to increase the site
class from “D” to “C”. Examples include:
•
•
•
•
Meridian Office Building and Parking Garage
First Citizens Headquarters Building
Gervais & Main Street Office Tower
Adesso Condominiums
This method employs non-linear optimization technology to derive one-dimensional S-wave
velocities from refraction microtremor (ambient noise) recordings using a seismograph and
low frequency, refraction geophones. We will utilize 12 receivers (geophones) set along a
straight-line array. Based on the survey plot, a 250±-foot traverse should be available at the
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Sumter Street Parking Garage
Terracon Proposal No. P73090279
October 7, 2009
TERRACON
site. This should be sufficient to provide the depth of data needed. A number of unfiltered,
30 second records will be collected using the background noise.
The collected data, the response spectrum in the 5 to 40 Hz range, will be processed using
the computer software (SeisOpt® ReMi™ by Optim, LLC) with the results plotted as a
conventional shear wave vs. depth profile. The shear wave dispersion curve and the picked
point plot of the data will also be provided as an Appendix to the report, as well as the shear
wave velocity profile from the SeisOpt® ReMi™ method data reduction.
Laboratory Testing
The recovered soil samples would be returned to our laboratory and visually classified by a
geotechnical engineer in general accordance with industry standards. Where appropriate,
we may perform selective laboratory testing on representative split-spoon samples.
Laboratory testing may consist of natural moisture content, fines content (silt and/or clay),
grain size distribution, and organic content testing to aid in visual classification and to help
estimate the engineering properties of the soils tested.
Engineering Analysis and Report
After completion of the field and laboratory testing programs, the data and conditions will be
analyzed and a letter report will be prepared by or under the supervision of a registered
Professional Engineer in the state of South Carolina. The report will confirm or modify our
original recommendations based of the new boring data, regarding the following:
•
Graphical representation of the boring/sounding data and summary of the laboratory
test data;
•
Summary of the geologic setting, site conditions, and the subsurface conditions
encountered at the site;
•
Recommendations for foundation design, including recommended foundation type,
allowable bearing pressure/capacity, estimate of settlement magnitude and
discussion of recommended construction practices.
•
Recommendations for earthwork, including subgrade preparation, fill placement and
minimum relative density requirements;
•
Anticipated excavation conditions, including difficult excavation and groundwater
conditions.
•
Recommendations for slabs-on-grade, including subgrade preparation, need for
vapor retarder, etc.
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Sumter Street Parking Garage
Terracon Proposal No. P73090279
October 7, 2009
TERRACON
•
Recommendations for lower level ramp retaining wall including bearing pressure,
coefficients, sliding coefficient, etc.
•
Seismic site class based on the shear wave velocity data as subject to the limitations
indicated in Chapter 16 of the IBC Code.
One bound, signed, and sealed original of the geotechnical exploration report and a PDF
copy would be provided. Terracon would not be held responsible for performing services
outside the scope explicitly stated within this proposal.
Schedule
Typically, a drill rig can be scheduled to the site within 5 working days after receiving written
notice to proceed. The field testing activities should take about 2 to 3 days to complete.
Our preliminary assessment will be verbally provided to you and your designers within about
one to two days after the drilling is completed. We estimate that the report can be completed
within about three weeks from the authorization date. This is a typical schedule for the earlier
described scope of work. Please inform us if your needs are different.
C. COMPENSATION
We estimate that our fees for the previously described scope of services in Section B will be as
follows:
Field Exploration and Testing
$9,900.00
Including up to 450 feet of SPT drilling, 360 feet of CPT
Soundings
Seismic Shear Wave Velocity Testing
$950.00
Laboratory Testing
$450.00
Analysis and Reporting
$3,900.00
Total, Not to Exceed
$15,200.00
Our fee estimate assumes that the reasonably recommended number and depths of soil test
borings with power augers and other proposed testing would provide sufficient data for the
planned analysis and recommendations. If conditions are encountered at the site that require
significant changes in the scope of services or a significant increase in the anticipated
number of samples which will increase the cost of the survey, you will be contacted for
discussion and approval of such changes before we proceed. Further, there may be
6
PROFESSIONAL SERVICE FEE SCHEDULE
FIELD EXPLORATION
Mobilization of equipment Truck-mounted Drill Rig and 2-man crew.......................................... 3.00/mile
(275.00 minimum)
Mobilization of Track-mounted or ATV Drill Rig and 2-man crew................................................ 4.00/mile
(400.00 minimum)
Track-mounted or ATV Drill Rig ............................................................................................... 300.00/day
Locations and elevations of borings 2-man crew..................................................................... 120.00/hour
Auger drilling and sampling using split-barrel at 5-foot intervals in soil (2-1/4 in augers)
Depth-Feet
0 – 50 .......................................................................................................................................... 11.00/foot
50 – 100 ...................................................................................................................................... 13.00/foot
Surcharge for drilling in Partially Weathered Rock (N>50/6”)..................................................... 2.50/foot
Surcharge for drilling with 3-1/4 in. augers (needed for Shelby tube sampling) ........................ 2.50/foot
Shelby tube sampling ............................................................................................................. 80.00/attempt
Rock Coring Set Up.................................................................................................................. 90.00/boring
NX Coring (5' minimum) 0 - 40' .................................................................................................. 60.00/foot
+ 40' ............................................................................................................................................ 70.00/foot
Rental/subcontracted equipment and supplies, permits, etc. ....................................... Cost + 20%
Stand-by time or setup and movement from boring to boring on site ..................................... 125.00/hour
PROFESSIONAL STAFF
Staff/Field Engineer .................................................................................................................... 85.00/hour
Project Engineer ....................................................................................................................... 100.00/hour
Senior Engineer........................................................................................................................ 130.00/hour
CADD operator ........................................................................................................................... 55.00/hour
Clerical ........................................................................................................................................ 45.00/hour
Additional Report Copies.............................................................................................. 0.20/page ($25 min)
Faxed Report (on request) ........................................................................................................... 0.25/page
Travel via personal or company vehicle....................................................................................... 0.70/mile
LABORATORY TESTING
Unconfined Compression Test................................................................................................... 28.00/test
Hand Penetrometer Test .............................................................................................................. 3.50/test
Dry Density Determination ......................................................................................................... 10.00/test
Water Content Test .................................................................................................................... 10.00/test
USCS Classification ..................................................................................................................5.00/sample
Atterberg Limits Test .................................................................................................................. 60.00/test
Dry Gradation Test ..................................................................................................................... 60.00/test
Hydrometer Gradation Test...................................................................................................... 120.00/test
Swell Test - 3 pressures........................................................................................................... 225.00
Swell Test - 1 pressure............................................................................................................. 120.00/each
Consolidation Test.................................................................................................................... 350.00/test
Plotted Time Curves ................................................................................................................... 70.00/each
Standard Proctor ...................................................................................................................... 140.00/test
CBR (including standard Proctor test)...................................................................................... 300.00/test