Resultant force of lateral earth pressure in unstable slopes

Leshchinsky, DovTraditionally, resultant force of lateral earth pressure serves as the basis for design nearly vertical walls. Conversely, slopes are designed to be stable using a factor of safety approach. However, with the availability of heavy facing elements such as gabions or with soil reinforcement combined with some facing system, steep slopes are increasingly being constructed. Steep slopes are considered to be unstable unless supported; that is, such slopes require facings to resist lateral earth pressure. Extending Coulomb‟s formulation to such slopes may not be conservative as a planar slip surface may not be critical. Presented are the results of a formulation to find the resultant lateral force which utilizes the log-spiral failure mechanism. The friction at the interface soil-facing is assumed to act on vertical surface only thus replicating the geometry of stacked rectangular facing units. Given the batter, the backslope, the height, the unit weight and design friction angle of the backfill, and the interface friction, one can quickly determine the corresponding lateral earth pressure coefficient. Formulation equivalent to Coulomb‟s is also presented. Its results show that for batters up to 20°, the common approach of using Coulomb method, including the assumed direction to coincide with the batter, yield results that are quite close to those stemming from the log-spiral analysis. Hence, use of Coulomb‟s analysis for such small batters is a reasonable as its formulation is simple.University of Delaware, Department of Civil and Environmental EngineeringM.C.E