Landslide in Claystone Derived Soil

A landslide in a colluvial slope is described that occurred after excavation was made for the construction of a building. The geometry of the landslide mass before and after sliding was able to be established relatively well. Ground-water observations were made for a period 3 months after the slide occurred. The surface on which sliding probably occurred was established with reasonable confidence from observations and test-boring information. Large displacement reversal direct shear tests performed by the Pennsylvania Department of Transportation on samples of red clay soil obtained on or very near the failure plane yielded residual strength parameters. Stability analyses using the Morgenstern-Price method for non-circular failure surfaces indicate that the value of the angle of shear resistance in the field at failure probably was between 12? and 13? if it is assumed that the cohesion intercept is 0.