Active Earth Pressure on Walls with Base Projection

The effect of base projection on the active earth pressure, a classical problem in the calculation of earth pressure forces on retaining walls, is presented. Four conclusions may be drawn. The first is that the failure wedge is bounded by two surfaces, one of them intersecting into the soil and the ground surface and the other one intersecting the wall. The second is that for the case of level backfill and no wall friction, the Rankine solution may be always applied on the vertical plane connecting the heel with the ground surface, regardless of the base projections. The third is that the inclination of the resultant earth pressure force will always be greater than the slope of the backfill and less than the angle of wall friction. Finally, the fourth is that the magnitude of earth pressure force will always be greater than that given by Coulomb solution for a wall without base projection and less than the force given by a Rankine analysis on the vertical plane through the heel with no wall friction. These conclusions are made in the case of wall interference with the shear zone. If there is not interference then the Rankine solution is applicable.