直剪剪切速率对钙质砂强度及变形特征的影响

为深入研究剪切速率对钙质砂强度和变形特征的影响，对钙质干砂进行不同剪切速率条件下的直剪试验。研究结果表明，随剪切速率从0.1 mm/min增至2.4 mm/min时钙质砂抗剪强度先减小后增大，其内摩擦角亦呈现出先减小后增大趋势，临界剪切速率为1.6 mm/min；低法向应力条件下钙质砂试样随剪切速率的增加更易于呈现剪胀现象，高法向应力条件下剪切速率从0.1 mm/min增长至1.6 mm/min时试样整体剪缩量逐渐减小；当剪切速率继续从1.6 mm/min增长至2.4 mm/min时试样最大剪缩量逐渐增加；不同法向应力水平条件下钙质砂加载速率效应的细观机制不同，较低应力水平条件下钙质砂加载速率效应主要由试样内部颗粒错动、换位、重新排列引起，在较高应力水平条件下钙质砂加载速率效应主要由颗粒破碎引起。

Effect of shear rate on shear strength and deformation characteristics of calcareous sand in direct shear test

In order to further study the effect of shear rate on the strength and deformation characteristics of calcareous sand, direct shear tests are carried out on dry calcareous sand under different shear rates in this paper. With the increase in shear rates from 0.1 mm/min to 2.4 mm/min, the shear strength of calcareous sand decreases at first and then increases in the tests, and a similar change trend of the internal friction angle is also found. Meanwhile, the measured critical shear rate is 1.6 mm/min for dry calcareous sand. Under a low normal stress condition, the shear dilatancy phenomenon in calcareous sand sample is more likely to occur with an increase in the shear rate. Under a relatively high normal stress condition, overall shear shrinkage decreases gradually with the shear rate increases from 0.1 mm/min to 1.6 mm/min. When the shear rate continues to increase from 1.6 mm/min to 2.4 mm/min, the maximum shear shrinkage increases gradually. The micro-mechanism of loading rate effect of calcareous sand varies under different normal stress conditions. Under the low stress conditions, the loading rate effect of calcareous sand is mainly caused by the dislocation, displacement and rearrangement of particles, while the particle breakage plays an important role at higher stress levels.