Simulating Hydraulic and Mechanical Responses of Unsaturated Expansive Soil Slope to Rainfall: Case Study

Abstract

This paper presents simulation results of the performance of an unsaturated expansive soil slope during artificial rainfall events from a field investigation. The field study, conducted on an intake canal of a major water transfer project in Zaoyang, Hubei, China, indicated that the water percolation under rainfall was limited to a near-surface vadose zone, in which substantial changes of the mechanical stress regime and deformation were observed due to the swelling of wetted soils. In this paper, the hydraulic responses of this slope are simulated with a finite-element model, followed by modeling of its mechanical response on wetting using an expanded infinite slope formulation. The soils’ mechanical behavior is described using a Mohr-Coulomb elastoplastic model extended for unsaturated soils. A new elastic moduli equation, which can consider the influence of degree of saturation on nonlinear variations of elastic moduli (E and H) with suction, is proposed to describe the unsaturated soils’ nonlinear deformation behavior in the elastic stage. Incorporating this new model is advantageous for smoothly modeling the transition between saturated and unsaturated states. The simulation results using the infinite slope formulation that incorporates these constitutive relationships are in reasonable agreement with the field observations, highlighting the capability of the expanded infinite slope formulation to interpret the complex response of this expansive soil slope to rainfall infiltration.