主应力轴旋转条件下黄土变形特性试验

为研究黄土在主应力轴循环旋转条件下的变形特性，采用空心圆柱扭剪仪（HCA）开展了2种不同应力路径下的扭剪试验。第1种应力路径为保持主应力轴方向不变，改变偏应力大小，研究黄土在不同主应力轴方向角α和不同中主应力系数b下的变形特性；第2种应力路径为保持偏应力大小不变，改变主应力轴方向，研究主应力轴循环旋转周期对黄土性状的影响。试验结果表明：土样剪切强度与中主应力系数b、主应力轴方向角α相关，当b相同，α=30°时土样剪切强度最大，α=60°时土样剪切强度略大于α=45°时；α相同时，剪切强度>b=1时的剪切强度>b=0.5时的剪切强度；纯主应力轴旋转会使土体产生塑形应变，并且随着旋转周期的增加，土体产生的塑形应变将不断累积。

Experimental Study on Deformation Characteristics of Loess Under Condition of Principal Stress Axes Rotation

To study the deformation characteristics of Loess under the cyclic rotation of the principal stress axes, two different torsional shear tests are performed under different stress paths using the hollow cylindrical torsional shear apparatus (HCA). The first stress path keeps the direction of the principal stress axes unchanged, but the size of deviator stress applied to the soil is changed. The first test is to study the deformation characteristics of the soil under the condition of different principal stress direction angle α and different intermediate principal stress parameter b values. The second stress path changes the direction of the principal stress axes, but the size of the deviator stress applied to the soil is unchanged. The second test is to study the effects of the cyclic rotation periods of the principal stress axes on the characteristics of the soil. The experimental results show that the deformation characteristics of Loess have a certain relationship with the principal stress direction angle and intermediate principal stress parameter. When b is constant, the shear strength is the largest when α=30° and when α=60°, the shear strength is slightly larger than that when α=45°. When α is constant, the shear strength when b=0 is larger than that when b=1, which larger than that when b=0.5. Pure principal stress axes rotation causes the soil to produce plastic strain, which will accumulate with the increase in the rotation cycles.