Dams and Extreme Events —
Reducing Risk of Aging
Infrastructure under Extreme
Loading Conditions
34th Annual USSD Conference
San Francisco, California, April 7-11, 2014
Hosted by
San Francisco Public Utilities Commission
On the Cover
Aerial view of the Calaveras Dam Replacement Project taken on January 27, 2014. The San Francisco Public
Utilities Commission is building a new earth and rock fill dam immediately downstream of the existing dam. The
replacement Calaveras Dam will have a structural height of 220 feet. Upon completion, the Calaveras Reservoir will
be restored to its historical storage capacity of 96,850 acre-feet or 31 billion gallons of water. The project is the
largest project of the Water System Improvement Program to repair, replace and seismically upgrade key
components of the Hetch Hetchy Regional Water System, providing water to 2.6 million customers.
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CONSTRUCTION TECHNIQUES FOR RCC PLACMENT
SAN VICENTE DAM RAISE
Frank Collins, P.E.1
Gerard E. Reed III, P.E. 2
Wade Griffis, P.E. 3
Jim McClain 4
Richard Burdette 5
ABSTRACT
The San Diego County Water Authority (Water Authority) is near completion of raising
the original San Vicente Dam, owned and operated by the City of San Diego, to provide
both emergency and carryover storage to increase local reservoir supplies in San Diego
County, California. The $1.5 billion Emergency Storage Project (ESP) and Carryover
Storage Project (CSP) will also provide a more-flexible conveyance system, and increase
water supply reliability in case of catastrophic failure to the delivery system due to a
major earthquake. The San Vicente Dam Raise (SVDR) project is a major component of
the last phase of the ESP and consists of raising the original 220-foot-high gravity dam
with 90,063 acre-feet of storage, by 117 feet to increase reservoir storage capacity by
152,000 acre-feet. Scheduled to be completed in 2013, the SVDR will be the tallest
concrete dam raise in the United States and tallest roller compacted concrete (RCC) dam
raise in the world. The reservoir capacity will be more than doubled, making it the
largest water storage reservoir in the region.
This paper presents the unique construction, scheduling, and coordination techniques
associated with placing RCC on the downstream face of the original dam. Additionally,
construction techniques of dam features such as the dam crest, spillway ogee crest,
parapet walls, spillway guide walls, and flip bucket are discussed.
INTRODUCTION
Original Dam
The San Vicente Dam is located in Lakeside, CA, an unincorporated community of San
Diego County. The original dam, pictured in Figure 1, constructed between 1941 and
1943, is a conventional concrete gravity dam founded on bedrock. Construction of the
1
Project Manager, Parsons, 110 West A Street, Suite 1050, San Diego, CA 92101, (858) 342-9183, Email:
frank.collins@parsons.com
2
Engineering Manager, San Diego County Water Authority, 4677 Overland Avenue, San Diego, CA
92123, (858) 522-6835, Email: JReed@sdcwa.org
3
Sr. Construction Manager, San Diego County Water Authority, 4677 Overland Avenue, San Diego, CA
92123, (619) 390-2310 x3206, Email: WGriffis@sdcwa.org
4
Construction Manager, Black & Veatch Corporation, 300 Rancheros Drive, Suite 250, San Marcos, CA
92069, (760) 602-7528, Email: jmcclain@bv.com
5
Construction Engineer - Asst. Construction Manager, Parsons, 110 West A Street, Suite 1050, San Diego,
CA 92101, (951) 252-3520, Email: richard.burdette@parsons.com
Construction Techniques for RCC Placement
799
concrete dam was performed using an on-site batch plant and placed via an overhead
cable-way. Blocks for construction of the concrete gravity dam generally consisted of
50-foot-wide by about 5-foot-thick sections and extended from the upstream face to the
downstream face of the dam, consistent with dam construction methods of the time. The
original San Vicente Dam had a structural height of 220 feet, with a crest elevation at 660
feet, a crest length of 963 feet, and a crest width of 14 feet. The dam contains a
275-foot-long spillway, consisting of an uncontrolled ogee-crest overflow section near
the center of the dam.
Figure 1. Original San Vicente Dam Prior to Dam Raise Construction
Concrete aggregate for the original dam was obtained from nearby sources (canyons and
creeks). The main source of aggregate consisted of Poway Conglomerate located
approximately one mile from the dam site. Other sources of aggregate reported for
construction material included a gravel deposit in the San Diego River as well as sand
from San Vicente Creek. Two types of cement were used for the dam. The original
design mix specified Type IV cement. However a second mix utilizing Type II (low
alkali) cement was also used due to cement shortages during World War II. Core tests
obtained during the dam raise design for compressive strength of the Type IV cement
resulted in a mean average of 4,115 psi while the Type II resulted in a mean of 4,370 psi.
Tensile stresses for the Type IV and Type II cement were measured to be 198 psi and 188
psi respectively.
800
Dams and Extreme Events
Figure 2. Original San Vicente Dam Prior to Dam Raise Construction
New Raised Dam
For the new raised dam, the foundation was determined to be expanded by 75 feet
downstream of the original dam with RCC placed against the downstream face and above
the crest of the original dam, creating a composite, monolithic structure (see Figure 3).
Figure 3. Schematic of Cross Section of San Vicente Dam
The design required that the new RCC dam has the following target strength properties:
• The laboratory compressive strength is 4,840 psi in two years
Construction Techniques for RCC Placement
801
•
The tensile strength across the RCC joint is 200 psi in two years
The RCC mix consists of materials matching the original concrete as closely as possible.
The selected mix was comprised of aggregates manufactured from a conglomerate
deposit nearby the dam with properties very similar to the original aggregates in strength
and thermal properties. The RCC ultimate compressive and tensile strength are expected
to closely match that of the existing dam as well.
Figure 4. San Vicente Dam Onsite Aggregate Borrow Area
Construction Phasing and Contractor Selection
Through lessons learned on the construction of the Olivenhain Dam Project, completed in
August 2003, the Water Authority elected to package the main features of the San
Vicente Dam Raise project into three separate contracts:
•
•
•
802
Phase 1 consisting of a test quarry and test crushing.
Phase 2 consisting of the preparation of the original dam to receive concrete
(through hydro-demolition of the dam face, and saw-cutting of the dam crest and
other features), excavation of the new dam foundation, filling cracks and crevices
within the new foundation with dental concrete, and installing a new pipeline
through the original dam.
Phase 3 consisting of implementing curtain, check, and consolidation grouting
program, focusing on manufacture and placement of RCC for the new dam, and
the construction of new flow regulating structures.
Dams and Extreme Events
Phase 2 of the San Vicente Dam project was awarded to Barnard Construction Company
(Barnard) on May 28, 2009 for a lump sum contract amount of $23,749,500 and
completed on September 24, 2010.
Phase 3 of the San Vicente Dam project was awarded to Shimmick/Obayashi, A Joint
Venture (SOJV) on April 22, 2010 for lump sum contract amount of $140,206,050.
Phase 3 is scheduled to be completed June 2014.
FOUNDATION PREPARATION
The geology of the site in the area of the dam excavation consisted of two types: slightly
weathered granodiorite underlying the right abutment of the dam from about 5 to 20 feet
deep while slightly weathered metavolcanic rock underlay the central part and left
abutment of the dam and ranging from 5 to 30 feet deep. The surface layer of the
excavation consists of a mixture of soil and highly weathered rock. This top layer was
able to be removed during excavation with an excavator ripping loose and degraded
material down to the slightly weathered bedrock. The granodiorite/metavolcanic areas
below this zone was a very hard rock and was removed using conventional drill and shoot
techniques.
The construction procedures generally consisted of working from the top of the slope to
the bottom, preparing the rock foundation. The first step of the cleaning procedure was
to excavate all overburden material, and loose rock from the mass excavation.
Rock fractures, faults, and shear zones were sinuous and variable in nature with some
areas being difficult to identify. The onsite construction management and geotechnical
staff assisted in the identification of these areas, which were treated differently than the
other competent rock areas with tight seams. At these shear areas, material was
excavated beyond the design elevation until competent (fresh) rock/granite was revealed
or up to a depth acceptable to the Design Engineer of Record and the California Division
of Safety of Dams (DSOD). The depth of excavation varied with the width of the shear
zone. Per the project requirements loose material in shear zones, cavities, and seams was
removed to a depth 2 times the width for a feature less than 2 inches wide, three times the
width for features between 2 inches and 12 inches wide, and to a depth no greater than
five feet for a feature greater than 12 inches wide. These areas were cleaned with highpressure water and/or air jets and then surface treated with grout at the time of dental
concrete placement.
Construction Techniques for RCC Placement
803
Two major fault areas required special treatment prior to commencement of the next
foundation preparation phase. One of the faults, located on the right abutment above the
top of the original dam, was oriented perpendicular to the dam axis. This fault area was
excavated extensively, stepped in five-foot increments and filled in with shaping concrete
(see Figure 5). The Design Engineer of Record in coordination with DSOD determined
that the stair type of shaping concrete was necessary in order to buttress the upstream and
downstream cuts and facilitate the placement on the steep foundation. This would allow
the complete covering of the fault zone across the new dam foundation while elevating
the excavated foundation grade close to the original design-intended grade and ultimately
improve performance of the new dam structure. The second fault area, located on the left
abutment near an original adit exit from the dam, was similarly remediated. Both faults
were discovered during the original dam construction and extensively investigated prior
to the new dam raise; both are classified as “inactive” according to the DSOD’s record.
Figure 5. Right Abutment Foundation Shaping Concrete Placement
When completed, Barnard excavated approximately 86,000 cubic yards of rock and
material for the new dam foundation and 27,000 cubic yards for the saddle dam
foundation.
HYDRO-DEMOLITION OF DOWNSTREAM FACE
In order to achieve a proper bonding surface on the downstream face of the original dam
and prepare for new RCC, the Design Engineer of Record in coordination with DSOD,
determined that hydro-demolition of existing concrete would be required. RCC placed
against this joint would be strengthened at the interface through the use of Grout
Enriched Vibratable RCC (GEVR).
804
Dams and Extreme Events
The downstream face of the existing dam was prepared by removing up to three inches of
surface concrete using high pressure air/water jets (20,000 psi). It was determined during
design that the zone of oxidation, or “weathering” was determined to be one to two
inches deep. Barnard was required to conduct three field test sections, at different
locations, along the downstream face of the existing dam to demonstrate its proposed
hydro-demolition equipment and methods. The first section removed one inch of
material, the second two inches and the third three inches. Cores were extracted and
examined petrographically to determine the appropriate depth of weathered concrete to
be removed from the face of the original dam.
Barnard selected American Hydro as its specialty subContractor for hydro-demolition of
the downstream face. American Hydro designed and built a custom robot equipped with
a single nozzle that traversed a pre-determined distance across a beam to achieve the
depth of cut (see Figure 6). The depth of cut (two inches) was determined after the test
sections were developed and analysis of core samples was conducted to confirm design
information.
Figure 6. Hydro-demolition Robotic Unit and Rail System
The hydro-demolition system consisted of a five-cylinder, 20,000 psi Hammelmann highpressure pump, powered by a 1000 hp Cummings diesel engine, high-pressure delivery
hoses, and the hydro-demolition robot which traversed on rails, manufactured by Fraco
Products, from the bottom of the dam to the top. The rails were placed plumb on the
overflow and non-overflow sections of the dam, maintaining an absolute minimum of 24inch standoff from the original concrete dam surface. The waterjet nozzle directed a high
pressure water stream to the concrete to be removed. The Hammelmann pump was
mounted on a trailer and needed to remain within 700 feet of the robot at all times.
Construction Techniques for RCC Placement
805
The rail system was installed on the dam face by Barnard. The spacing of the rails was at
a maximum of 30 feet on center and extended 5 feet above the desired cut line. The
American Hydro machine performed the cuts between rails in three consecutive passes.
During setup, the nozzle traversed horizontally along the rail until the programmed
distance was achieved, at which time the cross feed beam advanced a prescribed distance
vertically and the programmed cycle began again. The width of cut was adjusted by
controlling the transverse movement of the nozzle, using sensors that were manually
adjusted along the crossbar. The locations of these sensors determined the width that the
nozzles would traverse; this feature was particularly useful when working on angled
surfaces such as the left and right abutments.
The hydro-demolition started at the spillway section (see Figure 7). The work progressed
from the far right of the overflow section to the left and from the bottom to the top.
When the concrete removal was completed on a rail, the rail was removed in sections
prior to remounting the robot. Upon completion, Barnard hoisted the 20,000-pound robot
from the completed rail to the succeeding rail located to the left. Once the rail was
removed, American Hydro performed the third cut from the climber; this allowed the area
to be hydro-demolished where the previous rail was placed.
Figure 7. Rail Layout for Hydro-Demolition Spillway Section
When completed, American Hydro hydro-demolished approximately 145,000 square feet
surface area of the downstream face of the original San Vicente Dam.
806
Dams and Extreme Events
RCC CONSTRUCTION
This section provides a description of the RCC construction means and methods used by
the Contractor to raise San Vicente dam. In addition, this section highlights issues faced
during construction and provides a brief overview of the instrumentation installed during
construction.
Approximately 600,000 CY of RCC were placed in the Main Dam from
September 12, 2011 to September 20, 2012, as shown in Figures 8 and 11. The average
daily production was approximately 2,400 CY/day with a daily maximum of 6,725 CY.
The monthly RCC production ranged from 4,150 CY in September 2011 to a peak of
86,195 CY in June 2012, with a monthly average of 46,303 CY. The maximum weekly
RCC volume reached 36,265 CY with a weekly average of approximately 12,500 CY.
Monthly RCC Placement in Main Dam
100,000
90,000
86,195
79,380
80,000
74,650
70,260
70,000
Volume (CY)
61,062
64,465
60,000
50,427
50,000
39,290
40,000
28,346
30,000
20,000
10,000
16,341
15,057
12,310
4,150
0
Sep-11 Oct-11 Nov-11 Dec-11 Jan-12 Feb-12 Mar-12 Apr-12 May-12 Jun-12 Jul-12 Aug-12 Sep-12
As of September 21, 2012
Figure 8. Monthly RCC Production in the Main Dam
Shimmick-Obayashi Joint Venture (SOJV), the main Contractor for the SVDR, was in
charge of the RCC operation. SOJV assisted by Group Delta provided the Quality
Control for the RCC Construction, as well. The Construction Manager PARSONS/Black
& Veatch, Joint Venture provided Quality Assurance (QA) Inspection on the RCC dam.
Construction Techniques for RCC Placement
807
The RCC production plant, as shown in Figure 12 located on the South end of the Marina
area consisted of two main components: cooling and batching plants. Once RCC
ingredients were blended, the mix was transported via conveyor belt system to the dam
where articulated trucks completed the delivery to the point of placement.
RCC placements activities are summarized below:
•
•
•
•
•
•
•
•
The first RCC was placed for Trial Placement on March 14, 2011.
Trial Placement was complete in 11 lifts on April 1, 2011.
The first RCC placement for the main dam occurred on September 12, 2011.
The RCC placement for the main dam was complete on September 21, 2012.
The first RCC placement for the saddle dam occurred on July 7, 2011.
RCC placement for saddle dam (first phase) was complete on August 18, 2011.
RCC placement for saddle dam resumed on September 24, 2012.
The last RCC was placed for the saddle dam on October 4, 2012.
Figure 9. RCC Trial Placement
808
Dams and Extreme Events
Figure 10. First RCC Placement at Toe of Main Dam
The following Table 1 shows the quantity of RCC placed, aggregate plant production and
Quality Control samples:
Table 1. Quantity of RCC Placed, Aggregate Plant, QC Samples
RCC
Placement
Aggregate
Plant
Quality
Control
Item
Total RCC placed for the main dam
Total RCC placed for the saddle dam
Number of placement shift
Materials processed through Primary Plant
Materials wasted at the Primary Plant
Materials produced at the Primary Plant
Aggregate Group 1produced at the Secondary Plant
Aggregate Group 2/3 produced at the Secondary Plant
Aggregate Group 4 produced at the Secondary Plant
Number of density tests
Number of VeBe tests
Number of temperature tests
Number of cast cylinders
Number of gradation tests
Number of Sand Equivalent tests
Construction Techniques for RCC Placement
Quantity
600,237
12,470
367
2,587,629
1,352,146
1,235,483
423,266
371,786
427,613
3,096
2,031
2,349
6,492
2,365
1,142
Unit
Yd3
Yd3
each
ton
ton
ton
ton
ton
ton
each
each
each
each
each
each
809
As of 9/20/12
RCC Volume Placed on Main Dam
Cumulative Volume
650,000
600,237
600,000
550,000
500,000
RCC Volume (CY)
450,000
400,000
350,000
300,000
250,000
200,000
150,000
100,000
Cumulative Vol. (CY)
50,000
3-Nov-12
6-Oct-12
20-Oct-12
8-Sep-12
22-Sep-12
25-Aug-12
28-Jul-12
11-Aug-12
14-Jul-12
30-Jun-12
2-Jun-12
16-Jun-12
5-May-12
19-May-12
7-Apr-12
21-Apr-12
24-Mar-12
25-Feb-12
10-Mar-12
28-Jan-12
11-Feb-12
14-Jan-12
31-Dec-11
3-Dec-11
17-Dec-11
5-Nov-11
19-Nov-11
8-Oct-11
22-Oct-11
24-Sep-11
10-Sep-11
27-Aug-11
13-Aug-11
0
Figure 11. RCC Production in the Main Dam
The major challenges encountered during construction included:






Maintaining minimum production rate as required by project specifications
Consistently preparing the lift surface prior to RCC placement efficiently
Consistently and continuously performing water curing procedure
Excessive amount of unplanned (warm and cold) lift joints
Multiple interruptions of fly ash delivery
Consistently producing Group 4 materials that met the minimum Sand Equivalent
value
RCC Cooling
All the cooling capacity for water and aggregate cooling was provided by a single 1,200ton centrifugal chiller as shown Figure 12. The water supplied to the chillers, wet belts,
and batch plant was kept in a recycle pit or pond, capable of holding about 140,000
gallons of usable chilled water. As batch water was used for mixing, the water level at
the pond decreased during the production hours. The chiller ran during non-production
hours to replenish the pond. The temperature of the water in the pond was typically
around 40ºF.
810
Dams and Extreme Events
Project specifications required RCC to be placed at the following temperatures:
Location
Trial Placement
Main Dam below EL 516
Main dam between EL516 and EL 587
Main Dam between EL 587 and EL 658
Main Dam above EL 658
(top of original dam)
Saddle Dam
Placing Temperature at or below (ºF)
60
60
62
64
68
68
The Group 4 (fine aggregate) was air cooled via a counter-current rotary cooling drum from
an ambient temperature at the entrance to a target exit temperature of 63 F. After exiting the
sand drum, fine aggregate was fed to the batch plant overhead bin for use.
The coarse aggregates were cooled on two, 140-f00t-long “wet” belt conveyors, one belt for
Group 1 (1-1/2") rock and the other for Group 2/3 (3/4") rock. Prior to entering the wet belt,
the coarse aggregates were washed on high frequency wash screens. The wet belts were
housed in an insulated cover to reduce ambient heat effects. The aggregates on the belt were
sprayed with chilled water, which dropped the aggregate temperature to about 50°F. Total
belt retention time was in the 2-3 minute range for a combination of cooling and excess water
draining. Belt speed was adjustable to modify retention time, if required. The wet belt
design used perforated belts for removing most of the excess water from the coarse
aggregates. After leaving the belt, coarse aggregates were stored in the batch plant insulated
overhead bins for use. At the beginning of the RCC production, it was observed that the
excessive moisture was carried over to the overhead bins, thus the system was modified as
necessary.
Batching
The batch plant consisted of a “Con-E-Co Lo-Pro 10” batching module modified to a
nominal capacity of 500 CY/hour (based on 30-second mixing time and 6-CY batch in
dual twin-shaft mixers), as shown in Figure 13.
To meet mixer uniformity requirements, the mixer load was reduced to 5 CY/load and
mixing time was kept at 40 seconds. After experiencing problems with the original
electronic batch plant control system, the plant was equipped with a new Command
Alkon Batch system. During the entire production period, the plant’s peak production
rate was about 430 CY/hr.
The batching section consisted of three individual aggregate overhead bins with a total
capacity of 200-tons each, where cooled aggregate was stored. The plant was equipped
with individual weigh batchers for each aggregate group. Weighed aggregate were
transferred via a 48-inch batch transfer belt to holding hoppers located directly above the
mixers.
Construction Techniques for RCC Placement
811
The mixing section consisted of two 6 CY SICOMA model 7500 twin-shaft compulsory
mixers, as shown in Figure 13. Above each mixer, there was a separate weigh batcher for
cement and fly ash. Each weigh batcher was fed by a screw auger from the 1000-ton
cement and fly ash silos. Each silo contained a 24-hour throughput capacity of bulk
material. Each mixer was equipped with an individual water weigh hopper mounted
above the mixer with fast and slow discharge. Once the mixing cycle was complete, the
bomb bay gates discharged the mix to a conveyor belt, which, in turn, discharged it onto
the main belt to the dam.
Figure 12. RCC Batch Plant
812
Dams and Extreme Events
Figure 13. Mixing Section with Cement and Fly Ash Silos
RCC Conveying and Hauling
Project specifications required RCC for the main dam to be delivered by conveyor belt as
shown in Figure 14. The RCC delivery system to the main dam below elevation 642’
consisted of three main components:
a) Conveyor belt from the plant to the crest of the original dam,
b) 200-foot-long chute from EL. 658 to the hopper/conveyor to load trucks and,
c) Articulated trucks to move RCC on the lift.
Once RCC was on the dam, trucks were allowed to move it from the loading point to the
point of placement. On the other hand, RCC for the trial placement or the saddle dam
could be truck hauled from the batch plant to the placement area.
SOJV’s original plan was to deliver RCC by conveyor belt to both the saddle and main
dams. Also, their original intention was to construct the main dam first and the saddle
dam later to allow the conveyor to pass through the saddle dam area for the main dam
placement. The conveyor belt for the main dam would be demobilized before saddle dam
construction began. However, in the end, SOJV opted to partially construct the saddle
dam up to elevation 762; complete the main dam, and come back to top out the saddle
dam at the end of the RCC operation.
Construction Techniques for RCC Placement
813
Figure 14. General View of Conveyor System
The SOJV-selected overland RCC conveyor system to the main dam consisted of a
500 ft/min mine duty Superior Industries truss framed conveyors with a nominal capacity
of 1,200 tons per hour of RCC (approximately 600 CY/hour) and an approximate length
of 2700 feet from the batch plant to the dam. The belt capacity was designed to handle
the scheduled batch plant output. The conveyor was covered almost in its entire length
for RCC temperature and moisture control. Figure 14 shows the general views of the
conveyor system and the saddle dam crossing.
Conveyor segments 1A, 2A, 3A, 3B, as shown in Figure 14, delivered RCC to the right
abutment of the main dam. Truss frame conveyors 4A, 4B, and 4C extended down the
right abutment to approximately station 3+00 to reach the top of the existing dam, as
shown in Figure 15. The truss-framed conveyors (4A, 4B, 4C) were supported in three
locations: at the tail end, at the middle, and at the head of the conveyor. During RCC
placement, the tower supports were removed before the RCC lifts reached their
foundation elevation; but the pipe bents were left within the RCC and grouted after the
conveyor belts were removed.
814
Dams and Extreme Events
Figure 15. Conveyors 3B through 5C
Conveyors 5A, 5B, 5C, and 5D traversed across the top of the existing dam to
approximately station 7+00. Conveyor 5D transferred the RCC into a 200-foot-long drop
chute. The chute installed down the face of the original dam discharged the RCC onto an
18-CY hopper/conveyor unit to be used for loading trucks on the dam. The
hopper/conveyor unit was mounted on a CAT D350E truck for mobility during
placement. Initially, the vertical drop chute was made of a 30-inch-diameter HDPE pipe.
However, this pipe did not last more than a few shifts of placement because the RCC
abraded through the pipe wall.
The first alternate chute system trial consisted of a shallow rectangular channel section
covered with rubber conveyor belt segments. The chute system invert followed the
original dam downstream profile. The shallow, square corner channel section and the
misalignments of the field welded channel beams created frequent chute plugging and
placement interruptions. After repeated problems, the Contractor abandoned this system.
The next alternate trial chute system consisted of a 34-inch-diameter half round metal
pipe covered with segments of rubber conveyor belt. In contrast to the previous chute
system invert profile this chute invert profile was straight. This alignment was achieved
by mounting the chute on EFCO super-stud metal supports. For easy inspection and
intervention in case of plugging, the chute was covered with rubber conveyor belt
sections. The new chute system introduced an additional conveyor belt segment
(Conveyor 5E) at the end of the chute. Conveyor 5E was supported by an EFCO super
stud structure attached to the face of the existing dam and used a vertical plastic chute at
the end of the conveyor to direct the RCC stream to the trucks, as shown in Figure 16.
Construction Techniques for RCC Placement
815
Conveyor 5E was shifted to higher elevation when the clearance between the conveying
system and RCC lift was too short for truck loading.
Figure 16. Conveyors 5 Series, Half Round Pipe Chute, and Truck Mounted Hopper
816
Dams and Extreme Events
When the RCC dam construction reached elevation 642’, SOJV introduced another major
change to the RCC conveying and delivery plan by deploying a 150-foot crushing plant
“Thor Stacker” to deliver RCC to the trucks. The original submitted plan showed
conveyor 4C dropping into the hopper/conveyor unit after the removal of conveyors 5A,
5B, 5C, and 5D from the top of the existing dam. However during construction,
conveyor 4B head chute was connected to the tail hopper of the “Thor Stacker”, which
then discharged RCC on the trucks. The stacker was positioned on top of a temporary
base pad or top of concrete pedestals, which remained in place after stacker removal.
Initially, trucks were loaded directly from the stacker belt, but after approximately
elevation 658’, SOJV brought in a belly dump hopper to load the trucks as shown in
Figure 17. The use of the hopper provided some surge capacity to the delivery system
and helped to control excessive RCC mix segregation.
Once dam construction progressed to elevation 682’, Conveyor 4C and the stacker were
removed to allow conveyor 4B to drop directly into the belly dump hopper. When the
dam construction progressed to elevation 688’, conveyors 4A and 4B were removed and
conveyor 3B dropped RCC into the “Thor Stacker”, which discharged in the belly dump.
Once the dam reached approximately elevation 730’, the stacker was jumped to the
access road bench on the right abutment at approximately elevation 780’ and discharge in
the belly dump hopper. The stacker remained in that position until the end of the main
dam RCC operation.
Due to space limitations, at about elevation 738’, lighter 25-ton capacity articulated
trucks replaced the original 40-ton trucks used since the beginning of the RCC placement.
When the main dam reached elevation 755’, RCC placement between the right abutment
and the start of the left abutment chimney was stopped to allow the left chimney
construction. To complete the left chimney, the RCC was transferred from conveyor 3B
to the “Thor Stacker”, which loaded trucks via belly dump hopper positioned near the
right abutment at spillway elevation 755’. The trucks hauled RCC from the hopper and
dumped it on a reload conveyor belt positioned in the vicinity of the start of the left
abutment. The Reload belt dumped on the tail of a second “Thor Stacker”, which loaded
the single 25-ton truck hauling RCC to the final point of placement on the left abutment
chimney. After completing the left chimney, placement on the right side of the spillway
proceeded using the RCC conveyor belt, belly dump hopper and trucks only. The RCC
was hauled from the hopper to the point of placement using one 25-ton articulated truck.
RCC Placing: Depositing, Spreading, and Compacting
Except for the locations with special features, such as galleries, conduit crossings, and
sections above the spillway, the new dam was constructed essentially at the same
elevation across its entire length and width. Typically, RCC was placed from abutment
to abutment (parallel to the dam axis) for the full width of the dam. The width of the
placement was covered by several RCC strips; however, the leading edge of adjacent
RCC strips was typically kept at no more than 30 feet apart.
Construction Techniques for RCC Placement
817
Trucks hauling RCC on the lift, deposited the material far enough from the leading edge
to allow for the dozer to re-blend to minimize segregation. For most of the main dam
construction, RCC was spread with a D-6 dozer equipped with an extended blade. For
areas where dozer maneuverability was limited, a D-4 dozer equipped with a slope-blade
was used. Occasionally a “Bobcat” was used to assist the spreading material in tight
areas not accessible for the dozer and to create GEVR dikes.
At the bottom of the dam, once the rock foundation was covered with RCC, placement
typically proceeded from the farthest opposite end to the point of delivery. At higher
elevations, as RCC lift length increased, the relative location of the chute created two “far
ends” towards each abutment, with the left abutment being the farthest. For that reason,
the Contractor would typically place a “pad” on the right abutment first and then move to
the left abutment to complete the lift from left to right. This practice also continued when
placement was conducted with the “Thor Stacker” and the belly dump hopper.
Figure 17. Thor Stacker Loading Trucks via Belly Dump Hopper
RCC compaction was achieved by a single drum CAT CS563 12-ton vibratory roller.
Typically, two static passes and six vibratory passes were required to achieve the
minimum required density. A smaller BOMAG 120 or INGERSOLL RAND double
drum vibratory roller was used to compact on restricted areas and to finish the lift surface
close to the forms. The conveying, hauling, depositing, spreading, and compacting
equipment type and maker are shown in Table 2.
818
Dams and Extreme Events
Table 2. Conveying, Hauling, Depositing, Spreading, and Compacting Equipment
Function
Conveying
Equipment Type
Maker and Model
Thor Stacker
Conveyor
Small Stacker
CAS RL 34
Reload Conveyor
Volvo AD 40, John Deere 400 D
Hauling
Truck
CAT 725, CAT 2532
Spreading
Dozer
Skid Steer
Loading
Loader
Compacting
Roller
Plate Compactor
Hydraulic Vibrator
Vibrating
Plate Vibrator
Vacuuming
Vacuum truck
Brooming
Mechanical brush
Blower
Blowing
Air compressor
Crane
Lifting
Forklift
Man lifter
CAT D6, CAT D4
CAT 248B
CAT 980, CAT 966, CAT 936F,
Komatsu WA 250
CAT CS 563, Bomag BW-211D40
Bomag 120 AD4 DD
Vibratory Plate Compactor
Gang Vibrators attaced to CAT
307C, Gang Vibrators attached
to CAT 305CR
Plate Vibrator attached to
PC88MR
Vermeer LP 555, Vactor 2100,
Supersucker
CAT 244B with Lay Mor mech.
brush
Mobile sweeper
Billy Goat blower
Atlas Copco XAS 756
Sullivan-Pallatek
Grove RT870, Grove 5240, Grove
RT 855, Kobelco CK 2500, Maeda
LC785, Grove 58D
Skytrak 10054, CAT TL 1055,
Terex
JLG 660 SL
Note
From elevation 642 to
the top
For Left Chimney
For Left Chimney
From the bottom to
elevation 737
From elevation 738 to
775
For tight area
For tight area
For finishing GEVR
For GEVR
For contraction joint
Grout Enriched Vibratable RCC (GEVR)
The faces of the raised dam were treated using the Grout Enriched Vibratable RCC
(GEVR) method. This technique was applied on a 18-24” wide band for both
downstream and upstream faces, interface with the dam foundation rock, interface with
the original concrete dam, and interface with the precast gallery panels. GEVR
placement consisted in forming small RCC dikes by shoveling and filling them with
grout as shown in Figure 18. Once the dikes had been filled with grout, RCC was pushed
over the dikes to fill the area to grade. Then, gang-mounted 3½-inch, 9000 rpm hydraulic
vibrators were used to consolidate the grout enriched RCC mix as shown in Figures 19
and 20. After internal vibrator application, vibratory plates and float were used to finish
the GEVR surface at the downstream steps as shown in Figure 21.
Construction Techniques for RCC Placement
819
Figure 18. GEVR Dikes against the Original Dam Downstream Face
Grout for GEVR consisted of a mixture of water and cement with a target water/cement
ratio by weight of 0.55 and an optimum range between 0.50 and 0.60. The cement for
GEVR grout was the same as the one used for RCC mix. Also, grout for GEVR used the
same proportions as the grout used for lift joint treatment. At Contractor’s discretion,
PLASTIMENT ES manufactured by SIKA was used to control grout setting time. At the
beginning of RCC placement, SOJV selected to use 7 oz/CWT, but later in the project the
Contractor decided to reduce the dosage to about half the initial rate to allow for a faster
GEVR hardening. Grout was produced in a standard 60-gallon grout turbo mixer
equipped with a 25 tons capacity mobile cement silo. The grout plant was located outside
and above of the RCC placement area so that the grout could flow by gravity through
rubber hoses to the RCC placement work area.
820
Dams and Extreme Events
Figure 19. Vibrating GEVR at the Downstream Steps
Figure 20. Four 3.2-inch Hydraulic Vibrators on Mini Excavator
Construction Techniques for RCC Placement
821
The Contractor used a magnesium float after GEVR procedure at the downstream step to
create a smooth finish.
Figure 21. Magnesium Float to Create Smooth Finish for the Downstream Steps
Formwork
Two formwork systems were used to construct the upstream and downstream faces of the
dam. For smoother GEVR face and better performance during vibration, form systems
were specified to be metal.
The downstream form basic unit manufactured by DOKA was approximately 16 feet long
by 2 feet high. The system was a multiple stage “jump” form system that relied on
anchors embedded in the RCC to resist the loads. Once the RCC at the lower stage was
strong enough, the form was released and installed on top of the downstream formwork
system. The form “jumping” was made by crane and carpenters on the lift. The
downstream formwork system was demonstrated in the trial placement. Initially the
Contractor used at least four form stages, but as the dam increased in length, the number
of stages dropped to three. The downstream formwork is shown in Figure 22.
The upstream forms consisted of a DOKA climbing Formwork MF, which is designed for
structures where formwork has to be shifted upwards in successive lifts. This formwork
was used during the trial placement; however, it relied on stiff-backs and supports on the
ground. On the dam, the DOKA formwork used was solely supported by 8-foot-long
tiebacks with plates embedded in the RCC in the lower portion of the RCC raise section.
822
Dams and Extreme Events
In the top two-thirds of the raised section, down-pins were added and driven into RCC to
provide additional support to the tiebacks. The basic form unit was 12 feet long by 8 feet
high. The upstream formwork was moved by a 70-ton crane (stay-on-the-lift). A picture
of the upstream formwork is shown in Figure 23.
Figure 22. Downstream Formwork
In general, maintaining geometrical tolerances, in particular upstream, posed a major
challenge for the Contractor. In one occasion, upstream surface tolerance deviations
became so large that RCC placement was stopped to correct misalignments. When the
upstream form encroached on the outlet tower alignment, correction to the upstream form
alignment had to be made.
Maintaining downstream steps quality was a challenging task for the Contractor.
Stripping and “jumping” forms frequently damaged the steps. Extensive repairs were
required to restore quality and maintain required line and grade tolerances. The
Contractor performed significant patching work in an effort to repair the damaged stairs.
Curing
Project specifications required exposed RCC faces to be continuously moisture cured for
28 days after placement. Water for curing was drawn from the existing reservoir and
pumped to holding tanks located above the dam crest elevation on the right abutment.
For dam faces, water was delivered via sprinkler system. The Contractor elected to use
workers with hoses to keep the RCC lift surface moist. Dam face and RCC lift surface
Construction Techniques for RCC Placement
823
curing was a significant issue throughout RCC construction due to the frequent curing
system malfunctions and non-uniform moisture coverage by hand held hoses.
Figure 23. Upstream Formwork General View
Lift Joint Treatment
There were four lift joint categories and the lift joint treatment was determined based on
the lift joint maturity, which is related to temperature and time of exposure to the
environment. The joints were classified as “Hot”, “Warm”, “Cold” or “Super Cold” joint
depending on the exposure duration and the ambient air temperature, which was
quantified by a Modified Maturity Factor (MMF). The MMF was evaluated by
accumulating the average hourly ambient air temperature on the lift in degrees
Fahrenheit, minus 10.5 degrees. Air temperature on the lift was recorded by using a
recording thermometer.
The maturity (MMF) ranges defining each type of joint and the treatments applied to each
one of them are summarized in Table 3 below.
824
Dams and Extreme Events
Table 3. RCC Lift Joint Classifications and Treatments
Joint Type
Hot
Warm
Cold
Modified Maturity
Factor (mod ºF-hr)
< 1000
1000-2500
2500-3500
Super cold
>3500
Basic Treatment
Cleaning with Air
Vacuum/air cleaning; apply grout right before RCC placement
Roller brush & low pressure washing (As established in trial
placement); apply grout right before RCC placement
Hydro blasting with 10,000 psi max; apply grout right before RCC
placement.
The most frequent joint types encountered during construction were hot or warm joints.
Hot joints occurred at exposure below 1000 ºF-hr and required the minimum preparation
effort, which consisted of removing all loose materials, pools of water and other foreign
matter by blowing the surface off with air. Warm joints occurred at maturities between
1000 and 2500 ºF-hr and required treatment similar to hot joints with the requirement to
vacuum as necessary and apply a layer of grout before the placement of the next RCC
lift. Cold joints were the least common type of joint encountered during construction as
they often evolved to super cold joints. Cold joints occurred between 2500 and 3500 ºFhr and, as established during the trial placement, treatment consisted of roller brush
followed by a light pressure water wash, vacuum cleaning and the application of a layer
of grout before the placement of the next RCC lift. Super cold joints were experienced at
exposures beyond 3500 ºF-hr, which typically occurred during conveyor moves,
equipment breakdown, long gallery section setup, or planned holiday. Super cold joints
were treated with high pressure (10,000 psi max.) hydro blasting to expose surface
aggregates, vacuum cleaning and the application of a layer of grout before placing the
next RCC lift.
Contraction Joints
Contraction joints (CJ) in the raised dam followed the joint pattern established by the
existing dam. The typical spacing for the CJ was approximately 50 feet. Contraction
joints were formed by inserting a 14 gauge, 9” wide galvanized metal plate in the freshly
compacted RCC lift as shown in Figure 24. Initially, the project documents required a
standard 48-inch long plate; however, the Contractor requested to use plates with
different lengths (48, 60, 72, and 84 inches) to better accommodate the dam width. Plate
insertion was accomplished using a mini excavator with vibratory plate attachment.
Sometimes, installed CJ deviated from the location specified in the project drawings and
had to be corrected while the RCC was still fresh. Occasionally, trucks struck and
destroyed recently inserted CJ plates, which also required immediate replacement. In
total, more than 200,000 feet of CJ plates were installed during the RCC construction.
Construction Techniques for RCC Placement
825
Figure 24. Contraction Joint Installation
Precast Gallery Units
The location of the inspection and drainage gallery in the raised dam followed the layout
of the gallery in the original dam and extended into the new RCC sections. The gallery
and adits were constructed using full section precast gallery units. The precast unit
manufactured by US Precast Group showed minimal defects upon arrival on site. SOJV
experienced problems at the beginning of the installation process, in particular in the adit
main entrance and the adit leading to the Gallery Access Building (GAB).
Misalignments and cracking caused during installation were the most common problems.
However, once the learning curve was overcome, precast unit cracking became less
frequent. Figure 25 depicts an inclined roof precast unit installed near the downstream
face of the original dam. In general, inclined roof gallery sections were no major
obstacle to the RCC placement equipment; however, horizontal roof gallery sections like
the ones installed for the main gallery adit and the GAB branch adit at elevation 474 were
an obstacle to RCC equipment (accessibility) and impacted RCC productivity.
826
Dams and Extreme Events
Figure 25. Inclined Precast Gallery Unit
Instrumentation
The instrumentation for the Main Dam body consisted of the following items:
•
•
•
•
•
•
Multiple-Point Borehole Extensometers (MPBX)
Piezometers (Vibrating Wire and Manual Piezometers),
Thermocouples
Accelerometers
Drainage/Seepage Flow Weir
Surface Monuments
Extensometers, vibrating wire piezometers and thermocouples were installed on the main
dam during RCC construction. Installation of manual piezometers, accelerometer,
surface monuments, and weirs were installed after RCC placement. This section provides
a summary of the instrumentation installation during the RCC dam construction and data
collected from the temperature instruments monitored by the CM Team (thermocouples).
A three-point MPBX was installed at 45-degree inclination at STA 6+72 near the existing
extensometer borehole 407 in the existing inspection and drainage gallery (elevation
468’). Extensometers EX-3, EX-4 and EX-5 were installed at depths of 70, 140, and 280
feet, respectively. The extensometer used was Model A-3 from GEOKON, which was
supplied by PROUSYS and installed by Group Delta. Extensometers were monitored
during construction by the designer.
Construction Techniques for RCC Placement
827
A total of seven foundation vibrating wire piezometers were installed during RCC
construction.
In order to monitor the temperature rise in the RCC after being placed, project drawings
specified the installation of several layers of Type T thermocouples at various elevations
in the body of the dam. Each thermocouple layer consisted of eleven units which covered
from the upstream to downstream side of the new RCC dam. Thermocouple wires were
routed to an 8-inch PVC conduit embedded in the RCC. These wires ended at the
reading units installed in the inspection gallery at elevation 468 in the original dam.
Except by the thermocouples installed at elevation 601, which were moved one foot up,
all other thermometers were installed according to plan.
Due to the fluctuations observed in the Contractor’s thermocouple readings, the CM
Team installed additional quality assurance (QA) thermometers to validate the
Contractor’s (QC) thermocouples. These temperature loggers supplied by Intellirock,
were installed and monitored by the RCC Inspection team. The temperature history
curves recorded by these instruments at various elevations and offsets are shown in
Figure 26. A comparison of these values with the thermal study during design indicates
that they are within the range expected by the designer.
The peak temperatures recorded by Contractor’s and CM Team’s thermometers in the
new dam at different elevations indicates that comparable peak readings were obtained
with both sets of instruments.
Temperature Rise Main Dam
CM Temperature Loggers at Elev. 476, 520, 601,679,720 & 740
Oct 29, 2012
130
122
120.2
120
115
110
Temperature (ºF)
108
107.6
100
96
95
95
90
89.6
86
80
70
EL 740
EL 720
60
EL 679
EL 476
EL 601
EL 520
50
0
30
60
90
120
150
Day zero is Nov. 8, 2011
5109476 MAIN DAM EL 476 STA 6+52 25 DS
8235885 SAN VICENTE 520 1 (8' from existing dam)
8235893 San Vicente 520 3 (8' from D/S)
8235887 EL 601 2 (Mid RCC section)
8235890 SAN VICENTE DAM EL 679 1
8235892 SAN VICENTE DAM EL 679 3
8235891 SAN VICENTE DAM EL 740 1
180
210
240
270
300
330
360
390
Time (Days)
5109475 MAIN DAM EL 476 STA 8+25 30 DS
8235894 San Vicente-520-2 (Mid RCC Section)
8235888 EL 601 1 (8' from existing dam)
8235886 EL 601 3 (8' from D/S steps)
8235889 SAN VICENTE DAM EL 679 2
8275905 SAN VICENTE DAM EL 720 2
8235895 SAN VICENTE DAM EL 740 2
Figure 26. CM Temperature Readings at Various Elevations and Offsets in Main Dam
828
Dams and Extreme Events
Spillway, Crest Slab, and Parapet Wall
San Vicente Dam is essentially an “all RCC” structure; however, some components of
ancillary structures as spillway, crest slab, and parapet wall are constructed with
conventional concrete. The spillway of San Vicente Dam takes advantage of the RCC
downstream steps to dissipate energy and uses conventional concrete training walls to
channel the water flow downstream to the flip bucket. The concrete in the training wall
was typically placed with crane and bucket. Training wall placement followed RCC
placement. The spillway ogee and flip bucket and training walls were constructed with
structural concrete, which was delivered in mixer trucks from a concrete producer located
nearby the project.
The purpose of flip bucket is to deflect the flow downstream such that the energy is
transferred to a position where impact, turbulence, and resulting erosion will not
jeopardize safety of the dam. Conventional concrete was used to create the curve shape
of flip bucket as shown in Figure 27.
Figure 27. Concrete Pour for the Flip Bucket
Construction Techniques for RCC Placement
829
Figure 28. Finishing Crest Slab Concrete Pour
The top of the dam is one-foot-thick conventional concrete slab, also known as crest slab.
On the downstream and upstream sides at the top, a three-and-half-foot-high parapet wall
was also constructed from conventional concrete. A picture of in-progress crest slab
construction and the parapet wall steel reinforcement is provided in Figure 28.
The dam crest spillway is an ogee shape with a crest at elevation 766. A flat sloping
surface connects the upstream face of the dam at elevation 756 with the upstream
quadrant of the ogee at elevation 765.46. The equation for the shape of an uncontrolled
ogee crest downstream from the apex to the point of tangency with the circular flip
bucket is given by the USBR Standard (1987a). Steps have been designed into the ogee
shape (downstream) beginning at elevation 763. The outer point of the step is on the
ogee profile.
A picture of in-progress crest spillway ogee construction concrete placement and steel
reinforcement is provided in Figure 29.
A picture of in-progress crest spillway ogee construction concrete placement and overall
formwork layout is provided in Figure 30.
830
Dams and Extreme Events
Figure 29. Ogee Spillway Concrete Placement
Figure 30. Ogee Placement Formwork Layout
Construction Techniques for RCC Placement
831
SUMMARY
The presented construction, scheduling, and coordination techniques associated with
placing RCC on the downstream face of the original San Vicente Dam were use to raise
the original San Vicente Dam 117 feet from 220 feet to a new full height of 337 feet.
The near finished full height San Vicente RCC Dam is as shown in Figure 31.
Figure 31. New Full Height San Vicente Dam
832
Dams and Extreme Events