Dynamic Response and Progressive Failure of Moraine‐Covered Slopes Under Combined Rainfall and Earthquake Loading

ABSTRACT Rainfall and seismic loading are major factors triggering the instability of moraine slopes widely distributed in the mountainous regions of western China. To investigate the dynamic response and failure mechanisms of moraine soil slopes under combined rainfall and seismic loading, a numerical model was established based on shaking table tests, and a systematic investigation was conducted. A heterogeneous numerical model of moraine soil–rock mixtures (SRMs) was developed using a grid‐mapping method. The van Genuchten unsaturated seepage model was then incorporated to simulate the coupled rainfall‐seismic response of SRM slopes. Multidomain analysis methods were employed to investigate the topographic amplification effects of the slope under coupled rainfall and seismic loading and to summarize its dynamic response characteristics. On this basis, the progressive failure process from initial deformation to overall instability under hydromechanical coupling was clarified. Rock content (RC) changed the response markedly. For the tested slopes, the response changed least at RC = 20%–25%: acceleration amplification and displacement were smaller, and the difference between dry and postrainfall cases narrowed. Infiltrating water raised pore pressure primarily along soil–rock contacts. Liquefaction first appeared there, followed by sliding. Increasing the gravel fraction slowed the advance of this zone. This behavior results from changes in contact stress and drainage during wetting. Field assessments of moraine slopes exposed to strong shaking should thus include antecedent rainfall and interface drainage.