Simple Testing Method for Measuring the Triaxial Stress-Strain Relations of Unsaturated Soils at High Suctions

Abstract

Unsaturated soils at high suctions are widespread in arid and semiarid areas. Test data on the mechanical behavior of unsaturated soils are scarce at high suctions. In this article, the effect of void ratio or density on the soil-water retention behavior was discussed on the basis of measured data of various compacted soils at high suctions. According to the test data, the soil-water retention behavior is independent of the dry density or void ratio over a high suction range, namely, if the water content of a soil specimen is kept constant, the suction will be constant and independent of the void ratio (deformation) at high suctions. Therefore, a simple testing method for measuring the stress-strain relations of unsaturated triaxial specimens at high suctions is proposed by combining the vapor equilibrium technique (VET) with saturated salt solutions and the triaxial shear tests at constant water contents. First, a known initial high suction is imposed on the specimen by using the VET with a saturated salt solution. Then, the specimen is triaxially sheared under a constant water content, thereby resulting in a constant high suction during triaxial shearing. The proposed testing method can substantially shorten the testing period for one triaxial test. Finally, the results of triaxial shear tests on silt, silty clay, and expansive soil at high suctions obtained by the proposed testing method are presented.