交通荷载作用下软黏土的耗散能开展特征分析

Dissipation energy analysis of pore pressure and deformation characteristics of soft clay under traffic loads

交通、波浪等循环荷载的作用将引起土体主应力轴方向的连续变化,对软土路基的变形与稳定产生显著影响.现实工程中常以临界动应力水平作为路基设计的控制标准.为研究长期交通荷载下饱和软黏土处于临界动应力水平时的动力特性,利用空心圆柱扭剪仪开展一系列心形线应力路径及其他复杂应力路径下的不排水试验.基于耗散能理论,对交通荷载作用下软黏土的变形特征和耗散能的累积规律进行了分析,对比分析了不同应力路径和频率条件下广义剪应变和耗散能的发展规律.试验结果表明,临界动应力比条件下试样均会发生拐点破坏,可称之为临界破坏.在轴向拉压幅值比变化的心形线和圆形的不同应力路径下,土体发生临界破坏,虽然破坏特征差别很大,但累积耗散能的大小均较为接近,在88.007~91.807kJ/m3之间.故可考虑以耗散能作为不同应力路径临界破坏的判别标准.频率会影响土体的结构损伤程度,频率越低,损伤越充分,耗散能前期的累积速率越快.随着频率的增大,土体发生临界破坏时刻的累积耗散能越小,且呈一定的递减规律.建议可以采用累积耗散能作为确定临界应力水平下土体发生临界破坏的重要参考标准.

The continuous change of the principal stress axis direction of the soil will be caused by cyclic loads such as traffic and wave loads,which have a significant effect on the deformation and stability of the soft soil subgrade.In practice,the critical dynamic stress level is often used as the control standard of subgrade design.In order to study the critical dynamic characteristics of the saturated soft clay under the long term traffic load,a series of undrained tests under heart-shaped stress path and other complex stress paths were carried out by the hollow cylinder apparatus.Based on the dissipative energy theory,the deformation characteristics and the dissipative energy accumulation of soft clay under traffic load were analyzed.The develop-ment law of generalized shear strain and dissipative energy were compared and analyzed under different stress paths and frequencies.The test results show that the drastic changes damage will occur under the critical dynamic stress ratio,which can be called the critical damage.Under the different stress paths of the heart-shape and the change of axial tension and pressure amplitude ratio,the critical damage of the soil occurs,although the damage characteristics are quite different,but the cumulative dissipative energy is close to that of 88.007—91.807 kJ/m3.Therefore,dissipative energy can be considered as the criterion for determining the critical damage of different stress paths.Frequency affects the structural damage degree of soil.The lower the frequency,the more sufficient the damage is,and the faster the accumulation rate of dissipation energy is.With the increase of frequency,the cumulative dissipation energy of the soil at the time of critical damage is smaller and declining.It is suggested that cumulative dissipation energy can be used as an important reference standard for determining critical damage of soil under critical stress level.