This project is the first phase of dam seismic retrofit that establishes new water supply tunnels, drop shaft, and lake intake structures required prior to rebuilding the dam itself in subsequent phases. With the site located directly adjacent to the operating dam and nearby neighborhoods, there were serval stakeholders to remain in compliance with that included environmental agencies, safety regulators, and federal oversight. Underground coring was performed in advance of tunnel excavation to adequately analyze the rock, which varied from extremely weak to strong, and the variable quantities of groundwater and intermixed saturated soils.

Drill Tech performed the portal construction and utilized SEM techniques for both the shaft and tunnel. Drill Tech also designed the shaft, which was supported by lattice girders and shotcrete, that somewhat varied in depth geometry to facilitate future pipe elbow placement. Coordination of the organization and transportation for onsite shotcrete batching was required due to the 24/7 underground excavation operations. Vadnais, Drill Tech’s subsidiary microtunneling company, constructed the 8′ diameter microtunnel that connects the tunnel to Anderson Lake.