考虑变围压因素的饱和软黏土循环纯压动力特性试验研究

Undrained dynamic behaviors of saturated clays under compressive stress paths considering cyclic confining pressure

饱和土体的动力特性表现出对应力路径的依赖性。越来越多基于变围压动三轴的试验结果表明:循环围压应力路径对砂土等颗粒材料的变形和回弹特性存在较大的影响。基于变围压动三轴试验,通过循环偏应力与循环围压的耦合模拟真实交通荷载下竖向循环正应力与水平循环正应力的耦合,研究了循环围压对饱和软黏土孔压、永久和回弹变形的影响。试验结果表明:在不排水条件下,与常规恒定围压动三轴试验结果相比,循环围压的存在较大程度地改变了孔压的发展规律,减少了永久变形的累积速度,同时增加了回弹变形(即减少了回弹模量);循环围压幅值与循环偏应力幅值的比值(RPD)越大,永久应变的减少值与回弹应变的增加值越大;并进一步建立了考虑循环围压因素的饱和软黏土永久沉降和回弹模量预测模型。

The dynamic properties of saturated soils are dependent on the stress paths.More and more test results based on cyclic triaxial tests with cyclic confining pressure show that the stress paths with cyclic confining pressure have great influences on the deformation and resilient characteristics of granular materials such as sands.In this study,the cyclic triaxial tests with cyclic confining pressure are employed to study the coupling effects of cyclic deviatoric stress and cyclic confining pressure on the dynamic behaviors of saturated clays,which simulate the coupling effects of cyclic axial normal stresses and cyclic lateral normal stresses in real traffic loading.The test results show that： under undrained conditions,in comparison with the results in conventional cyclic triaxial tests with a constant confining pressure,the cyclic confining pressure influences greatly the development of the excess pore water pressure,reduces the accumulation rates of the permanent axial stain and increases the resilient strain（i.e.,decreases the resilient modulus）;and with the increasing ratio of the amplitude of cyclic confining pressure to the amplitude of cyclic deviatoric stress,the decrease of the permanent axial strain and the increase of the resilient strain are getting larger.Two prediction models of permanent settlement and resilient modulus considering the cyclic confining pressure are proposed.