定轴剪切条件下砂土强度与非共轴性试验研究

Experimental Study on Strength and Non-Coaxiality of Sand under Fixed Principal Stress Axes Shearing

针对现有定轴剪切试验大多忽略中主应力系数b值变化这一问题,基于不同力系之间的映射关系,严格推导了空心圆柱扭剪仪4个外荷载的加载参数。采用重塑福建标准砂试样,分别在2组围压下开展主应力方向固定的剪切试验,研究主应力方向角α不同时,砂土变形、强度、非共轴性等力学特性的差异。结果表明:砂土的强度、应力应变关系等力学特性均具有显著的应力方向依赖性;随着应力方向从0°到90°变化,应力路径表现为2个变化阶段,峰值强度先减小后增大,在α为67.5°附近取极小值;对比大主应变增量方向与大主应力方向之间的关系,发现当偏应力比较小时,试样存在明显的非共轴现象,随着偏应力比的增大,应变增量方向逐渐趋近于应力方向。

Given the problem that most of the existing shear tests with fixed principal stress direction ignore the change of intermediate principal stress coefficient b.The loading parameters of the four external loads of the hollow cylindrical apparatus were strictly deduced based on the mapping relationship between different force systems.The shear tests with fixed principal stress direction were carried out under two groups of confining pressures using remodeled Fujian standard sand specimens.The differences in mechanical properties such as deformation,strength,and non-coaxiality of the sand were studied when the principal stress directionαwas different.Test results show that the stress path,strength,and other mechanical properties of sand have a significant stress direction dependence.With the principal stress direction changes from 0°to 90°,the stress path shows two variable phases,the peak strength decreases and then increases,and the minimum value of strength nearαof 67.5°.The specimen has an obvious non-coaxiality when the deviatoric stress ratio is small,according to a comparison of the major principal strain increment direction and the major principal stress direction.However,as the deviatoric stress ratio increases,the direction of the principal strain increment gradually approaches the principal stress direction.