SGER: Failure of Teton Dam: A New Theory

Washington State University, Pullman WA

Investigators

Abstract

0234103, Balasingam Muhunthan, Washington State University "Failure of the Teton Dam: A New Theory" The objective of this research is to verify a new theory regarding the failure of the Teton Dam. The Teton Dam, in Idaho, failed during its first filling on 5 June 1976. It resulted in 14 fatalities and a very large economic loss. Its failure was one of the most publicized events involving a large earth fill dam in recent times. The dam was designed and built using modern standards; therefore its failure received considerable attention from engineering experts. However the failure assessment and prognosis by experts, including the Independent Panel (IP) and the Interior Review Group (IRG), failed to arrive at a consensus. Failure mechanisms suggested, included hydraulic fracture, internal erosion, the wet-seam theory, and defects in the abutment rock. None of the investigations, however, was able to explain satisfactorily why the dam breached when the reservoir reached El. 5301.7 ft and only in the vicinity of Sta. 15+00 on the right abutment. This investigation is based on a preliminary work using fundamental "state based soil mechanics". It indicates that a deep open transverse vertical crack(s) existed in the core (Zone-1) to EL.5300 ft and the deepest crack(s) occurred only in the right abutment and in the vicinity of Sta. 14+00 to Sta.15+00. When the reservoir rose above El. 5300 ft in the early hours of 5 June 1976, water flowed through the open transverse vertical crack(s) into the pervious downstream Zone-2, which was seated on bedrock at El. 5200 ft. The water flow slowly eroded the crack into a large tunnel leading to the major breach of the dam hours later. This preliminary work is based on the critical state soil mechanics framework. It assumes that the mechanical behavior of soils, such as the compressibility, pore pressure response, shear behavior with respect to yield, rupture and fracture, is dependent on the "state of soil" in q-p-e (shear stress-mean stress-void ratio) space or equivalently the LI - p (Liquidity Index - mean stress) space. A one-day workshop will be held at the conclusion of the program, at which a panel of experts will meet with the investigators to examine the research results and provide a critique in light of past investigations of the Teton failure. The expert committee will include professionals from the US Bureau of Reclamation, the US Army Corps of Engineers, and academics. The proceedings of the workshop, along with a detailed analysis of the Teton Dam failure and recommendations, will be disseminated via the worldwide web.