Tolt Dam Spillway Conduit Repair

Client: Seattle Public Utilities Location: Tolt Dam, King County, WA Contact for geotechnical projects: John Peterson

Project Background & Challenges

Constructed in the early 1960's, the Told Dam is an earthen dam nearly 150-feet high, that impounds nearly half of the drinking water for the Seattle area. The spillway for the dam is an 18-foot diameter tunnel that is internal to the dam. Leaks have eveloped at construction joints in the spillway tunnel. One particular leak has been found to be passing small amounts of soil material.

Solution

Concerned that the eroding soil could eventually result in a void in the dam, SPU asked Aspect to evaluate the potential solutions for plugging the leak and filling the void. After performing tests to identify voids, Aspect collaborated with a specialty grouting supplier to enact a multi-staged grouting plan involving polymer grouts to seal the tunnel liner and fill any potential voids. We also developed an interim solution for preventing the passing of solids through the leak until grouting operations were completed..