Strength characteristics of slip zone soils of the Tongjiaping landslide in the Three Gorges Reservoir area under different ring shear conditions
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摘要: 研究不同环剪条件下库岸堆积层滑坡滑带土强度特性对滑坡稳定性评价具有重要意义。针对目前在库岸堆积层滑坡滑带土力学特性方面研究薄弱的问题, 以三峡库区童家坪滑坡滑带土为研究对象, 采用ARS-E2环剪仪开展了不同剪切速率下的剪切试验, 研究了等速剪切、加速剪切以及减速剪切作用下滑带土强度变化特征。试验结果表明: 滑带土试样在恒定的低速剪切条件下更容易得到稳定的残余强度, 并且达到峰值强度后易出现"应变软化"现象; 在相同剪切应力条件下, 滑带土加速环剪和减速环剪的剪应力变化趋势基本一致, 与法向应力均呈正相关关系; 剪切速率的变化会显著影响滑带土峰值黏聚力的大小。研究成果揭示了不同环剪条件下滑带土力学特性, 可以为揭示库岸堆积层滑坡变形破坏的力学机制提供理论依据。Abstract: Studying the strength characteristics of slip zone soils under different shear conditions is of great significance for the stability evaluation of reservoir landslides. Aiming at the weak research on the mechanical properties of landslide zone soil in the reservoir bank accumulation layer at present, in this paper, the Tongjiaping landslide slip zone soil in the Three Gorges Reservoir area is taken as an example to research the strength variation characteristics of slip zone soils under different shear test conditions. The ARS-E2 ring shear apparatus is employed to operate the shear modes of constant velocity, acceleration and deceleration on the strength variation characteristics of the slip zone soil. The experimental results indicate that the stable residual strength of slip soil samples tends to be obtained under constant low-speed shear conditions; meanwhile, the phenomenon of 'strain softening' is prone to appearing after reaching the peak strength. Moreover, the change trend of shear stress is basically the same whether accelerated ring shear or decelerated ring shear under the same shear stress condition, which both have a positive correlation with the normal stress. However, the change in shear rate will significantly affect the peak cohesion of slip zone soils. The research results reveal the mechanical properties of the sliding zone soil under different ring shear conditions, which provide a theoretical basis for revealing the mechanical mechanism of the deformation and failure of reservoir bank accumulation landslides.
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图 1 童家坪滑坡平面图(a)及其变形特征(b~e)
Figure 1. Plane of the Tongjiaping landslide (a) and its deformation characteristic (b-e)
图 7 等速环剪峰值强度-剪切速率关系
Figure 7. Relationship between peak strength and shear rate in constant velocity ring shear
图 8 中部土样变速环剪τ-t曲线
Figure 8. τ-t curves of ring shear at variable speed for the middle soil sample
图 9 后缘土样变速环剪τ-t曲线
Figure 9. τ-t curves of ring shear at variable speed for the rear soil sample
图 10 变速环剪下滑带土峰值强度包线
Figure 10. Peak strength envelope of slip zone soil with variable speed ring shear
表 1 滑带土基本物理力学性质指标
Table 1. Basic physical and mechanical property indexes of the slip zone soil
取样位置 天然含水率/% 饱和含水率/% 天然干密度/(g·cm-3) 相对密度 液限/% 塑限/% 中部 19.58 29.43 1.51 2.72 28.85 17.81 后缘 20.14 27.51 1.56 2.70 28.42 16.33 
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表 2 滑带土环剪试验方案
Table 2. Scheme of the ring shear test for slip zone soil
环剪方法 试样编号 有效法向应力/kPa 剪切速率/(mm·min-1) 滑带土位置 等速环剪 HJ1-(1, 2, 3, 4, 5) 200 0.06, 0.6, 2, 6, 10 滑坡中部 HJ2-(1, 2, 3, 4, 5) 滑坡后缘 变速环剪 HJ3-(1, 2, 3) 50, 100, 200 0.02~15(加速) 滑坡中部 HJ3-(4, 5, 6) 15~0.02(减速) HJ4-(1, 2) 50, 100 0.06~30(加速) 滑坡后缘 HJ4-(3, 4) 30~0.06(减速)
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表 3 等速环剪试验滑带土峰值强度特征
Table 3. Peak strength characteristics of slip zone soil of ring shear at constant velocity
中部滑带土 后缘滑带土 剪切速率/(mm·min-1) 峰值强度/kPa 达到峰值强度最小位移/mm 剪切速率/(mm·min-1) 峰值强度/kPa 达到峰值强度最小位移/mm 0.06 106.73 32.94 0.06 112.88 8.17 0.60 98.07 68.88 0.60 117.33 6.85 2.00 107.30 217.30 2.00 105.18 273.68 6.00 104.56 556.42 6.00 115.50 123.30 10.00 90.92 130.09 10.00 104.32 334.38
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表 4 变速环剪试验滑带土峰值强度特征参数
Table 4. Strength characteristic parameters of slip zone soilof ring shear at constant velocity
试验条件 法向应力/kPa 强度参数 50 100 200 φp/(°) cp/kPa 峰位强度/kPa 中部加速 32.06 62.22 111.61 27.92 7.37 中部减速 24.24 61.02 104.45 27.47 2.53 后缘加速 56.85 82.84 / 27.46 30.86 后缘减速 54.95 81.72 / 28.37 28.18
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