Time-variant failure probability of critical slopes under strong rainfall hazard including mitigation effects

The time-variant failure probability for critical slopes under strong rainfalls, which cause reductions on the soil shear strength, is calculated and compared to the target failure probability. The soil properties and the rainfall characteristics are considered as random and the correlation between rainfall intensity and duration is included to assess the impact of water infiltration on the slope failure probability. The failure probability, defined as the probability that the safety factor is less than 1, is calculated through a Monte Carlo simulation process. The paper emphasizes the importance of the time during the water infiltration into the soil, as the rainfall sequence occurs. The target failure probability, derived from the minimum expected life-cycle cost, is compared to the slope failure probability to decide if the slope requires mitigation measures. If mitigation is required, the slope model is modified and a new annual failure probability is calculated. The slope annual failure probability, for three sites under strong rainfall hazard, is found to be around 0.78. However, by introducing mitigation actions, the failure probability reduces to 0.037. The slope failure probability allows for the risk-based prioritization of the attention for many slopes at several sites by stablishing basis for optimal resources allocation.