Influence of Rainfall Conditions and Loading Modes on the Stability of Expansive Soil Cut Slopes: Insight from In Situ Borehole Shear Test

Abstract

Given the frequent occurrence of expansive soil slope failures during rainy season, in situ borehole shear tests were conducted to investigate how loading-added modes and rainfall conditions affect the shear strength parameters of expansive soils. The results obtained were used to analyze an actual engineering project under various construction practices and depths of rainfall infiltration, with the goal of elucidating the mechanisms behind expansive soil landslides. The test results indicate that rainfall infiltration leads to a significant reduction in cohesive force, while the internal friction angle decreases slightly. Cohesive force increases linearly with greater preload pressures, whereas the internal friction angle decreases linearly as preload pressure increases. Numerical simulations revealed that rainfall-induced sliding occurs at shallow depths along a broken-line sliding surface. For unprotected expansive soil cut slopes, the safety factor experiences a sharp decline as the depth of rainfall infiltration increases. Timely support measures significantly enhance slope stability; however, the supporting load can mitigate the softening effect only up to a certain extent. Additionally, two methodologies for selecting preload pressures in practical engineering applications have been proposed.