Shear Properties of Paleosol Containing Calcareous ConcretionsBased on Ring Shear Tests

Paleosol containing calcareous concretion is widely distributed in the shear zone of loess landslides and affects the shear failure characteristics of landslides. Based on ring shear tests, the shear characteristics of paleosol with different contents of calcareous concretions under different normal stresses were discussed, and the test results were analyzed from macro-and micro-aspects. The results indicate that under low axial (normal) stress, the stress-displacement curves are of softening type and have obvious residual strength characteristics. With the increase of calcium nodule content, the strain softening characteristics become weak. Under high axial (normal) stress, the stress-displacement curves show strain hardening. Calcareous nodule particles can increase the shear strength and peak friction angle of soil and reduce the cohesion. The thickness of shear band is positively correlated with the content of calcareous concretions and negatively correlated with D50. Particle crushing occurred under the larger deformation. According to the particle size distribution analysis before and after shearing, the breakage of calcareous concretions mainly occurred to particles in the size range of 3−5 mm, with a breakage percentage of 19.5%−55.5%, and the paleosol was broken from 0.01−0.05 mm into smaller particles of 0.002−0.010 mm. Based on macroscopic observation and mechanical analysis of shear failure surfaces, all samples can be divided into two groups with “—” and “U” failure surface patterns, respectively, and three failure modes, including sliding shear mode, turbulent and transitional shear mode.