Progressive failure of a dam abutment: A fracture mechanics analysis

During the construction of Baldhill Dam, the bedding of the sloping Pierre Shale bedrock and overburden was exposed along the inlet and outlet channels. Small scale earth slides developed and stabilized soon after filling of the reservoir, but instrumentation within the hillside detected movements intermittently over the past 50 years. Various remedial measures were taken to stabilize the slide, including the construction of a drilled shaft wall. Nevertheless, movements did not completely cease, especially when piezometric conditions in the abutment were high. From inclinometer readings, it was determined that the zone of sliding was confined to a relatively narrow shear band. The extent of the sliding zone encompassed 70% of the right abutment, much larger than the original assumption used in the limit equilibrium analysis when designing the drill shaft wall. It is clear that failure is progressive and that the shear band is propagating. In this paper, a fracture mechanics analysis is introduced to provide an explanation for the progressive failure. It is shown that the energy release rate (G) in the field may satisfy the failure criterion, G = G _c, where the material parameter G _c was determined from plane strain compression testing. Copyright ASCE 2008.