A numerical study on undrained passive earth pressure

This paper presents a numerical study on passive earth pressure under undrained conditions. First, a simplified problem is investigated in order to evaluate the resulting earth pressure for a parallel movement of a rigid wall. It is shown that for undrained conditions the type of constitutive model employed has an influence on the limiting passive earth pressure. Comparison with limit analysis is provided whenever possible, giving confidence that the finite element results are reliable. In a second study, a simplified deep excavation problem is analysed where the positive effect of negative excess pore water pressures developed during undrained excavation increases the factor of safety against global failure. However, this effect is only temporarily and it is shown that standard strength reduction procedures to calculate factors of safety, as applied frequently in practice, are not well suited for this type of problems. An alternative way is therefore suggested. Again, the influence of the constitutive model is addressed, and it is shown that simple elastic-perfectly plastic models may not be conservative. In addition the influence of geometric effects is highlighted.