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砂砾土的地震液化至今仍存较大的争议,相应的液化机理解释主要沿用传统的砂土液化分析思路和方法。利用动态圆柱扭剪仪开展了100 mm直径、3组典型级配(含砾量分别为37%,45%和60%)的饱和砂砾土试样循环动三轴实验。基于实验得到的应力–应变率关系曲线,定义了反应饱和砂砾土流动性的平均流动系数和流动性水平。实验发现,初始动应力比对不同含砾量下的平均流动系数–孔压比关系曲线无影响;相对密度越大、含砾量越大,饱和砂砾土的流动性水平越低;有效固结压力对饱和砂砾土平均流动系数–孔压比关系曲线的影响与含砾量相关。推测饱和砂砾土在循环荷载下的流动性由其粗粒接触状态和数量决定;粗粒间的接触在高孔压状态下不能顺利解除是饱和砂砾土与饱和细粒土抗液化性能的本质区别。提出的基于流动性的饱和砂砾土液化机理较好地解释了以上现象。
The liquefaction of gravelly soil is still a big controversy. The corresponding explanation of liquefaction mechanism mainly follows the traditional ideas and methods of sand liquefaction analysis. A dynamic triaxial test of saturated gravel soil specimens with 100 mm diameter and 3 typical gradations (gravel content of 37%, 45% and 60% respectively) was carried out by dynamic cylindrical torsion shear tester. Based on the experimentally obtained stress-strain rate curves, the average flow coefficient and liquidity level of the fluidity of saturated gravel soil are defined. The experimental results show that the initial dynamic stress ratio has no effect on the average flow coefficient-pore-pressure ratio curve under different gravel content. The larger the relative density is, the larger the gravel content is and the lower the fluidity of saturated gravel soil is. The influence of pressure on the average flow coefficient - pore pressure ratio curve of saturated gravel soil is related to the amount of gravel. It is inferred that the fluidity of saturated grit-gravel under cyclic loading is determined by the contact state and the number of coarse grains. The contact between coarse grains can not be successfully removed under high pore pressure. The essential difference between liquefaction resistance of saturated gravel soil and saturated fine grained soil . The proposed fluidity-based mechanism of liquefaction of saturated gravel soils well explains the above phenomenon.