Landslide mechanism of metamorphic sandstone area containing weak interlayers in Shuangqiaoshan Group
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摘要:
双桥山群地层在华东地区广泛揭露，岩性与地层复杂，断层及褶皱发育，常形成软弱夹层斜坡，在降雨入渗的作用下极易发生滑坡。为揭示其在降雨条件下变形演化机理，以江西省修水县一典型含粉质黏土软弱夹层堆积体滑坡为例，分析了该软弱夹层滑坡的形成原因和变形破坏特征，建立了堆积体滑坡的地质力学模型，采用GeoStudio数值分析软件模拟了该滑坡在不同降雨强度条件下的形成机理。研究结果表明：（1）滑坡后缘EW向断层与韧性断裂带共同作用，发育了4组控制坡体稳定性的裂隙，在滑床之上形成厚达8.8 m的船形软弱夹层。（2）降雨入渗到碎屑和黏土物质组成的滑带，使滑体经历前期蠕变-中期滑动面贯通-后期剪切变形3个变形破坏阶段。（3）当降雨强度达9.9 mm/d时，滑坡坡体开始蠕变；当降雨强度增加到40 mm/d时，坡体沿着软弱结构面剪切变形增大；当降雨强度上升至120 mm/d时，坡体沿着软层结构面产生贯通性破碎面，最终加速失稳破坏。研究结果对今后该类似岩群的滑坡灾害的防治具有一定的参考价值。
Abstract:Objective The Shuangqiaoshan Group strata are widely exposed in East China, with complex lithology and stratigraphy, developed faults and folds, often forming weak interlayer slopes. These characteristics often create weak interlayer slopes that are prone to landslides under rainfall infiltration.
Methods This study aims to reveal the deformation and evolution mechanisms of such slopes under rainfall conditions. Taking a typical silty clay-bearing soft interlayer landslide in Xiushui County as an example, the formation reasons and failure characteristics of the weak interlayer landslide were analyzed. A geomechanical model of accumulation landslides was established, and the landslide's response under different rainfall intensities was simulated using GeoStudio numerical analysis software.
Results The findings are as follows: (1) An EW-trending fault zone and ductile fault zone at the landslide's rear edge combine to form four groups of cracks that control slope stability, forming a boat-shaped weak interlayer approximately 8.8 m thick in the sliding bed; (2) Rainfall infiltrates into the sliding zone composed of debris and clay, triggering the sliding body to undergo three deformation stages: early creep, mid-stage sliding surface penetration, and late-stage shear deformation; (3) Creep deformation begins when rainfall intensity reaches 9.9 mm/d. At 40 mm/d, shear deformation increases along the weak structural plane and progressively intensifies. At 120 mm/d, a connected fracture surface forms along the weak interlayer structure, ultimately accelerating instability and landslide failure.
Conclusion These findings provide valuable insights into the prevention and management of landslide disasters in similar lithological settings.
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图 3 滑坡体二维数值模型和监测点布置图
Figure 3. Two dimensional numerical model of landslide and layout of monitoring points
图 4 滑坡各岩层的持水曲线（a）和渗透曲线（b）
Figure 4. Water retention curve (a) and permeability curve (b) of each rock layer of landslide
图 5 不同降雨工况下孔隙水压力随时间变化曲线
Figure 5. Variation curve of pore water pressure with time under different rainfall conditions
图 6 不同降雨工况下边坡总位移等值线分布图
Figure 6. Isogram distribution of slope total displacement under different rainfall conditions
表 1 滑坡A区物理力学参数
Table 1. Physical and mechanical parameters of landslide in Area A
工况 岩层 γ/(kg·m3) E/GPa 泊松比 C/kPa φ/(°) 工况一 变质岩屑石英杂砂岩 26.8 4.3 0.2 22.0 37.0 变质凝灰质砂岩 26.8 4.3 0.2 22.0 37.0 变质粉砂岩 26.8 4.2 0.25 22.0 37.0 工况二 变质岩屑石英杂砂岩 27.0 2.2 0.24 17.5 33.7 变质凝灰质砂岩 27.0 2.2 0.24 17.5 33.7 变质粉砂岩 27.0 2.1 0.28 17.5 33.7 工况三 变质岩屑石英杂砂岩 27.3 1.1 0.30 13.0 28.0 变质凝灰质砂岩 27.3 1.1 0.30 13.0 28.0 变质粉砂岩 27.3 1.05 0.35 13.5 28.0 
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表 2 滑坡B区物理力学参数
Table 2. Physical and mechanical parameters of landslide in Area B
工况 岩层 γ/(kg·m3) E/GPa 泊松比 C/kPa φ/(°) 工况一 古崩滑堆积体 26.8 4.3 0.18 22 37 软弱夹层 16.2 0.16 0.3 17.6 25.4 工况二 古崩滑堆积体 27 2.2 0.23 17.5 33.7 软弱夹层 19.8 0.09 0.34 14.2 24.6 工况三 古崩滑堆积体 27.2 1.1 0.28 13.2 28 软弱夹层 21.4 0.075 0.4 11.1 23.8
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表 3 岩土层的持水曲线和渗透曲线相关参数
Table 3. Related parameters of water retention curve and permeability curve of rock and soil layer
岩土层 材料模型 饱和含水率θs/
(m3·m−3)残余含水率θr/
(m3·m−3)饱和渗透系数Ks/
(10−5 m·s−1)变质粉砂岩 饱和/非饱和 0.28 0.028 2.2 变质凝灰
质砂岩饱和/非饱和 0.25 0.025 2.0 变质岩屑石
英杂砂岩饱和/非饱和 0.24 0.024 2.0 软弱夹层 饱和/非饱和 0.32 0.032 0.3 基岩 饱和 0.005 0.0005 0.1 堆积体 饱和/非饱和 0.33 0.033 4.0
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表 4 不同降雨工况下降雨1 d监测点位移
Table 4. Displacement of monitoring points under different rainfall conditions after one day
工况 降雨类型 降雨强度/(mm·d−1) 后缘位移/m 中部位移/m 前缘位移/m 坡脚位移/m 工况一 小雨 9.9 0.102 0.096 0.090 0.039 工况二 大雨 40 0.229 0.234 0.203 0.153 工况三 大暴雨 120 0.386 0.426 0.390 0.324
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