Influence of Excavation Time, Tension Crack, and Rainfall on the Stability of Unsupported Vertical Cuts in Unsaturated Soil

Abstract

This study focuses on the stability of unsupported vertical cuts in unsaturated soil. For this, a series of numerical analyses were carried out to estimate the stability of unsupported vertical cuts excavated in an unsaturated glacial till considering three possible practical scenarios: (1) excavation time, (2) depth and location of a tension crack, and (3) rainfall infiltration into a tension crack. The results showed that the influence of excavation time and rainfall infiltration into a tension crack may not be significant if an unsupported vertical cut is made with a certain safety margin (i.e., safe height). A tension crack did not affect the overall safety of an unsupported vertical cut in a case where the location and depth of the tension crack are within 30% and 20% of safe height, respectively. The proposed approaches were then applied to the deep unsupported vertical cut made into a clay (9.75 m; Kwan 1971) for the validation. The failure in the vertical cut was initiated due to the development of a tension crack, which matched the numerical analyses results obtained extending both effective and total stress approaches considering the influence of matric suction.