Stability of Shale Embankments

Abstract

The performance of embankment slopes along a section of I‐77 is summarized. Slope failures occurred mostly in embankments constructed of red shales of the Conemaugh, Monongahela, and Washington formations. Soil moisture, soil suction, pore pressure, and slope movements were measured in four embankments. The results of measurements indicated that saturation of the embankment slopes occurred near the surface by infiltration of rainfall. Laboratory shear tests were used to measure the shear strengths of the embankment materials and of the red shales in their intact state and after various manipulations that simulated compaction and weathering. With seepage parallel to the slope, failure could occur if the in‐situ shear strength was close to the lower limit of the peak shear strength measured in laboratory tests on samples of the embankment material. With vertical seepage, failure could occur if the in‐situ shear strength was slightly less than the softened shear strength of samples of intact shale. Since it was not possible to verify the actual seepage conditions, both scenarios are considered possible.