Kinematic limit analysis of unsaturated stepped excavation slopes subjected to surcharge loads

Abstract

Stability assessment and design of stepped excavation slopes are of great practical significance and require explicit consideration of the three-dimensional (3D) effect and the suction-related effects. In the realm of 3D kinematic limit analysis theorem, this paper presents a semi-analytical method to quantify the suction impact in the 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 effect, surcharge loads and seismic actions in the safety assessments. An example is presented to show the practical use of this method in engineering practice with respect to the determination of the optimum shape of a stepped excavation slope that characterized with 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 those of single-stage slopes and the optimum depth coefficient (αopt) falls in 0.55 ∼ 0.7 for 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 the 3D effect tends to be more pronounced as the surcharge load increases.