深井富水砂岩冻结解冻后的渗流应力耦合试验研究

发布时间：2018-08-18 09:46

【摘要】：由于对深部软岩冻融劣化问题关注较少,冻结壁解冻后,冻结管环形空间内岩体导水性增强,出现串水淹井事故。目前有关冻融的研究由于没有考虑应力边界条件的影响,无法准确评价深部岩体冻融后的劣化影响。针对西部中生代地层中立井冻结工程中面对的问题以及现有研究的不足,本文采用试验和理论结合的方法,对冻结完整砂岩、冻结裂隙砂岩的力学性质,砂岩冻融劣化后孔隙结构的发展以及渗流-应力耦合特性开展研究。选取鄂尔多斯某矿500-600m深度富水地层中典型的红砂岩、中砂岩和细砂岩为研究对象,制作了不同倾角的裂隙试样。在-5°C、-10°C、-15°C温度下对冻结完整砂岩和裂隙砂岩进行了单轴和三轴压缩试验。结果表明,在-5°C~-15°C温度范围内,红砂岩、中砂岩和细砂岩的冻结强度均随着温度的降低呈线性增加,但随着围压的增加,温度对强度的影响程度有所减弱。三种砂岩的冻结强度均随着围压的增加而线性增加,符合莫尔-库伦准则。温度从-5°C降低至-15°C,冻结红砂岩、冻结中砂岩和冻结细砂岩内摩擦角分别增加9.74%、12.54%和10.67%,粘聚力分别增加15.03%、18.69%和15.39%。温度对冻结砂岩粘聚力的影响大于对内摩擦角的影响。冻结裂隙红砂岩的强度随围压的增加而增加,满足线性关系。随着裂隙倾角的增加,冻结裂隙红砂岩强度逐渐减小,当裂隙倾角大于30°后,试样强度几乎保持不变。冻结水平裂隙红砂岩破坏模式在单轴压缩下为张拉破坏,三轴压缩下为张拉和剪切复合模式;15°-45°倾角的冻结裂隙红砂岩,单轴和三轴压缩下,破坏模式均为冰的屈服破碎和沿岩-冰界面的剪切滑移。选取石拉乌素煤矿地下450m深度的饱和中砂岩进行了不同应力条件下的冻融试验以及冻融后的渗流-应力耦合试验。基于CT图像,重构了中砂岩冻融前后的三维孔隙结构,分析了冻融对CT尺度孔隙发展的影响。结果表明,中砂岩冻融前后孔隙半径主要分布在10-80μm之间,占所有孔隙比例的80%以上。冻融会导致半径在10-60μm的小孔隙有明显的发展,比例增加,而半径在60-200μm的中等孔隙比例有明显的降低,200μm以上的大孔隙比例小幅度增加。冻融时应力越大,冻融后,孔隙率增加幅度越大,渗透率也越大,而渗流条件下的强度却越低。渗透压存在临界值5MPa。渗透压低于此值时,中砂岩渗透率随渗透压增加有明显增加;渗透压高于此值时,中砂岩渗透率保持不变,甚至减小。在中砂岩冻融后渗流条件下的全应力-应变加载过程中,当围压为24MPa时,中砂岩全部试样的渗透率随着轴向应变的增加保持不变或有所减小;当围压为6MPa时,全部试样的渗透率均在初始阶段,随体应变增加而减小,进入剪胀阶段后,随着体应变的减小而增大;围压介于12-18MPa时,渗透率在加载过程中的演化规律较为复杂,进入塑性段后,可能增大,可能减小,也可能保持不变。在统计损伤本构理论的基础上,考虑损伤过程中刚度劣化对Biot系数的影响,构建了考虑渗流影响的统计损伤本构模型,采用不同应力条件下冻融后中砂岩渗流条件下的全应力应变曲线对模型进行了验证,模型能够较好反应中砂岩渗流条件下受荷后的力学性能。
[Abstract]:Because there is little concern about the deterioration of deep soft rock by freezing and thawing, the water conductivity of rock mass in the annular space of freezing pipe increases after thawing, and a series of flooding accidents occur. In this paper, the mechanical properties of frozen intact sandstone, frozen fractured sandstone, the development of pore structure after freeze-thaw deterioration of sandstone and the coupling characteristics of seepage and stress are studied by combining experimental and theoretical methods. Uniaxial and triaxial compression tests of frozen intact sandstone and fractured sandstone were carried out at temperatures of - 5 C, - 10 C and - 15 C. The results show that the frozen strength of red sandstone, medium sandstone and fine sandstone varies with the temperature range of - 5 C ~ - 15 C. The freezing strength of the three sandstones increases linearly with the increase of confining pressure, which conforms to the Mohr-Coulomb criterion. The temperature decreases from - 5 C to - 15 C, and the internal friction angles of frozen red sandstones, frozen medium sandstones and frozen fine sandstones increase by 9, respectively. The cohesion increases by 15.03%, 18.69% and 15.39% respectively. The influence of temperature on the cohesion of frozen sandstone is greater than that on the internal friction angle. The strength of frozen fractured red sandstone increases linearly with the increase of confining pressure. The strength of frozen fractured red sandstone decreases gradually with the increase of fracture dip angle. The failure mode of frozen horizontal fissured red red sandstone is tension failure under uniaxial compression, tension and shear composite mode under triaxial compression, and frozen fissured red red sandstone with inclination of 15 to 45 degrees under uniaxial and triaxial compression, the failure mode is ice yield fracture and shear slip along rock-ice interface. The freeze-thaw test and seepage-stress coupling test of saturated medium-sized sandstone with 450 m depth underground in Shilawusu Coal Mine were carried out under different stress conditions. Based on CT images, the three-dimensional pore structure of medium-sized sandstone before and after freeze-thaw was reconstructed, and the influence of freeze-thaw on CT-scale pore development was analyzed. The pore radius mainly distributes in the range of 10-80 micron, accounting for more than 80% of all the pore ratios. Freezing and thawing will lead to the obvious development of small pores with a radius of 10-60 micron, and the proportion of medium pores with a radius of 60-200 micron decreases obviously. The proportion of large pores with a radius of more than 200 micron increases slightly. When the osmotic pressure is lower than this value, the permeability of medium sandstone increases with the increase of osmotic pressure. When the osmotic pressure is higher than this value, the permeability of medium sandstone remains unchanged or even decreases. In the process of strain loading, when the confining pressure is 24 MPa, the permeability of all samples of medium sandstone remains unchanged or decreases with the increase of axial strain; when the confining pressure is 6 MPa, the permeability of all samples is in the initial stage, decreases with the increase of volumetric strain, and increases with the decrease of volumetric strain when entering the dilatancy stage; the confining pressure is between 12 and 18 MPa. On the basis of statistical damage constitutive theory and considering the effect of stiffness degradation on Biot coefficient during damage process, a statistical damage constitutive model considering seepage effect is constructed and different stress strips are adopted. The full stress-strain curves of frozen-thawed medium-sized sandstone under seepage conditions were validated. The model can well reflect the mechanical properties of medium-sized sandstone under seepage conditions.
【学位授予单位】：中国矿业大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TU45

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