Uncertainty analysis of seismic response of soil layer in deep overburden area
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摘要: 以上海地区作为深厚覆盖层地区代表，在丰富的地质资料基础上，全面、系统地分析了100 m以深地层的土层分布、剪切波速、土动力特性参数、密度和地震输入界面这5个不确定因素可能的分布范围，并采用逻辑树分析方法，利用等效线性化土层地震反应分析，计算得到了这5种不确定因素在23种工况下3个超越概率、4个典型地质孔的地表峰值加速度和反应谱结果。经分析表明，100 m以深地层的土动力特性参数、剪切波速、土层分布、密度属于低敏感性因素，其不确定性对地表地震动参数影响较小，峰值加速度差异基本在5%以内；地震输入界面属于高敏感性参数，对地表地震动参数（尤其是低频段）影响较大，最大差异可达30%—40%。地震安全性评价工作中应合理设定地震输入界面，以避免可能对工程抗震设防参数带来的不利影响。Abstract: Taking Shanghai area as the representative of deep overburden area, based on abundant geological data, this paper comprehensively and systematically analyzes the possible distribution range of 5 uncertain factors, including soil layer distribution, shear wave velocity, soil dynamic characteristic parameters, density and seismic input interface, in a depth of 100 m, and uses the logic tree analysis method and equivalent linearization method for seismic response analysis of soil layers, the surface peak acceleration and response spectrum results of 5 uncertain factors, 3 exceedance probabilities and 4 typical geological holes under 23 working conditions are calculated. It shows that the parameters of soil dynamic characteristics, shear wave velocity, soil layer distribution and density in the depth of 100 m are low sensitive parameters, and their uncertainty have little impact on the ground motion parameters, the difference of peak acceleration are basically within 5%. The seismic input interface is a highly sensitive parameter, which has a great impact on the ground motion parameters (especially to the low frequency band), with the maximum difference of 30%—40%. The seismic input interface should be reasonably set in the seismic safety evaluation to avoid the adverse impact on the seismic fortification parameters of the project.
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图 1 深部地层地震反应分析不确定性分析的逻辑树
Figure 1. Logic tree for uncertainty analysis of seismic response analysis of deep strata
图 2 200 m深度处黏性土（a）和砂土（b）的动力特性参数变化工况
Figure 2. Dynamic characteristic parameter change conditions of cohesive soil (a) and sandy soil (b) at 200 m depth
图 4 4种典型地层基准工况下地质剖面图
Figure 4. Geological profile under four typical stratigraphic reference conditions
图 5 不同工况条件下的地表峰值加速度计算结果分布图
Figure 5. Distribution of calculated results of surface peak acceleration under different working conditions
图 6 不同工况条件下的地表周期1.0 s处反应谱值计算结果分布图
Figure 6. Distribution of response spectrum values calculated at 1.0 s of surface period under different working conditions
图 7 不同周期处反应谱（Sa）在5个地层参数变化情况下的偏差分布图
偏差为与基准工况计算结果差异百分比值的绝对值；GL1代表50年超越概率63%，GL2代表50年超越概率10%，GL3代表50年超越概率2%
Figure 7. Deviation distribution of response spectrum values at different periods under the change of five formation parameters
图 8 典型地层2超越概率50年10%反应谱值时不同工况与基准工况的偏差最大值分布图
与基准工况的偏差：土层分布(a)，土动力特性参数(b)，剪切波速(c)，密度(d)和地震输入界面(e)；不同地震输入界面工况反应谱分布(f)对比
Figure 8. Distribution diagram of the maximum deviation between the response spectrum value of the 50-year exceedance probability of 10% of the typical stratum 2 and the reference condition under different working conditions
表 1 上海地区土层土动力特性参数特征
Table 1. Characteristics of dynamic characteristics parameters of soil layer in Shanghai
土类 土层层号、名称及深度范围 土动力参数特征 黏
性
土②1层粉质黏土（2—4 m） 模量最小、阻尼最大 ⑤1层粉质黏土（20—30 m） ⑤3层粉质黏土（30—50 m） ⑤4层粉质黏土（35—50 m） 模量最大、阻尼最小 ⑥层粉质黏土（17—35 m） ⑧1层黏土（40—70 m） 砂
土②3层粉性土（5—15 m） 模量最小、阻尼最大 ⑤2层粉性土（20—40 m） ⑦1层砂质粉土（25—40 m） ⑦2层粉砂（35—70 m） ⑨1粉细砂（60—90 m） ⑨2中粗砂（80—100 m） 模量最大、阻尼最小 
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