Geomechanical evolution model of bedding rock landslides in construction areas: A case study of the Maidiping landslide in Tiefeng Town, Wanzhou
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摘要:
工程建设是诱发滑坡的主要原因和风险承灾对象，其中坡脚的开挖对斜坡的稳定性产生了较大的影响。在万州区内的顺层斜坡区，泥岩、页岩等软弱夹层在自然条件与工程活动共同作用下渐进破坏，导致滑坡大范围发生，造成无法挽回的经济损失，因此需要对滑坡的破坏过程进行分析与讨论。根据调查万州铁峰乡典型顺层岩质滑坡，建立了降雨与工程活动作用下滑坡演化过程的地质力学模型。通过环剪实验获得软弱泥化层的力学参数，应用FLAC3D模拟了滑坡在人工开挖和降雨条件下滑动面的剪切变形，与刚体极限平衡法相结合分析了滑坡稳定性的变化趋势，并结合野外调查结果进行了对比验证。计算结果表明，软弱夹层经历了自然缓慢软化和人工开挖快速软化2个阶段，受剪切位移控制，属于应变软化模型，强度随剪切位移增大而不断衰减，在达到某一临界位移时强度快速衰减，进而转化为滑动面，降低了斜坡稳定性。研究区内的麦地坪滑坡大变形出现在坡脚开挖后的降雨期，与实验分析结果相符。实验和模拟结果与野外调查相匹配，验证了建设区顺层岩质滑坡地质力学模型的合理性，研究结果对于顺向坡的建设活动和防灾减灾具有指导意义。
Abstract:Objective Engineering construction is the main cause and risk-bearing object for landslides, where excavation at the foot of a slope has a great impact on the stability of a slope. In the cascading slope areas, the progressive damage of soft inclusions such as mudstone shale under the combined effect of natural conditions and engineering activities has led to the occurrence of landslides on a large scale, which cause irreparable economic losses. Therefore, the destruction process of landslides needs to be analysed and discussed.
Methods A geomechanical model of the landslide evolution process under the action of rainfall and engineering activities was established based on the investigation of a typical bedding rock landslide in Tiefeng Town, Wanzhou. The mechanical parameters of the soft muddied layer were obtained by ring shear experiments. FLAC3D was applied to simulate the shear deformation of the landslide under the conditions of manual excavation and rainfall, which was combined with the rigid body limit equilibrium method to analyse the trend of landslide stability and compare with the field survey results.
Results The results show that the weak interlayer goes through two stages of natural slow softening and artificial excavation rapid softening and belongs to the strain softening model. The strength decreases continuously with the increasing shear displacement, and the strength decreases rapidly when a critical displacement is reached. The large deformation of Maidiping landslide occurs during the rainfall period after the excavation of the foot of the slope, which is consistent with the experimental results.
Conclusion The experimental and simulated results agree with the results of field investigation, which verify the present geomechanical model of the cis-layered rock landslide. The results are of guidance for construction activities and disaster prevention and mitigation of cis-slopes.
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Key words:
- bedding rock landslide /
- weak interlayer /
- geomechanical model /
- ring shear test /
- Maidiping landslide
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图 2 研究区软弱夹层分布柱状图(a)和野外观测图(b, c, d)
b.自流井组炭质页岩; c.自流井组泥质页岩; d.珍珠冲组石英砂岩和泥岩夹层
Figure 2. Column chart (a) and field observation chart (b, c, d) of weak interlayer distribution in the study area
图 4 麦地坪滑坡航拍图(a)及剖面图(b)
Figure 4. Aerial view (a) and section view (b) of the Maidiping landslide
图 6 环剪样品制备过程
a.环刀样品制备; b.环形样品制备; c.装配剪切盒; d.完整剪切盒
Figure 6. Sample preparation process of ring shear test
图 7 不同含水率下应力-位移曲线
Figure 7. Stress-displacement curves under different moisture contents
图 8 不同含水率下剪应力拟合曲线
Figure 8. Shear stress fitting curve under different moisture contents
图 9 不同含水率下样品剪切刚度
Figure 9. Shear stiffness of samples under different moisture contents
图 11 麦地坪滑坡第一阶段软弱夹层剪切位移量模拟
Figure 11. Displacement magnitude of the weak interlayer in the Maidiping landslide at the first stage
图 12 麦地坪滑坡第二阶段软弱夹层剪切位移量模拟
Figure 12. Displacement magnitude of the weak interlayer in the Maidiping landslide at the second stage
图 13 各阶段和工况下滑坡稳定性系数
Figure 13. Stability coefficient of landslides at various stages and working conditions
表 1 软弱夹层强度参数
Table 1. Strength parameter of weak interlayer
含水率 峰值强度参数 残余强度参数 σ=100 kPa σ=250 kPa σ=500 kPa cp/kPa φp/(°) cr/kPa φr/(°) τp/kPa τr/kPa τp/kPa τr/kPa τp/kPa τr/kPa 10% 22.4 34 21.0 20 75 50 200 125 350 225 17% 22.0 29 14.9 15 75 50 160 100 325 175 24% 22.1 21 7.3 11 60 40 120 75 225 125 注: c.黏聚力；φ.内摩擦角；τ.剪切强度；σ.法向应力；p, r代表峰值阶段、残余阶段 
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表 2 数值模拟参数取值
Table 2. Values of the simulation parameters
材料名称 γ/(kN·m3) c/kPa φ/(°) K/MPa G/MPa RM/kPa cp/kPa cr/kPa φp/(°) φr/(°) 砂岩(自然) 25.9 20 6 1.8×103 1.2×103 7×103 — — — — 砂岩(降雨) 26.1 18 4 1.8×103 1.2×103 7×103 — — — — 泥岩(自然) 17.2 — — 9.2 8.6 1 22.4 21 34 20 泥岩(降雨) 17.8 — — 6.4 6.3 22.1 7.3 21 11 注：γ.重度；K.体积模量；G.剪切模量；RM.抗拉强度；其他同表 1
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