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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。
In view of the large deformation and mechanism of liquefaction flow in the inclined field in inclined earthquakes, taking Nanjing fine sand with obvious flaky structure as the research object, the dynamic hollow cylinder torsional shear instrument of GDS company in the United Kingdom was used to carry out the saturated Nanjing fine sand Cyclic torsional shear tests on the characteristics of large flow deformation after liquefaction are carried out. The influence laws of rubber membrane effect, effective confining pressure, cyclic loading amplitude and initial static shear stress on the large deformation of Nanjing fine sand liquefaction flow and its mechanism . The experimental results show that the anti-liquefaction strength and the cumulative deformation strength of saturated Nanjing fine sand are increased with the increase of effective confining pressure under other conditions. When the confining pressure is kept constant, the strength of saturated Nanjing fine sand resistant to unidirectional liquefaction flow tends to increase. As the initial static shear stress ratio becomes larger, the anti-liquefaction and anti-unidirectional cumulative deformation strength characteristics of fine sand in Nanjing can be divided into three different stages. In the absence of initial static shear stress, the saturated liquefaction of fine sand in Nanjing is still dominated by cyclic liquefaction flow deformation and cumulative one-way flow deformation. However, with the increase of initial static shear stress ratio, the strength of anti-liquefaction of saturated fine sand and the cumulative deformation strength of anti-unidirectional liquefied flow are obviously reduced, that is, the cumulative deformation of unidirectional liquefied flow occurs mainly. When the initial static shear stress ratio is close to or exceeds the cyclic dynamic shear stress ratio, the strength of saturated Nanjing fine sand in liquefaction resistance and anti-unidirectional flow accumulation increases obviously, but it is still dominated by cumulative liquefaction unidirectional flow. When the initial static shear stress ratio continues to increase to a certain extent, the saturated Nanjing fine sand has been very difficult to liquefy, and its strength against one-way cumulative deformation is also significantly reduced. The main reason for this is that the plastic deformation damage. At the same time, the experimental results show that the large deformation characteristics of saturated Nanjing fine sand after liquefaction are also significantly different from that of Japan-based Toyobo sand which is mainly composed of round particles.