Analyses of Waco Dam Slide

Abstract

The investigation was performed to study the factors influencing the undrained shear strength of Pepper shale, a stiff-fissured clay, and to apply the results of the study to the analysis of a slide which occurred during construction of Waco Dam, founded on the Pepper shale. Unconsolidated-undrained triaxial compression tests were performed on undisturbed samples of Pepper shale to investigate the influence of anisotropy, sustained loading and specimen size. The study showed that the Pepper shale is highly anisotropic, possessing a much lower strength along a horizontal plane than along other planes. The influence of sustained loading and of specimen size was found to be negligible. Analyses showed that the assumption of isotropic shear strengths, measured on vertical specimens, indicated stable conditions, while the use of anisotropic shear strengths produced results in agreement with the observed failure and pronounced noncircular failure surface.