基于环剪试验的含钙质结核古土壤剪切特性

Shear Properties of Paleosol Containing Calcareous Concretions Based on Ring Shear Tests

含钙质结核古土壤在黄土滑坡的剪切带中广泛分布,影响滑坡的剪切特性.通过固结排水环剪试验,改变轴应力大小,研究不同钙质结核含量下古土壤的剪切力学特性;基于对剪切破坏面的宏观结构分析,总结并提出剪切破坏面的“一”型和“U”型两种破坏形态及平稳、过渡、波动3种破坏模式.研究结果表明:在低轴应力下,应力-位移曲线均为软化型,具有明显的残余强度特性,随钙质结核含量增大,应变软化特性变弱;在高轴应力下,则表现为硬化型;钙质结核颗粒能增大土的剪切强度、摩擦角,减小黏聚力;剪切带厚度与钙质结核含量正相关,与D50负相关;在大位移剪切作用下,颗粒会发生破碎,通过对剪切前后粒径分析,确定了钙质结核主要破碎区间为3~5 mm,破碎率为19.5%~55.5%;古土壤由0.01~0.05 mm颗粒破碎为0.002~0.010 mm的较小颗粒.

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.