Seismic vulnerability assessment of gravity retaining walls based on performance
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摘要: 位于高烈度地震区的支挡结构时刻面临着特大震灾的严峻考验,迄今国内外还没有人针对重力式挡墙系统地做过易损性方面的研究工作。采用增量动力分析方法,考虑地震动输入的不确定性,选取PGA为地震强度参数,挡墙的位移指数DI为性能参数,基于振动台模型试验划分了挡墙的抗震性能水准,利用FLAC3D对8 m高的重力式挡墙进行了地震动力响应分析和地震易损性分析,通过易损性曲线对挡墙在不同地震动作用下的易损性进行了评估和对比分析。研究表明：PGA与挡墙的位移指数近似呈指数关系,当地震动加速度小于0.4g时,场地条件对墙体位移指数的影响不显著,当地震动加速度大于0.4g时,土质场地挡墙位移指数与岩石场地挡墙相比显著增大,墙体位移指数受场地条件的影响显著。当PGA<0.4g时,挡墙基本保持完好或以轻微损伤破坏为主；当PGA>0.6g时,挡墙已完全损伤,发生严重损坏的概率也较大；当PGA>0.8g时,会造成挡墙的严重损坏,甚至可能造成整体倒塌,需要采取一定的抗震加固措施。Abstract: The retaining structures in the high earthquake intensity areas face the severe tests of devastating earthquake, and so far, the seismic vulnerability of gravity retaining walls has not been studied systematically at home and abroad. The increment dynamic analysis method is used in this study. Taking into account the uncertainty of seismic input, the PGA and displacement index are selected as the seismic intensity parameter and performance parameter, respectively, and the classification of the performance level of retaining walls is determined based on shaking table tests. The seismic response and seismic vulnerability of a 8 m-high gravity retaining wall are analyzed by applying FLAC3D, and the fragility curves are derived to assess and compare the seismic performances of the retaining wall under different ground motions. It is shown that the displacement index exponentially relates to the PGA. When the PGA is less than 0.4g, the displacement index increases slowly. When it exceeds 0.4g, the displacement index increases quickly, and it is greatly affected by site conditions. When the PGA is less than 0.4g, the retaining wall keeps slight damage or good situation; when it is more than 0.6g, the retaining wall is damaged completely, and the probability of severe damage increases. When the PGA is more than 0.8g, the retaining wall suffers serious damage, and even collapse is caused, and reinforcing measures should be taken to maintain the stability of the retaining wall.
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图 6 位移指数随地震系数变化
Figure 6. Change of displacement indexes under different intensity earthquakes
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图 10 地震作用下挡墙的位移云图
Figure 10. Displacement nephogram of retaining wall under earthquake
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图 12 不同强度的地震作用下的位移指数变化
Figure 12. Change of displacement indexes under different intensity earthquakes
表 1 模型试验主要相似常数
Table 1 Primary similitude coefficients of model
物理量 相似关系 相似常数 12 m 8 m 4 m 长度L Cl 8.000 5.333 2.667 密度ρ Cρ 1 1 1 加速度a Ca 1 1 1 速度v Cv=Cρ1/4Cl3/4 4.75 3.51 2.09 位移u Cu=Cρ1/2Cl3/2 22.63 12.32 4.36 黏聚力c Cc=CρCl 8.00 5.33 2.67 内摩擦角φ Cφ=1 1 1 1 时间t Ct=Cρ1/4Cl3/4 4.75 3.51 2.09 频率ω Cω=Cρ-1/4Cl-3/4 0.210 0.285 0.479 
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表 2 挡墙抗震性能水准的划分
Table 2 Quantitative indexes of seismic performance of retaining wall
性能水准 损伤描述 评判标准 功能状态描述 位移指数DI I 完好 无明显震害 可正常使用 0≤DI<1% II 基本完好 出现裂缝或轻微变形 按常规方法养护后使用 1%≤DI<2% III 损伤 有明显变形,但主体结构保持完好 可维持使用,在后期运营中逐步修复 2%≤DI<4% IV 严重损坏 出现过大变形或局部破坏,但未倒塌 必须采取紧急加固措施 4%≤DI<6% V 毁坏 倒塌 重建 DI>6%
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表 3 各材料的物理力学参数
Table 3 Physical and mechanical parameters of materials
材料 干密度/(kg·m-3) 体积模量/MPa 剪切模量/MPa 泊松比 内摩擦角/(°) 填土 2150 50 23.1 0.31 35 挡墙 2300 10500 10500 0.17 — 基岩 2400 17900 12300 0.17 —
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表 4 地震动记录
Table 4 Far-field seismic information
序号 地震记录 地震名称 记录台站 PGA/g 1 NGA#15 Kern County Taft Lincoln School 0.159 2 NGA#175 Imperial Valley-06 Delta 0.237 3 NGA#176 Imperial Valley-06 EL Centro Array #12 Hills-Mulhol 0.145 4 NGA#266 Imperial Valley-06 EL Centro Array #12Country-WLC 0.229 5 NGA#326 Northridge Camarillo 0.198 6 NGA#522 Hector Mine Hector 0.231 7 NGA#582 Hector Mine Mecca-CVWD Yard 0.236 8 NGA#729 Chi-Chi, Taiwan CHY041 0.149 9 NGA#737 Chi-Chi, Taiwan CHY031 0.158 10 NGA#778 Chi-Chi, Taiwan CHY028 0.143 11 NGA#884 Chi-Chi, Taiwan CHY080 0.968 12 NGA#985 Manjil-Iran Rudsar 0.167 13 NGA#978 Imperial Valley EI Centro Array #11 0.367 14 NGA#1000 Chalfont Valley 54171 LADWP 0.143 15 NGA#1116 Loma Prieta Capotola 0.227 16 NGA#1637 Loma Prieta Agnews State Hospital 0.225 17 NGA#1762 Bishop Rnd Val 1661 Mc Gee 0.128 18 NGA#1810 Kobe, Japan Shin-Osaka 0.267 19 NGA#1823 Victoria-Mexico Chihuahua 0.387 20 NGA#3265 N. Palm Springs Indio 0.365
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