Shear strength of weakly expansive soils and its prediction in a wide range of suction

A series of suction-controlled triaxial tests are conducted on unsaturated weakly expansive soils experiencing different suctions in a wide range of suction. With regard to the suction applied, the low and high suctions are imposed by using the axis translation technique and the vapor equilibrium method. The test results show that under the same net stress, the specimen experiencing larger suction shows a higher stress-strain relationship and small contractive volumetric strain shearing, and its deviatoric stress-strain relationship and volumetric strain behavior become more and more similar to deformation characteristics of overconsolidated soils with the increase of the imposed suction. The reason of the above phenomenon is that when the specimen experiences a larger suction, the weakly expansive soils shrink significantly due to the loss of water, and its void ratio decreases obviously, thus the specimen exhibits the deformation characteristics of overconsolidated soils during shearing. In a wide range of suction, the volume shrinkage of weakly expansive soils is significantly caused by the suction, and it cannot be ignored. In addition, on the basis of test data of the mercury intrusion porosimetry (MIP), the Bishop’s equation for unsaturated soils is modified by introducing the concept of the effective degree of saturation. A comparison between the measured and the predicted results shows that the modified equation can predict the strength of unsaturated Nanyang weakly expansive soils well in a wide range of suction.