Seismic stability analysis of slopes with cracks in unsaturated soils using pseudo-dynamic approach

Abstract

In practice, soil slopes are commonly unsaturated and may suffer from the adverse effects of earthquakes. Stability assessment of slopes subjected to earthquakes tends to consider whether the soils are dry or saturated while neglecting the time and spatial effects of seismic waves; in such assessments, the actual features cannot be reflected sufficiently. In the present study, a framework considering unsaturated soils was developed to investigate the seismic stability of slopes accounting for tension cracks using the pseudo-dynamic approach. Several expressions for apparent cohesion were applied to analyze the influence of matric suction, and seepage under different phreatic levels was also included. The pseudo-dynamic approach was applied to characterize the time and spatial effects of earthquakes. Two types of cracks, open cracks (cracks existing prior to slope failure) and formation cracks (cracks forming as part of a slope failure mechanism), were considered. A closed-form solution for the critical height of the slopes was derived from the energy balance equation of the Limit Analysis upper bound method, and the safety factor was obtained. The validity of this approach was verified by comparison with published solutions. Through the parametric analysis, it was found that higher amplification factors and seismic coefficients led to a smaller discrepancy in the safety factor between the slopes with open cracks and formation cracks, yet a reverse trend was observed at a higher value of matric suction. The effect of matric suction on slope stability was more apparent with a lower water level. Different shear strength models of unsaturated soils led to different safety factors.