三维应力状态下饱和软黏土循环动力特性试验研究

在三维应力空间中，基于循环大主应力与循环中主应力的耦合模拟交通荷载下竖向循环正应力与平行于道路方向的水平向循环正应力的耦合，构建了循环大、中主应力耦合应力路径，定义了循环应力路径表征参数——循环中主应力系数bcyc。通过GDS动静真三轴仪，对正常固结饱和软黏土进行了一系列循环大、中主应力耦合应力路径下的不排水循环加载试验，重点分析了循环中主应力系数及循环应力比对正常固结软黏土长期循环动力及安定特性的影响。试验结果表明：三维应力状态下，循环中主应力系数的增大提升了土体回弹模量，抑制了累积大主应变的发展，并且累积大主应变与循环中主应力系数呈线性关系。基于安定理论，确定了循环大、中主应力耦合应力路径下饱和软黏土的容许循环应力比，同时发现循环中主应力系数的增加引起了容许循环应力比的上升。

Experimental study of cyclic dynamic behaviors of saturated soft clay in three-dimensional stress state

A coupling condition of cyclic major and intermediate principal stresses was applied to simulate the coupling of vertical cyclic normal stress with the horizontal cyclic normal stress parallel to the road direction under traffic load in three-dimensional stress space. A stress path with coupling of cyclic major and intermediate principal stresses was then proposed, and the coefficient of cyclic intermediate principal stress bcyc was defined as the characterization parameter of cyclic stress path. A series of undrained cyclic true triaxial tests under coupling of cyclic major and intermediate principal stresses was performed in normally consolidated saturated soft clay by GDS cyclic true triaxial apparatus. The effects of coefficient of cyclic intermediate principal stress and cyclic stress ratios on the long-term shakedown characteristics of normally consolidated soft clay under undrained conditions were analyzed. The experimental results show a significant increase of resilient modulus induced by increasing the coefficient of cyclic intermediate principal stress, which restrains the development of cumulative major principal strain. The cumulative major principal strain has a linear relationship with the coefficient of cyclic intermediate principal stress in the three-dimensional stress state. On the basis of the shakedown theory, the allowable cyclic stress ratios under coupling of cyclic major and intermediate principal stresses were determined, and it was also found that the allowable cyclic stress ratios increased with increasing the coefficient of cyclic intermediate principal stress.