饱和南京细砂初始液化后特大流动变形特性试验研究

针对地震中倾斜场地砂土液化流动大变形特征与机理,以具有明显片状颗粒结构特征的南京细砂为研究对象,采用了英国GDS公司的动态空心圆柱扭剪仪,开展了饱和南京细砂液化后特大流动变形特性的循环扭剪试验研究,主要分析了橡皮膜效应、有效围压、循环加载幅值和初始静剪应力等因素对南京细砂液化流动大变形特性的影响规律及其机理。试验结果表明:在其它条件不变时,随着有效围压增加,饱和南京细砂抗液化强度和抗单向液化流动累积变形强度都有所增加。当保持围压不变时,饱和南京细砂抗单向液化流动累积变形的强度有增加的趋势。随着初始静剪应力比的变大,南京细砂的抗液化和抗单向累积变形强度特征可以分为三个不同阶段。在无初始静剪应力条件下饱和南京细砂液化后仍以循环液化流动变形为主和单向流动累积变形为辅。但是,随着初始静剪应力比的增大,饱和南京细砂抗液化强度和抗单向液化流动累积变形强度明显降低,即主要发生单向液化流动累积变形破坏。当初始静剪应力比接近或超过循环动剪应力比时,饱和南京细砂的抗液化和抗单向流动累积变形的强度又明显增大,但仍以液化单向流动累积破坏为主。当初始静剪应力比继续增大到一定程度时,饱和南京细砂已经很难液化,其抵抗单向累积变形的强度也明显降低,主要原因应为此时试样发生的是塑性累积大变形破坏。同时,试验结果表明饱和南京细砂的液化后流动大变形特性也明显区别于含圆形颗粒为主的日本丰浦砂。

Cyclic torsional shear loading tests on the extremely large post-liquefaction flow deformation of saturated Nanjing sand

To investigate the post-liquefaction flow deformation of saturated Nanjing sand mostly composed of flaky grains, the hollow column torsional shear apparatus is used to simulate the loading states of the soils in the site with large liquefaction-induced lateral deformation. The results show that the resistance of Nanjing sand against the liquefaction and the post-liquefaction accumulation deformation increase with the effective confining pressure, and they also have increasing tendency under the same effective confining pressure. Without the initial shear forces, the post-liquefaction deformation of saturated Nanjing sand is mainly the cyclic liquefaction-induced deformation, and single direction accumulated flow deformation is also found, which also increases with the cyclic loading. The effect of the initial shear forces should be divided into three stages. In the first stage, the resistance of Nanjing sand against the liquefaction and the post-liquefaction accumulation deformation decrease severely with the increasing initial shear forces, and the soil samples are mainly damaged by the large liquefaction-induced flow deformation. However, when the initial shear forces are close to the cyclic shear forces, the resistance of Nanjing sand against the liquefaction and the post-liquefaction accumulation deformation increase quickly with the increasing initial shear forces, and the soil samples are mainly damaged by the large liquefaction-induced flow deformation in this stage. When the initial shear force is large enough, the saturated Nanjing sand is not liquefied until the single direction accumulated deformation reaches 30%, which proves that the large deformation of the saturated Nanjing sand is mainly caused by the large plastic deformation. Meanwhile, the large post-liquefaction deformation of saturated Nanjing sand is also different from that of the Toyoura sand mainly composed of round grains.