Earth Slide on Geomembrane

This note describes slide failures of the inside slope of a water reservoir, following a prolonged period of heavy rainfall. The reservoir had just been completed and was empty. Sliding took place along the plane of the smooth-surfaced geomembrane high-density polyethylene (HDPE), which had been installed 0.4 m below the face of the slope to contain stored water. Sliding cannot be explained by gravity forces only. By considering the combined effect of gravity and seepage forces acting on the surface of the membrane at the time of sliding, under wet conditions, it was calculated that the coefficient of friction between the geomembrane and the nonplastic silty sand of the soil cover is between 0.325–0.360. Under wet conditions, either of these values agree with previously published coefficients of friction between HDPE geomembrane and sand, or between smooth-surfaced concrete and steel, and plastic silt.