Unsaturated Soil-retaining Wall Interaction: Experiments And Theoretical Modelling

In this paper experimental observations and theoretical modelling outcomes are presented which show the significant effect suction has on the interaction between unsaturated soils and retaining walls. Firstly, a new testing facility and set of procedures for performing retaining wall model tests in unsaturated soils are described. The facility enables a rigid model wall to be rotated into or away from a soil sample about its toe. Results for samples of unsaturated decomposed granite are presented. Suction changes were measured using vibrating wire piezometers. Pressures on the wall were measured by earth pressure cells embedded in the wall face. Integrating the earth pressure profile enabled an equivalent load acting on the wall to be calculated, and was in reasonable agreement with the measured applied load. Soil deformations were recorded using particle image velocimetry. The pattern of soil deformation observed, particularly strain localisations, was similar to those in tests on dry sands. The suction increases measured during the test were consistent the volumetric dilation that occurred in the sample. Secondly, an extension of slip line theory to unsaturated soils is presented and applied to the rigid retaining wall problem. Suction is introduced using the effective stress concept. The predicted effective normal stresses were found to be in reasonable agreement with experimentally measured values.