Idaho Power Construction

LOCATION:  The State of Idaho   |   OWNER:  Idaho Power
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McMillen Jacobs was awarded a contract from Idaho Power Company for the construction services throughout Idaho. This contract is utilized for the execution of a broad range of construction projects. Typical projects include emergency repairs to spillway structures, bridges, and canals.

Upper Salmon Spillway Repairs (Phases 1, 2, 3)

Hagerman, Idaho. McMillen Jacobs completed repairs to the Upper Salmon Spillways on the Snake River to fix significant cracking and failures to the entire shell of the concrete piers of the spillway, near the embed trunnion pins, and the overhead bridge column supports.

During initial demolition phases, our team identified that the concrete structure lacked the reinforcing steel, which we had anticipated. McMillen Jacobs’ structural engineers and construction division manager visited the jobsite along with Idaho Power Company’s project managers to assess the conditions and develop a new construction approach.

McMillen Jacobs’ engineers developed a new design approach of installing a reinforcing cage around the entire exposed perimeter of the concrete pier and drilling holes through the existing 10-foot-wide piers and connected the newly reinforced exterior faces of the spillway piers with through-bolts and lock washers. Once accomplished, a custom concrete forming system was constructed and secured to the piers as required to pour and place concrete to the new dimensions. Remaining work included the installation of a weather-protected work platform that attached to the piers and was suspended above the flowing river, demolition of the outer 9” of concrete, installation of reinforcing steel cages, drilling of 3” core holes, installation and tightening of 10’ through-bolts, placement and curing of cast-in-place concrete, and reinstallation of gate limit switches. Our team made concrete and slide gate repairs at each location of the Upper Salmon spillway. Phase 3 repairs included concrete repairs to Pier #1. Work required the demolition of the existing electrical control building positioned on Pier #1. Pier #1 featured a small metal stair structure which had to be removed and replaced following completion of the repair work. Our innovative construction approach provided consistent pricing, which allowed for additional piers.

Access was limited to work from a floating barge at the upstream face of the spillway, and from a narrow, single lane access road which limited the size of equipment that could access the work area. Despite challenges, this project was delivered to the client on budget and ahead of schedule.

Reconstruction of Thousand Springs Snowbank Bridge

Hagerman, Idaho. McMillen Jacobs was retained to reconstruct the existing bridge that leads to the Thousand Springs Power Plant. The existing bridge remained open to traffic throughout the construction period. Our team provided traffic control to ensure public safety throughout the construction period. We installed two 40-ft long, 2-ft diameter heavy walled HDPE pipe to divert the stream flow around the disturbed streambed during the work in order to comply with permitting requirements along with the necessary energy dissipation required for discharge at the end of the diversion pipe.

Upper Salmon Emergency Intake Canal Concrete Repairs

Hagerman, Idaho. Our team performed emergency repairs to the crest of the intake canal which was in a state of disrepair The structure was experiencing spalled and crumbling concrete, full-depth cracking that had led to extensive leaking, and considerable erosion and loss of backfill due to burrowing animals. Idaho Power was unable to operate the canal at maximum capacity because of the conditions of the canal wall crest, requiring the urgency of the corrective action. Repairs to the concrete canal were required to both the south canal walls, which were accessible by road, as well as the north canal walls that could only be accessed for repair by boat.

Logistics required that concrete was pumped over an active 120′ canal. The power plant remained operational during the construction. This project required significant safety measures for work above an active waterway including the installation of downstream safety line, and strict use of personal floatation devices, and the constant presence of a manned and dedicated rescue boat. Deteriorated concrete was removed down to sound conditions and new reinforcing steel was drilled and anchored into the walls to accept the new concrete. Much of the formwork was installed from boat. This work was performed under a “time and material” contract, under which McMillen Jacobs executed the work to a high level of quality and efficiency while providing the client with complete transparency of all incurred costs.

Bliss Tailrace Repairs, Bliss, Idaho

Our team provided structural repairs by resurfacing rock to concrete in deteriorated areas. Safety and time were key components as there were extremely hazardous conditions for both McMillen Jacobs employees performing this work and Idaho Power employees performing their normal maintenance activities on the power plant. We implemented a stringent safety program due to extremely hazardous conditions. McMillen Jacobs was able to fabricate a rolling, cantilevered scaffolding to access the leading edge of the tailrace and set formwork and temporary safety rails while the repairs were performed. Elements include saw cutting concrete and rolling cantilevered scaffolding over water.