Engineering geology properties and creeping strength characteristics of the silty mudstone in Gongjue County in Tibet of China
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摘要:
川藏铁路在穿越西藏贡觉地区时遇到三叠系粉砂质泥岩，在高地应力条件下容易发生大变形等危害。文章开展了不同围压下的岩石三轴压缩和和三轴蠕变试验，结合PFC数值模拟，研究了粉砂质泥岩在不同围压下的蠕变特性和长期强度研究，结果表明：贡觉粉砂质泥岩流变具有西原蠕变模型特征，蠕变与常规三轴试验条件下，随着围压不断增大，粉砂质泥岩试样均由拉-剪破坏向单剪破坏过渡，剪切破裂面与水平线的夹角逐渐减小，微裂纹数量减少；蠕变试验相较于常规三轴试验，由拉应力引起的压碎带影响范围更广；在高围压条件下，粉砂质泥岩更容易发生流变，随着围压的增大，轴向应变、侧向应变和体积应变均增大，微裂纹数量呈下降趋势；瞬时弹性模量及黏弹性系数与围压呈线性递增关系，黏弹性模量与围压呈对数型增长关系，黏塑性系数与围压呈指数型增长关系。在荷载长期作用下，岩石长期强度低于瞬时强度。
Abstract:The Triassic silty mudstone is encountered in the Sichuan-Tibet Railway, when it passes through Gongjue County in Tibet of Chian, and the rock is prone to cause large deformation under the condition of high geo-stress. In this study, we carried out the triaxial rock compression and triaxial creep tests under different confining pressures. Combined with the PFC numerical simulation, we have also studied the creeping characteristics and long-term strength of the silty mudstone under different confining pressures. The results show that the rheology of the Gongjue silty mudstone is characterized by the Nishihara creep model. With the continuous increase of the confining pressure, under the conditions of the creep and conventional triaxial tests, the silty mudstone specimens all undergo transition from tensile-shear failure to single-shear failure. The angle between the shear fracture surface and the horizontal line gradually decreases, and the number of microcracks decreases. Compared with the conventional triaxial test, the creep test has a wider range of influence on the crush zone caused by tensile stress. Under the conditions of high confining pressure, the silty mudstone is more prone to rheology. The numerical simulation results show that when the confining pressure increases, the axial strain, lateral strain and volumetric strain will increase, while the number of microcracks decrease. There is a linear increasing relationship between the instantaneous elastic modulus and the viscoelastic coefficient with the confining pressure, the viscoelastic modulus has a logarithmic growth relationship with the confining pressure, and the viscoplastic coefficient has an exponential growth relationship with the confining pressure. Under long-term loading, the long-term strength phase of the rock is lower than the instantaneous strength.
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表 1 岩石力学实验加载方式
Table 1. Experimental loading method
试验类别 试样编号 围压/MPa 加载方式 常规三轴 GJ-1 5 先以1 MPa/min的速率施加围压，
待围压达到设定围压并稳定后，
轴向荷载以5 MPa/min速率
加载至试样产生破坏GJ-2 10 GJ-3 15 三轴蠕变 GJ-4 5 以1 MPa/min的速率施加围压，
待围压达到设定围压并稳定后
分级施加轴向荷载，轴向荷载
以5 MPa/min速率加载，每一
级应力恒定时间为24 hGJ-5 10 GJ-4 15 
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表 2 贡觉粉砂质泥岩室内试验基本力学参数
Table 2. Basic mechanical parameters of the laboratory tests
试样编号 密度/
（g·cm−3）围压
σ3/MPa轴向压力
σ1/MPa偏应力峰值
qf/MPa黏聚力
c/MPa内摩擦角
φ/（°）1 2.64 5 40.95 35.95 6.47 37.47 2 2.61 10 71.71 61.71 3 2.67 15 88.09 73.09
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表 3 用于PFC数值模拟的粉砂质泥岩细观参数
Table 3. PFC microscopic parameters of silty mudstone
细观参数 参数类型 参数值 颗粒参数 颗粒模量/GPa 1.486 刚度比 1.4 摩擦系数 0.5 平行粘结参数 粘结模量/GPa 27.5 刚度比 1.4 抗拉强度/MPa 105 黏聚力/MPa 275 内摩擦角/（°） 42
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表 4 长期强度参数
Table 4. Long-term strength parameter
围压
σ3/MPa长期流动极限
σs/MPaσs/σ0 黏聚力
c/ MPa内摩擦角
φ/（°）5 28.08 0.71 4.11 28.81 10 42.93 0.60 15 56.57 0.64
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表 5 西原模型各流变参数
Table 5. Rheological parameters of the visco-elastoplastic creep model
σ3 /MPa σs /MPa E0/GPa E1/GPa η2/（GPa·h） η1/（GPa·h） 5 28.08 1.35 4.85 14.76 20.54 10 42.93 1.88 9.16 111.75 49.60 15 56.57 1.67 10.31 291.25 63.88
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