ASSESSMENT AND REPAIR OF ACTIVE FOUNDATION PIPING AND EROSION AT FERN RIDGE DAM, OREGON

摘要

Significant distress of the downstream slope (depressions) and the internal drainage system (sediment, drain envelope gravels, and fragments of pipe coating materials in the discharge water) was observed beginning in August 2002 at the 60-year-old Fern Ridge Dam located near Eugene, Oregon. Subsequently, the Portland District of the U.S. Army Corps of Engineers began an in-depth data-gathering program and engineering assessment of seepage concerns. In December 2004, a Senior Board of Review was convened by the Corps to review available information and engineering evaluations. The Board members were Messers. Francke Walberg, James Talbot and Keith Ferguson. The Board confirmed that the internal drainage system in the dam was in an active state of failure and the immediate corrective actions were needed to mitigate the potential for dam failure. Subsequently, the Corps, working with the Board, prepared final designs of modifications to the dam that have recently been constructed. Key considerations of the design and construction included foundation dewatering and excavation stability; construction materials; the dimensioning and construction of the replacement drain system; and the sequencing of work activities. The design and construction of the repairs to Fern Ridge Dam were completed in less than 1 year.