考虑不同单次加载时长影响的循环荷载作用下软土动力特性

Dynamic characteristics of soft soil under cyclic loading considering influence of different single loading durations

为研究不同单次加载时长循环荷载作用下软土的动力特性,设计并进行软土试样的动三轴试验,分析不同围压、动荷载幅值和动荷载单次加载时长作用下软土的累积变形发展和刚度软化特性。从应变-循环周次曲线、软化指数-循环周次曲线等方面研究围压、动荷载幅值和动荷载加载时长对软土累积变形及刚度软化特性的影响,并建立考虑加载时长作用的软土累积变形发展和刚度软化经验模型。研究结果表明:软土的累积塑性应变与围压负相关,与动荷载幅值和动荷载作用时间正相关;土体应变-循环周次曲线存在拐点,循环周次未加载到拐点时,累积塑性应变发展迅速,循环周次加载达到拐点后,累积塑性应变增长速率减缓并逐渐趋于平稳;土体刚度软化指数与围压正相关,与动荷载幅值和动荷载作用时间负相关;土体刚度软化指数以临界加载次数为界,加载次数小于临界加载次数时,软化指数急剧衰减,衰减幅度达到70%以上;建立的考虑加载时长作用的软土累积变形发展和刚度软化经验模型具有较高的预测精度。

To study the dynamic properties of soft soil under cyclic loading with different single loading duration,dynamic triaxial tests of soft soil specimens were designed and carried out to analyze the cumulative deformation development and stiffness softening characteristics of soft soil under different perimeter pressures,dynamic load amplitudes,and dynamic loading durations.The effects of confining pressure,dynamic load amplitude,and loading duration on the cumulative deformation and stiffness softening characteristics of soft soil were investigated in terms of the strain-cycle curve and softening index-cycle curve.And an empirical model of cumulative deformation development and stiffness softening of soft soil was established by considering the effect of loading duration.The results show that the cumulative plastic strain of soft soil is negatively correlated with the confining pressure,and positively correlated with the dynamic load amplitude and dynamic load duration.There is an inflection point in the strain-cycle curve of the soil body,and the cumulative plastic strain develops rapidly when the cycle times are not loaded to the inflection point.The growth rate of the cumulative plastic strain is slowed down and tends to be stable after the cycle times are loaded to reach the inflection point.Soil stiffness softening index is positively correlated with the confining pressure,and negatively correlated with the dynamic loading amplitude and dynamic loading time.The stiffness softening index is bounded by the critical loading times.When the loading times are less than critical,the softening index decreases sharply,and the attenuation amplitude accounts for more than 70%.The empirical model of cumulative deformation development and stiffness softening of soft soil established in this paper considering the role of loading duration has high prediction accuracy.4 tabs,11 figs,31 refs.