Shear Creep Characteristics of Red Sandstone Discontinuities Considering Different Morphologies
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摘要:
工程岩体开挖会遇到各种复杂应力条件，岩体在荷载作用下随时间会产生流变现象，这种“累进性破坏”导致工程岩体常出现滑坡、塌方、大变形和支护困难等问题.为解释天然岩体结构面的流变现象，以天然红砂岩结构面为研究对象，基于结构面三维形貌扫描试验、结构面分级加载剪切蠕变试验，对天然岩体结构面的剪切蠕变特性进行系统研究.研究发现，岩体结构面蠕变变形量与蠕变应力和结构面三维形貌特征指标正相关；岩体结构面蠕变曲线可分为3个阶段，即过渡蠕变、稳态蠕变和加速蠕变阶段，当法向应力一定时，结构面三维形貌特征指标越大，发生的蠕变破坏越剧烈；基于结构面剪切蠕变曲线与剪切蠕变速率曲线特征，建立了参数物理意义明确的岩体结构面剪切蠕变经验模型.
Abstract:Engineering rock excavation will encounter a variety of complex stress conditions, and the rock will produce rheological phenomena over time under a loading effect. The "progressive damage" leads to landslides, collapses, large deformations and support difficulties in the engineering rock. In order to explain the rheological phenomena of natural rock discontinuities, the shear creep characteristics of the discontinuities of red sandstone are systematically studied based on the three-dimensional morphological scanning test and the graded loading shear creep test. It is found that the amount of creep deformation of the discontinuities is positively correlated with the creep stress and the three-dimensional morphological parameters of the discontinuities. The creep curve of the discontinuities can be divided into three stages, i. e. transition creep, steady-state creep and accelerated creep stage. When the normal stress is certain, the larger the three-dimensional morphological parameters of the discontinuities, the more intense the creep damage occurs. Based on the characteristics of shear creep curve and shear creep rate curve of the discontinuities, an empirical model of shear creep of the discontinuities is established with clear physical meaning of parameters.
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图 2 剪切蠕变试验岩体结构面三维形貌示意图(单位：mm)
Fig. 2. Three⁃dimensional morphologies of rock mass discontinuities tested by shear creep
图 3 分级加载剪切蠕变试验应力与时间关系
Fig. 3. Relationship between stress and time in shear creep test under graded loading
图 4 不同三维形貌岩体结构面蠕变全过程曲线
Fig. 4. Whole⁃process creep curves of rock mass discontinuities with different 3D morphologies
图 7 C⁃2破坏阶段剪切蠕变曲线与蠕变速率关系曲线
Fig. 7. Relationship between shear creep curve and creep rate at C⁃2 failure stage
图 8 C⁃4、C⁃1破坏阶段剪切蠕变曲线与蠕变速率关系曲线
Fig. 8. Relationships between shear creep curve and creep rate at C⁃4, C⁃1 failure stage
图 9 过渡蠕变与稳态蠕变的分界点确定方法
Fig. 9. Determination method of boundary point between transition creep stage and steady creep stage
图 10 不同三维形貌节理岩体结构面剪切蠕变分级曲线
Fig. 10. Shear creep grading curves of jointed rock masses with different three⁃dimensional morphologies
图 11 不同三维形貌结构面蠕变速率-时间曲线
Fig. 11. Creep rate ⁃ time curves of jointed rock masses with different three⁃dimensional morphologies
图 12 不同三维形貌结构面稳态蠕变阶段蠕变速率曲线
Fig. 12. Creep rate curves of discontinuities with different three⁃dimensional morphologies in steady creep stage
图 14 经验模型拟合效果($ \overline{{R}^{2}}=0.996 $)
Fig. 14. Fitting effect of empirical model ($ \overline{{R}^{2}}=0.996 $)
图 18 参数$ a $、参数$ b $与蠕变应力$ \tau $之间的关系
Fig. 18. Relation between parameter a, parameter b and creep stress τ
表 1 剪切蠕变试验岩体结构面三维形貌特征指标
Table 1. Three-dimensional morphological characteristics of rock mass discontinuities in shear creep test
试件编号 上结构面 下结构面 平均值 Z2+ Z2w+ Z2+r Z2+ Z2+w Z2+r C-1 0.215 0.114 0.25 0.174 0.109 0.256 0.186 C-2 0.247 0.126 0.273 0.187 0.129 0.261 0.204 C-3 0.235 0.177 0.261 0.205 0.172 0.298 0.225 C-4 0.271 0.191 0.272 0.279 0.185 0.305 0.251 
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表 2 分级加载蠕变试验应力
Table 2. Stress of creep test under graded loading
试样
编号法向应力(MPa) 水平剪切应力(MPa) 破坏应力(MPa) C-1 10.4 3.0、5.0、7.0、8.0、9.0、10.0 10.0 C-2 10.0 C-3 - C-4 10.0
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表 3 岩体结构面各级蠕变变形量(mm)
Table 3. Creep deformation of rock mass discontinuities at all levels
蠕变
应力3.0 MPa 5.0 MPa 7.0 MPa 8.0 MPa 9.0 MPa 10.0 MPa C-1 0.014 0.028 0.047 0.064 0.159 - C-2 0.017 0.018 0.029 0.028 0.04 - C-3 0.012 0.017 0.02 0.018 0.022 0.033 C-4 0.027 0.036 0.041 0.036 0.057 -
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表 4 C⁃4结构面敏感性分析参数选取
Table 4. Parameters for sensitivity analysis of C⁃4
τ=3.0 MPa a b 基准参数 3.64 759 拟合参数对蠕变曲线的影响 10 759 20 759 30 759 3.64 500 3.64 600 3.64 700 拟合参数对蠕变速率曲线的影响 10 759 20 759 30 759 3.64 7 3.64 70 3.64 700
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