成都平原粘性土动力学参数统计分析

Research on Dynamic Parameters of Clay Soil in Chengdu Plain

成都平原地震构造环境主要受近场中强地震和外围大地震的影响。成都平原内的第四系分布广泛,主要为河流相的砂卵石层夹粘土、粉土层。这种地层在土层地震反应计算时往往会产生一个峰值,具有显著的放大作用。本文共收集了107组土动力学参数的实验资料,统计分析了粉质粘土和粘土两种粘性土的实测土动力学参数,给出了它们在不同深度的动剪切模量比和阻尼比的统计值。然后,选取1个典型钻孔,建立了土层地震反应分析模型,分别运用本文"统计值"、"十五结果"、"规范值"、"推荐值"进行地震土层反应计算,从反应谱形状、地表峰值加速度和反应谱特征周期等方面,验证了本文"统计值"的适用性和针对性,结果表明在盆地内使用"规范值"和"推荐值"时应谨慎,不然可能会对工程的抗震设防产生不利的影响。本文的"统计值"比"规范值"和"推荐值"更适用于成都平原地区,对各类工程建设的场地地震安全性评价具有一定的借鉴和参考价值。

Earthquake tectonic environment of Chengdu plain is relatively stable, mainly suffering from strong earthquakes in the near field and the peripheral impact of the large earthquakes. The Quaternary sediments within the plain are mainly fluvial sand and gravel with clay and silt interlayers. Such stratum in regarding to soil seismic response calculation tends to produce a peak, with significant amplification. In this paper we collected the soil dynamic parameters from 107 experiments, and divided the data into 2 groups based on lithology, such as, silty clay and clay. Statistical analysis of the dynamic parameters of these soils was carried out to obtain the mean values of dynamic shear modulus ratio and damping ratio at different depths. Furthermore, selecting one typical engineering site, we analyzed the influences of four different soil dynamic parameters, mean values, experimental values, values recommend by former researchers, and values recommend in the code for seismic safety evaluation of engineering sites （DB001-94）. The results show that in Chengdu plain using specifications and recommended values can have adverse effects on the earthquake fortification work. The results can be taken as a reference of the soil dynamic value in this area and can be used in the seismic risk assessment of engineering projects.