不同循环加载方式下饱和珊瑚砂的液化流动特性

Liquefaction flow characteristics of saturated coral sand subjected to various patterns of cyclic loading

循环荷载作用下饱和砂土的超静孔压累积是导致土体液化的原因,将可液化砂土视为流体是一种较新的液化研究思路。通过循环应力主轴90°跳转和连续旋转的均等固结、不排水循环剪切试验,探究了不同循环加载方式下饱和珊瑚砂的液化流动特性,发现以初始表观黏度η0规准的表观黏度比η/η0与超静孔压比ru的关系受循环应力路径的影响显著,η/η0随ru的增大而渐进衰退;而平均流动系数k随r_(u)的增长呈指数函数形式增大。循环应力比CSR(CSR=0.25~0.40)和循环加载频率f(f=0.1~1 Hz)对η/η0-ru和k-r_(u)关系的影响均不敏感。不论循环应力主轴90°跳转或连续旋转,发现表观黏度梯度和平均流动系数梯度均随ru的增大呈现出先增后减的特征,其反转点的ru≈0.9,可视为饱和珊瑚砂由固态向液态转变的相变孔压比ruth,以相应的相变平均流动系数k_(th)规准的k/k_(th)-r_(u)的所有试验数据点处于一个窄带内,且k/k_(th)随r_(u)增长服从指数函数关系。

The accumulation of the excess pore water pressure of saturated sand under various cyclic loadings is the cause of soil liquefaction,and it is a relatively new research idea to treat the liquefiable sand as a fluid.A comprehensive experimental investigation of the liquefaction flow characteristics is performed for the saturated coral sand subjected to the jump of 90°and the continuous rotation of the principal stresses with cyclic loading frequency(f)at isotropic consolidations.The test results show that the relationship between the normalized apparent viscosity(η/η0)and the excess pore water pressure ratio(ru)is significantly affected by the cyclic stress paths,the degradation ofη/η0 with ru is a progressive process,and a positive exponential correlation exists between the average flow coefficient(k)and ru.The correlations betweenη/η0 and ru and between k and ru seem to be independent on the cyclic stress ratio(CSR=0.25~0.40)and f(=0.1~1 Hz).Another significant finding is that the apparent viscosity gradient and the average flow coefficient gradient both increase first and then decrease with the increase of ru regardless of the jump of 90°and the continuous rotation of the principal stresses,and ru approximately equal to 0.9 at the reversal point can be regarded as the threshold value of the excess pore water pressure ratio(ruth)at the phase transformation state from the solid state to the liquid one,by denoting the correspondingk/k(th)as k_(th).The data points of k as k_(th)ru for all testing conditions are distributed in a narrow band,and a virtually positive exponential relationship exists between k/k_(th)and ru.