Kinematic limit analysis of unsaturated stepped excavation slopes under surcharge loads

Abstract

Stability assessments and design of stepped excavation slopes are of great practical significance and require explicit consideration of the three-dimensional (3D) effect and suction-related effects. In the realm of 3D kinematic limit analysis, this paper presents a semi-analytical method to quantify the impact of suction in stability assessments of stepped excavation slopes. The influences of surcharge load and seismic excitation are both considered from a kinematic perspective. Numerical experiments were conducted regarding the roles of soil suction, 3D effects, surcharge loads and seismic actions in safety assessments. An example is presented to show the practical use of the proposed method in engineering practice with respect to determination of the optimum shape of a stepped excavation slope characterised with a fixed slope toe and slope crest positions. The results demonstrate that the stability of stepped excavation slopes can be improved by 10–25% compared with the stability of a single-stage slope and the optimum depth coefficient (αopt) falls in the range 0.55–0.70 in most cases. For steeper excavation slopes, αopt might exceed this range while, for gentler slopes, αopt tends to be smaller than this range. The critical slip surface and 3D effects tend to be more pronounced with an increase in surcharge load.