重庆主城区粉质黏土动力特性研究

Study of silty clay dynamic characteristics in Chongqing downtown area

采用自振(共振)柱和动三轴试验方法,得到重庆主城区粉质黏土动剪切模量和阻尼比随剪应变变化试验结果,比较分析试验值、文献[1]给出的推荐值和文献[2]给出的规范值的差异,并通过土层反应计算初步给出了这种差异对地表反应谱的影响,结果表明:(1)G/Gmax-γ关系中,规范值在中等应变时给出的G/Gmax比试验值和推荐值低;大应变时,相比较于试验值和推荐值,规范值衰减更快;(2)相比较于λ-γ关系,G-γ关系经过Gmax归一化后,更具有一致性,粉质黏土阻尼离散性较大;(3)试验值和推荐值计算的地表反应谱相差较小,但试验值和规范值计算的地表反应谱相差较大,特别是在随着输入地震动强度增大,这种差异性更显著。分析表明,重庆主城区进行土动力计算过程中,当无土动力特性试验资料时,选用规范值具有一定的局限性和风险,相比较于规范值,推荐值在一定程度上更具适用性。

The testing results of dynamic shear modulus and damping ratio of silty clay in Chongqing downtown area are attained with the change of shear strain by natural(resonance) column test and dynamic triaxial test.Besides,the differences between test value and recommended value from Reference [1] and code value from Reference [2] are compared and analyzed.Furthermore,the influence of such difference on surface response spectrum is initially given through soil response calculation;and main conclusions are drawn as follows:(1) In Relation G/Gmax-γ,G/Gmax given by code value is lower than that of test value and recommended value during moderate strain;code value attenuates faster than test value and recommended value during large strain.(2) After Gmax normalization,relation G-γ bears more consistency than relation λ-γ;and damping discreteness of silty clay is relatively large.(3) The difference of surface response spectrum calculated by test value and recommended value is relatively small;while the difference calculated by test value and code value is relatively large.And such difference is more obvious with the increase of input ground motion strength.Analyses show that in the process of soil dynamic calculation in Chongqing downtown area without testing data of soil dynamic characteristics,the application of code value has certain limitation and risk;and to some degree recommended value bears more applicability than code value.