Hydroelectric, Reservoirs and Water Conveyance Systems
Dam License Implementation Program
Location: Sierra Mountains, California
This project involved the installation of nine slide gates into the face of existing gates on the dam, part of a hydroelectric generating network. On behalf of the diving and salvage company, L123 provided project management services by completing contract negotiations, planning the project, producing the Contractor Work Plan meeting stringent environmental agency requirements, procured the necessary engineering support, supervised the engineering tasks, procured the prefabricated materials, mobilized the project, produced all project management tracking and reporting processes to meet the owner’s requirement by being on schedule and budget, met all site safety requirements, and provided onsite management ensuring that field operations were established and operating efficiently.
Work Trestle and Cofferdam Construction
Location: Washington State
This design-build project by our strategic partner, Pacific Pile and Marine, involved a pile supported work trestle and braced cofferdam in the Columbia River just downstream of the Chief Joseph Dam. Work included 90-ft long pile support work trestle to support a 110 ton crane, excavation and concrete placement equipment. The cofferdam included 85 pairs of 25- to 30-ft long sheet piles, two levels of internal bracing, and a structural tremie slab supported by tension rock anchors.
Cofferdam Design, Build, Install
Location: Washington State
Pacific Pile and Marine, an L123 strategic partner, designed, furnished, installed, and removed a cofferdam for a dam Improvements project. The cofferdam provided access for construction of a fish passage structure downstream of the existing dam and adjacent to the powerhouse. The cofferdam was required to resist up to 28 ft of differential water pressure, stream flow pressure, and construction surcharge live load. The cofferdam consisted of an earth filled double-sheet pile system connected by two levels of tie-rods spaced at 9 ft on center. The river had significant flow. Directly adjacent was a working hydro dam spillway. The flows and water elevation were influenced by unpredictable schedules from the dam operators. To install the cofferdam, large fractured boulders needed to be removed.
Intake Tower Inspection
Location: Sierra National Forest, California
In compliance with the stability standards outlined by FERC and the operational requisites of DSOD, the dam owner engaged L123 to plan, oversee and document the necessary intake tower Inspections. The purpose of the underwater inspection activities was to produce an engineered report to document the as-built geometry and overall condition of the intake tower as part of the seismic stability retrofit project. The dam is a hydraulic fill and rockfill embankment with a reinforced concrete core wall with a maximum height of 150-feet.
Hydro Facilities Construction
Two new hydro facilities were constructed consisting of two powerhouses and intakes with 20MW capacity. The first Intake structure required a penstock consisting of 48-in welded steel pipe, switching station, and powerhouse which generated 12MW of power. The second Intake consisted of dam and stream diversion, 3 km new forest roads, 2 km restored forest roads, 950 m of buried 72-in welded steel pipe, switching station and powerhouse capable of generating 8MW of power. Over 5,000 m3 cast-in-place concrete was placed for the intake structures, power houses, penstock saddles, and cable crane system anchor slab utilized to install the 1,100 m of exposed penstock over 500 m of elevation change. The skyline cable crane system used for materials delivery was the first built for temporary construction site access in North America. This project was a design-build project by Pacific Pile and Marine.