西安近断层区黄土动力特性研究

Study on dynamic characteristics of loess in Xi′an near-fault zone

为研究近断层区黄土的动剪切模量和阻尼比特性,以近骊山断层区黄土为研究对象,采用GDS动三轴试验仪进行动三轴试验,分析黄土动剪切模量和阻尼比在围压、饱和度、频率三种因素影响下的变化规律.结果表明:近断层区黄土动剪切模量和饱和度、固结比呈负相关关系,且降幅逐渐减小;与振动频率呈正相关关系,并且随着振动频率的增加,增幅逐渐减小.近断层区饱和黄土的动剪切模量出现反弹现象,其值高于非饱和黄土,其原因可能为断裂带黄土次生裂隙更为发育.其孔隙水溶解土骨架中的可溶盐增多,土体趋于软化,黏滞性增强,所需的动剪切应力增加.近断层区黄土阻尼比与饱和度、围压和固结比呈负相关关系,且降幅逐渐减小,最后趋于稳定.饱和度对黄土阻尼比影响最大,围压和固结比对阻尼比影响较小.近断层区原状黄土与重塑黄土阻尼比大致近似,近似可认为土体扰动对骊山山前断裂场地黄土影响较小.本文采用半对数坐标系下的线性函数来量化动剪切模量、阻尼比与动应变的关系,且拟合效果较好.这一研究结果可为近断层区的动力响应机制分析提供参考.

In order to study the characteristics of dynamic shear modulus and damping ratio of loess in the near-fault area,the dynamic triaxial test was carried out by GDS dynamic triaxial tester with the loess in the near-fault area as the research object,and the dynamic shear modulus and damping ratio of loess were analyzed under the influence of confining pressure,saturation and frequency.The results show that the dynamic shear modulus of loess in the near-fault area is negatively correlated with saturation and consolidation ratio,and the decline decreases gradually,but it is positively correlated with the vibration frequency,and the amplification gradually decreases with the increase of vibration frequency.The dynamic shear modulus of saturated loess in the near-fault zone rebounds,and its value is higher than that of unsaturated loess,which may be due to the fact that the secondary fissures of loess in the fault zone are more developed.The dissolution of soluble salts in the soil skeleton by pore water increases,causing the soil to soften and enhance its viscosity,resulting in an increase in the required dynamic shear stress The damping ratio of loess in the near-fault zone is negatively correlated with saturation,confining pressure and consolidation ratio,and the decrease gradually decreases and finally tends to be stable.Saturation has the greatest influence on the damping ratio of loess,while confining pressure and consolidation ratio have little influence on the damping ratio.The damping ratio of undisturbed loess and remolded loess in the near-fault zone is roughly similar,indicating that soil disturbance has a relatively small impact on the loess at the Lishan Mountain front fault site.In this paper,the linear function in semi logarithmic coordinate system is used to quantify the relationship between dynamic shear modulus,damping ratio and dynamic strain,and the fitting effect is good.The results of this study can provide a reference for the analysis of the dynamic response mechanism in the near-fault zone.