Effect of Rainfall on Stability of Unsaturated Earth Slopes Constructed on Expansive Clay

Abstract

Rainfall induced slope failure is a common geotechnical hazard in many parts of the world. Infiltration of rain water results in reduction in soil matric suction and shear strength, which eventually leads to reduction in slope stability. This reduction in slope stability has been identified to be affected by both rainfall intensity and duration, while the response of unsaturated earth slopes to different rainfall conditions is critically dependent on soil type. The objective of current paper is to investigate the influence of different rainfall events (intensity and duration) on slope constructed on expansive clay in Waxahachie, Texas by using numerical modeling. The factor of safety has been evaluated for a range of one (1) day to seven (7) day rainfall conditions for the current study. A fully coupled flow deformation analysis was carried out using the finite element-based software PLAXIS. The change in soil's shear strength, due to changes in matric suction, is taken into consideration by using the Bishop's effective stress concept. Results obtained from the numerical study indicates a drop in factor of safety from 2.13 to 1.3 after seven day rainfall period. Based on the current study the critical duration that yielded the lowest possible factor of safety has been identified to be seven (7) days.