Horizontal drains to stabilize clay slopes

Abstract

Five horizontal drains were installed in a natural clay slope and the piezometric heads in the slope were monitored with piezometers. Decreases of piezometric head in the vicinity of the drains were measured and indicated that horizontal drains can be used to improve the stability of clay slopes.Based on the theory of consolidation, estimates were made of the changes of piezometric head within the test slope due to the installation of drains. Good comparisons were obtained between the predicted and the measured values, demonstrating that the method of prediction can be used with confidence for design purposes. The three-dimensional pattern of piezometric levels was averaged to give an equivalent two-dimensional pattern, and this was used in slope stability calculations to determine the improvement in safety factor of the slope.The effectiveness of horizontal drains depends on the spacing and diameter of the drains, and on their location relative to the critical slip zone.The study has shown that installation of horizontal drains is a viable method of improving the stability of certain clay slopes. Keywords: slope, clay, stability, drains, field test, theory.