复杂受力状态下裂隙岩体渗透特性试验研究

发布时间：2018-02-13 19:14

  本文关键词： 裂隙岩体 荷载水平 渗透特性 水力梯度 导水系数 非线性流动特征　出处：《中国矿业大学》2017年博士论文　论文类型：学位论文

【摘要】：由于地质运动和人为扰动,天然岩体内部通常赋存裂隙或裂隙网络。裂隙岩体渗流问题涉及核废料处置、地热资源开发、油和天然气开采及CO2地质封存等工程领域。深入理解应力作用下裂隙岩体的渗流行为对保证这些地质工程的安全性能有着重要意义。本文以裂隙岩体为研究对象,通过自主研发裂隙网络岩石渗流综合模拟和分析系统,综合采用室内试验、理论分析和数值模拟相结合的方法,对不同荷载作用下裂隙岩体的渗透特性展开一系列研究工作,对裂隙岩体非线性流动特征与裂隙形式、剪切位移、荷载水平之间的相关性进行讨论,对丰富裂隙岩体水力学理论起到一定的积极作用。(1)采用高分辨率岩石CT扫描系统对不同应力路径作用后花岗岩试样内部裂隙发育特征进行三维重构。渗流试验结果表明,单轴压缩后花岗岩试样渗流试验过程中流速和压力梯度之间呈现明显的非线性特征,可以用Forchheimer方程进行描述,系数a'和b'均随围压σs的增加逐渐增大。导水系数随着压力梯度的增加逐渐降低。常规三轴和三轴峰前卸荷试验后花岗岩试样流速和压力梯度之间均呈现近似线性关系,试样等效渗透系数均随围压σs的增加逐渐减小,而随围压σ_3的变化特征存在一定差异。(2)自主研发一台裂隙网络岩石渗流综合模拟和分析系统,展开一系列含不同剪切位移三维粗糙单裂隙的渗流试验。流体的流动行为均可以用Forchheimer和Izbash定律进行描述。随着剪切位移的增加,Forchheimer拟合方程中线性和非线性项系数a和b均逐渐减小,Izbash拟合方程中系数λ减小了 2～3个数量级,而系数m在1.35～1.80范围内波动。裂隙剪切渗流过程中导水系数和雷诺数之间可以用多项式函数进行拟合分析。随着剪切位移的增加,裂隙导水系数、临界水力梯度和等效水力隙宽均逐渐增大。(3)裂隙网络岩石试样的渗流特征均可以用Forchheimer和Izbash函数进行描述。回归拟合系数a和b随荷载水平的增加逐渐增大,而随裂隙网络夹角和交叉点个数的增加逐渐减小。随着裂隙网络夹角和交叉点个数的增加,试样导水系数均逐渐增大,而临界水力梯度和临界雷诺数总体呈现逐渐减小的趋势。随着侧压力系数的增加,试样的渗透特性逐渐减弱,而临界水力梯度和临界雷诺数均逐渐增大。与荷载水平Fx=Fy作用下相比,对于不同侧压力系数,(F_y-F_x)越大,试样的渗流特性差异越明显。(4)建立应力作用下裂隙岩体渗透特性理论模型,采用COMSOL Multiphysics多物理场仿真软件对单裂隙和裂隙网络的渗透特性进行计算。对于单裂隙,随着时间的增加,平均导水系数先逐渐增加后趋于稳定,稳定后平均导水系数随裂隙倾角和上覆岩层压力的增加逐渐减小,而随进水口压力和初始裂隙隙宽的增加逐渐增大。裂隙网络夹角和交叉点个数对裂隙有效应力、裂隙隙宽、水压力和渗流通道均产生影响,随着裂隙网络夹角和交叉点个数的增加,模型出水口处整体流速均逐渐增大。
[Abstract]:Due to the geological and anthropogenic disturbance, natural rock mass usually occurrence crack or crack network. Seepage problems involving nuclear waste disposal, exploitation of geothermal resources, oil and gas exploration and geological sequestration of CO2 and other engineering fields. Understanding should be seepage behaviors of fractured rock under the action of force is very important to ensure the safety of these geological engineering. The fractured rock mass as the research object, through independent research and development of rock fracture network seepage simulation and analysis system, combined with indoor test, method of combining theoretical analysis and numerical simulation, seepage characteristics of fractured rock mass under different loads to launch a series of research work on flow characteristics and fracture forms, nonlinear fractured rock mass shear displacement, the correlation between the load level are discussed, to enrich the rockmass hydraulic theory will play a positive role . (1) using high resolution CT scanning system of rock stress after the granite specimen fracture characteristics of three-dimensional reconstruction of different seepage. Test results show that the obvious nonlinear characteristics between velocity and pressure gradient in uniaxial compression after granite sample seepage test process can be described by Forchheimer equation, and the coefficient of A'B' increases with confining pressure. S increases gradually. The water conduction coefficient with the increase of pressure gradient decreases gradually. Between the conventional three axis and three axis pre peak unloading test of granite after sample flow rate and pressure gradient showed a linear relation with the equivalent permeability coefficient increases, confining pressure. S decreased gradually, and the change with confining pressure. _3 there are certain differences. (2) developed a comprehensive rock fracture network seepage simulation and analysis system, launched a series of shear displacement with different roughness A single fracture seepage test. The flow behavior of the fluid can be used Forchheimer and Izbash law are described. With the increase of shear displacement, Forchheimer equation in linear and nonlinear coefficient of a and B were decreased, Izbash coefficient in fitting equation is reduced by 2~3 orders of magnitude, and the coefficient of m in the range of 1.80 ~ 1.35 fluctuations between fracture shear seepage problems of water coefficient and Reynolds number can use polynomial fitting analysis. With the increase of shear displacement, fracture conductivity, critical hydraulic gradient and the equivalent hydraulic aperture increase gradually. (3) the characteristics of seepage in fracture network of rock specimen can be used Forchheimer and Izbash functions are described. The regression coefficients of a and B with the load level increases gradually, and with the increase of fracture network angle and the intersection number decreases. With the fracture network and cross angle Increase the number of samples, the water conduction coefficient increased, while the critical hydraulic gradient and the critical Reynolds number showed a decreasing trend. With the increase of the lateral pressure coefficient, permeability of specimens gradually weakened, while the critical hydraulic gradient and the critical Reynolds number increased gradually. Compared with the level of load under the action of Fx=Fy, for different side pressure coefficient, the greater the difference (F_y-F_x), the seepage characteristics of samples is more obvious. (4) shall establish a theoretical model of permeability characteristic of fractured rock mass under the force of permeability by COMSOL Multiphysics multiphysics simulation software of single fracture and fracture network were calculated. For a single fracture, with the increase of time, average the water conduction coefficient first increased and then tended to be stable, increase the stability of the average water conduction coefficient with dip angle and the overburden pressure gradually decreases, while with the inlet pressure and the initial crack width. With increasing gradually, the number of intersection points and the number of intersections of fractured network will influence the effective stress, the width of the fracture gap, the water pressure and the seepage channel. With the increase of the number of intersection points and the number of intersection points, the flow velocity at the outlet of the model will gradually increase.

【学位授予单位】：中国矿业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TU45
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本文编号：1508900