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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。
The monotonic torsional shear undrained and drained water tests and the cyclic undisturbed undrained tests were carried out on the saturated Nanjing sand with different relative densities by means of a hollow cylindrical torsional shear instrument. The experimental results show that in the monotonic torsional shear test, the position of the sample phase change line has nothing to do with the drainage conditions, but the slope of the phase transition line of the sample with larger relative density is smaller than the sample with the smaller relative density. In the cyclic undisturbed undrained test, when the effective stress path is close to the phase transfer line with the same initial conditions under monotonic torsional shear loading, the pore pressure increases sharply and the torsional shear The strain rapidly increases and the sample shows instability, then the initial liquefaction occurs. For the sample with relatively high density, the sample appears when the effective stress path approaches the phase transition line of the sample under the monotonic torsional shear load With the continuous application of cyclic torsional shear stress, the effective stress path appears as a series of overlapping hysteresis loops with the “butterfly” shape as the boundary and the pore pressure at a constant value Fluctuation up and down, cumulative pore pressure no longer increases. The same initial conditions of the sample in the cycle and monotonic torsion shear load obtained phase transition line is almost the same, this rule is not affected by the relative density.