Swelling and shrinkage behaviour of expansive soil during wetting-drying cycles

Two groups of laboratory cyclic wetting-drying tests are conducted on expansive soil to study the swelling and shrinkage behaviour. In suction-controlled wetting-drying tests, two suction control methods are used: the osmotic method for low suction range (0.4 ～ 4 MPa) and the vapor equilibrium technique for high suction range (4 ～ 262 MPa). At each suction level, water content and volume of soil specimen are determined after equilibrium is reached. In conventional wetting-drying tests, soil specimen is allowed to swell , and either shrinks fully or partially to the initial height in each cycle. Simultaneously, axial deformation is measured. After each cycle, the water content of specimen is also assessed. The results show that the void ratio of specimen varies with the suction in three typical stages in both drying and wetting paths, i.e., sharp variation stage (0.4 ～ 9 MPa), transition stage (9 ～ 82 MPa) and peace stage (82 ～ 262 MPa). The reversibility in the swelling and shrinkage deformation is found when the suction is higher than 113 MPa, but significant hysteresis is observed as the suction is lower than 113 MPa and the hysteresis extent increases with decreasing suction. In conventional wetting-drying tests, it is observed that the swelling and shrinkage behaviour gradually reaches equilibrium with increasing cycles and is significantly influenced by shrinkage pattern. The measured swelling potential of specimen subjected to full shrinkage cycle is higher than that of specimen subjected to partial shrinkage cycle. Swelling velocity increase with the increase of the wetting-drying cycle is noted when the specimen fully shrinks. Generally speaking, the swelling ability of specimen in wetting-drying cycle significantly depends on water absorption capability.