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Project Considerations

Rehabilitation of the Dam: Improving Cost Effectiveness by Including Bridge Placement

was found to be in “Poor” condition due pri- Combining efforts to address marily to the deteriorating/leaking spillway dam safety issues with access and downstream masonry wall and the erodi- bility of the “emergency spillway” over the and transportation issues main embankment section of the dam. provided a win-win situation To address most of the main dam safety concerns, a reconstructed spillway with a for all of the involved hydraulically actuated crest gate was chosen parties. as the preferred alternative. The crest gate option provided additional hydraulic capacity while also improving the DCR’s ability to MATTHEW A. TAYLOR & JOHN G. DELANO manage the reservoir level, most importantly, he Department of Con- during the annual winter drawdown. ser vation and Recreation (DCR) owns During the planning stages of the project, Tand operates the Otis Reservoir Dam in maintaining access to the west side of the Otis, Massachusetts, for recreational purposes. reservoir during construction was identified In 2006, the 145-year-old, 31.5-foot-tall, earth- as a critical component in the viability of the en embankment dam with downstream project. At the time, the bridge over the spill- masonry wall and stone masonry spillway way was a one and one-half lane, temporary

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“Bailey bridge” installed in 1995. It was sup- ered by about 3 feet to create an “emergency posed to have been replaced with a permanent spillway,” although no erosion protection, bridge in 1998. Given that the dam is a large, other than the asphalt pavement roadway, high hazard structure, the dam repairs needed was provided. The dam was originally built to move forward to protect the public safety. with a 38-foot-long stone masonry primary To expedite the project, the DCR elected to spillway located near the dam’s left (west) incorporate the bridge replacement into the abutment. The spillway was divided into two, dam rehabilitation project. The dam rehabili- 19-foot-long segments by a stone masonry tation project was transformed, by necessity pier. and creative planning, into a combined dam In 1995, MassHighway replaced the deteri- and bridge replacement project that ultimate- orating original bridge over the spillway with ly benefited the DCR and the town of Otis. a temporary one and one-half lane Bailey bridge. This bridge was intended to be in serv- Project Background ice for three years. A permanent, two-lane Otis Reservoir Dam is located within Tolland bridge was slated for construction in 1998. State Forest on the Fall River in the town of However, the project was delayed and post- Otis, in Berkshire County (see Figure 1). The poned, apparently due to MassHighway’s dam was originally constructed in 1866 by the bridge project prioritizations. By 2009, the per- Water Power Company in manent bridge replacement at the Otis order to provide supplemental water to power Reservoir Dam had been officially postponed mills on the Farmington River in . until 2014. The Commonwealth acquired the reservoir in Prior to the recent dam rehabilitation, there 1967. Otis Reservoir is a 1,000-acre impound- were two gatehouses/outlet structures at the ment with a 16-square-mile drainage area that dam. The original gatehouse, located in the encompasses portions of three towns (Otis, middle of the upstream side of the embank- Tolland and Blandford). Having a storage ment, was taken out of service in 1984 when capacity of 22,000 acre-feet (7.1 billion gallons) the outlet works at the dam were rehabilitat- at normal pool, it is the largest recreational ed. The original sluice gates, stems and opera- body of water in the Commonwealth of Mas- tors were removed and a 4-foot-high by 8- sa chusetts. foot-wide intake conduit, with an upstream Tolland Road, owned by the town of Otis, steel trash rack, was installed within the reser- passes over the dam and provides the only voir. The intake conduit extends into the reser- access to the western side of the reservoir dur- voir about 40 feet upstream of the dam. A ing the winter months. The majority of the res- downstream outlet tower was constructed in idents on the western side of the impound- 1984 with a second gatehouse opposite to the ment are seasonal, with only four full-time original upstream gatehouse. The outlet tower residents present during the winter. Because has two, 48-inch-square slide gates. One gate of the recreation industry supported by the serves as a low-level outlet and the other reservoir, the population in the town of Otis serves as a mid-level outlet. The outlet tower swells from a few thousand in the winter to also has a 10-foot-wide by 3-foot-high over- near 10,000 during the summer months. flow weir at the same elevation as the primary The Otis Reservoir Dam consists of an spillway crest (with the flashboard in place). earthen embankment with a downstream The two original 30-inch-square stone sluice- stone masonry wall. The dam has a maximum ways through the dam had been retrofitted structural height of about 31.5 feet and a with 26-inch-square steel conduits and then length of about 630 feet. The exposed portion grouted in place. of the downstream masonry wall of the dam is The Otis Reservoir is operated by the approximately 480 feet in length. Tolland DCR’s park staff according to an order of Road, a paved public roadway, traverses the conditions from the Otis Conservation top of the dam. In 1955/1956, after Hurricane Commission, which defines the target sea- Diane, the top of the embankment was low- sonal reservoir levels and governs the rates

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FIGURE 1. The location of the Otis Reservoir and dam.

of reservoir drawdown and refill. In October for an annual weekend canoe race. The DCR of every year, the DCR opens the low-level subsequently dials back the release to lower outlet gate to provide a flow of around 300 the reservoir to about 2 inches per day until cubic feet per second (cfs) into the Fall River the winter pool elevation (6 to 8 feet below

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FIGURE 2. View of the deteriorated and leaking conditions at the spillway prior to rehabili- tation.

the primary spillway crest elevation) is ice. An excessive water release could cause the reached. The purpose of the annual draw- development of a void between the bottom of down is to allow for the inspection of the the ice and the surface of the reservoir. The dam structure, to prevent ice damage to the presence of such a void would be a major safe- shoreline docks and piers, and to provide ty concern, given the year-round recreational meltwater storage and discharge control use of the reservoir, which includes ice fishing during the spring freshet. Beginning in and snowmobiling on the reservoir. The January of each year, the DCR begins to raise DCR’s staff would use a chain saw to cut holes the reservoir level. The reservoir is raised to through the ice in order to evaluate the reser- within 4 feet of the summer pool level by voir level. Obviously, this practice was not an April, depending on the ice conditions on ideal approach. So, the DCR indicated that the the reservoir. The goal is to have the reser- dam rehabilitation project should also include voir level restored to the summer pool level provisions to improve the reservoir operation by July 4th each year. The 1984 outlet works procedures. configuration requires constant adjustment to manage the reservoir level, especially Engineering Evaluations & prior to or after storm events. Alternative Analyses With the winter pool being maintained by Following an inspection of the dam in May releasing water from the low-level outlet in 2006 by an engineering consulting firm, the the downstream outlet tower, the DCR could dam was judged to be in “poor” condition. not easily monitor the water level below the The primary deficiencies of the dam were:

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• The deteriorated masonry and leakage (PFMA) was performed with several members conditions at the spillway (see Figure 2) of consultant’s dam engineering team and and the downstream masonry wall; and, representatives from the DCR who were • The erodibility of the “emergency spill- responsible for the operation and maintenance way” over the main embankment section of the dam. The objective of the PFMA was to of the dam. assess possible failure modes and to deter- mine the most likely failure mechanisms, In 2007, the engineering consultant per- thereby allowing the design of the rehabilita- formed a Phase II Engineering Evaluation and tion project to address each of these deficien- Alternatives Analysis of the dam. This study cies. included field investigations covering wet- Using the information obtained from the lands delineation, a topographic survey of the detailed engineering evaluations and the dam and nearby areas, rare species determina- PFMA, an alternatives analysis was per- tions, diving inspections of the intake conduit formed to evaluate the repair/rehabilitation and interior of the downstream outlet tower, options that could address the dam safety subsurface explorations with test borings and issues. These alternatives included: taking additional readings from the existing instrumentation (piezometers and inclinome- • no action; ters) at the dam. The consultant’s engineering • breach/remove; evaluations included interpretation of the sub- • raise the dam; surface conditions from the test borings, geot- • construct an emergency spillway; and, echnical laboratory testing (grain size analy- • spillway modification/reconstruction. ses) and existing instrumentation readings, as well as conducting engineering analyses Spillway reconstruction, along with raising including detailed hydrologic and hydraulic the crest of the dam, were selected as the pre- analyses, liquefaction and seismically induced ferred alternatives. settlement analyses, seepage analyses, slope stability analyses and gravity wall stability Selection of the analyses. Preferred Alternatives With Otis Reservoir Dam categorized as a To address both the dam safety issues and large, high hazard dam per the Massa chu - operational issues, reconstructing the spillway setts Dam Safety Regulations, its spillway with a bottom-hinged, 7.5-foot-tall by 38-foot- design flood (SDF) is one-half of the proba- wide steel crest gate was selected as a pre- ble maximum flood (½ PMF). The results of ferred alternative. When the crest gate is in the the detailed hydrologic and hydraulic analy- “up” or “closed” position, the top of the gate ses revealed that the original spillway was is at the current normal summer pool eleva- capable of passing only 10 percent of the SDF tion for the reservoir. The invert of the new and overtopping of the dam by about 3.3 feet spillway (i.e., with the crest gate in the was predicted. The seepage and stability “down” or “open” position) was set at the analyses indicated that the dam met most of winter pool elevation so that once the reser- the stability requirements set forth in the voir was drawn down it could “self-regulate” dam safety regulations except for the case the reservoir level without constant assess- where the dam was overtopped during the ment and adjustment by the DCR staff. SDF event. The factor of safety against slid- To safely pass the SDF, the DCR staff ing for the downstream masonry wall was would need to lower the summer reservoir below the recommended minimum value of level by 2 feet in advance of the ½ PMF 1.3 due to the likelihood for erosion occur- event and then operate the gate throughout ring at the base of the wall attributed to over- the storm to prevent overtopping of the topping during the SDF. dam. Without proper gate operation, the In concert with the detailed engineering dam will be subject to overtopping during analyses, a potential failure mode analysis the SDF. However, the proposed dam modi-

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Reconstruct spillway & bridge Raise top of dam, improve roadway alignment & pedestrian access

Rehabilitate outlet tower controls Construct spillway control building

Repair downstream masonry & Demolish unused construct new toe drain upstream building

Rehabilitate upstream slope

N

FIGURE 3. The locations of repairs/improvements on the dam.

fications would allow the spillway to safely • raising the top of the dam by adding up pass the 500-year flood event with about 2 to 3 feet of embankment fill; feet of freeboard without lowering the crest • repointing the downstream masonry gate. wall; Typically, relying on human operations to • extending the downstream toe drain; pass the SDF is not a recommended dam safe- • adding a reinforced concrete splash pad ty practice. The reason it is not recommended at the base of the downstream masonry is the potential for improper or lack of opera- wall; tion that can result from human error. How- • restoring the rip-rap slope protection on ever, Otis Reservoir Dam is not a typical dam the upstream and portions of the since it has a full-time dam operations staff in downstream slopes; and. the DCR’s Office at the • installing new slide gates on the inside right abutment of the dam. The DCR also has upstream face of the downstream outlet staff who live locally who are “on-call” should tower. an emergency situation develop at the dam. Therefore, the design of the new spillway was Solving Resident Access Issues able to take advantage of the DCR’s somewhat Access to the west side (left side of the dam) of unique on-site staffing situation. the reservoir was identified as a critical issue Other improvements included in the dam early in the project development. The towns of rehabilitation, as shown in Figure 3, were: Otis and Tolland fully understood the benefit of the project. However, residents of both • adding a new gatehouse on the left towns were concerned about the potential for abutment of the dam; short-term impacts on the recreational-based

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economy. Several concepts and options were bridge was closed. The detour route (see evaluated by the project team in order to Figure 4), which was about 8 miles in length, address this concern. included a 2.8-mile section of gravel road that Initially, a bypass route upstream of the was typically not plowed during the winter. spillway was evaluated. A temporary earthen The DCR included a construction contract embankment was considered that would con- provision for liquidated damages to be levied vey traffic around the spillway construction against the contractor if the bridge over the while also serving as a temporary cofferdam spillway was not reopened on time. The town for the work area. A significant amount of fill of Otis accepted the DCR’s offer for the new would have been needed to be placed in wet- bridge and the temporary detour route, and lands area fro the embankment. This option granted the DCR permission to close Tolland was eliminated when the constructability, cost Road for five months. and permitting requirements were evaluated more closely. Dam & Bridge Design A second approach that was considered Considerations was to construct the spillway in two segments: The design of the dam rehabilitation and the upstream and downstream. The existing bridge replacement occurred between 2007 Bailey bridge would be left in place initially to and 2010. The engineering consultant retained allow the upstream portion of the spillway to another engineering firm to provide structur- be constructed. The Bailey bridge would then al, mechanical and electrical engineering be moved to the upstream side of the dam and design services for the new crest gate and for the downstream half of the spillway would be two new slide gates in the outlet tower. constructed. However, this option was also Under a separate contract, the Massachustts eliminated when the costs associated with the Department of Transportation (MassDOT) phased construction, the extended construc- engaged another consultant to perform the tion duration, the need for a more robust tem- bridge design. The DCR supervised the bridge porary cofferdam capable of remaining in designer and reported progress to MassDOT. place throughout the higher summer pool sea- As overall project manager and the dam engi- son and the additional risks were evaluated neer-of-record, the contracting engineering more closely. consultant was responsible for providing To limit the impact of the project on the engineering design for the dam, including the recreational use of the reservoir, it was decid- hydrologic/hydraulic, geotechnical and civil ed that the majority of the work needed to be designs, in addition to coordinating the other performed in off-season (i.e., winter construc- project team design responsibilities and merg- tion). It was also obvious that with the signifi- ing of the contract documents into a single bid cant improvements being considered for the package. spillway, it did not make sense to reinstall the A performance-based specification was cre- temporary Bailey bridge over the newly ated for the crest gate. Two Massachusetts- reconstructed spillway. Therefore, the DCR based gate manufacturers were consulted to decided to incorporate a permanent bridge provide input in establishing the crest gate replacement into the dam rehabilitation proj- design criteria and to understand the implica- ect. In exchange for adding the new bridge to tions of the DCR’s intended operation proce- the project, the DCR was granted permission dures. The DCR was committed to providing from the towns of Otis and Tolland to close redundancy with the crest gate operations. Tolland Road for five months (from October The DCR wanted the gate to have twin top- 2010 to March 2011) in order to facilitate con- mounted actuators, but the DCR also wanted struction. to have the ability to operate the gate with a To address the access issue to the west side single actuator in the event that one failed. of the reservoir, the DCR offered to establish Based on this requirement, a hydraulically and maintain a detour route around the reser- actuated operation system was selected for the voir during the five-month period when the project. Velocity fuses (i.e., a hydraulic valve

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Dam Site

FIGURE 4. The 8-mile detour route that was used during construction.

used to stop flow if the maximum speed of the included provisions to raise or lower the gate fluid is exceeded) were also added to the sys- manually in an emergency situation. A new tem to prevent the gate from opening uninten- gatehouse was also added on the left (west) tionally in the event of a power loss or a break abutment of the dam to house the crest gate’s in the hydraulic system. The gate system also hydraulic system.

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With the reservoir’s annual drawdown and the necessity for limited road closure pre- schedule, there is a need to operate the gate in cluded any of the bridge types that used cast- cold-weather months. However, the rubber in-place decks. Therefore, a decision was side and invert seals could be damaged if the made by the project team to only consider crest gate is operated while it is subjected to bridge types that used prefabricated elements, ice accumulation. As such, robust electric side since they could be brought on-site and low- seal and invert heaters were incorporated into ered into place once the spillway training the structure. Operational procedures to turn walls/bridge abutments were completed. The on the heaters in advance of any winter gate prefabricated bridge types that were operations were also written into the dam’s considered included: new operations and maintenance plan. The new gatehouse constructed near the spillway • Prefabricated concrete/steel composite to house the crest gate controls included pro- superstructure units (formally known as visions for connecting a portable generator if Inverset); spillway operations were required during • NEXT beam system; power outages. • Fiber reinforced polymer (FRP) deck on The existing masonry spillway was steel stringers; removed and replaced with a reinforced con- • Full depth precast concrete deck panels crete structure to support the crest gate and to on concrete or steel stringers; and, convey the spillway flow through the dam. • Butted boxes/deck slab with no cast-in- The new spillway structure served dual pur- place deck. poses: spillway training wall and bridge abut- ments. (In addition to the hydraulic loads The effects of each system on the imparted due to the spillway flows, the new hydraulic performance of the spillway, their concrete walls were also required to support relative maintenance costs and their impact the lateral loads from the embankment, verti- on construction schedule (if any) were eval- cal dead forces from the bridge structure and uated. The first alternative — prefabricated HS-25 vehicle loading, and earthquake loads.) concrete/steel composite superstructure The training walls/abutments were to be units with an asphalt wearing course — was founded directly on bedrock, which provided chosen. The composite system included adequate bearing capacity and erosion resist- steel stringers and a precast concrete deck. ance. The main benefits of this bridge type includ- Several types of superstructure for the new ed design flexibility, adaptability to the bridge were considered in the early part of the winter construction schedule and quick project. Initially, the bridge types considered installation. included: Improving Constructability by • Single span, precast, prestressed concrete Modifying the Spillway Design spread box beams with cast-in-place The winter-only construction schedule, cou- concrete deck. pled with the five-month road closure limita- • Single span, rolled steel stringers with a tion, dictated that the total construction sched- cast-in-place deck. ule for the project occur over a two-year peri- • Single span, built-up steel plate girders od. And, with the crest gate design, submittal with a cast-in-place deck. review process and fabrication requiring up to • Single span, rolled steel stringers with a six to eight months, the crest gate installation timber deck. was not scheduled until the second winter construction season. This schedule would The initial recommendation for a bridge have not been possible if the project had been type was for a single span, precast concrete awarded in the fall since the spillway con- spread box beams with a cast-in-place deck. struction would have needed to have been However, the winter construction schedule completed during the winter road closure of

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FIGURE 5. Improvements to the dam crest and upstream slope.

the first construction season. In order to • The stop logs would also be used to cre- accommodate this scheduling issue, the deci- ate a controlled upstream water condi- sion was made to add stop logs bays to the tion that would allow testing of the crest spillway upstream of the proposed crest gate. gate and the training of the DCR opera- The addition of the upstream stop logs pro- tions staff. vided the following benefits: Combined Dam & Bridge Design • The stop logs provide a permanent mech- Benefits Project Financing anism to allow the crest gate to be taken With the project design and constructability off line for servicing and maintenance. issues resolved, the next step was to figure out • The stop logs could be installed early in how the project would be funded. The initial the spillway construction in order to limit construction cost estimate was on the order of the amount of time needed for a tempo- $2 million. The DCR Office of Dam Mainten - rary cofferdam for the project. ance used this figure in their capital planning • The stop logs could be installed and kept for FY2010/2011. However, the initial cost in place to serve as the water control estimate did not include a new bridge nor did mechanism until the crest gate was fully it consider a two-season construction sched- installed. Doing so would allow the crest ule. Consequently, the updated project cost gate design, submittal review and fabri- estimate was about $1 million higher than cation to proceed without the added pres- originally estimated. In order to address the sure of being the critical path element for cost increase, the DCR needed to look at other the project. funding options.

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FIGURE 6. Bedrock excavation at the spillway.

Because this “dam” now included a new ed in a greater way with the expanded proj- bridge, it became obvious that it should quali- ect scope and the DCR’s ability to see the big fy for “bridge monies.” The bridge and por- picture. tions of the spillway construction that served a dual capacity (both spillway training walls First-Year Construction and bridge abutments) were funded via the Highlights MassDOT Accelerated Bridge Program and The project was advertised for bid in the sum- not solely through the DCR’s Office of Dam mer of 2010. The project was awarded to the Maintenance dam rehabilitation budget. low bidder, with a bid price of $3,057,496.50. Second, by extending the project to two con- Seven prequalified contractors submitted bids struction seasons, the project was also extend- on the project. The four lowest bidders were ed over two fiscal years. Consequently, the within $150,000 of each other, and all four of DCR was able to spread the project budget out these bids came within $300,000 (roughly 10 over two years, which provided the DCR with percent) of the engineering consultant’s esti- greater fiscal flexibility when compared to the mate for the project. initial approach when the dam rehabilitation On September 15, 2010, the DCR and the was scheduled to occur over one construction contractor began first construction season. season. Approximately one month later, the portion of Even though the project scope and budget Reservoir Road across the top of the dam was were increased by the addition of the bridge officially closed and the detour route around replacement to the project, the DCR, the the site was established. The first-year town of Otis and the general public benefit- construction work included:

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FIGURE 7. Concrete work during winter 2010/2011 at the spillway.

• the construction of the toe drain and was approximately 100 by 80 feet in area, and splash pad; required cuts into the bedrock of up to about 7 • raising of the embankment crest by 3 feet; feet. • placement of new upstream and down- Excavation of the gneissic bedrock was stream riprap slope protection (see Figure accomplished with a combination of ripping 5 on page XX); with an excavator and hoeramming. Due to • demolition of the masonry spillway; the fracture patterns in the bedrock, con- • construction of the new reinforced con- trolled blasting was not required. Figure 6 crete spillway/bridge abutments; (on the previous page) shows an example of • installation of the new stop logs; typical rock excavation at the spillway. • installation of the new bridge; Because the bedrock was fractured and rip- • demolition of the upstream gatehouse; pable, the contractor utilized line drilling and, techniques on the outer perimeter of the • construction of the new crest gate gate- excavation area to control the limit of the house at the left abutment. rock removal. Construc tion-induced vibra- tions were limited to the criteria set forth in Because the invert of the new crest gates 527 CMR 13.00, which provide vibration lim- was almost 8 feet lower than the original spill- its based on a relationship between peak par- way crest, bedrock excavation and removal ticle velocity and frequency. Continuous and within the spillway footprint was required for event-specific vibration monitoring was per- foundation construction. The excavation formed for the existing downstream masonry required for the new spillway foundations face of the dam, the downstream gate-

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FIGURE 8. New spillway bridge installation.

house/outlet tower, and at locations where As shown on Figure 7, concrete was formed new concrete was being poured. and poured in heated tents, and was typically The bedrock conditions in the area of the allowed to cure for at least three days within spillway were generally less competent than it the heated tents prior to stripping forms. was anticipated during design. Because the Diligent maintenance of the heating system by top of competent bedrock was generally about the contractor allowed for concrete placement 1 to 4 feet deeper than the design bottom of to occur relatively unimpeded despite the cold footing grades, approximately 150 additional weather. Rock excavation was not allowed for cubic yards of concrete were required to reach 24 hours after concrete had been poured on the design footing subgrade elevations. The the site, and backfilling was not permitted final bedrock surface was cleaned out with until the concrete had achieved its required compressed air prior to the placement of the 28-day compressive strength. Field-cured concrete. At the east bridge abutment, a “shear cylinders were used to determine whether key” into the bedrock subgrade was added required 28-day compressive strengths were because of the lower than anticipated compe- achieved, which, thus, allowed backfilling to tent bedrock surface. This shear key was be performed at an accelerated schedule. The added to increase the passive resistance for the stop log bays foundations, crest gate founda- training wall/bridge abutment foundation. tion, as well as upstream and downstream December 2010 marked the beginning of training walls/bridge abutments were all concrete placement for the new spillway. It poured throughout the winter in this manner also marked the beginning of one of the cold- with great success. Side seals and heating ele- est winters in recent years in the . ments for the hydraulic crest gate were

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FIGURE 9. Spillway flow due to Tropical Storm Irene.

installed as part of the training wall construc- in addition to the rainy/wet weather that tion. became more prevalent in the early spring of By February 2011, work on the spillway 2011, caused delays in the backfilling opera- had progressed sufficiently to allow backfill- tion. The wet backfill issues were addressed ing between the existing embankment and primarily by providing better control of mois- spillway training/abutment walls. Freezing ture in both the on-site and off-site borrow temperatures required a diligent effort on the area stockpiles. In some instances where mois- contractor’s part to provide ground heaters ture could not be properly controlled, the and frost blankets. The specifications for back- amount of fill placed in a single day had to be fill material were geared toward providing limited to allow porewater to dissipate prior control of seepage through the embankment, to the placement of the next lift of fill. Despite as opposed to the free-draining materials com- the adverse conditions, the backfilling was monly associated with roadway and bridge completed, the stop logs were installed and construction. Because of the relatively high the temporary cofferdam was removed in time fines content (between 15 and 30 percent) of for the scheduled bridge/road reopening in the off-site embankment fill material, moisture March 2011. content significantly impacted the contractor’s The new bridge has a 20-foot-wide road- ability to compact the material to the required way (curb-to-curb) and a 6-foot-wide side- density. The backfill material was brought walk on the north side, resulting in an overall from an off-site borrow pit to the site with a width of 29 feet. The bridge can accommodate moisture content that was typically well over two travel lanes, where the previous “tempo- its optimum moisture content. This condition, rary” Bailey bridge could not accommodate

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FIGURE 10. Water flowing over the completed crest gate.

travel in both directions. The wider bridge A Little More Than required the location of the new bridge to be Just a “Wet Test” shifted southward, with respect to the previ- ous bridge, which resulted in a straightening Between the first and second construction sea- of the layout of Tolland Road. sons, on August 27-28, 2011, Otis Reservoir The bridge installation was performed received between about 7 and 10 inches of rain using a 60-ton crane set up at the east (right) from Tropical Storm Irene. In anticipation of abutment of the spillway (see Figure 8 on page the storm, the DCR began to lower the reser- XX). Completing the spillway backfilling voir level with the outlet gate two days prior operation was critical since it needed to be to the storm’s arrival in the area. The outlet completed ahead of the bridge installation in tower slide gate was kept open during and order for the bridge and Tolland Road to be after the storm to help control the reservoir reopened to the public by March 2011. The level. By the time the storm hit, the DCR had bridge was fabricated in the three sections, removed up to three rows of stop logs (1.5 which were trailered individually to the dam feet). The reservoir level eventually rose to and staged on the dam crest. The crane was about 12 inches over normal pool (as seen in able to set each bridge section into place in one Figure 9) on August 29, 2011, which is about 6 day. The grouting of the bridge sections and inches above the maximum reservoir level the installation of the bridge railings were used to design the stop logs. On September 1, completed over a two-week period and the 2011, the DCR reported that the three rows of bridge was opened on schedule on March 18, stop logs had been replaced and gate in the 2011. outlet tower was closed. The DCR inspected

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FIGURE 11. Complete crest gate in in the spillway.

the spillway and did not observe any notice- The crest gate (shown in Figures 10 & 11) able damage. was installed by the end of December 2011. The hydraulic system was installed and tested Second Year Construction: as part of the “dry test” in January 2012. A The Home Stretch “wet test” of the crest gate system was also The contractor re-mobilized to the site full- performed shortly thereafter. Although the time in October 2011 in order to begin con- reservoir was at the winter pool elevation, struction on the last parts of the project. Final water could be pumped from the reservoir pavement of the road and bridge was placed into the area between the stop logs and crest and the pedestrian railings were completed. gate. So, once again, the inclusion of the stop Construction of the new gatehouse began con- logs provided a benefit to the project that went currently with the installation of the hydrauli- beyond their primary objective. cally actuated crest gate. The new gatehouse The crest gate system was substantially was constructed on the left (west) side of the complete by mid-March 2012 when a spillway: training session was held for the DCR personnel who would be operating the • to house equipment and controls associ- new system. ated with the hydraulic crest gate; The new slide gates were installed “in-the- • to house the remote water level wet” inside the downstream tower on its instrumentation system; and, upstream face. The new slide gates included • to provide secure storage for the alu- new electric actuators (with manual backup). minum stop logs. These new slide gates were installed with new

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FIGURE 11. Upstream view of the completed dam between winter and summer pool levels.

anchor bolts drilled into the downstream face tiated by the dam safety inspections, led to a of the outlet tower, with cement grout bedding project that ultimately benefited the DCR, the installed between the gate flange and the out- town of Otis and the general public. The crest let tower wall. However, the contractor had gate spillway provides the needed hydraulic problems during the installation of the new capacity to the dam in order to mitigate over- gates. During startup testing, the slide gates topping and the potential failure of a high haz- leaked significantly through the grout bed- ard dam. The crest gate also provides a self- ding and flowed behind each gate’s flange regulating winter pool level that significantly and through several of the anchor bolt holes. improves the DCR’s reservoir operations. The The reason for the leakage was attributed to new bridge replaces a temporary one-lane problems encountered by divers used during bridge that was in place for approximately 15 the installation of the grout bedding. Several years beyond its intended service life and pro- repair attempts were made. However, the vides a permanent two-lane bridge that will leakage remained beyond the specified allow- benefit the users of the Otis Reservoir. Even able limit. As of 2013, the DCR is evaluating though the project initially started out with repair options to address the slide gate leak- the primary goal of addressing the dam safety age. issues at the dam, the evolution of the project ultimately provided a broader and more sub- Summary stantial benefit to each of the project stake- The Otis Rehabilitation Dam and Bridge holders. Rehabilitation Project (see Figure 12) was a success. The planning efforts, which were ini- ACKNOWLEDGEMENTS — GZA GeoEnviron men -

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tal, Inc., was the firm that provided the inspection of the dam and all engineering analyses and reports on this project. Working with the DCR, GZA was proj- ect manager. GZA retained Wright-Pierce of Topsham, Maine, to provide structural, mechanical JOHN G. DELANO (bio to come). and electrical engineering design services for the new crest gate and for two new slide gates in the outlet tower. Under a separate contract, MassDOT engaged Amman Whitney of Boston, Massachusetts, to perform the bridge design. Contractor for the proj- ect was MIG Corporation of Acton, Massachusetts. The bridge superstructure was manufactured by Fort Miller Company, Inc., of Schuylerville, New York. The crest gate was fabricated by Rodney Hunt of Orange, Massachusetts.

MATTHEW A. TAYLOR (bio to come).

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