Abstract：A series of suction balance，equal suction drainage consolidation and equal suction and equal b-value shear tests were carried out on intact expansive soil by using unsaturated soil true triaxial apparatus to investigate the effect of intermediate principal stress and matric suction on the strength and deformation characteristics of intact expansive soil. The swelling and shrinking characteristics，yield characteristics and strength change characteristics of intact expansive soil were studied. The results show that the intact expansive soil shows an elasto-plastic volumetric strain in the process of wetting and drying，and yield suction is equal to 71 kPa. When 0 kPa≤s≤37 kPa，the expansive soil exhibits elastic swelling，when 37 kPa＜s≤71 kPa，the expansive soil exhibits elastic shrinkage，when s＞71 kPa，the expansive soil exhibits plastic shrinkage，indicating the existence of the Suction-Increase(SI) yield locus in the drying path of the expansive soil elastoplastic model. The isotropic compressive yield stress increases with an increase in suction，which verifies the existence of Loading Collapse(LC) yield locus in the elastoplastic model of expansive soil. As the suction increases，the dilatancy of the intact expansive soil increases. The dilatancy is not only closely related to the net confining pressure and suction，but also affected by the intermediate principal stress，and the dilatancy is weaker as the intermediate principal stress is larger. The cohesion increases nonlinearly with an increase in suction at different b values，and when the suction is constant，the cohesion increases with an increase in intermediate principal stress. For a given b value，the internal friction angles of expansive soils with different suctions have little difference，and the internal friction angle decreases with an increase in the intermediate principal stress. While，the suction friction angle increases nonlinearly with an increase in intermediate principal stress.
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2021, Vol. 40 
