冻融循环对重塑青藏粉质黏土阻尼比影响的试验研究

Experimental study of influence of freeze-thaw cycles on damping ratio of remolded Qinghai—Tibet silty clay

阻尼比是土的重要动力学参数之一。为研究动荷载作用下重塑青藏粉质黏土的阻尼比特性,在室内冻融循环试验的基础上开展动三轴试验,考虑冻融循环次数、含水率及动荷载频率等影响因素,得到重塑青藏粉质黏土的阻尼比–动剪应变(λ-γd)关系曲线及模型参数。结果表明:动荷载作用下重塑青藏粉质黏土的阻尼比受含水率的影响最为显著,受冻融循环作用的影响次之,受动荷载频率的影响较小。随冻融循环次数的增加,λ-γd关系曲线向上偏移,同一动剪应变对应的阻尼比增大,经历1次冻融循环后的λ-γd关系曲线变化最为显著,3次冻融循环后趋于稳定;随含水率的增加,λ-γd关系曲线不断向上抬升,曲线形态也由缓变陡,同一动剪应变对应的阻尼比普遍增大;随频率的增加,λ-γd关系曲线缓慢下移,同一动剪应变对应的阻尼比略有减小。研究成果可为寒区场地地震反应分析、路基动力响应分析中阻尼比参数的选取提供参考。

Damping ratio is one of the important dynamic parameters of soil. Based on the freeze-thaw cycles tests,the dynamic triaxial tests are carried out to study the damping ratio of remolded Qinghai-Tibet silty clay under dynamic loading. In the test,the influences of the freeze-thaw cycles,water content and dynamic loading frequency are considered. The relationship curve and model parameters of damping ratio vs. dynamic shear strain( λ-γd) are obtained. The results indicate that the damping ratio of remolded Qinghai-Tibet silty clay under dynamic loading is most significantly affected by moisture content,significantly affected by freeze-thaw cycles,and less affected by dynamic loading frequency. With the increase of the number of freeze-thaw cycles,the λ-γd curve shifts upward and the damping ratio corresponding to the same dynamic shear strain increases,the λ-γd curve changes most significantly after one freeze-thaw cycle,then tends to be stable after three freeze-thaw cycles. With the increase of the water content,the λ-γd curve keeps moving upward,the shape of the curve also changes gradually from gentle to steep,and the damping ratio corresponding to the same dynamic shear strain generally increases. With the increase of the dynamic loading frequency,the λ-γd curve moves down slowly,and the damping ratio corresponding to the same dynamic shear strain decreases slightly. The research results can provide a reference for the selection of the damping ratio parameters in the seismic response analysis and foundation dynamic response analysis in cold region.