考虑应力水平影响的冻结黏土变形特性

Deformation characteristics of frozen clay with considering the influence of mean principal stress

为研究应力水平对应力主轴旋转过程中冻结黏土变形特性的影响,采用冻土空心圆柱仪,对冻结黏土开展不同应力水平p值下的应力主轴单向旋转试验,试验温度为-10℃,试验结果表明:平均主应力p值对单向旋转中的轴向应变和剪应变均有较大影响,轴向应变的最大变幅达121.7%,p值的增加会使轴向拉应变减小;剪应变峰值滞后于剪应力峰值,表现出较强的黏塑性变形特性,加载过程中的剪应变越大,剪应变的滞后性越大。当p值较小时,p值的增加会使冻结黏土的强度增大,超过临界p值后,冻结黏土的强度随p值的增加开始减小,但中主应力的增加会使临界p值减小。只发生应力主轴的旋转,也会在冻结黏土中产生较明显的塑性剪应变,通过对p-塑性剪应变曲线的分析,发现塑性剪应变随p值的增加呈现出四阶段变化趋势:强化→弱化→弱强化→再弱化。

In order to study the effect of stress level on the deformation characteristics of frozen clay during loading process,a series unidirectional rotation of the principal stress axis tests was conducted on frozen clay under different mean principal stress at-10℃using a frozen soil hollow cylindrical apparatus in this study.The experimental results indicate that,the mean principal stress p has a great influence on the axial strain and shear strain in unidirectional rotation loading process.The ratio of difference between maximum and minimum axial strain to minimum axial strain can reach 121.7%,and axial tensile strain decreases with the increase of p-value.The peak value of shear strain lags behind the peak value of shear stress,showing strong viscoplastic deformation characteristics.And the larger the shear strain is during loading process,the greater the degree of lag behind of shear strain is.At lower p-value,the strength of frozen clay increases with the increase of p-value.However,when the p-value exceeds the threshold value,it will decrease with the increase of p-value.The threshold p-value is reduced with the increase of intermedia principal stress.After the unidirectional rotation tests,there is obvious plastic shear strain in specimen.By analyzing the curve of p-value versus plastic shear strain,four stages can be got,which is strengthening,weakening,weak strengthening and weakening again.