Stability of slopes in red conemaugh shale of Ohio

Nine slopes excavated in soft Conemaugh shales containing slickensides were investigated. The trace lengths and orientations of the slickensides found in exposures were measured. The shear strengths of the intact shales and slickensides were measured by means of direct shear tests. Stability analyses were performed to calculate the shear strength of the shale in the failed slopes. For the stable slopes, the strength required to attain a safety factor of 1 was calculated. The in situ strength must exceed this strength. The estimated strengths are examined in the light of the average density and the average length of slickenside traces and the stress distribution. Estimates are made of the effect of slickensides and stress distribution on the reduction of shear strength below its peak value.