循环荷载下重塑黄土变形特性

为研究主应力方向和大小耦合变化对土体应力-应变状态及非共轴性的影响, 采用空心圆柱扭剪仪对饱和重塑黄土开展一系列循环扭剪试验, 分析了应力-应变状态和非共轴角的变化规律及影响因素。试验结果表明: 轴向应变始终处于压缩状态, 环向应变先负向累积再正向累积, 径向应变基本处于受拉状态, 剪切应变的受拉与受压状态交替出现, 轴向、环向和剪切应变曲线的波动特性明显, 而径向应变曲线的波动特性弱, 说明循环荷载作用下各应变分量表现出不同的发展规律; 轴向和径向应变及环向和剪切应变变化幅值随中主应力系数的增大先增大后减小, 说明中主应力系数影响各应变分量的累积; 随着主应力方向角旋转范围的增大, 轴向和径向应变逐渐减小, 环向应变由负向往正向变化的趋势提前, 剪切应变变化幅值逐渐减小, 说明主应力方向角旋转范围影响各应变分量的发展趋势; 剪切和正偏应力-应变曲线滞回现象明显, 且刚度发生循环强化, 但剪切刚度的循环强化比正偏刚度更明显, 说明土体出现次生各向异性, 这是引起非共轴现象的内在因素; 非共轴角变化曲线随中主应力系数的增大先下移后上移, 随循环次数的增大而逐渐上移, 随偏应力幅值的增大其变化范围增大。可见, 循环荷载下中主应力系数、循环次数和偏应力幅值可显著影响饱和重塑黄土的应力-应变状态及非共轴性, 在黄土工程设计和本构关系研究中应加以考虑。

Deformation properties of remolded loess under cyclic loading

To study the effect of coupling changes in principal stress direction and magnitude on the stress-strain state and non-coaxiality of soil, a series of cyclic torsional shear tests were carried out on the saturated remolded loess by using a hollow cylindrical torsional shear apparatus, and the variation rules and influencing factors of stress-strain state and non-coaxial angle were analyzed. Experimental result shows that the axial strain is always in a compression state, the hoop strain accumulates negatively first and then positively, the radial strain is basically in a tension state, the tension and compression states of shear strain alternate, the fluctuation characteristics of axial, hoop and shear strain curves are obvious, while the fluctuation characteristic of radial strain curve is weak, indicating that each strain component shows different development laws under the cyclic loading. The axial and radial strains and the variation amplitudes of hoop and shear strains increase first and then decrease as the intermediate principal stress coefficient increases, indicating that the intermediate principal stress coefficient affects the cumulation of each strain component. With the increase of rotation range of principal stress direction angle, the axial and radial strains decrease gradually, the trend of hoop strain changing from negative to positive advances, and the variation amplitude of shear strain decreases gradually, indicating that the rotation range of principal stress direction angle affects the development trend of each strain component. The hysteresis phenomena of shear and normal differential stress-strain curves are obvious, and the stiffness consolidates cyclically, but the cyclic strengthening of shear stiffness is more obvious than that of normal differential stiffness, indicating that the secondary anisotropy occurs in the soil. This is an intrinsic cause of the non-coaxial phenomenon. The non-coaxial angle curve moves down first and then moves up as the intermediate principal stress coefficient increases, and moves up gradually as the cycle number increases. The variation range of non-coaxial angle curve increases as the deviating stress amplitude increases. Thus, the intermediate principal stress coefficient, cycle number and deviating stress amplitude can obviously affect the stress-strain state and non-coaxiality of saturated remolded loess, which should be considered in loess engineering design and constitutive relationship research.