A Suction-Controlled Ring Device to Measure the Coefficient of Lateral Soil Pressure in Unsaturated Soils

Abstract

A suction-controlled ring device has been developed to continuously measure the coefficient of lateral soil pressure in deformable unsaturated soil samples from the at-rest to the active condition under application of increasing vertical pressure and controlled matric suction. The device incorporates a thin aluminum specimen ring equipped with horizontal strain gages for recording the lateral soil strains. In addition, a sensor recording water volume changes is utilized to continuously monitor the degree of saturation of the soil sample during tests. The matric suction within the soil texture is controlled using the axis translation technique. In order to verify the performance of the ring device, twenty suction-controlled tests under application of five different constant matric suctions have been performed on two different unsaturated soil types, namely Firouzkouh Clay and Sand-Kaolin mixture, each with two different initial densities. During tests, the lateral soil pressure and corresponding lateral strains have been continuously recorded from the at-rest to the active state of the soil. Accordingly, the coefficients of the lateral soil pressure for the at-rest and the active states of the soil are calculated based on the experimental data and by considering the effective stress concept in unsaturated soils. Finally, the observed responses have been analyzed and the effects of initial density and matric suction on the ratio of lateral to vertical soil pressure have been discussed.