Fragility Curves for Highway Embankment Slope Stability under Extreme Rainfall

Highway embankment slopes are subject to potential failure due to extreme rainfall patterns. This study uses a fragility framework to examine the failure probability of a highway slope consisting of Yazoo clay in the northern part of Jackson, Mississippi, USA. A finite-element model of the slope is calibrated with available site data. Total rainfall depths between 47 mm and 630 mm are considered in the application of the model under different high-to-low intensity and short-to-long duration categories for return periods up to 1,000 years. Uncertainties in the rainfall patterns are incorporated through Monte Carlo simulation. The effects of extreme rainfall are integrated by applying the intensity and frequency of rainfall events that are greater than those of typical design considerations. Fragility curves, the continuous failure probability functions corresponding to a wide range of rainfall depths, are constructed using simulation outputs for different limit states. Rainfall duration is identified as the key factor affecting the embankment’s fragility. Low-intensity and long-duration rainfalls are found to be more detrimental to the slope compared to high-intensity and short-duration rainfalls. This study revealed that the major limit state is only exceeded by post-200-mm rainfall depths, with an increasing exceedance likelihood at greater rainfall depths. Limit states showed higher exceedance probability from higher frequency rainfalls due to the long rebound period of Yazoo clay. The findings from this study may be utilized in the design of new embankments within the same region and in safety assessments of existing embankment slopes under a range of rainfall conditions.