Abstract：A series of isotropic consolidation tests，three-dimensional net principal stresses loading tests and wetting tests were carried out on intact expansive soils under measuring suction by using unsaturated soil collapsible true triaxial apparatus to simulate the swelling deformation characteristics of expansive soils in practical engineering. The effects of net average stress on suction and compression deformation were studied. The variation of suction under three-dimensional net principal stresses loading，and the effects of intermediate principal stress，stress ratio and net confining pressure on suction and swelling deformation are discussed. The results show that the suction decreases with an increase in net average stress，and the smaller net average stress(p≤100 kPa) has little effect on the variation of suction and pore ratio，while the larger net average stress(p＞100 kPa) has a great influence on the change of suction and pore ratio. From the e-lnp relationship curve，it is determined that the yield stress of expansive soil is = 100 kPa，and the yield suction is = 86.4 kPa. When shearing，the suction decreases slightly or remains unchanged at first，q/p＞1，the suction decreases again and then tends to be stable，q/p≤1，the suction increases again and then tends to be stable. When humidifying，the suction decreases with an increase in moisture content， intermediate principal stress parameter b and net confining pressure ，but increases with an increase in k value. There is a three-dimensional deformation when the intact expansive soil is humidified. In this paper，the deformation forms of expansive soils can be summarized into four forms，which is closely related to the intermediate principal stress parameter b，stress ratio k and net confining pressure .
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2022, Vol. 41 
