Dam Failure Case Study: Fort Peck Dam (Montana, 1938)

Beginning at about 1:15 pm on September 22, 1938, the upstream slope of the dam adjacent to the right abutment experienced a large failure as the construction work had progressed to within 20 feet of the final dam crest elevation. One hundred eighty men were working in the area. Thirty-four men were injured. Eight men lost their lives, six of whom were never found and are buried somewhere in the dam.

This case study presents a summary of 1) the efforts to investigate and understand the cause of the failure, and 2) the controversy concerning the root cause evaluation. The Board of Consultants for the project found that the failure was due to the inadequate shearing resistance of the weathered shale and bentonite seams in the upstream right abutment and dam foundation. They further indicated that “the extent to which the slide progressed upstream, may have been due, in some degree, to a partial liquefaction of the material in the slide.”