Stability of Retaining Walls against Overturning

The safety factor of wall stability against overturning is defined as the ratio between the sum of resisting moments and the sum of overturning moments. In evaluating these moments, the vertical component of the active thrust on the wall may be considered in two different ways: as decreasing the overturning moment, or increasing the resisting one. This technical note shows that both these definitions are false because the safety factor value depends on the thrust surface being arbitrarily assumed in the analysis. Wall stability against overturning can, however, be assessed using the position of the resultant force on the base, which is unaffected by the assumed thrust surface. Contrary to overturning, safety factors against sliding and bearing capacity are unaffected by the assumed thrust surface.