中文摘要：

通过空心圆柱扭剪仪对不同相对密实度的饱和南京砂分别进行了单调扭剪不排水、排水试验以及循环扭剪不排水试验。试验结果表明：在单调扭剪试验中，试样相转换线的位置与排水条件无关，但相对密实度较大试样的相转换线斜率小于相对密实度较小的试样。在循环扭剪不排水试验中，对于相对密实度较小的试样，当其有效应力路径接近单调扭剪荷载作用下具有相同初始条件试样的相转换线时，孔压急剧增加，扭剪应变迅速增大，试样出现不稳定现象，随后发生初始液化；对于相对密实度较大的试样，当其有效应力路径接近单调扭剪荷载作用下试样的相转换线时，试样出现循环活动现象，随着循环扭剪荷载的继续施加，有效应力路径表现为以破坏线为边界且呈“蝴蝶”形状的一系列重叠的回滞环，此时孔压在某一常值上下波动，累积孔压不再增加。具有相同初始条件的试样在循环和单调扭剪荷载作用下得到的相转换线几乎相同，这一规律不受相对密实度的影响。

英文摘要：

Undrained and drained monotonic as well as undrained cyclic torsional shear loading tests are carried out on saturated Nanjing sand at various relative densities in a hollow cylinder apparatus. The test results indicate that the phase transformation line appears to be independent of drainage conditions, but is lower when relative density is denser under monotonic torsional shear loading. In the cyclic torsional shear loading tests under undrained condition, as to the loose specimen, the excess pore pressure and the torsional strain increase rapidly when the stress path approaches the phase transformation line defined under monotonic torsional shear loading with identical initial conditions, which lead to specimen in instable state. Subsequently, initial liquefaction occurs. For the dense specimen, it shows cyclic mobility when the stress path approaches the phase transformation line defined under monotonic torsional shear loading with identical initial conditions. With the loading going on, the stress path presents a series of papilionaceous overlapped hysteresis loops with the border of failure line. At the moment, the excess pore pressure fluctuates around a nearly constant value and cumulative pore pressure no longer increases. The phase transformation line defined under cyclic loading appears to coincide with the phase transformation line defined under monotonic loading, which seems independent of the relative density.