饱和松砂的双向耦合剪切特性试验研究

Liquefaction of sand under bi-directional cyclic loading

为了模拟海床及海洋建筑物遭受波浪荷载时所引起的循环应力,进行了一系列均等固结条件下的应力控制式轴向-扭转双向耦合循环剪切试验。试验时在竖向和扭转向同时施加动应力,使加载路径在正应力偏差(σz-σθ)/2与剪应力τzθ应力空间内为椭圆。分别控制竖向和扭转向循环荷载的大小,以此来探讨双向耦合剪切试验中竖向应力与剪应力幅值的变化对饱和松砂变形特性的影响。试验结果显示,所有的竖向应变均以拉伸向为主。对于椭圆应力路径所包围的椭圆面积相同的一组试验,当竖向荷载分量与扭转向荷载分量之比小于某一临界值时,竖向应变完全表现为单拉伸方向的变形,大于临界值时则呈现出拉伸向更为显著的双向循环累积特性破坏。剪应变虽都表现为双向循环累积,但是两个荷载分量的比值不同,应力应变关系的滞回圈曲线形状不同。而椭圆面积的大小对土样的变形特性几乎没有影响。

To simulate the continuous rotation of principal stress axes, a set of stress controlled bi-directional cyclic loading tests were conducted. Tests were performed with two cyclic stress components involving the horizontal shear stress （torsional shear stress） and the vertical shear stress （stress difference between vertical normal stress and horizontal normal stress） to provide an approximate presentation of wave or seismic loading conditions. The stress path shown in the orthogonal coordinates of stress difference and shear stress had an elliptical shape. The ratio of the shear amplitude between the longer axis and shorter axis and the area enclosed by elliptical rotational loading path were controlled in a planned way. Test results showed that the stress-strain behavior was significantly affected by the ratio of amplitude of the two shear stress components. But it was nearly independent on the area enclosed by elliptical rotational loading path. The deformation behaviors were classified as two different types based on the ratio value.