Dynamic analysis of Fort Peck Dam

Abstract : During the investigation the following conclusions were reached: (1) Active faults have not been found on either the Hinsdale or the Brockton-Froid-Weldon trends; (2) An earthquake of magnitude 5.5 at Tiger Butte appears possible; (3) The split-spoon blow counts that were obtained at Fort Peck Dam indicate the relative density of the Shell to be substantially greater than that obtained by WES using undisturbed samples and laboratory tests; (4) Cyclic tests conducted on specimens of remolded material have significantly less dynamic strength than tests conducted on tapped undisturbed specimens; (5) The results of the static analysis show that a 2.5-ft displacement imposed in the shale under the upstream and downstream toes does not cause a significant change in the static stresses in the dam; and (6) The Fort Peck Dam is not expected to experience 5% strain if an earthquake of magnitude 5.5 occurs at a distance of 10 miles. It is concluded that the dam is safe for earthquakes considered possible at the site.