埋深对黏性土动剪切模量和阻尼比影响试验研究

Experimental study on the influence of buried depth on dynamic shear modulus and damping ratio of cohesive soil

动剪切模量和阻尼比是两个重要的土动力学参数,在场地地震反应分析中是不可或缺的基础内容。本文通过对取自江苏地区的397个原状黏性土样进行自振柱试验,深入研究了土的埋藏深度对各类土的最大剪切模量、动剪切模量比和阻尼比与剪应变的关系影响,结果发现:各类土的最大剪切模量均随埋深的增大而增大,二者在统计意义上呈指数关系;埋深对黏性土的动剪切模量比和阻尼比与剪应变关系曲线也有较明显的影响,且这种影响的程度随埋深的增大而减小;动剪切模量比和阻尼比关系曲线受埋深变化影响的敏感性因土类的不同而有明显差异,从本次结果来看,埋深对粉质黏土与粉砂互层的影响最大,对淤泥质土和粉土的影响次之,对黏土和粉质黏土的动力特性影响最小,且每种土动剪切模量与剪应变的关系和阻尼比与剪应变的关系受埋深的影响表现出了不同的变化趋势。此外建立了土层模型进行了地震反应分析,验证了考虑埋深对土动力学参数影响的必要性,在工程上具有一定的参考意义。

Dynamic shear modulus and damping ratio are two important soil dynamic parameters. They are indispensable basic datum for seismic response analysis of important projects. Through the free vibration column tests on397 undisturbed cohesive soil samples from Jiangsu area,the effects of buried depth on the maximum shear modulus,the relationships of dynamic shear modulus ratio and damping ratio versus shear strain of each kind of soil have been investigated in detail. The results show that the maximum shear modulus of each kind of soil increased with the increase of buried depth. The two follows the exponential function. The effect of buried depth on the relationships of dynamic shear modulus ratio and damping ratio versus shear strain of cohesive soil is obvious and the degree of influence decreases with the increase of buried depth. The sensitivity of relationships of dynamic shear modulus ratio and damping ratio versus shear strain to the influence of buried depth is significantly different due to the difference of soil types. Judging from this experimental,silty clay and fine sand interbedded strata get the greatestinfluence of buried depth,followed with mucky soil and silt. Clay and silty clay get the minimal impact on the dynamic characteristics. The relationships of dynamic shear modulus ratio versus shear strain and damping ratio versus shear strain of each kind of soil show different variation tendency for the influence of buried depth. Besides,a case of foundation model is established for seismic response analysis,which verifies that it is necessary to consider the influence of buried depth on soil dynamics parameters in reality projects.