Fatigue damage mechanism of soft-hard interbedded rock joints subjected to pre-peak cyclic shear loading
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摘要: 三峡库区频发微小地震下岩体节理循环剪切疲劳损伤对边坡动力稳定性具有重要影响。通过室内峰前循环剪切试验和PFC2D细观数值计算，研究了考虑一阶起伏角、含水率、剪切速率、剪切幅度、法向应力及循环剪切次数影响的软-硬互层岩体节理宏细观疲劳损伤机理。研究表明：①岩体节理剪切应力-剪切位移曲线历经初始非线性压剪变形、近似线弹性压剪变形、循环剪切疲劳损伤变形、应力缓升压剪变形、应力陡升压剪变形及应力脆性跌落压剪变形六个演化阶段。②岩体节理峰值（残余）剪切强度和疲劳剪切（法向）位移在相同一阶起伏角、含水率、剪切速率、剪切幅度或法向应力下随循环剪切次增多而分别降低和增大；且其在相同循环剪切次数下随一阶起伏角或法向应力变大而分别增大和降低，而随含水率、剪切速率或剪切幅度变大则分别降低和增大。③宏细观结果总体上吻合较好，且岩体节理细观剪切疲劳损伤裂纹数量随剪切位移变化呈前期微增-陡增、中期缓增及后期陡增-缓增-陡增的发展特征，而其随循环剪切次数变化则呈前期陡增和后期缓增的发展特征。④岩体节理宏细观剪切疲劳损伤典型演化过程可概述为压密-起裂破坏、循环错动-贯通破坏及分离-啃断破坏3个渐进性发展阶段，且宏细观剪切疲劳损伤裂纹近似呈“倒U形”密集分布于岩体节理附近。
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关键词:
- 软-硬互层岩体节理 /
- 峰前循环剪切试验 /
- PFC2D细观数值计算 /
- 演化过程 /
- 疲劳损伤机理
Abstract: The cyclic shear fatigue damage of rock joints under frequent micro-earthquakes in the Three Gorges Reservoir area has an key impact on the dynamic stability of slopes. The macro-meso fatigue damage mechanism of soft-hard interbedded rock joints is studied via the laboratory pre-peak cyclic shear tests and PFC2D meso numerical calculation considering the effects of the first-order asperity angle, moisture content, shear rate, shear amplitude, normal stress and cyclic shear number. The results show that: (1) The curve of shear stress versus shear displacement of rock joints experiences six evolution stages, i.e., initial nonlinear compression-shear deformation, approximate linear elastic compression-shear deformation, cyclic shear fatigue damage deformation, compression-shear deformation with slowly rising stress, compression-shear deformation with sharply rising stress and compression-shear deformation with brittle stress drop. (2) Under the same first-order asperity angle, moisture content, shear rate, shear amplitude or normal stress, the peak (residual) shear strength and cumulative shear (normal) displacement of rock joints decrease and increase with the increase of the cyclic shear number, respectively. Under the same cyclic shear number, they increase and decrease with the increase of the first-order asperity angle or normal stress, respectively. Meanwhile, they decrease and increase with the increase of the moisture content, shear rate or shear amplitude, respectively. (3) The macro-meso results are in good agreement on the whole. The number of meso shear fatigue damage cracks of rock joints exhibits the development characteristics of slight increase-steep increase, slow increase and steep increase-slow increase-steep increase in the early, middle and late stages, respectively, with the change of shear displacement; and it shows the development characteristics of steep increase and slow increase in the early and late stages, respectively, with the change of cyclic shear number. (4) The typical evolution process of macro-meso shear fatigue damage of rock joints can be described as three progressive development stages, i.e., compaction-crack initiation failure, cyclic dislocation-penetration failure and separation-gnawing failure, and the macro-meso shear fatigue damage cracks are densely distributed near the rock joints in an approximate inverted U-shape. -
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图 1 库区现场调研、取样及材料物理力学参数测定
Figure 1. Field investigation, sampling and determination of physical- mechanical parameters of materials in reservoir area
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图 2 试验原理及软-硬互层岩体节理设计与加工
Figure 2. Test principle and design and processing of soft-hard interbedded rock joints
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图 6 软-硬互层岩体节理剪切应力-剪切位移曲线
Figure 6. Curves of shear stress versus shear displacement of soft-hard interbedded rock joints
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图 7 各因素对软-硬互层岩体节理剪切疲劳损伤机理影响曲线
Figure 7. Influence curves of various factors on shear fatigue damage mechanism of soft-hard interbedded rock joints
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图 8 软-硬互层岩体节理剪切疲劳损伤裂纹数量变化曲线
Figure 8. Variation curves of shear fatigue damage crack number of soft-hard interbedded rock joints
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图 9 软-硬互层岩体节理宏观剪切疲劳损伤演化过程及破坏形态
Figure 9. Macro-shear fatigue damage evolution process and failure morphology of soft-hard interbedded rock joints
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图 10 软-硬互层岩体节理细观剪切疲劳损伤演化过程及颗粒分布特征
Figure 10. Meso shear fatigue damage evolution process and particle distribution characteristics of soft-hard interbedded rock joints
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图 11 软-硬互层岩体节理宏细观剪切疲劳损伤退化机理统一概化描述
Figure 11. Generalized description of macro-meso shear fatigue damage mechanism of soft-hard interbedded rock joints
表 1 材料物理力学参数
Table 1 Physical-mechanical parameters of materials
类别 含水率/% 密度/(g·cm-3) 抗压强度/MPa 弹性模量/MPa 泊松比 黏聚力/kPa 内摩擦角/(°) 软层 5.0 1.55 1.33 106.43 0.30 118.33 30.13 10.0 1.69 1.13 97.49 0.28 107.28 29.34 15.0 1.74 0.92 88.74 0.27 99.86 27.19 硬层 — 2.65 57.26 6600 0.24 5260 44.53 
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表 2 峰前循环剪切试验工况
Table 2 Working conditions of pre-peak cyclic shear tests
工况编号 一（二）阶起伏角/(°) 含水率/% 剪切速率/(kN·s-1) 剪切幅度/% 法向应力/MPa #1 30（45） 10.0 1.5 50τp 0.3 #2 45（45） 10.0 1.5 50τp 0.3 #3 60（45） 10.0 1.5 50τp 0.3 #4 45（45） 5.0 1.5 50τp 0.3 #5 45（45） 15.0 1.5 50τp 0.3 #6 45（45） 10.0 1.5 50τp 0.4 #7 45（45） 10.0 1.5 50τp 0.5 #8 45（45） 10.0 0.5 50τp 0.3 #9 45（45） 10.0 1.0 50τp 0.3 #10 45（45） 10.0 1.5 30τp 0.3 #11 45（45） 10.0 1.5 40τp 0.3
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表 3 细观物理力学参数
Table 3 Meso physical-mechanical parameters
圆形颗粒 光滑节理 平行键 摩擦系数 0.6 键合模式 1 半径乘子 1.0 密度/(kg·m-3) 2750 剪胀角/(°) 0 剪切强度/MPa 62.5 最大半径/mm 0.54 摩擦系数 0.5 法向强度/MPa 48.5 弹性模量/GPa 12 拉伸强度/MPa 0 弹性模量/GPa 25 法向与切向刚度比 1.5 剪切刚度/(GPa·m-1) 80 法向与切向刚度比 2.5 最大半径与最小半径比 1.42 法向刚度/(GPa·m-1) 80 剪切和法向强度标准差/MPa ±5
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