南京饱和细砂液化后大变形条件下动剪切模量衰减特征研究

Shear moduli reduction of saturated Nanjing sand under large deformation induced by liquefaction

针对南京饱和细砂液化后特大变形条件下(双幅剪应变接近100%)应力-应变关系特征,分析了有效围压和初始静剪应力比等因素对南京饱和细砂初始液化后特大变形条件下应力-应变关系曲线的影响规律,即在液化后多次循环加载条件下零有效应力阶段、剪胀阶段和反向卸载阶段的剪切模量随单向流动累积变形的衰减特征。结果表明:有效围压、初始静剪应力和循环加载幅值对南京饱和细砂初始液化后特大变形条件下应力-应变关系曲线在零有效应力阶段和剪胀阶段的剪切模量大小及其衰减特征的影响不明显,而对反向卸载阶段的剪切模量大小和衰减特征的影响相对较大。随着有效围压和加载幅值分别增大,南京饱和细砂初始液化后特大变形条件下应力-应变关系曲线反向卸载阶段剪切模量都有明显增大的趋势,同时其剪切模量随后续循环加载次数的衰减速度也变快。但随着初始剪应力的增大,该阶段剪切模量随后续循环加载次数的衰减速度有减慢的趋势。同时,基于试验结果,给出了南京饱和细砂初始液化后特大变形条件下应力-应变关系曲线在不同阶段的剪切模量与单向流动累积变形有关的衰减函数及其拟合参数确定方法。

To study the post-liquefaction stress-strain relationship of saturated Nanjing sand, shear moduli reduction in the liquefaction state, the dilation state and the unloading state were investigated under different loading conditions. As results, the effective confining pressure, the initial shear loading, and the amplitude of cyclic loading have less effect on shear moduli reduction of saturated Nanjing sand in the liquefaction state and the dilation state. However, these factors have great effect on shear moduli reduction of saturated Nanjing sand in the unloading state. As the effective confining pressure and the cyclic loading amplitude increasing, the post-liquefaction shear moduli of saturated Nanjing sand in unloading stage are all stronger and the shear moduli soften faster under the subsequent cyclic loadings. Meanwhile, as the initial shear stress increasing, the post-liquefaction shear moduli of saturated Nanjing sand are also stronger, but it softens slower under the subsequent cyclic loadings. Based on the test results, the decay function of the shear moduli of saturated Nanjing sand in different loading stages are also given.