裂隙岩体渗透系数确定方法研究

裂隙岩体渗透系数以及渗透主方向的确定对研究岩体渗透性大小及各向异性具有重要意义。高放废物地质处置库介质岩体的渗透性能将直接影响其使用安全性。本文运用离散裂隙网络模拟的方法对我国高放废物处置库甘肃北山预选区3#钻孔附近裂隙岩体进行了渗透性质分析。通过对3#钻孔1715～1780m段压水试验数据的反演,标定了离散裂隙网络渗流模型中的裂隙渗透参数(导水系数T)。利用标定的离散裂隙网络模型对场区裂隙岩体进行了渗流模拟,确定了该区域裂隙岩体的渗流表征单元体(REV)的尺寸大小以及渗透主值和主渗透方向。运用离散裂隙网络模型计算得出的渗透主值的几何均值与现场压水试验计算结果较接近,证明了计算结果的有效性。     

初应力条件下超临界CO2气爆致裂规律研究

为研究地下爆破工程中初始地应力条件下超临界CO2气爆的致裂规律,利用自主研发的三轴加载式超临界CO2气爆实验系统,对不同应力组合工况下混凝土试件进行了超临界CO2气爆致裂实验,实验结果表明超临界CO2气爆爆破峰值压力低且高压持续时间长,致裂过程不同于传统炸药爆破,分为动态和准静态过程：应力波将气爆孔附近介质压碎形成粉碎区,在环向拉应力作用下粉碎区周围介质产生径向裂隙的动态过程,高压CO2气体进入裂隙形成气楔,促使裂隙继续扩展的准静态过程,得到了气爆后试件沿最大初始压应力方向开裂的规律。通过理论计算的方法分析了初应力作用下气爆过程中介质应力状态的变化规律,揭示了初应力影响裂纹起裂和扩展的机理：位于气爆孔最大初始压应力方向的介质产生初始环向压应力最小,在超临界CO2径向冲击产生的环向拉应力作用下首先发生开裂;位于气爆孔最小初始压应力方向介质中初始环向压应力最大,开裂所需的径向冲击压力增大,开裂滞后;垂直裂隙方向的应力抑制裂隙的张开而阻碍CO2气体的进入,同时增大了裂隙扩展所需的气楔压力,气楔作用效果大幅减弱,对裂隙扩展的阻碍作用显著。裂隙的扩展速度与扩展距离呈“S型”曲线关系,初始压应力越大,裂隙扩展相同距离降低的速度值越大,且压碎区和裂隙扩展范围逐渐减小。     

单裂隙流-固耦合渗流的试验研究

通过对较大尺寸的单裂隙岩体试块进行不同侧面加载的渗流试验,在实验室里开展了单裂隙流 固耦合渗流研究,模拟核废料贮藏库的围岩自由面的最危险部位的渗流量 应力耦合状态。分析了裂隙岩体渗流与应力的耦合机理,获得了几种典型情况下的试验数据,并拟合出不同应力条件下单裂隙岩体渗流量与应力间数学经验公式。从而说明并非任一方向的应力增加都能使渗流量减小,而是裂隙岩体的渗流量随着双向压应力的增加而减少,随着平行于裂隙面方向的单向压应力的增加而增加。缝隙开度虽然随着法向应力的增加而逐渐减小,但最终不可能完全闭合,所以,此时流量不可能为零。同时,在试验过程中还通过闭环控制来实现被加载面的均匀受力,这为大尺寸岩体试验提供了一种很好的加载方法。     

岩体渗流及参数敏感性对块体稳定性影响研究

首先利用离散单元法中的流固耦合技术模拟出裂隙岩体渗流场,并计算得到作用在可动岩石块体上的渗流压力;然后基于块体理论,研究渗流压力对岩石块体动力稳定性的影响,得到有无渗透水压力作用两种情况下块体动安全系数对比曲线.结果表明,渗透水压力的存在使得块体的动力稳定性降低.同时,发展了一种基于参数敏感性的块体稳定分析技术,利用该技术可对粘聚力和摩擦角在各种不同取值组合下的稳定性进行快速计算,已在实际边坡工程中应用,实践证明其简单、方便且准确,具有很高的工程应用价值.     

围岩应力重分布对隧洞爆生裂隙区比例半径的影响

基于爆炸应力波作用下爆生裂隙形成机理的研究,采用莫尔库伦准则及最大拉应力准则,研究了围岩应力重分布对爆炸应力波作用下爆生裂隙区比例半径的影响。研究结果表明,围岩应力重分布对爆生裂隙区比例半径有重要影响,隧洞围岩应力重分布将减小隧洞径向爆生裂隙区比例半径,压剪破坏模式下,爆生裂隙区比例半径可降低20％以上,拉伸破坏模式下可降低10％以上。爆炸应力波作用下,岩体更容易沿结构弱面发生压剪破坏。利用围岩的应力重分布作用,可以降低爆破对保留岩体的损伤作用。     

作用在裂隙中的渗透力分析

裂隙岩体中流体对岩体的作用力, 是研究岩体稳定性的重要问题。本文认为流体作用于裂隙壁面上的力包括两部分, 即垂直于裂隙壁面的流体静水压力 (导致裂隙垂向变形)和平行于裂隙壁面的拖曳力 (导致裂隙切向变形), 此拖曳力为面力。文中以单裂隙水流的立方定律为基础, 运用流体力学的动量方程, 推导出了单一平直光滑无充填裂隙、有充填的裂隙及水流和充填物一起运动情况下, 裂隙壁面承受的切向拖曳力公式。该公式对于分析流体对裂隙岩体变形性能及强度的影响具有重要价值。     

修正的拉应力裂纹扩展准则及裂隙\=水压对裂纹扩展的影响

对脆性材料的第一主应力--拉应力裂纹扩展准则进行了补充和修正,修正的裂纹扩展准则能确定裂纹扩展步长.以平面斜置裂纹扩展为例,利用无网格Galerkin方法,对不含裂隙水压的二维裂纹扩展进行数值模拟,计算结果与试验结果一致,表明最大周向拉应力准则的正确性.在不同裂隙水压条件下,研究了二维裂纹初始破裂,并在给定水压下对二维裂纹扩展路径进行了数值模拟跟踪.结果表明裂隙水压对裂纹初始破裂方向、破裂步长、破裂载荷和裂隙岩体破裂强度有显著影响.有水压和无水压的扩展迹线不同,但后续的扩展趋势相同.     

非连续变形分析方法的改进及应用1）

首先,采用位移收敛判据对非连续变形的岩石断裂分析进行改进并程序实现. 其次,将非连续变形分析方法和裂隙网络渗流模型结合起来,建立了渗流应力耦合分析模型,研究了裂隙岩体变形对渗流的影响以及渗流与应力耦合作用下裂隙岩体的变形破坏特征. 研究发现,主干裂隙控制着渗流场分布,考虑耦合作用时的水头值比不考虑耦合作用时大,说明考虑耦合后坡体更容易变形失稳. 改进前后裂纹扩展形态基本不变,表明程序计算的收敛判据是有效的.     

单轴压缩荷载下“十字形”交叉裂隙类岩石试件的破坏模式与力学特性试验研究

通过在类岩石材料中预制特定裂隙的方法,来模拟含"十字形"交叉裂隙的岩体,并对其在单轴压缩情况下的力学特性与破坏模式进行了试验研究。研究表明:(1)交叉裂隙试件中,次裂隙倾角对主裂隙倾角为45°时试件的抗压强度与起裂应力的影响最大,而对主裂隙倾角为90°时的影响最小。(2)单裂隙试件的抗压强度与起裂应力小于完整试件。交叉裂隙试件相对于单裂隙试件而言,当主裂隙倾角为0°和45°时,其抗压强度与起裂应力减小;当主裂隙倾角为90°时,其抗压强度与起裂应力增大。(3)在单裂隙试件中,当裂隙倾角为0°、45°和90°时,试件分别发生拉剪复合型破坏、剪切破坏和张拉破坏;相对于单裂隙试件而言,交叉裂隙试件破坏时产生的裂纹相对较多,破坏模式大多为拉剪复合型破坏,同时,在破坏过程中交叉裂隙试件发生复合其他破坏模式或直接导致试件破坏的滑移。上述结果对岩体工程的开挖和建设具有一定的参考价值。     

流体饱和弹性半空间裂隙对平面P_I波的衍射

采用间接边界元法,求解了饱和半空间裂隙对平面PI波的二维衍射问题。基于单层位势理论,将边界离散并直接在边界单元上施加虚拟荷载(水平作用力、竖向作用力和流量源的叠加)以构造散射波场,并由边界条件确定虚拟荷载密度,总波场由自由波场和散射波场共同组成。通过参数分析研究了入射波频率、入射倾角、埋深、孔隙率、边界渗透条件等因素对饱和半空间中裂隙对平面PI波衍射的影响规律。结果表明:裂隙随埋深增大,地表位移谱振荡加剧,峰值有所降低;随着入射频率增加,孔隙率影响逐渐增大;垂直入射时,水平位移的放大区域主要分布在裂隙两端,斜入射时,主要集中在裂隙正上方地表附近;透水和不透水两种情况下的地表位移幅值和相位差别较小,但干土情况与饱和情况下的位移幅值相差较大。     

Modeling Free-Surface Seepage Flow in Complicated Fractured Rock Mass Using a Coupled RPIM-FEM Method

The prediction of the free-surface seepage flow behavior in fractured rock mass is of significance in geotechnical engineering. There are two major issues in solving the seepage flow in complicated fractured rock mass based on the fractured porous medium (FPM) flow model, in which groundwater is assumed to flow simultaneously in both rock matrix and embedded fractures: One is the mesh generation of rock mass in the presence of the fracture network, especially when there exist a large number of stochastic fractures; the other is that a robust iteration algorithm is required since the free surface is unknown at the beginning of solution. Aiming at these two issues, this paper proposes a novel numerical method by coupling radial point interpolation method (RPIM) and finite element method (FEM), in which RPIM is utilized to model the rock matrix and FEM is utilized to model the fractures. On the basis of the variational inequality (VI) theory for free-surface seepage analysis, the computation formulations of the numerical method are derived and the corresponding computation program is developed. Three examples are solved with the present method. It is found that the VI theory can be extended to solve the free-surface seepage problem based on the FPM flow model. A crucial advantage of the present method is that the mesh generation can be greatly simplified. The present method has been verified to be a robust, efficient and reliable method for modeling the groundwater flow in complicated fractured rock mass.     

Stress-induced fluid flow anisotropy in fractured rock

Anisotropic stress states are common in the upper crust and result in fracture apertures being dependent on fracture orientation. Fractured rocks should therefore display an anisotropic permeability determined by the aperture, length, and orientation of those fractures remaining open. In this paper, a numerical study of this effect is made for a rock containing two orthogonal fracture sets subject to a uniaxial compressive stress applied perpendicular to one of the sets. With increasing compressive stress, the decreasing aperture of fractures orientated perpendicular to the stress axis leads to a decrease in permeability both parallel and perpendicular to the stress. For flow parallel to the stress direction, this is a consequence of the finite length of the fractures, flow in fractures perpendicular to the stress being required to connect fractures orientated parallel to the stress direction. As the number of fractures is decreased towards the percolation threshold, the average permeability tensor is found to become increasingly isotropic. This behaviour results from the highly tortuous nature of the flow paths just at the percolation threshold.     

岩体中饱和渗流应力耦合模型研究进展

在大坝渗流与控制、各种水工隧洞和交通隧道以及地下各种洞室开挖、采矿工程与油藏开采中的水力劈裂、 岩坡和坝基的稳定性研究等领域中经常会遇到岩体的饱和渗流应力耦合问题.本文对这些领域中的渗流应力耦合问题分为6种力学模型: 等效连续介质模型、 裂隙网络模型、 双重介质模型、 断裂力学模型、 连续损伤力学模型和统计模型.前3种主要从经典的黏弹塑性本构着手考虑, 着重对渗流场的处理, 后3种则是从考虑岩体在耦合作用下发生损伤破裂行为方面切入, 着重于岩体结构内部发生质的改变带来的更加复杂的耦合效应.对这些模型进行了详细的介绍, 指出了这些模型的优缺点与适用范围, 给出了一些有代表性的研究成果, 并对该研究领域中未来的研究方向进行了展望.     

Nonlinear Coupled Mathematical Model for Solid Deformation and Gas Seepage in Fractured Media

Based on detailed investigation into the interactional physical mechanism of solid deformations and gas seepage in rock matrix and fracture, a nonlinear coupled mathematical model of solid deformation and gas seepage is put forward and the FEM model is built up to carry out numerical analysis. The coupled interaction laws between solid deformations and gas seepage in rock matrix and fractures has been emphasized in the model, which is a vital progress for coupled mathematical model of solid deformation and gas seepage of rock mass media. As an example, the methane extraction in fractured coal seam has been numerically simulated. By analyzing the simulation results, the law of methane migration and exchange in rock matrix and fractures is interpreted.     

FEM ANALYSIS FOR INFLUENCES OF A FAULT ON COUPLED T-H-M-M PROCESS IN DUAL-POROSITY ROCK MASS

For the case in which a large geological structure like fault existing within the surrounding rock mass in the near field of a repository for high-level radioactive nuclear waste, one kind of coupled thermo-hydro-mechanical-migratory model of dual-porosity medium for saturatedunsaturated ubiquitous-joint rock mass was established. In the present model, the seepage field and the concentration field are double, but the stress field and the temperature field are single, and the influences of sets, spaces, angles, continuity ratios, stiffness of fractures on the constitutive relationship of the medium can be considered. At the same time, a two-dimensional program of finite element method was developed. Taking a hypothetical nuclear waste repository located at a rock mass being unsaturated dual-porosity medium as a calculation example, the FEM analysis for thermo-hydro-mechanical-migratory coupling were carried out under the condition of radioactive nuclide leaking for the cases with and without a fault, and the temperatures, pore pressures, flow velocities, nuclide concentrations and principal stresses in the rock mass were investigated. The results show that the fracture water in the fault flows is basically along the fault direction, and its flow velocity is almost three orders of magnitude higher than that of fracture water in rock mass; the nuclide concentration in the fault is also much higher than that without fault, and the nuclides move along the fault faster; moreover, the fault has obvious influences on the pore pressures and the principal stresses in the rock mass.     

岩体三维裂隙网络地质熵与渗透特性关系研究

裂隙网络是岩体地下水的主要流动通道,而工程岩体中裂隙网络错综复杂,裂隙网络的几何特征和连通性对其渗透性有着重要影响.为了综合量化裂隙迹长、间距、倾角、开度对裂隙网络连通性和渗透性的影响,基于信息熵原理,提出了三维裂隙网络地质熵理论和连通性指标-熵尺度,对比熵尺度与其他传统三维裂隙网络连通性指标,验证了熵尺度评价三维裂隙网络连通性和渗透性的合理性.结合锦屏一级水电站左岸边坡裂隙统计分布,建立三维裂隙网络渗流数值计算方法,分析不同裂隙迹长、倾角、间距、开度条件下三维裂隙面密度、无量纲逾渗密度、熵尺度和渗透系数的变化关系.结果表明:当体积率一定,考虑开度影响时,三维裂隙面密度和无量纲逾渗密度无法定量表征迹长和间距对裂隙网络连通性的影响;裂隙迹长与熵尺度和渗透系数呈负相关关系,裂隙间距和开度与熵尺度和渗透系数呈正相关关系,裂隙倾角变化对熵尺度和渗透系数影响较小;熵尺度与渗透系数的非线性关系近似满足二次多项式.     

岩体系统渗流场与应力场耦合的广义双重介质模型的应用研究

本文通过实验资料分析, 提出了裂隙岩体应力与渗流之间的分形几何关系式。以研究区岩体系统结构为基础, 提出了岩体系统应力场与渗流场耦合的广义双重介质模型, 并将该模型应用于某水利水电工程的渗流与控制中, 对坝区岩体进行了应力场和渗流场的耦合分析, 取得了比较满意的结果。     

考虑单元劈裂的流-固耦合连续-非连续方法及定向水力压裂模拟

为了更真实地模拟水力压裂过程中的岩石变形、裂缝扩展及流体流动,在自主开发的拉格朗日元与离散元耦合的连续-非连续方法的基础上,发展了一种流-固耦合方法。在该方法中,裂缝可沿四边形单元对角线和单元边界扩展,流体流动满足立方定律。通过与单一裂缝非稳态渗流模型及KGD模型的理论解进行对比,验证了该方法的正确性。由定向射孔水力压裂的模拟结果可以发现,(1)距离射孔越远,流体压力越小;随着时间的增加,裂缝中流体压力降低。(2)随着射孔角度的增加,裂缝起裂和扩展过程中的流体压力及转向距离增加;随着x方向水平应力的增加,裂缝起裂和扩展过程中的流体压力增加;两个方向水平应力之差越大,裂缝转向距离越小。(3)随着时间的增加,裂缝区段数目的增速变慢,这与裂缝体积增加变快有关。