Insight into soil cyclic triaxial testing using a high capacity tensiometer

Unsaturated soils often form part of geo-infrastructure such as road and railway substructures subjected to repeated traffic and train-induced loading. However, the principles of Unsaturated Soil Mechanics have commonly been neglected in design protocols of such infrastructure mainly due to the lack of appropriate experimental data and poor understanding of the response of unsaturated soils to complex loading. Advances in suction measurements using tensiometers have enabled practical analysis of the behaviour of unsaturated soils under laboratory and field conditions. This paper discusses the advantages of using a high-capacity tensiometer in studying the cyclic response of unsaturated clayey sand taken from a railway formation. The tests were carried out using a cyclic triaxial apparatus while suction was continuously monitored during testing using a tensiometer mounted on the body of soil samples. The soil cyclic behaviour including accumulated axial strains and resilient modulus was observed to be dependent on the soil suction levels as well as the confining pressure and cyclic deviatoric stress applied. The Bishop’s stress ratio (defined as the ratio between the cyclic deviatoric stress and mean Bishop’s stress) was used to interpret the test results where the accumulated axial strain was
consistently found to increase and resilient modulus to decrease with the Bishop’s stress ratio.