Instability mechanism of massive oblique bedding rock landslide in the Three-Gorges Reservoir: A case study of the Longjing landslide in Shizhu County of Chongqing City
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摘要:
长江三峡库区位于我国地形第二、三级阶梯过渡地带,地质环境复杂,斜倾顺层基岩滑坡较为发育。本文以重庆石柱龙井滑坡为例,详细分析了大型斜倾顺层基岩滑坡的变形特征、成因机理和破坏模式、并采用极限平衡法计算了滑坡在四种工况条件下的稳定性。结果表明:(1)龙井滑坡位于扬子准地台石柱向斜北西翼,体积约1.42×106 m3,主滑方向162°,前缘发育两个次级滑坡;(2)受地形地貌、地层构造、地下水和降雨等因素影响,滑坡目前处于蠕滑变形阶段,变形方式主要为拉张裂缝、剪切裂缝和局部鼓胀变形;(3)滑坡同时处于暴雨和前缘次级滑坡滑动条件下,稳定性为1.03,处于欠稳定状态,滑坡易沿软弱夹层发生整体滑动破坏。
Abstract:The Three Gorges Reservoir is located in the transition zone of the second and third terrains in China. Taking the Longjing landslide in Chongqing as an example, this paper analyzes in detail the deformation characteristics, formation mechanism and failure pattern of the oblique bedding slope, and calculates the stability of the slope under four working conditions by using the limit equilibrium method. The results show that: (1) Longjing landslide is located in the northwest wing of the syncline of the stone pillar of the Yangtze platform, with a volume of 142.83×104 m3 and the main sliding direction of 162°. (2) Under the influence of topographical features, stratigraphic structure, groundwater, rainfall and other factors, the slope is currently in the stage of creep deformation. The deformation pattern are mainly tensile fractures, shear fractures and local bulging deformation. (3) The slope is under the sliding conditions of rainstorm and leading secondary landslide at the same time, and its stability factor is 1.03, so it is in an under-stable state. The slope is prone to overall sliding failure along the weak intercalated layer.
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图 8 传递系数法计算简图[19]
Figure 8.
表 1 滑体物理力学参数表
Table 1. Physical and mechanical parameters of the sliding body
滑体岩性 天然重度
/(kN·m−3)饱和重度
/(kN·m−3)天然 饱和 c/kPa φ/(°) c/kPa φ/(°) 粉质粘土
夹碎石20.10 20.40 16.60 22.69 14.30 19.94 砂土 17.50 17.80 11.70 27.76 9.50 22.80 泥岩 25.20 25.30 800 34.35 500 33.17 砂岩 24.60 24.70 790 36.62 550 35.39 表 2 滑带物理力学参数
Table 2. Physical and mechanical parameters of rockmass at the sliding zone
滑带岩性 天然(峰值) 饱和(峰值) 饱和(残余值) c/kPa φ/(°) c/kPa φ/(°) c/kPa φ/(°) 泥化软弱夹层 15.90 10.60 13.50 8.86 11.10 6.36 表 3 稳定性系数计算成果表
Table 3. Calculation results of FOS
工况 滑面
型态剪出口
位置剩余
下滑力
/(kN·m−1)稳定性
系数稳定
状态工况1 折线 悦黄公路内侧 1035.30 1.20 基本稳定 工况2 1765.97 1.13 基本稳定 工况3 1328.89 1.16 基本稳定 工况4 2317.68 1.03 欠稳定 -
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