循环荷载下南京片状细砂的动应力--应变关系

Dynamic Stress-strain Relationship of Nanjing Flake-shaped Sands in Cyclic Loading

以片状颗粒成分为主的片状结构砂与常用的圆形颗粒标准石英砂相比,在物理力学特性上有显著的差异。循环荷载作用下,饱和砂土振动孔压上升会导致土体刚度发生软化,当振动孔压累积达到一定水平时,会产生液化现象,从而引起土体结构发生破坏。采用英国WFI动三轴仪,研究了南京片状细砂在循环荷载作用下,静偏应力水平、循环应力比水平和循环次数对其动应力—应变关系的影响,考虑每一次循环过程中动应力—应变关系滞回曲线的卸载及再加载割线动剪切模量G_(sec)和最大割线模量G_(max)的变化特性,建立了动剪模量软化的经验公式;静偏应力水平对动剪模量软化有显著影响,随着循环次数的增加,动应力—应变滞回圈逐渐向应变累积方向滑移和向应变轴方向倾斜,且彼此分离;考虑循环软化特性,采用修正的Masing准则,描述了循环荷载下南京片状细砂的动应力—应变关系。

Physical properties of flake-shaped sand soils are remarkably different from those of the common standard quartz sand soils composed of circular-shaped particles. The rising of pore-water pressure under cyclic loading will lead to stiffness degradation of fully-saturated sand soils. And liquefaction of the soil will be triggered when its pore-water pressure reaches to a threshold, breaking down the soil mass. Considering different values of static deviatoric stress, ratios of alternating stresses and the number of cycles, a series of tests were performed with the WFI cyclic tri-axial apparatus to study the dynamic stress-strain relationship of Nanjing flake-shaped sands. It has been observed that initial static deviatoric stress ratio, axial cyclic stress ratio and the number of cycles have remarkable effect on the stress-strain relationship of Nanjing flake-shaped sands. An empirical equation on degradation of secant shear modulus has been for-mulated on the properties of secant shear modulus in each unload-reload loop of dynamic stress-strain relationship. The static deviatoric stress ratio has remarkable influence on the degradation of shear modulus. With the numbers of cycles increasing, the stress-strain hysteretic loops separate from each other gradual- ly and the stress-strain hysteretic loops are leaning gradually towards the coordinate axis of strain. In addition, the empirical equation of shear modulus degradation has been based to describe the dynamic stressstrain relationship of Nanjing flake-shaped sands with the modified Masing＇s criteria.