考虑循环围压和加载频率影响的间歇循环荷载作用下软黏土变形特性试验研究

    Coupling effects of cyclic confining pressure and loading frequency on deformation behavior of saturated soft clay under intermittent cyclic loading

    • 摘要: 列车运行时,下卧土体会经历循环加载和间歇停振阶段,间歇停振阶段的存在会影响土体力学性质。在循环加载阶段,交通荷载引起的土单元应力场中,轴向偏应力和围压循环变化,土体响应频率也不断变化。因此,通过对软黏土开展循环三轴试验,研究了间歇循环荷载作用下软黏土变形特性,分析了循环加载阶段循环围压和加载频率对软黏土累积轴向变形影响。结果表明,不同试验条件下各加载阶段产生的累积轴向应变增量均随加载阶段而减小,且应变增量的衰减程度与循环围压和加载频率有关,即循环围压的存在使试样各加载阶段产生的累积轴向应变增量衰减程度更为明显,且加载频率越大对应的应变增量衰减程度愈剧烈;与此同时,不同试验条件下应变增量的差异性在第1加载阶段中最为显著,即应变增量随循环围压和加载频率的增大而减小,但这一应变增量差异性在后续加载阶段中则可以忽略不计。结合上述试验结果,提出了一个考虑循环围压和加载频率影响的计算间歇循环荷载作用下软黏土累积应变表达式,且预测结果与实测值较为吻合。上述研究成果有助于加深对间歇循环荷载作用下软黏土动力特性的认知,也可为交通工程的设计工作提供一定技术支撑。

       

      Abstract: After the train passes away, the subgrade soils undergo cyclic loading and intermittent periods. The existence of the intermittent period can also affect the mechanical properties of soil. During the cyclic loading period, the stress field of the soil element caused by the traffic loads undergoes cyclic changes in deviator stress and confining pressure, and the response frequency of the soil also changes. Therefore, the deformation characteristics of saturated soft clay under intermittent cyclic loading are studied by conducting the cyclic triaxial tests, and the effects of the cyclic confining pressure and loading frequency are also analyzed. The results show that the accumulated axial strain increment generated at each loading stage under different experimental conditions decreases with the loading stage, and the attenuation degree of strain increment is related to the cyclic confining pressure and loading frequency. The existence of the cyclic confining pressure makes the attenuation degree of the accumulated axial strain increment of each loading stage more obvious. The larger the loading frequency, the more severe the attenuation degree of strain increment. Besides, the differences in the strain increments under different experimental conditions are most significant at the first loading stage, where the strain increment decreases with the increasing cyclic confining pressure and loading frequency. However, the differences in the strain increment can be ignored at subsequent loading stages. Based on the above experimental results, a model for calculating the accumulated axial strain of soft clay under intermittent cyclic loading considering the influences of the cyclic confining pressure and loading frequency is proposed, and the predicted results are in good agreement with the measured values. The above research results contribute to a deeper understanding of the dynamic characteristics of soft clay under the intermittent cyclic loading, and can also provide technical support for the design of transportation engineering.

       

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