地震荷载作用下粗颗粒含量对川西混合土动剪切模量和阻尼比的影响

Effect of Coarse Grain Content on the Dynamic Shear Modulus and Damping Ratio of Mixed Soil Under Seismic Load in Western Sichuan

为分析川西地区混合土地震荷载作用下的动力特性,针对该地区保留全部粒径的天然混合土,对3组土分别采用筛分法剔除60,20,10,5 mm粒径颗粒,制备粗颗粒含量不同的天然混合土土样,利用DJSZ-150粗粒土动、静两用三轴试验机进行大型动三轴试验,采用Hardin-Drnevich双曲线模型(H-D模型)拟合动应力-应变关系曲线,获得Gd/Gmax-γ和λ-γ曲线变化规律,分析不同围压和粗颗粒含量对川西混合土动剪切模量Gd和阻尼比λ的影响作用。结果表明:混合土动剪切模量Gd、阻尼比λ均随围压及大于5 mm的粗颗粒含量的增大而增大,原因是随着围压增大,粗细颗粒的接触增多,土体结构更加紧实,提高了颗粒壁隙间的动摩擦力,增大了能量传递时的耗损,导致动剪切模量与阻尼比随之增大;当粗颗粒含量小于40%时,细颗粒构成土骨架,粗颗粒的接触被细颗粒阻隔,导致其对动剪切模量及阻尼作用贡献不大,此时动剪切模量和阻尼比随粗颗粒含量增加而增加的速度较慢,当粗颗粒含量为40%~60%时,混合土中粗颗粒骨架形成,且细颗粒有效填充了粗颗粒间的孔隙,粗颗粒在土中起主导作用,此时动剪切模量与阻尼比随着粗颗粒含量的增加而快速增加,当粗颗粒含量大于60%时,粗颗粒的增加无法进一步增强其骨架效应,而此时细颗粒间的胶结作用随粗颗粒的增多导致细颗粒的相应减少而减弱,动剪切模量和阻尼比随粗颗粒含量增加而增加的趋势不明显。

To analyze the dynamic characteristics of mixed soil under seismic loading in the Western Sichuan area,in view of the natural mixed soils retaining all particle sizes in this area,we screened out three groups of soils(with particle sizes of 60,20,10,and 5 mm),and then prepared natural mixed soils with different coarse particle content.Large-scale dynamic triaxial tests were carried out using a DJSZ-150 dynamic and static dual-purpose triaxial testing machine for coarse-grained soils.Moreover,a Hardin-Drnevich hyperbolic model(H-D model)was used to fit the dynamic stress-strain relationship curve,and the variation rules of the Gd/Gmax-γandλ-γcurves were obtained.The effects of different confining pressures and coarse particle content on the dynamic shear modulus(Gd)and damping ratio(λ)of the mixed soils were analyzed.The results demonstrate that Gd andλincrease with increasing confining pressure and in soils with a content of coarse particles greater than 5 mm.This is because the contact between coarse and fine particles increases with increasing confining pressure,the structure of the soil is more compact,the dynamic friction force between particle gaps is increased,and the loss of energy transfer is increased.When the coarse particle content is less than 40%,fine particles constitute the soil skeleton and they block the contact of the coarse particles,which makes little contribution to Gd andλ.At this time,Gd andλincrease slowly with increasing coarse particle content.When the coarse particle content is 40%-60%,a skeleton of coarse particles is formed in the mixed soil and fine particles effectively fill the voids between the coarse particles.Here,coarse particles play a dominant role in the soil.At this time,Gd andλincrease rapidly with increasing coarse particle content.When the coarse particle content is more than 60%,the increase in coarse particles cannot further enhance the skeleton effect,whereas the cementation between fine particles decreases with increasing coarse particle content.Further,the increasing trend of Gd andλwith increasing coarse particle content is not obvious.