The Study of Effect by the Valley Site on Ground Motion
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摘要: 本文以梯形河谷场地为研究对象，采用二维显式有限差分和透射人工边界理论，根据设计的正交表建立计算模型，计算分析了梯形河谷场地对地震动的影响因素，对其影响程度进行了排名，并采用强震记录分析法对计算结果进行了初步验证。结果表明，4个因素对梯形河谷场地的地表地震动有重要的影响，但是其影响程度随着位置的变化表现也不同，不同位置的影响因素排名不同；距河谷谷坡40m以内的场地，各影响因素排位相同，首位是河谷坡角，其次是深宽比、覆盖层厚度，最后是输入地震动强度，因此，河谷场地距谷坡一定距离时各因素对地表地震动影响程度基本相同，该段场地河谷地形的几何参数对地震动影响起较大作用；随着场地距河谷谷坡越远，影响因素的排位也发生了变化，总体上是坡角排位后移，输入地震动和覆盖层厚度排位前移，河谷几何参数对地震动影响逐渐减弱，覆盖层厚度和输入地震强度2个因素的影响逐渐加大，该段场地对地震动影响与水平成层场地类似。对安宁河河谷场地强震记录分析验证的结果表明，河谷地形对地震动有显著的放大作用，同时也验证了本文的数值模拟结果是可信的。Abstract: Taking the trapezoid-shaped valley as a research site, according to numerous models based on orthogonal design, we studied the factors that influence ground motion in the valley site with two-dimensional finite difference method. Factors are ranked based on their importances, then the calculation results are verified by ground motion analysis. We found that there are four factors with important effect on ground motion of trapezoid valley site, but the effects are different as the sites changed. Within a distance 40m from river valley ranking factors of site are same. The fist factor is valley angle, the second is ratio of bottom width, the third is cover thickness, and the last one is input ground motion intensity. Therefore it is the same impact degree of factors on ground motion in some distances from the site to the slope of the valley, in which geometric parameters of the valley plays a great part in the effect on ground motion. With the further away from the valley slope, the ranking of factors have also changed, the angles of slope rating are moved back, input ground motion and cover thickness move ahead, the major factors have changed. The effect of valley geometric parameters motions are gradually weakened, but the other two factors influence is gradually increased, that is similar to levels of the layered site. Strong motion records in the Anning river valley site are analyzed as a study case, and the results show that effect of the valley topography on the ground motion is a significantly amplified, and the numerical results of this paper are credible.
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Key words:
- Valley site /
- Ground motion /
- Finite difference /
- Influencing factors
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图 2 计算编号3各观测点输入脉冲地震反应图
Figure 2. Seismic response of all observation points on input pulse of calculation No. 3
图 4 各台站加速度反应谱（阻尼：5%）
Figure 4. The response spectra of different stations (damping:5%)
图 5 汶川地震中安宁河土层场地对地震动的放大作用
Figure 5. Amplication of soil site on ground motion in Anning river during the Wenchuan earthquake
表 1 影响因素和水平的设置
Table 1. Settings of factors and calculation degree
计算水平 因素 倾角A/° 深宽比B 覆盖层厚度C/m 输入地震动D/gal 1 30 0.5 20 50 2 45 1 30 100 3 60 2 40 200 
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表 2 计算方案表
Table 2. Calculation plan
计算编号 因素 计算方案 A B C D 1 1 1 1 1 A1B1C1D1 2 1 2 2 2 A1B2C2D2 3 1 3 3 3 A1B3C3D3 4 2 1 2 3 A2B1C2D3 5 2 2 3 1 A2B2C3D1 6 2 3 1 2 A2B3C1D2 7 3 1 3 2 A3B1C3D2 8 3 2 1 3 A3B2C1D3 9 3 3 2 1 A3B3C2D1 注：计算编号1代表一次计算，选用的计算方案A1B1C1D1即倾角30°、深宽比0.5、覆盖层厚度20m、输入地震动50gal，以下以此类推。
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表 3 模型土物理力学参数
Table 3. The physical and mechanical parameters of the soil model
土类 土层 基岩 密度/kg·m－3 1850 2200 剪切波速/m·s－1 200 800 泊松比μ 0.3 0.2
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表 4 各计算点地震动放大倍数（M）
Table 4. The amplification of ground motion (M) at each calculated point
位置 计算编号 1 2 3 4 5 6 7 8 9 J1 2.88 2.97 2.39 3.30 4.90 3.09 8.80 12.29 5.32 J2 2.73 2.57 2.64 2.77 4.22 3.22 2.96 7.29 3.93 J3 3.40 2.82 2.58 2.73 2.73 3.29 3.33 11.59 3.86 J4 3.46 3.18 2.73 2.96 3.12 3.26 4.27 2.69 3.21 J5 4.63 2.88 3.15 3.16 3.04 3.92 4.40 2.96 3.03 J6 2.77 2.86 3.01 2.56 3.07 4.29 6.50 2.70 3.02 J7 2.63 3.46 2.98 2.80 5.13 8.04 5.12 2.65 2.73 J8 4.04 3.14 2.61 2.98 2.82 7.98 3.46 2.68 3.21 J9 2.05 2.69 2.77 2.72 2.84 3.47 2.53 2.60 2.94 J10 3.36 3.17 2.89 3.09 2.85 2.95 2.53 2.56 2.59 J11 3.23 2.61 2.67 2.44 2.84 2.52 3.05 2.97 3.07 J12 3.51 3.36 2.85 2.59 2.93 2.23 3.05 3.15 2.97 J13 1.00 2.96 2.55 2.80 3.17 2.31 2.31 2.46 2.67 J14 2.57 2.91 3.26 2.45 3.54 2.28 2.80 2.48 3.11 J15 2.88 2.51 2.41 3.06 2.98 2.62 2.62 2.94 2.91 J16 2.73 2.44 2.42 2.45 3.55 2.24 3.01 2.37 2.48 J17 3.40 2.66 2.60 2.65 5.14 2.32 2.74 2.42 2.58
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表 5 J3正交计算极差表
Table 5. Range analysis of orthogonal calculation for J3 point
计算项 因素 A B C D K1 8.80 18.28 9.42 9.98 K2 8.74 9.40 17.13 9.44 K3 18.77 8.64 9.73 16.89 k1 2.93 6.09 3.14 3.33 k2 2.91 3.13 5.71 3.15 k3 6.26 2.88 3.24 5.63 极差R 3.35 3.21 2.57 2.48 影响排位 1 2 3 4
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表 6 不同计算位置与影响因素排名表
Table 6. The rank of influence factors and different calculated position
位置/m 因素 倾角A/° 深宽比B 覆盖层C/m 输入地震动强度D/gal 20 1 2 3 4 40 1 2 3 4 60 1 2 3 4 80 3 2 4 1 100 4 1 2 3 120 3 4 2 1 140 2 4 3 1 160 4 3 2 1 180 2 1 3 4 200 4 2 1 3 220 2 4 3 1 240 4 3 1 2 260 3 2 1 4 280 4 3 1 2 300 2 3 4 1 320 4 3 1 2 340 4 2 3 1
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表 7 汶川地震中安宁河获得主震加速度记录的台站参数
Table 7. The parameters of stations in Anning river from that the mainshock acceleration histories were recorded during the Wenchuan earthquake
台站名称 场地类型 PGA/cm·s－2 EW NS UD 小庙 基岩 5.8 4.1 3.3 礼州 土层 15.9 22.1 11.5 冕宁 土层 14.5 17.7 10.7
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