Importance of variability in initial soil moisture and rainfalls on slope stability

A first-order moment analysis is developed to investigate the temporal and spatial propagation of uncertainty of slope stability during rainfall, considering spatial variabilities in initial soil water pressure and soil hydraulic properties, and temporal variability of rainfall. Results of the analysis indicate that the uncertainties resulting from variabilities in initial soil pore water pressure distributions and rainfalls are comparable with that from the variability in soil hydraulic properties. Further, the evolution of slope stability uncertainty is driven by the mean flow field, and a localized large-uncertainty zone along the slope profile could form, leading to a localized low-reliability zone, which may lead to the failure of the slope. In particular, when the slope is close to saturation, the reliability of the stability analysis of any elevation of the slope is low even at early rainfall times. On the other hand, when the slope is unsaturated and heavy rainfalls occur, the low-reliability zone exists at shallow parts of the slope at early times. The results also show that greater unreliability exists at shallow depths at early times when the rainfall has a descending trend in comparison with uniform and increasing trend. Lastly, the low-reliability zone is always near the impermeable bedrock if rainfall persists.