Research on the softening law of cyclic immersion strength of silty clay

Abstract

[Objective] To investigate the strength softening and recovery mechanisms of silty clay under cyclic wetting-drying actions and clarify the impact mechanisms of multiple rainfall events on soil strength degradation and slope deformation, [Methods] The strength change characteristics of silty clay in the process of water-soaking and air-drying were investigated through the cyclic soaking and softening test, and the strength recovery law in the stage of air-drying was investigated; combined with the monitoring data of the rainfall and deformation of a slope of a clayey soil in Guangxi, the effect mechanism of multiple rainfalls on the response of slope deformation was verified; the dynamic prediction of slope stability was realized through the construction of a function model and the refinement of parameter assignment method. [Results] The result show that:(1) Silty clay exhibits significant cyclic wetting-induced softening effects. With increasing wetting-drying cycles, the initial cohesion decreases by over 79%, while the initial internal friction angle declines by more than 47%. The stabilization time for cohesion and internal friction angle during re-wetting shortens to 3.6%~10.9% of the original duration.(2) Strength recovery during drying displays a three-phase characteristic: in the initial phase(<1 d), cohesion and internal friction angle decrease slowly by 25.6% and 5.4%, respectively; during the intermediate phase(1~5 d), cohesion increases at 0.13 kPa/h and internal friction angle recovers at 0.08 kPa/h; in the late phase(>5 d), cohesion growth rate decelerates to 0.03 kPa/h while internal friction angle fully recovers to natural state.(3) Slope deformation response time follows an exponential decay pattern with rainfall frequency, showing 56% shorter lag time after the third rainfall compared to initial events, which strongly correlates with laboratory-observed strength degradation.(4) The proposed damage accumulation function model with dynamic parameter calibration predicts critical rainfall cycles(N=8±1) for slope instability, achieving less than 10% error compared to actual failure cases. [Conclusion] The research findings reveal the strength evolution mechanism of silty clay under cyclic wetting-drying processes and establishes a quantitative correlation model integrating rainfall frequency, strength degradation, and slope deformation. The dynamic prediction framework provides quantifiable theoretical criteria for emergency early-warning of rainfall-induced landslides, offering significant engineering value for disaster prevention systems in cohesive soil slopes.

Keywords

silty clay / wetting-drying / strength recovery / function model / softening effect / mechanical properties / slope