Abstract:To investigate the deformation and strength characteristics of expansive soils after suction loading and unloading,this paper uses an improved true triaxial apparatus for unsaturated soil to realize the suction loading and unloading process,and conducts the true triaxial shear tests under different middle principal stress parameter b value on intact expansive soils. The hydraulic variation characteristics after suction loading and unloading and during the shearing process,as well as the change characteristics of volumetric strain and strength are studied. The results show that compared with those without suction loading and unloading,the void ratio,the degree of saturation and volumetric strain of expansive soil experienced wet-dry path increase,and the shear strength decreases,while the void ratio and the degree of saturation of expansive soil experienced dry-wet path decrease,the shear strength increases,and which have a greater strength and a smaller volumetric strain when it experienced greater suction. The cohesion increases with an increase in the middle principal stress,and the internal friction angle decreases with an increase in the middle principal stress. Under different values of b,the water contents of expansive soils without suction loading and unloading,experienced wet-dry path and dry-wet path(smaller suction) decrease with an increase in generalized shear strain,and the degree of saturation increase with an increase in generalized shear strain,and both water content and degree of saturation decrease with an increase in b value. The water content of expansive soil experienced dry-wet path(larger suction) increases with an increase in generalized shear strain. When b = 0,0.25 and 0.5,the degree of saturation first increases to the peak value and then decreases to the stable value. When b = 0.75 and 1,the degree of saturation first increases rapidly and then slowly increases to the stable value.
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