New excavation or tunnelling affects the stress state of soils in ground. The change of stress state due to excavation may affect the cyclic behaviour of soils. Cyclic loading, such as traffic and earthquake loading, induced ground deformation may be greater than expected if such effect is not considered. A series of cyclic triaxial tests were performed on Sydney sand with different relative densities. The effect of unloading sequence on deformation of the sand under cyclic loading was simulated by reducing lateral stress in steps between loading cycles. The dependence of strain accumulation on the magnitude of confining pressure reduction and on unloading stress paths was studied. The results indicate that the sand has a memory of stress history and the stress history of such unloading enlarges the strain accumulation during the subsequent cycles, and the greater the reduction of lateral stress, the greater the accumulated strain. Under cyclic loading, the accumulated axial strain could increase nonlinearly or linearly with the ratio of unloading magnitude to initial mean effective stress, depending on the stress state before cyclic loading. The unloading stress paths have limited effects on the final accumulated strain if the initial and final stress states are the same. The variation of strain accumulation direction attributes to the change of average stress ratio resulting from lateral stress reduction, but hardly depends on relative density and unloading stress paths. The strain accumulation direction after unloading roughly agrees with the modified Cam Clay flow rule.

新的开挖或掘进会影响地下土壤的应力状态。开挖引起的应力状态变化可能会影响土壤的循环行为。如果不考虑这种影响，则周期性荷载（例如交通和地震荷载）引起的地面变形可能会比预期的大。在具有不同相对密度的悉尼砂上进行了一系列的循环三轴试验。通过在加载循环之间逐步减小侧向应力，模拟了卸载顺序对循环加载下砂土变形的影响。研究了应变累积对围压降低幅度和卸载应力路径的依赖性。结果表明，砂具有记忆应力历史的特性，这种卸载的应力历史增大了后续循环中的应变累积，侧向应力的减小越大，累积应变越大。在循环载荷作用下，累积的轴向应变可能随卸载量与初始平均有效应力的比值非线性或线性增加，具体取决于循环载荷作用前的应力状态。如果初始应力状态和最终应力状态相同，则卸载应力路径对最终累积应变的影响有限。应变积累方向的变化归因于由横向应力减小引起的平均应力比的变化，但几乎不取决于相对密度和卸载应力路径。卸荷后的应变累积方向大致与修改后的“凸轮粘土”流动规则一致。累积轴向应变可能随卸载量与初始平均有效应力之比非线性或线性增加，具体取决于循环载荷之前的应力状态。如果初始应力状态和最终应力状态相同，则卸载应力路径对最终累积应变的影响有限。应变积累方向的变化归因于由横向应力减小引起的平均应力比的变化，但几乎不取决于相对密度和卸载应力路径。卸荷后的应变累积方向大致与修改后的“凸轮粘土”流动规则一致。累积轴向应变可能随卸载量与初始平均有效应力之比非线性或线性增加，具体取决于循环载荷之前的应力状态。如果初始应力状态和最终应力状态相同，则卸载应力路径对最终累积应变的影响有限。应变积累方向的变化归因于由横向应力减小引起的平均应力比的变化，但几乎不取决于相对密度和卸载应力路径。卸荷后的应变累积方向大致与修改后的“凸轮粘土”流动规则一致。如果初始应力状态和最终应力状态相同，则卸载应力路径对最终累积应变的影响有限。应变积累方向的变化归因于由横向应力减小引起的平均应力比的变化，但几乎不取决于相对密度和卸载应力路径。卸荷后的应变累积方向大致与修改后的“凸轮粘土”流动规则一致。如果初始应力状态和最终应力状态相同，则卸载应力路径对最终累积应变的影响有限。应变积累方向的变化归因于由横向应力减小引起的平均应力比的变化，但几乎不取决于相对密度和卸载应力路径。卸荷后的应变累积方向大致与修改后的“凸轮粘土”流动规则一致。