Discovery and Remediation of Deteriorating Timber Trestles within an Embankment

摘要

In October 2010, depressions on the downstream side of the left embankment at the Big Falls Hydroelectric Project were observed that led to the initiation of a Watch Condition of the Emergency Action Plan (EAP). The Federal Energy Regulatory Commission and other stakeholders were notified and a reservoir drawdown was initiated. Following initiation of the EAP, several potential mechanisms for the depressions were hypothesized and evaluated. Potential failure modes, construction records, record drawings, historic photographs and rock/soil conditions were all reviewed. The review of historic photographs indicated that numerous wooden trestles were utilized to transport materials from the bank/shoreline to the project features during the dam's construction in 1922. Drilling investigations were conducted and a repair was completed at twenty-two depression locations; repair consisted of augering into the depressions to remove loose or objectionable material and placing more suitable material.