Comparative analysis of shear characteristics of soilbag-canal expansive soil interface under positive and negative temperature conditions

Soilbags have been widely used in the prevention of frost damage of canal expansive soil in cold regions due to their excellent engineering properties. The mechanical behavior of the interface between the soilbags and the canal expansive soil is the key factor affecting the design of the canal slope. The interface shear test of soilbag-canal expansive soil samples with different initial water contents under positive and negative temperature conditions were carried out by a self-developed large-scale temperature-controlled direct shear test device. The effects of temperature and initial water content on the failure morphology, shear stress-shear displacement curves, strength behavior and shear dilatancy characteristics of the sample were studied. The test results show that: The failure characteristics of the frozen samples are typical strain softening type, and the samples under positive temperature show two failure characteristics of weak strain softening and weak strain hardening. Under negative temperature condition, with the increase of initial water content of expansive soil, the peak shear strength and interfacial cohesion of the sample increase gradually, while the residual shear strength and interfacial friction angle are almost unaffected. Under positive temperature condition, both the peak shear strength, residual shear strength, interfacial cohesion and friction angle of the sample decrease with the increase of water content of the soil. Additionally, the normal displacement of the frozen sample shows a three-stage growth trend of slow-fast-slow with the increase of the shear displacement, and it shows shear dilatancy behavior during the whole shear process, which is closely related to the effect of the ice cementation strength at the interface of soilbag-expansive soil. The normal displacement-shear displacement curve of the sample under positive temperature is relatively smooth, and the sample exhibits shear dilatancy under low normal stress but shear contraction under high normal stress. However, under the same normal stress condition, the final dilatancy displacement of the sample at the optimal moisture content (21.7%) is the smallest.