Coulomb wedge analysis of cuts in steep slopes

Abstract

Coulomb's trial wedge method for estimating the active force on retaining walls is applied to situations where there are steep slopes at limiting equilibrium behind the walls. The analysis is applied initially to slopes of dry cohesionless material; in this case the slope angle is equal to the friction angle of the material. The analysis produces two interesting, and perhaps surprising, results. The first is that the critical wedge angle equals the slope angle, and the critical wedge becomes a "slab" extending an unlimited distance up the slope above the wall. The second is that as the inclination of the slope and friction angle (which are equal) increase the active force on the wall decreases. The method is then applied to more general slopes involving cohesion, friction, and seepage. Back-analysis is first used to obtain combinations of cohesion and friction corresponding to limiting equilibrium; these are then used in the wedge analysis. The results obtained are similar to those for the dry cohesionless slope. The method provides a means of estimating required retaining forces for cuts made in steep slopes of residual soil or partly weathered rock where estimation of strength parameters is often very difficult.Key words: slopes, steep, back-analysis, Coulomb, wedge, analysis.