循环加卸载作用下贵阳红黏土损伤特性试验研究

EXPERIMENTAL STUDY ON DAMAGE CHARACTERISTICS OF GUIYANG RED CLAY UNDER CYCLIC LOADING AND UNLOADING

为研究贵阳红黏土在循环荷载作用下的损伤特性,揭示抗剪强度参数随加卸载过程的损伤演化规律,通过应力-应变控制式三轴剪切渗透仪中的应力路径试验模块,对ω=29%、32%、35%以及38%4种含水率的贵阳红黏土在σ_(3)=100 kPa、200 kPa和300 kPa围压下开展固结不排水剪循环加卸载试验。研究结果表明:卸载过程中土样表现出变形增强性,卸载后轴向应变增量越大,松弛时间越长,回弹变形量越大;综合考虑含水率与围压条件的影响,建立贵阳红黏土剪切过程中弹性变形演化的数学关系式,并与试验结果进行对比验证,拟合度达95%以上;采用等效塑性剪切应变作为塑性内变量,对贵阳红黏土剪切全过程强度损伤特性进行研究,发现其胶结强度不断损失,而摩擦强度不断增加;且随着含水率的增加,内摩擦角的变化范围为21.8°~16.1°,黏聚力的变化范围为83.7~57.5 kPa。研究成果可为路基压实及考虑加卸载工况的土坡稳定性评价提供理论指导。

This paper studies the damage characteristics of Guiyang red clay under cyclic loading and reveals the evolution of shear strength parameters with the loading and unloading process.Using the stress path test module in the stress-strain controlled triaxial shear penetrometer,we conducted consolidation undrained shear cyclic loading and unloading tests on Guiyang red clay with four water contents ofω=29%,32%,35%and 38% at σ_(3)=100 kPa,200 kPa and 300 kPa surrounding pressure,respectively.This study shows the follows.The soil samples exhibit deformation enhancement during unloading,the larger the axial strain increment after unloading,the longer the relaxation time,and the larger the rebound deformation.Taking into account the effects of water content and surrounding pressure conditions,we established the mathematical relational equation for the evolution of elastic deformation during shearing of Guiyang red clay.We compared the mathematical relational equation with the experimental results to verify that the fit was more than 95%.We adopted the equivalent plastic shear strain as the plastic internal variable to study the strength damage characteristics of Guiyang red clay during the whole shear process.The results found that its cementation strength kept losing while the friction strength kept increasing.With the increase of water content,the internal friction angle and cohesiveness range from 21.8°to 16.1°and 83.7 kPa to 57.5 kPa,respectively.The research is expected to provide theoretical guidance for the compaction of road base and the evaluation of soil slope stability considering the loading and unloading conditions.