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21st Century Dam Design
Advances and Adaptations
31st Annual USSD Conference
San Diego, California, April 11-15, 2011
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On the CoverArtist's rendition of San Vicente Dam after
completion of the dam raise project to increase local storage and
provide
a more flexible conveyance system for use during emergencies
such as earthquakes that could curtail the regions
imported water supplies. The existing 220-foot-high dam, owned
by the City of San Diego, will be raised by 117
feet to increase reservoir storage capacity by 152,000
acre-feet. The project will be the tallest dam raise in the
United States and tallest roller compacted concrete dam raise in
the world.
The information contained in this publication regarding
commercial projects or firms may not be used for
advertising or promotional purposes and may not be construed as
an endorsement of any product or
from by the United States Society on Dams. USSD accepts no
responsibility for the statements made
or the opinions expressed in this publication.
Copyright 2011 U.S. Society on Dams
Printed in the United States of America
Library of Congress Control Number: 2011924673
ISBN 978-1-884575-52-5
U.S. Society on Dams
1616 Seventeenth Street, #483
Denver, CO 80202
Telephone: 303-628-5430
Fax: 303-628-5431
E-mail: [email protected]
Internet: www.ussdams.org
U.S. Society on Dams
Vision
To be the nation's leading organization of professionals
dedicated to advancing the role of dams
for the benefit of society.
Mission USSD is dedicated to:
Advancing the knowledge of dam engineering, construction,
planning, operation,
performance, rehabilitation, decommissioning, maintenance,
security and safety;
Fostering dam technology for socially, environmentally and
financially sustainable water
resources systems;
Providing public awareness of the role of dams in the management
of the nation's water
resources;
Enhancing practices to meet current and future challenges on
dams; and
Representing the United States as an active member of the
International Commission on
Large Dams (ICOLD).
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Underwater Construction Engineering 721
CHEESMAN DAM OUTLET WORKS RENOVATION UNDERWATER CONSTRUCTION
ENGINEERING
Jeff Martin, P.E.1
Gordon Harbison, P.E.2
ABSTRACT
Denver Water is in the process of an Outlet Works Rehabilitation
at Cheesman Dam. The outlet works consists of tunnels bored through
the left abutment at elevations 6,780, 6,690, and 6,645,
respectively referred to as the Auxiliary, Mid-Level, and Low-Level
Outlets. The rehabilitation was accomplished by installing new
stainless steel slide gates through underwater construction diving
and at depths up to 210 feet. The Cheesman Upstream Control project
is a phased project spanning several years of design and
construction. The project begun in 2007 with the removal of the old
balance valve at the low level intake and is anticipated to finish
in 2011 with the removal of the old guard valves within the outlet
tunnel and replacement of the Larner-Johnson Needle Valve with a
new Jet Flow Gate. The entire project includes providing upstream
control by means of new slide gates at the inlets to the outlet
works tunnels, a new control building housing the hydraulic power
for the gates, and finally removal of the guard gates within the
outlet tunnel. The project design was based upon historical
information including the original survey note books, asbuilt
drawings, and photographs. The high costs of construction diving
coupled with the likelihood of differing subsurface conditions
required a good partnering effort between the Contractor, Resident
Engineer, and Design Engineers. A fast-paced construction schedule
(24-hours a day for approximately 15 weeks) required quick analysis
of existing conditions and subsequent design changes to avoid lost
production time and unnecessary costs.
FACILITY OVERVIEW
The Cheesman Dam is an on-stream facility located on the South
Platte River in Jefferson and Douglas Counties, Colorado, in the
Pike National Forest. The dam was constructed for storage of
municipal water supply by the South Platte Canal and Reservoir
Company, and was completed in 1905. At the time of construction
Cheesman was the worlds highest dam. In 1973 Cheesman Dam was
designated a National Historic Civil Engineering Landmark by the
American Society of Civil Engineers. The dam structure is a gravity
arch masonry dam constructed with solid granite blocks laid in
cement mortar as facing over a core consisting of granite rubble in
a bed of
1 Jeff Martin, Project Manager/Design Engineer, Denver Water
Department, 1600 West 12th Ave, Denver, CO 80202 2 Gordon Harbison,
Resident Engineer, Krech Ojard & Associates, 3580 Mount Hickory
Blvd., Hermitage, PA 16148
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21st Century Dam Design Advances and Adaptations 722
Figure 1. Site Layout
concrete. The dam is 221 feet in height and impounds 79,064
acre-feet of water, and is classified as a large high hazard dam.
The outlet works tunnels are bored through the left abutment at
approximate elevations 6,780, 6,690, and 6,645, respectively named
within the drawing set as the Auxiliary Outlet, Mid-Level Outlet,
and Low-Level Outlet. A fourth outlet tunnel at elevation 6734 was
originally constructed, but was abandoned with the inlet portion
being filled with concrete. The Auxiliary Outlet, built in 1925, is
an independent tunnel outlet with no connection to the other
tunnels and is controlled by the Larner-Johnson Needle Valve. The
Low and Mid Level outlet tunnels combine to one tunnel
approximately two-thirds of the way through the abutment. Both
tunnels are controlled by a total of six 42-inch gate valves prior
to the tunnel intersection, and then by various cone and
free-discharge valves in the downstream valve house. The site
layout is shown in Figure 1.
The only major work succeeding the original construction is a
valve house constructed at the toe of the dam in 1971. The original
waterway tunnel was extended with a 78-inch diameter steel pipe.
The pipe is manifold to provide passageways for two 42-inch, one
24-inch, one 12-inch, and one 8-inch Howell Bunger type outlet
valves. Each of the outlet valves are guarded by one or more ball
valves.
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Underwater Construction Engineering 723
The six 42-inch gate valves at one time controlled the release
flows to the South Platte River, after the 1971 Valve-House
addition the 42-inch gate valves act as guard gates to the valves
located within the Valve-House. The 42-inch gate valves internal to
the outlet works tunnels are equipped with hydraulic cylinders to
operate the gate stem. The hydraulic system consists of an original
Pelton Wheel connected to a triplex pump that furnishes hydraulic
water pressure to the cylinders attached to the gate valves. The
original Pelton Wheel, 42-inch gate valves, cylinders, and piping
were used to operate the system, until completion and startup of
the new slide gates as described in this paper. Figure 2 and Figure
3 the Primary outlet works and Auxiliary outlet works sections
through the left abutment.
Figure 2. Primary Outlet Works
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21st Century Dam Design Advances and Adaptations 724
PROJECT INITIATION
The project need and initiation was bore out of several key
factors: (1) An aging outlet works system dependent and operating
on 19th century equipment and technology, (2) maintaining key
infrastructure within the Denver Water system, (3) new sediment
loading from the Haymen Fire3, and (4) a desire to provide upstream
control of the outlet works tunnels for future work. The facility
needs and the Denver Waters organizational goals and Mission
Statement4 aligned and the project was selected for implementation.
Outlet Works modifications studies and alternatives were initiated
in 2005, followed by design concept selection in 2006. Early within
the alternatives development and evaluation phase, an underwater
construction approach was selected based on water storage risks
associated with draining the reservoir. Analyses showed there was a
significant probability of not filling the reservoir in a single
run-off season. Specifically, the analyses showed a 30% probability
of a storage shortfall in Cheesman Reservoir. A shortfall of the
magnitude evaluated would have system wide impacts to the water
supply system.
3 Colorados largest wildfire impacted the drainage area directly
above Cheesman Dam 4 Denver Water will provide our customers with a
reliable, high-quality water supply and excellent service. We will
be responsible and creative stewards of the assets we manage. We
will actively participate in and be a responsible member of our
communities. We will accomplish this mission with a productive and
diverse work force.
Figure 3. Auxiliary Outlet Works
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Underwater Construction Engineering 725
DESIGN PLAN The Cheesman Upstream Control project is a phased
project spanning several years of design and construction. The
project begun as an Outlet Works Modifications study in 2005, with
a selected design approach made in 2006. In 2007 Denver Water
contracted with Rodney Hunt (RH) for fabrication of three
hydraulically operated stainless steel slide gates and spools
(tunnel liners/thrust restraints). The installation design began in
2007 and lagged the slide gate design, and was based upon the
limited site knowledge and the pre-purchased slide gates designed
and fabricated on a similar but earlier schedule. During the design
phase it was understood that the project would be performed
underwater and by a limited amount of divers; likely just one diver
physically assembling the components of the design. The design and
installation of the slide gates was based upon the interpreted size
of the three inlet tunnel portal geometries. An interpretation of
the geometry from historical data was made, and the size of the
slide gates was maximized to maintain the current hydraulic
capacity of the outlet works system. As the condition of the rock
quality was not know at each of the inlets, a new tunnel liner,
referred to as a spool, was designed for each tunnel inlet. The
spool piece serves several key purposes, they are (1) Structural
support to the tunnel portal area, (2) form for annulus grouting
(seal) between the spool and tunnel, and (3) provide a clean
connection flange for the gate. Basically, the spool acts as a
traditional gate thimble, but also provides structural support to
the tunnel portal area. Rock excavation, tunnel shaping, and spool
placement and annulus sealing were the most critical steps for
project success. Rock excavation and tunnel shaping contained the
most contract risk, and a majority of the construction duration and
all change order work was spent on these activities. It was known
and understood by Denver Water that without a detailed physical
hands on survey of all three areas, the tunnel portal geometry as
related to the placement of the spools contained the most risk to
the project. In order to maintain the current hydraulic capacity of
the system the spool cross sections were maximized to within inches
of the assumed tunnel geometry. This condition resulted in a
minimal amount of room for the spool to fit within the tunnel. The
hydraulic design criteria for the outlet works governed the spool
size, and the risk of additional excavation and tunnel shaping was
known and accepted by Denver Water prior to project bidding. The
stainless steel slide gates and spools were designed specifically
for each level, the Auxiliary Level is the largest at 8x8, while
the Mid and Low Level gates are 4x7. The slide gates were designed
to simply be attached with 52 or 72 bronze hex head bolts
(depending on the size of the gate) secured to a flange piece on
the front of the spool piece. The hydraulic tubing could then be
connected to the gate, followed by the installation of the
trashrack sections.
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21st Century Dam Design Advances and Adaptations 726
Through lessons learned from a different underwater project, the
design team choose to drill inclined bore holes form atop the left
abutment to the gate locations to house the hydraulic control
lines. Two inclined rock borings were drilled, one to the Auxiliary
Level, and one boring servicing both the Mid Level and Low Level
Outlets. The inclined bore holes eliminated a great amount of risk
to the contractor and provided a protected conduit to house the
hydraulic control lines and bubblers air lines. Phase 2 of the
Cheesman Upstream Control project includes removal and replacement
of the Larner-Johnson Needle Valve with a new Jet Flow Gate, and
removal of the six gate valves located in both the Mid-Level and
Low-Level outlet tunnels. The opening left by the removal of the
gate valves will be sealed with new tunnel sleeves. Bulkheads will
be installed at this location for future access. In addition to the
valve removals, new platforms, handrails, and ladders will be
installed within the manways. Finally, a small tunnel air/fill line
will be constructed so that the upstream control gates can operate
under balanced head conditions. Phase 2 construction work is
planned for spring/summer 2011.
UNDERWATER CONSTRUCTION Contract Global Diving and Salvage
(Global) was contracted through a quality based selection process
to perform the underwater diving work and manage other ancillary
conventional construction that had impacts to the diving work and
schedule. Prior to executing the contract, Global and Denver Water
negotiated a predetermined daily rate for anticipated change order
work and standby (idle) time. The pre-negotiated rate for surface
diving was approximately $27,000/day and for saturation diving was
approximately $80,000/day. The surface air diving was based upon
12-hour days and would be implemented at the Auxiliary Level while
the saturation diving schedule was based upon 24-hour days and
would be used at both the Mid Level and Low Level with continuous
operation until the project was complete. Schedule Due to the high
contractor overhead costs for the dive barge, crane, saturation
diving life support system, and short weather window, the schedule
was aggressive and fast paced. The sequencing of the installation
work and owner restrictions for continued operation of the
facility, created a schedule with little to no float and a series
of activities dependent on finish-to-start relationships. In order
to continue with operation of the facility and bypass critical
water calls on the river, concurrent work was not allowed; limiting
the contractor to work on one level at a time and to completion.
With no schedule float, it was recognized at the beginning of the
project that a teaming effort between the contractor, resident
engineer, and the owner would be required to tackle project issues
in an effective and decisive manner. All project team members
strove for zero lost time production.
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Underwater Construction Engineering 727
Construction Sequencing The general sequencing of construction
was similar to what Denver Water had anticipated and designed. All
three levels followed the general sequencing shown in Figure 4.
Figure 4. Construction Sequencing (Typical for All Three
Levels)
CONSTRUCTION ENGINEERING Construction Engineering Team
The very nature of an underwater capital improvement project at
a 110-year facility contains risk. In this projects case the
greatest risk was changed underwater physical conditions of the
tunnel areas as related to pre-purchased owner furnished equipment.
The high mobilization fee and overhead for the specialized diving
equipment resulted in large daily operation costs for the
contractor. Cost of operation and cost of production was almost
identical, resulting in the same daily rate charge in the event of
change order work or standby time. In the event of a change of
conditions, the Contractor may be required to standby until an
approved owner solution was provided for the implementation. In
this event the contractor would be compensated at the predetermined
daily rate. Again, the daily construction/standby time daily rates
were approximately $28,000/day ($2,340/hour) for surface/air diving
and $80,000/day ($3,325/hour) for saturation diving. Construction
engineering as related to changed field conditions played a vital
role in the success of the project.
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21st Century Dam Design Advances and Adaptations 728
This construction engineering team consisted of the contractor,
resident engineer, and the owner. The contractor provided a full
time project manager and project engineer to develop work plans and
detailed submittals outlining the construction sequencing. In
addition, the contractor staffed a construction superintendent who
reviewed and revised the work plans for underwater
constructability. Denver Water contracted Krech Ojard and
Associates (KOA), through HDR, Inc., to provide Resident
Engineering (RE) services for the underwater diving construction.
The purpose of the Resident Engineer was to monitor the diving
construction progress and quality through a live feed closed
caption video mounted atop of the divers dive helmet. KOA monitored
the entire underwater construction process, including 3 months of
air/surface diving, and 101 days of 24-hour saturation diving. The
Resident Engineering position was critical to the success of the
project, by locating the RE onsite in close contact with the
contractors project manager and project engineer, the RE was able
to assist in submittal development, submittal review, and design
construction when issues were identified. The original Denver Water
design team and structural consultant5, URS, maintained close
contact throughout the project to ensure issues were identified and
resolved according to the original design criteria of the new slide
gates.
Risk Management and Issue Resolution
Early identification and timely resolution of project issues was
a key factor for project success. In order to manage the project
issues that would arise during execution, the construction
engineering team continuously evaluated potential project risks
through a risk management plan and created response plans for risks
that could seriously impact the project. The risk management plan
was developed by the project team and updated by Denver Water,
prior to each construction phase the construction engineering team
met and brainstormed potential project risks and issues that could
impact the project. The risk register outlined project risks that
could impact both the owner as well as the contractor. The project
team worked on these risks together for the common success of the
project. The risk register was constantly updated, and most
importantly, lessons learned from previously completed activates
were incorporated within the risk register to minimize the impact
of the same issue occurring multiple times. The risk management
plan also outlined a response plan in the event a risk item
occured. The risk response plan would generally consist of having
key decision makers available to review changed conditions and
design modifications, decreasing the owner response and direction
time to the contractor. The risk response plans proved valuable for
several of the risk scenarios, and allowed project issues to be
resolved in an expedited and pre-defined manner. The risk register
and notification to stakeholders of the potential risk was
extremely valuable to expediting the response plan.
5 URS designed the trashrack structures and grout mix used for
the spool annulus grouting. URS also provided structural design
analysis and review at the Mid Level spool cover structural
block.
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Underwater Construction Engineering 729
Most serious issues on this project were the result of a
differing underwater physical condition that was different than
what was shown within the construction drawings. Some of the issues
were small and others were large. Regardless, any changes to the
planned work as related to the contract drawings resulted in cost
increases to the contract. Along with the pre-negotiated daily
rates, a clear division was made between contract work and change
order work. Prior to implementation of any changes a meeting
between the contractor, owner, and resident engineer was had to
review the change order work and delineate a scope line for change
order work and what would be eligible for additional contract
charges. Because all change orders were based upon a time and
material rate it was very important to monitor true change order
work versus contract work. A good example of this is the rock bolts
used to secure the spool in place. At the Mid Level location, the
required length of the rock bolts was typically about 3 feet in
length according to the contract drawings. After, identification of
changed tunnel geometry, the required length of the bolts was
between 5 feet and 6 feet in length. In this case, the base
contract covered the first 3 feet of drilling for the bolts, while
the remaining 2-3 feet of drilling was completed as time and
material with the resident engineer tracking the additional time.
By agreeing to a clear delineation of the scope line there was very
little disagreements between the owner and contractor regarding the
costs for change order work.
Figure 5. Issue Flow Chart
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21st Century Dam Design Advances and Adaptations 730
Auxiliary Level Tunnel Widening: The first project issue
requiring field construction engineering related to the Auxiliary
Outlet tunnel. The Contractor identified a differing underwater
physical condition within the Auxiliary Outlet tunnel. The
differing underwater physical condition consisted of differing
tunnel geometry within the Auxiliary Level resulting in the tunnel
being too narrow to allow the pre-purchased spool piece to
physically fit within the tunnel, requiring additional widening of
the tunnel annulus. In order to minimize the cost and schedule
impacts of the additional work, the Contractor, Resident Engineer,
and Owner reviewed several alternatives, shown in Figure 6, for
relocating the spool alignment to reduce rock excavation. The final
chosen alignment (Alternative 2) reduced the amount of excavation
by adjusting the bearing and moving the entire spool south. The
re-alignment resulted in approximately 20% less tunnel excavation,
and a cost savings of about $76,000.
Figure 6. Auxiliary Level Widening
Auxiliary Level Trashrack: While installing the second trashrack
section, interference between the existing tunnel wing walls and
the trashrack was encountered. Either the wing wall or the
trashrack required modification to fit the trashrack assembly
properly around the gate. It was decided to remove the trashrack
from the water and make structural modifications in the dry. The
contractor had concurrent work to perform on the hydraulic piping,
and continued with their underwater operations and adjusted the
schedule for the trashrack to be installed 3 days later. The
trashrack manufacturer was immediately contacted and requested to
send a crew to the site along with material that was anticipated
for the construction modifications. The existing wing wall was then
resurveyed. The data was used to design the modifications necessary
to ensure the trashrack would fit the existing condition. The
Resident Engineer and Owner reviewed the interference areas and
designed a new cut out area within the trashrack that would allow
the rack to fit around the wing wall. The proposed modification
design was then reviewed and approved by the structural
engineer.
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Underwater Construction Engineering 731
Figure 7. Mid Level Spool Post Blast Void
The design was based upon immediately available materials on
hand at the jobsite and those available for local pickup by the
fabricators en route to the jobsite. The redesign of the trashrack
section took approximately 24 hours to complete while the
modifications to the rack itself took an additional 48 hours.
Topside modifications to the trashrack as opposed to additional
wall excavation saved the project approximately $40,000 and did not
impact the project schedule. Mid Level Tunnel Geometry: The
existing Mid level tunnel geometry and physical conditions was
identified as a risk item early in the design phase of the project.
The as-constructed drawings and histrocial photographs showed
conflicting information, and recent side sector scan survey
information continued to disagree with the historical information.
The design team choose to show the most conservative interpretation
of the data, but assumed the existing conditions would be different
than shown within the contract documents.
As anticipated, the actual tunnel geometry was different than
what had been shown in the contract drawings. The existing tunnel
geometry was too narrow to allow the pre-purchased spool piece to
physically fit within the tunnel, requiring additional widening on
the south tunnel wall. The widening was accomplished by drilling
additional blast holes and limited hand excavation similar to the
Auxiliary Level. In addition to the tunnel geometry issue, a larger
void space was identified along north wall adjacent to the spool. A
small cavity was shown the project drawings that anticipated this
feature, the feature turned out to be approximately 30% larger than
anticipated. The cavity was filled with additional reinforcement
consisting of No. 6 rebar doweled into the tunnel and fill grout.
Finally, interference outside of the tunnel between the rock and
trashrack was identified. Additional minor rock excavation would be
required to fit the trashrack. In order to reduce costs, the entire
spool, gate, and trashrack were adjusted to the south and
vertically. The realignment resulted in additional tunnel shaping,
but reduced the exterior rock excavation. This proved to be a cost
effective alternative because the additional tunnel shaping could
be performed as part of the contract underwater blast, while the
exterior hand chipping would be laborious and time consuming. The
estimated project savings in changing the original alignment are
estimated at $120,000. Mid Level Rock Fall: A large rock mass above
the tunnel portal released during the blast operation, resulting in
a large void space above the gate spool. Through a post blast
visual inspection of the area, it was reasonably concluded the rock
mass
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21st Century Dam Design Advances and Adaptations 732
Figure 8. Low Level Masonry at Tunnel Brow
contained a joint and fracture pattern that was present prior to
the blast operation. The removal of the underlying rock (as
required by the contract documents) and the joint and fracture
pattern of the rock caused the rock mass to fall. The result of the
rock fall left the spool piece with no cover above it as planned
within the design package, as seen within Figure 7. In order to
meet the original design criteria of at least one tunnel diameter
of solid competent rock cover above the spool, a new monolithic
reinforced concrete block was designed to provide structural cover
over the front half of the spool, and increase length of potential
seepage pathways. The design of the new cover block was developed
by the Resident Engineer and Owner and was based upon survey
information developed by the Contractor. A concept design was
developed and submitted to URS Corporation for structural analysis
review. The embedment lengths of the bar and the bar spacing was
checked and approved. Upon value engineering review with the
Contractor, the rebar sizing was increased to reduce the overall
length of rebar embedment within the rock. Through contract work
the contractor had learned drilling in the native granite rock for
rebar embedment was a laborious process, and reducing the length
and quantity of embedments would reduce the change order cost. The
reinforcement size was increased, decreasing the amount of drilled
hole for embedment within the rock. This exercise was estimated to
save approximately $60,000 in installation costs. Low Level Masonry
Removal: During the contract blasting and construction activities
at the low level tunnel portal a differing site condition was
identified. Unlike the previous differing conditions, the low level
tunnel geometry was as expected and could fit the
spool without further modifications. However, it was discovered
that the tunnel brow and ceiling areas consisted of a poor quality
masonry material (See Figure 8), not hard competent granite as
shown in the historical documents. The unstable masonry brow posed
several challenges to the project. The first was diver safety, the
area was unstable and exhibited signs of potential failure and rock
fall. This condition posed direct safety concerns to the
construction divers. The second was the portal stability above and
behind the spool piece, if the area was masonry and not granite
rock, the
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Underwater Construction Engineering 733
entire system would depend on this material with unknown
structural and seepage characteristics. The original design had
depended on strong competent granite to lie directly over the spool
and tunnel just downstream of the spool. It was clear the original
design intent and design basis criteria would not be achieved if
the masonry was left in place above the spool. In order to best
ensure the new installation was structurally sound, it was decided
to remove identified masonry material and reposition the spool
further within the tunnel. Additional surveying was required to
identify the vertical control of the spool based on the rise of the
original tunnel floor. Proper placement was required to minimize
any additional material removal and maintain the hydraulic capacity
of the tunnel. The reposition of the spool met the original design
intent and design basis criteria. The repositioned spool provided
over 15 feet of vertical granite rock above the back end of the
spool. This cover material was believed to be good quality
competent granite rock that could provide the required structural
stability for the tunnel ceiling. The repositioning required three
addition underwater blasts to remove the material to the desired
area. The addition work took approximately 18 days and resulted in
a change order close to $1,400,000. The construction engineering
was vital in identify the issue and to design a new alignment that
met the criteria of the original design. If the masonry condition
was not discovered by the contractor, this issue would likely have
caused failure of the tunnel ceiling area behind the downstream end
of the spool, leading to major impacts to the facility and Denver
Waters operation.
PROJECT RESULTS AND CRITICAL SUCCESS FACTORS
Project Results The project was a success in providing new
upstream control at the Cheesman Dam. The new stainless steel slide
gates were operated successfully during the startup and
commissioning of the system. Most notably, the combined tunnel
seepage and gate leakage results were extremely low, and are shown
in Table 1. When consideration is given to the fact that these
gates were installed underwater at depths of 200 feet, and that
there are significant portions of the outlet works tunnels that are
unlined (allowing reservoir seepage), the minimal seepage observed
is considered to be a success.
Table 1. Combined Gate Leakage and Tunnel Seepage Rates
Auxiliary Level 2.8 gpm Mid Level 45 gpm Low Level 7 gpm
Critical Success Factors The project can be considered a success
for many reasons, from no lost time injuries or incidents to a
working system with extremely low seepage/leakage rates. Some of
the predefined critical success factors that were accomplished are
listed below.
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21st Century Dam Design Advances and Adaptations 734
The new slide gates and upstream location meet present day
standards. The new slide gates provide guard function to the
downstream valves. The new slide gates were installed almost
exactly as designed. The new slide gates provide new flexibility in
operating the facility. The Low Level slide gate trashrack has the
ability to be simply modified in the
future to store approximately 10 feet of sediment. Contract
modifications (negotiations) were fair and managed on a current
time basis,
with no issues left to the end of the project. The risk register
and response plans created a teaming effort between the
construction team to tackle issues in an efficient and
predefined manner. No standby time was incurred for the project.
All change order work resulted in high
production rates. Very minimal disruption to the operation of
the water supply system.