TETON DAM FAILURE Group 22 Jayson Ladd Paddy Mac Cormack Elaine Casey Sadhbh Ni Hogain INTRODUCTION • On June 5th 1976 the TETON DAM failed suddenly • Located 44 miles northeast of Idaho Falls in south-eastern Idaho • It claimed the life of 14 people and caused hundreds of millions of dollars in damage. • Failure was due to a leak near the abutment of the dam, about 130 feet below the crest Flood waters advancing through Rexburg, Idaho SITE HISTORY • The first site investigation in the area took place in 1932 yet work on the dam did not begin until early 1972 • The Teton Dam is located on the Snake River Plain, a broad tectonic depression underlain by rhyolitic and basaltic volcanic rocks • The volcanic rock at the dam site consists of hard, welded, rhyolitic ash-flow tuff dated at 1.9 million years. • It has a hard ash-flow turf and sits upon think sedimentary rock • This geological configuration causes a high level of permeability in the surrounding area. CONSTRUCTION • The earth fill dam required 10 million cubic meters of materials, most of which was dug from the river bed around the site • The dam consisted of a centre zone made up of clay, silt, gravel and cobbles mixture tightly compacted by tamping rollers The Five zones of the Dam: • Zone 1: • Zone 2: • Zone 3: • Zone4\5: Core - Moisture content 1.5% dry of optimum permeability 0.3 m/yr Compacted Sandy Gravel – Overlies Zone 1 and extends downstream into the floodplain Miscellaneous Fill – Properties similar to Zone 1 Rock Fill-Compacted on outer surface of dam View northwest toward right abutment. The hole in the dam face enlarges upward View northwest toward right abutment. Muddy water issues out of the hole about two-thirds up the face of the dam and begins to pond at the toe The hole in the dam face continues to enlarge upward near the crest of the dam, the rush of water increases markedly, and erosion cuts deep into bedrock of the abutment COLLAPSE • Failure occurred rapidly with out much advance warning • June 3rd: small seepages become visible in the north abutment wall • June 5th: the first major leak was noticed on the right abutment with a flow of about 500 to 800 l/s which increased to 1,400 l/s. Seepage was observed about 40 meters below the crest of the dam. • At 11am a whirlpool was noticed 5m from the edge of the embankment. • At 11.30am bulldozers filling the hole on the embankment were lost • The dam finally broke at 11.57am • The 251,000 acres were emptied within 5 hours CONCLUSIONS • The dam failed due to internal erosion of the core of the dam deep in the foundation • Eroded particles found exits through the channels in and along the interface of the dam, exits existed through cracks in the core • The design team did not believe that these cracks were sufficient to cause failure but the build up of water pressure pushed the waster through • Politics played a huge part in pushing on this project and as a result design mistakes were made, which ultimately caused the failure of the dam • A report in 1947 showed that none of the site investigations were sufficient • “It was shown that the reservoir rim could transmit water in large quantities and that seepage form the reservoir could occur.”