中文摘要：

动剪切模量和阻尼比是岩体重要的动力特性参数，其取值的合理性对场地地震响应分析的结果有重要影响．利用WDT1500多功能材料试验机，对砂岩、砾岩和砂砾岩等软岩试样进行了循环荷载试验，研究了软岩的动剪切模量和阻尼参数对应力、应变幅值和应力水平的响应特性，得到了动剪切模量和阻尼参数随应力幅值、应力水平及含水率的变化规律，讨论了其变化机理．结果表明，在不同应力水平和不同应力幅值下阻尼参数随着应力幅值的增大而增大，与应力幅值成线性拟合关系．当应力幅值较小时，含水率对岩石动剪切模量的影响较小，而对阻尼比和阻尼系数的影响较大；当应力幅值较大时，恰好相反．含水率，应力水平和应力幅值都相同时，应力水平逐级增大的应力路径下测得的阻尼参数大于应力幅值逐级增大的应力路径下测得的阻尼参数．建立的不同应力水平和不同应力幅值条件下软岩的动剪切模量与阻尼比关系模型能够描述分级循环荷载过程中阻尼行为．研究成果对抗震工程的地震反应分析和场地安全性评价有着重要参考价值．

英文摘要：

Shear modulus and damping ratio are two important dynamic parameters of rock, the values of which can have great impacts on the analysis results of seismic response. To investigate the damping be haviour of soft rock under stepped axial cyclic loading,cycle loading tests in different stress levels and dif ferent stress amplitudes were carried out for sandstone, conglomerate and glutenite specimens on a WDT- 1500 material testing machine. Based on the experimental results, the responses of dynamic shear modulus and damping parameters to stress amplitude,strain amplitude and stress level under cyclic loading were in- vestigated, and the comparative analysis of damping behaviour under different loading conditions was made. It was shown that the dynamic shear modulus and damping parameters varied in different ways with stress level, stress amplitude and moisture. The interrelation of dynamic shear modulus and stress amplitude of soft rock .was obtained under stepped axial cyclic loading. The results showed that the damping parameters increased linearly with the increase of stress amplitude under different stress amplitudes and stress levels. It was clearly shown that the lower the stress amplitude was,the less the effect of moisture content on the dynamic shear modulus was, and the greater the effect of moisture content on the damping parameters was. Furthermore,with the same stress level and stress amplitude,the damping parameters under stepped stress level cyclic loading were greater than those under stepped stress amplitude cyclic loading. The hyperbolic model was used to describe the stress strain relationship of soft rock under stepped axial cyclic loading. Fi- nally,a model of relationship between dynamic shear modulus and damping ratio of soft rock in different stress levels and different stress amplitudes was proposed,which showed a superior capacity in describing the damping behaviour of soft rock under stepped axial cyclic loading. The results provided useful knowl- edge for seismic response analysis and on