A study of the pro-water pressure for initiation of a large landslide triggered by a strong earthquake based on fluid-structure coupling
-
摘要:
2008年汶川Ms8.0级强震触发了体积近12×108 m3的大光包滑坡。该滑坡发生于古生代碳酸盐岩地层,滑带地质背景为斜坡内部深埋400 m、最大厚度达5 m的先期层间构造错动带。最新调查表明,该错动带是斜坡内部地下水通道,错动带岩体处于饱和状态。为揭示强震过程与地下水相关的大光包滑坡启动机制,提出了一种具有软弱层带的硬质碳酸盐岩边坡简化模型,将层间构造错动带概化为碳酸盐岩硬层内部软弱层带,采用FLAC3D程序中的流固耦合算法模拟了模型的响应特性。研究结果表明:强震过程中软弱层带上下碳酸盐岩硬层的变形响应时间、波型、大小出现明显差异,上硬层相对于下硬层产生了张离、压缩和剪切3种非协调变形模式,由此对软弱层带产生了振动冲压-张拉和振动剪切动力学行为,饱水软弱层带形成了具有瞬间放大和累积增涨特征的超孔隙水压力。这里将上下硬层差异性变形称为非协调变形,认为非协调变形是软弱层带应力放大成因,推测软弱层带应力瞬间放大以及放大应力长持时作用下的岩体致损是超孔隙水压力激发和累积的成因;强震过程软弱层带超孔隙水压力导致其内有效应力快速降低,使得斜坡前部锁固段应力快速集中,而后被突然剪断,滑坡骤然启动,揭示了强震过程中超孔隙水压力是大光包滑坡启动的主要原因。
Abstract:The Daguangbao landslide is the largest co-seismic landslide with a volume of approximately 12×108 m3, which triggered by the Wenchuan earthquake (Ms 8.0) occurred on May 12, 2008. The slide zone is located in the Paleozoic carbonate strata and it is an interlayer structural dislocation zone with a depth of 400 m and a maximum thickness of 5 m inside the slope. A previous study concluded that the shear failure of the Daguangbao landslide developed within the bedding fault. Our latest investigation showed that this bedding fault was under the water table, and its rock mass was saturated before the landslide. To reveal the initiation mechanism of the Daguangbao landslide related to the groundwater, a simplified model of a hard carbonate slope with an inter-weak layer is given. The response characteristics of the model are stimulated by a fluid-structure coupling algorithm using the FLAC3D. The results show that significant differences in deformation patterns during the earthquake, such as response time, wave shape, and amplitude exist between the upper and lower hard layers. Three uncoordinated deformation patterns, i.e., tension, compress, and shearing coming from the upper layer to the weak layer, are identified. The deformation pattern results in the amplification of compress and shear forces within the weak layer. The stress amplification subsequently induces excess pore water pressure with instant amplification and accumulation features. It is reasonably inferred that the excess pore water pressure essentially reduces the effective stress of the bedding fault. Our simulation confirms that the excess pore-water pressure can be generated within a saturated bedding fault deep situated in a slope during a strong earthquake. We propose that the excess pore water pressure within the saturated fault at 400 m underground is the cause of the Daguangbao landslide.
-
图 1 大光包滑坡构造地质平剖面图[14]
Figure 1.
表 1 数值模拟参数与本构模型综合选取表
Table 1. Comprehensive selection of the numerical simulation parameters and constitutive model
岩层 本构模型 干密度/(kg·m−3) 内聚力/Pa 内摩擦角/(°) 体积模量/Pa 剪切模量/Pa 抗拉强度/Pa 孔隙率/% 渗透系数/(cm·s−1) 白云岩 弹性 2700 1.8×107 42 3×1010 2.6×1010 1×107 2 1×10−12 软弱层带 摩尔-库伦;
Finn(Byrne)2300 3×105 25 1.1×108 3.5×107 1×106 20 5.9×10−7 表 2 模拟工况一览表
Table 2. Test of the numerical simulation conditions
水位 垂直向振动 水平向振动 双向振动
(垂直与水平向同时振动)无水位 √ √ √ 有水位 √ √ √ -
[1] DAI F C, XU C, YAO X, et al. Spatial distribution of landslides triggered by the 2008 Ms 8.0 Wenchuan earthquake, China[J]. Journal of Asian Earth Sciences,2011,40(4):883 − 895. doi: 10.1016/j.jseaes.2010.04.010
[2] 许强, 裴向军, 黄润秋, 等. 汶川地震大型滑坡研究[M]. 北京: 科学出版社, 2009: 1 − 18
XU Qiang, PEI Xiangjun, HUANG Runqiu, et al. Large-scale landslides induced by the Wenchuan earthquake[M]. Beijing: Science Press, 2009: 1 − 18. (in Chinese)
[3] 殷跃平. 汶川八级地震滑坡特征分析[J]. 工程地质学报,2009,17(1):29 − 38. [YIN Yueping. Features of landslides triggered by the Wenchuan earthquake[J]. Journal of Engineering Geology,2009,17(1):29 − 38. (in Chinese with English abstract) doi: 10.3969/j.issn.1004-9665.2009.01.004
[4] 黄润秋, 裴向军, 张伟锋, 等. 再论大光包滑坡特征与形成机制[J]. 工程地质学报,2009,17(6):725 − 736. [HUANG Runqiu, PEI Xiangjun, ZHANG Weifeng, et al. Further examination on characteristics and formatiom mechanism of Daguangbao landslide[J]. Journal of Engineering Geology,2009,17(6):725 − 736. (in Chinese with English abstract) doi: 10.3969/j.issn.1004-9665.2009.06.001
[5] 崔圣华. 强震过程软弱层带地震动响应及大型滑坡启动机理研究[D]. 成都: 成都理工大学, 2017
CUI Shenghua. Seismic responses of wake interlayer and initiation mechanisms of large landslide during strong earthquake[D]. Chengdu: Chengdu University of Technology, 2017. (in Chinese with English abstract)
[6] 崔圣华, 裴向军, 黄润秋. 大光包滑坡启动机制: 强震过程滑带非协调变形与岩体动力致损[J]. 岩石力学与工程学报,2019,38(2):237 − 253. [CUI Shenghua, PEI Xiangjun, HUANG Runqiu. An initiation model of DGB landslide: Non-coordinated deformation inducing rock damage in sliding zone during strong seismic shaking[J]. Chinese Journal of Rock Mechanics and Engineering,2019,38(2):237 − 253. (in Chinese with English abstract)
[7] 殷跃平, 王猛, 李滨, 等. 汶川地震大光包滑坡动力响应特征研究[J]. 岩石力学与工程学报,2012,31(10):1969 − 1982. [YIN Yueping, WANG Meng, LI Bin, et al. Dynamic response characteristics of Daguangbao landslide triggered by Wenchuan earthquake[J]. Chinese Journal of Rock Mechanics and Engineering,2012,31(10):1969 − 1982. (in Chinese with English abstract) doi: 10.3969/j.issn.1000-6915.2012.10.003
[8] ZHANG Y B, CHEN G Q, ZHENG L, et al. Effects of near-fault seismic loadings on run-out of large-scale landslide: A case study[J]. Engineering Geology,2013,166:216 − 236. doi: 10.1016/j.enggeo.2013.08.002
[9] SONG Y X, HUANG D, CEN D F. Numerical modelling of the 2008 Wenchuan earthquake-triggered Daguangbao landslide using a velocity and displacement dependent friction law[J]. Engineering Geology,2016,215:50 − 68. doi: 10.1016/j.enggeo.2016.11.003
[10] XU X W, WEN X Z, YU G H, et al. Coseismic reverse- and oblique-slip surface faulting generated by the 2008 Mw 7.9 Wenchuan earthquake, China[J]. Geology,2009,37(6):515 − 518. doi: 10.1130/G25462A.1
[11] YANG C W, ZHANG J J, LIU F C, et al. Analysis on two typical landslide hazard phenomena in the Wenchuan earthquake by field investigations and shaking table tests[J]. International Journal of Environmental Research and Public Health,2015,12(8):9181 − 9198. doi: 10.3390/ijerph120809181
[12] 许向宁, 李胜伟, 王小群, 等. 安县大光包滑坡形成机制与运动学特征讨论[J]. 工程地质学报,2013,21(2):269 − 281. [XU Xiangning, LI Shengwei, WANG Xiaoqun, et al. Characteristics of formation mechanism and kinematics of Daguangbao landslide caused by Wenchuan earthquake[J]. Journal of Engineering Geology,2013,21(2):269 − 281. (in Chinese with English abstract) doi: 10.3969/j.issn.1004-9665.2013.02.013
[13] 崔圣华, 裴向军, 黄润秋, 等. 大光包滑坡不连续地质特征及其工程地质意义[J]. 西南交通大学学报,2019,54(1):61 − 72. [CUI Shenghua, PEI Xiangjun, HUANG Runqiu, et al. Discontinuities and engineering geological significances of strong earthquake-induced Daguangbao landslide[J]. Journal of Southwest Jiaotong University,2019,54(1):61 − 72. (in Chinese with English abstract)
[14] 裴向军, 崔圣华, 黄润秋. 大光包滑坡启动机制: 强震过程滑带动力扩容与水击效应[J]. 岩石力学与工程学报,2018,37(2):430 − 448. [PEI Xiangjun, CUI Shenghua, HUANG Runqiu. A model of initiation of Daguangbao landslide: Dynamic dilation and water hammer in sliding zone during strong seismic shaking[J]. Chinese Journal of Rock Mechanics and Engineering,2018,37(2):430 − 448. (in Chinese with English abstract)
[15] CUI S H, YANG Q W, PEI X J, et al. Geological and morphological study of the Daguangbao landslide triggered by the Ms. 8.0 Wenchuan earthquake, China[J]. Geomorphology,2020,370:107394. doi: 10.1016/j.geomorph.2020.107394
[16] 朱凌, 裴向军, 崔圣华, 等. 基于动三轴试验的大光包滑坡层间错动带动力特性研究[J]. 工程地质学报,2018,26(3):647 − 654. [ZHU ling, PEI Xiangjun, CUI Shenghua, et al. Triaxial tests for dynamic characterstics of the bedding fault material within basal layer of Daguangbao landslide[J]. Journal of Engineering Geology,2018,26(3):647 − 654. (in Chinese with English abstract)
[17] CUI S H, PEI X J, JIANG Y, et al. Liquefaction within a bedding fault: Understanding the initiation and movement of the Daguangbao landslide triggered by the 2008 Wenchuan Earthquake (Ms = 8.0)[J]. Engineering Geology,2021,295:106455. doi: 10.1016/j.enggeo.2021.106455
[18] 崔圣华, 裴向军, 黄润秋, 等. 强震过程滑带超间隙水压力效应研究: 大光包滑坡启动机制[J]. 岩石力学与工程学报,2020,39(3):522 − 539. [CUI Shenghua, PEI Xiangjun, HUANG Runqiu, et al. Excess interstitial water pressure within sliding zone induced by strong seismic shaking: An initiation model of the Daguangbao landslide[J]. Chinese Journal of Rock Mechanics and Engineering,2020,39(3):522 − 539. (in Chinese with English abstract)
[19] 范宣梅, 许强, 张倬元, 等. 平推式滑坡成因机制研究[J]. 岩石力学与工程学报,2008,27(增刊2):3753 − 3759. [FAN Xuanmei, XU Qiang, ZHANG Zhuoyuan, et al. Study on genetic mechanism of translational landslide[J]. Chinese Journal of Rock Mechanics and Engineering,2008,27(Sup2):3753 − 3759. (in Chinese with English abstract)
[20] XU Q, LIU H X, RAN J X, et al. Field monitoring of groundwater responses to heavy rainfalls and the early warning of the Kualiangzi landslide in Sichuan Basin, southwestern China[J]. Landslides,2016,13(6):1555 − 1570. doi: 10.1007/s10346-016-0717-3
[21] 高杨, 卫童瑶, 李滨, 等. 深圳“12.20”渣土场远程流化滑坡动力过程分析[J]. 水文地质工程地质,2019,46(1):129 − 138. [GAO Yang, WEI Tongyao, LI Bin, et al. Dynamics process simulation of long run-out catastrophic landfill flowslide on December 20th, 2015 in Shenzhen, China[J]. Hydrogeology & Engineering Geology,2019,46(1):129 − 138. (in Chinese with English abstract)
[22] 彭建兵, 王启耀, 庄建琦, 等. 黄土高原滑坡灾害形成动力学机制[J]. 地质力学学报,2020,26(5):714 − 730. [PENG Jianbing, WANG Qiyao, ZHUANG Jianqi, et al. Dynamic formation mechanism of landslide disaster on the Loess Plateau[J]. Journal of Geomechanics,2020,26(5):714 − 730. (in Chinese with English abstract) doi: 10.12090/j.issn.1006-6616.2020.26.05.059
[23] 李浩, 乐琪浪, 孙向东, 等. 巫溪县西溪河北岸高位高危碎屑流滑坡特征与机理研究[J]. 水文地质工程地质,2019,46(2):13 − 20. [LI Hao, LE Qilang, SUN Xiangdong, et al. A study of the characteristics and mechanism of high-risk debris flow landslide on the northern bank of the Xixi River in Wuxi county[J]. Hydrogeology & Engineering Geology,2019,46(2):13 − 20. (in Chinese with English abstract)
[24] 陈育民, 徐鼎平. FLAC/FLAC3D基础与工程实例[M]. 北京: 中国水利水电出版社, 2009: 193 − 259
CHEN Yumin, XU Dingping. FLAC/FLAC3D foundation and engineering examples[M]. Beijing: China Water & Power Press, 2009: 193 − 259. (in Chinese)
[25] 工程地质手册编委会. 工程地质手册[M]. 5版. 北京: 中国建筑工业出版社, 2018: 210
Geological engineering handbook editorial board. Geological engineering handbook[M]. 5th ed. Beijing: China Architecture & Building Press, 2018: 210. (in Chinese)
[26] 李远征, 陈强, 潘远阳, 等. 西南某电站坝址右岸含软弱层带岩质斜坡变形破坏机制[J]. 中国地质灾害与防治学报,2020,31(4):1 − 10. [LI Yuanzheng, CHEN Qiang, PAN Yuanyang, et al. Deformation and failure mechanism of rock slope with soft strata in the right bank of a power station dam site in Southwest China[J]. The Chinese Journal of Geological Hazard and Control,2020,31(4):1 − 10. (in Chinese with English abstract)
[27] 范昊天, 孙少锐, 王亚山, 等. 基于离散元的含软弱夹层岩质边坡滑移机理分析[J]. 中国地质灾害与防治学报,2019,30(3):12 − 17. [FAN Haotian, SUN Shaorui, WANG Yashan, et al. Sliding failure mechanism of bedding rock slope with weak intercalated layer based on discrete element method[J]. The Chinese Journal of Geological Hazard and Control,2019,30(3):12 − 17. (in Chinese with English abstract)
[28] 李宏儒, 张盼, 王神尼, 等. 降雨条件下顺倾向煤系地层边坡稳定性的影响研究[J]. 地质力学学报,2018,24(6):836 − 848. [LI Hongru, ZHANG Pan, WANG Shenni, et al. A study of the influence of rainfall on slope stability along the tendency of coal measure strata[J]. Journal of Geomechanics,2018,24(6):836 − 848. (in Chinese with English abstract) doi: 10.12090/j.issn.1006-6616.2018.24.06.087
[29] 李夕兵. 论岩体软弱结构面对应力波传播的影响[J]. 爆炸与冲击,1993,13(4):334 − 342. [LI Xibing. Influence of the structural weakness planes in rock mass on the propagation of stress waves[J]. Explosion and Shock Waves,1993,13(4):334 − 342. (in Chinese with English abstract)
[30] 杨峥, 许强, 刘汉香, 等. 地震作用下含反倾软弱夹层斜坡的动力变形破坏特征研究[J]. 振动与冲击,2014,33(19):134 − 139. [YANG Zheng, XU Qiang, LIU Hanxiang, et al. Dynamic deformation and failure of slopes with an anti-dip weak interlayer under earthquakes[J]. JournalL of Vibration and Shock,2014,33(19):134 − 139. (in Chinese with English abstract)