A modified ring shear test device for determining the hydro-mechanical behaviour of unsaturated soils

Abstract

This thesis presents the design details of an automated modified ring shear apparatus for the testing of unsaturated soils using the axis translation technique. The system is fully automated and it can be used for conducting Constant Load and constant Suction (CLS) shear tests, Constant Volume and constant Suction (CVS) shear tests, Constant Load and constant Water content (CLW) shear tests as well as Constant Volume and constant Water content (CVW) shear tests. In addition to shear tests, the soil-water retention curve (SWRC) can also be generated for the same specimen in the same testing device. The principal advantages of the device include its ability to shear unsaturated soils to very large deformations as well as conducting tests under constant volume conditions. Analysis of the experimental data using these characteristics suggests that the volumetric changes of the sheared specimen are not the only factor affecting the changes of its water content under constant matric suction conditions. In addition, the experimental evidence suggests that shear deformations much greater than those typically used in the testing of unsaturated soils are required if an ultimate water content equilibrium condition is to be reached. Such an equilibrium condition is required if critical state data is to be determined for unsaturated soils. The thesis also presents the design and use of additional equipment utilised for testing unsaturated soils. This includes the use of an electronic balance to measure the change in water volume of the specimen, and provides details on how the readings of the balance can be stabilized to remove the noise caused by the connection of the tubes to the overflow jar. A simple technique relying solely on the measurement of the water volume change to determine the volume of diffused air removed by the flushing operations is also presented. The other pieces of equipment described include a volume gauge/air trap that can be used to measure the water volume changes of unsaturated soil specimens, and a simple, robust, and precise pressure gauge.