岩体非连续裂隙网络三维面状渗流模型

模拟了一个野外实际入渗试验的岩体裂隙网络及其中的渗流。通过逆方法建立岩体三维裂隙网络模型,其指导原则是使模型能够再现野外通过露头和钻孔所观察到的裂隙现象。逆方法由于可以对模拟和实测裂隙进行相同条件统计抽样,因此避免了实测数据统计分析中复杂的误差矫正。裂隙面状渗流分析采用了任意多边形有限差分法。讨论了通过模型校正确定裂隙导水系数的方法,进行了随机模型重复实现,验证了模型的稳定性。     

裂隙岩体渗流模拟的三维离散裂隙网络数值模型(Ⅰ)：裂隙网络的随机生成

对于裂隙岩体中的渗流来说，离散裂隙网络模型比等效连续体模型更能刻画其基本规律。发展了用于模拟裂隙岩体渗流的三维离散裂隙网络数值模型，并编制了裂隙岩体渗流模拟程序FracFlow。该模型可以利用野外露头上采集到的裂隙的观测数据，通过计算机处理最终形成三维裂隙网络的人工几何模型，然后用边界元法求解所生成的裂隙网络中的渗流问题。在此第一部分中，介绍了利用计算机随机生成三维裂隙网络的详细过程，然后利用算例校核了程序的正确性。     

岩体裂隙非规则几何水力学特性研究

不规则裂隙的渗流问题是岩体水力学中一个比较复杂的问题。本文通过单裂隙渗流规律的模拟试验，提出了用正弦渗流模型模拟面外曲度渗流，用“地毯”状锥体渗流模型模拟面内曲度渗流。试验结果的统计分析表明，不规则裂隙的渗流存在分形效应     

二维任意裂隙网络裂隙–孔隙渗流模型的两种解法

 与裂隙网络渗流模型相比,裂隙–孔隙渗流模型(双重介质渗流模型)假定裂隙及裂隙切割而成的岩块均透水。这样可以只考虑较大裂隙形成的裂隙网络,而岩块及其内部的较小随机裂隙均作为连续孔隙介质进行渗流分析,从而减少裂隙网络中的裂隙数量以增加计算容量。讨论裂隙–孔隙渗流模型研究存在的问题,归纳剖析2种解法,即整体求解法与流量交换法。整体求解法中,裂隙作为有一定宽度的介质并划分为实体计算单元,与岩块单元的单元渗透矩阵合并成总体渗透矩阵进行求解。裂隙实体单元无需在网格划分时划出,只需在计算程序中对裂隙节点进行扩展。流量交换法中,裂隙系统和岩块系统分别形成渗透矩阵和渗流方程组,分别计算2个系统的渗流,2个系统之间通过流量交换,最终实现流量平衡和同一节点的水头一致,并指出水交换量只修正下游节点的渗流平衡方程。通过算例,比较2种解法的特点。还提出任意封闭回路在不增加节点前提下的三角形划分法。     

盐岩裂隙渗流–溶解耦合模型及试验研究

根据盐岩溶解机制，对盐岩裂隙的溶解过程进行合理简化和假设；在此基础上，考虑盐岩裂隙溶解和渗透性变化的耦合条件，建立盐岩裂隙渗流–溶解耦合模型。利用自行设计研制的盐岩裂隙渗流–溶解耦合试验装置对特定条件下的盐岩裂隙渗流–溶解耦合过程进行试验研究，并应用盐岩裂隙渗流–溶解耦合模型进行模拟分析与验证，计算结果与试验结果非常吻合，表明所建立的盐岩裂隙渗流–溶解耦合模型可以很好地描述盐岩裂隙的渗流–溶解耦合机制。该研究成果为进一步研究盐岩的应力–渗流–溶解耦合机制奠定重要的理论和试验基础。     

盐岩裂隙渗流-溶解耦合模型及试验研究

根据盐岩溶解机制，对盐岩裂隙的溶解过程进行合理简化和假设；在此基础上，考虑盐岩裂隙溶解和渗透性变化的耦合条件，建立盐岩裂隙渗流溶解耦合模型。利用自行设计研制的盐岩裂隙渗流-溶解耦合试验装置对特定条件下的盐岩裂隙渗流-溶解耦合过程进行试验研究，并应用盐岩裂隙渗流-溶解耦合模型进行模拟分析与验证，计算结果与试验结果非常吻合，表明所建立的盐岩裂隙渗流-溶解耦合模型可以很好地描述盐岩裂隙的渗流-溶解耦合机制。该研究成果为进一步研究盐岩的应力-渗流溶解耦合机制奠定重要的理论和试验基础。     

裂隙膨胀土渗流研究进展

膨胀土在反复干湿循环中,吸水膨胀失水收缩,先出现主裂隙逐步发展更多的次裂隙,最后把土体分割成碎块。蒸发速度、含水率梯度、试样的水分蒸发量等是影响裂隙发育的主要因素。采用拍照法可得到二维平面上裂隙情况,通过处理图像和三维建模可得到空间裂隙情况。介绍了几种裂隙渗流模型的研究现状,分析了各自的优缺点,等效连续介质渗流模型应用最为广泛。裂隙的存在为渗流提供了通道,膨胀土渗流应考虑裂隙的影响。     

双重裂隙系统渗流模型研究

根据岩体裂隙系统发育规律及其渗流特征，提出双重裂隙系统渗流原理，将裂隙网络渗流理论模型变成能详细描述主次裂隙系统渗流机制的裂隙岩体渗流实用模型，为解决工程中的岩体裂隙渗流分析提供了新方法。     

裂隙岩体渗流概述

从岩体应力场对渗流的控制作用、渗流对岩体的作用机理、应力—渗流耦合三方面,分析了裂隙岩体渗流的主要问题,阐述了裂隙岩体三个基本模型的原理和优缺点,为合理选取裂隙岩体渗流计算模型提供了参考。     

基于连续介质离散元的双重介质渗流应力耦合模型

 为模拟边坡在库水涨落和降雨作用下的渐进破坏过程,发展基于连续介质离散元的双重介质渗流应力耦合模型。它分为固体计算模型、孔隙渗流应力耦合模型和裂隙渗流应力耦合模型3个部分。固体计算模型能够反映地质体的破坏规律,可以模拟从连续到非连续的破坏过程;孔隙渗流应力耦合模型可以方便地计算出自由水位线(浸润线)的位置;裂隙渗流应力耦合模型可以避免由于不连通裂隙(孤立裂隙)存在所导致的收敛性问题;假设只考虑库水涨落和降雨的最终状态,裂隙渗流产生的水头分布和由库水涨落所引起的水头改变作为孔隙渗流的变边界条件,从而实现孔隙渗流场和裂隙渗流场的耦合。典型算例计算结果表明,基于连续介质离散元的双重介质渗流应力耦合模型对于库区古滑坡的研究是很有效的。     

裂隙单元修正等效渗透率模型及其验证

 采用裂隙单元表征裂隙网络,引入裂隙单元等效渗透率的概念,按照流量等效的原则计算其大小,然而阶梯状裂隙单元造成渗流流程的增加,同时压差不变导致流量的减少,为解决这一问题,用裂隙在网格中的实际流程长度与裂隙迹长之比来修正裂隙单元等效渗透率,并且针对复杂裂隙网络,对其进行预处理--删除孤立裂隙、死端裂隙、孤立裂隙簇等非连通裂隙。用此修正模型对单裂隙、相交裂隙、复杂裂隙网络进行渗流数值模拟,并与理论解及离散裂隙网络模型方法渗流结果进行比较,结果显示：研究区域下游出口总流量及出口处流量分布均取得较好一致性;同时,此裂隙单元修正等效渗透率模型也能反映出裂隙岩体渗流的非均质和各向异性。     

Longitudinal mixing in meandering channels: new experimental data set and verification of a predictive technique

Evaluation of longitudinal mixing processes in open channel flows is important in environmental management, requiring the quantification of mixing coefficients. Estimates of these coefficients sufficiently accurate for environmental impact assessments cannot be achieved using current theoretical or semi-empirical methods for natural channels. This inaccuracy is caused by a limited understanding and quantification of the interaction of the dominant mechanisms resulting from natural channel features, such as plan form curvature and changes in cross-sectional shape. Experimental results are presented here from studies conducted in three self-formed channels, developed by known discharges. Longitudinal mixing was investigated at various flow rates within each of the channels by monitoring the development of tracer plumes during transit through the channels. Using an optimisation procedure, coefficients required for solution of the one-dimensional advection dispersion equation (1D-ADE) were found in the range 0.02-0.2m(2)/s. The coefficients were found to vary as functions of longitudinal meander location, channel form and discharge. Predictions of these longitudinal mixing coefficients were made using a mathematical technique requiring only channel form properties and flow rate as inputs. Predicted values were typically within 20% of the measured values, although deviation of up to 50% was found for the lowest discharge in each channel. This large error is likely to have been caused by increased dead zone effects associated with channel bathymetry at low discharges that are not captured by the method. The method was shown to be capable of capturing the variation in the longitudinal mixing coefficient with longitudinal meander location, with channel form and with discharge.     

Hydro-mechanical interaction effects and channelling in three-dimensional fracture networks undergoing growth and nucleation

The flow properties of geo mechanically generated discrete fracture networks are examined in the context of channelling.Fracture networks are generated by growing fractures in tension,modelling the low permeability rock as a linear elastic material.Fractures are modelled as discrete surfaces which grow quasi-statically within a three-dimensional(3 D) volume.Fractures may have their locations specified as a simulation input,or be generated as a function of damage,quantified using the local variation in equivalent strain.The properties of the grown networks are shown to be a product of in situ stress,relative orientation of initial flaws,and competitive process of fracture interaction and growth.Fractures grow preferentially in the direction perpendicular to the direction of maximum tension and may deviate from this path due to mechanical fracture interaction.Flow is significantly channelled through a subset of the fractures in the full domain,consiste nt with observations of other real and simulated fractures.As the fracture networks grow,small changes in the geometry of the fractures lead to large changes in the locations and scale of primary flow channels.The flow variability and formation of channels are examined for two growing networks,one with a fixed amount of fractures,and another with nucleating fractures.The interaction between fractures is shown to modify the local stress field,and in turn the aperture of the fractures.Pathways for single-phase flow are the results of hydro-mechanical effects in fracture networks during growth.These are the results of changes to the topology of the network as well as the result of mechanical self-organisation which occurs during interaction leading to growth and intersection.     

A Graph-theoretic Pipe Network Method for water flow simulation in discrete fracture networks: GPNM

In order to simulate water flow in discrete fracture networks, a Graph-theoretic Pipe Network Method (GPNM) is proposed. Firstly, identification of water flow pathways is considered and a tree cutting technique is adopted. Then each fracture in a discrete fracture network is treated as a weighted pipe with a starting node and an ending node in an oriented graph. A node law of flow rate and a pipe law of pressure in discrete fracture networks are derived based on the conservation of mass and energy, respectively. Boundaries and fractures are unified with the same form of a unified governing equation. Solutions of water pressures and flow rates in discrete fracture networks are obtained by solving a system of nonhomogeneous linear equations. Since no discretization is needed, GPNM is demonstrated with high efficiency. In addition, a few case studies are implemented and compared with those from analytical solutions or numerical analysis using the software, Universal Distinct Element Code (UDEC). It shows that the proposed Graph-theoretic Pipe Network Method (GPNM) is effective in analyzing water flow in discrete fracture networks. Moreover, GPNM is promising for more engineering applications, and can be used for large scales of water simulation problems with numerous fractures.     

基于双重逾渗模型的裂隙多孔介质连通性研究

 孔隙和裂隙是裂隙多孔介质的2种渗流通道。在低渗和特低渗情况下,孔隙和裂隙能否构成贯穿的通道,决定介质能否发生渗流。针对低渗和特低渗裂隙多孔介质的连通性,结合孔隙逾渗理论和裂隙逾渗理论,提出一种双重逾渗模型。基于该模型,提出能够反映和比较裂隙多孔介质连通性的2个量化参数 和D,并重点讨论这2个量化参数物理意义。根据 和D这2个参数分析裂隙多孔介质的连通性特征。分析结果表明,以 为临界值,可以将裂隙多孔介质分为3种类型：“弥散型”、“临界型”、“指向型”。当 时,介质具有自封闭趋势,属于“指向型”;随着孔隙连通和裂隙方向随机性的增强,这种自封闭趋势会被破坏,使介质趋向于“弥散型”,即利于连通。少量长裂隙的存在对介质的连通性起决定作用。     

破断岩体裂隙的流体流动特性分析

 讨论立方定律成立的前提条件,指出立方定律只有在裂隙隙宽波动极小的情况下才能近似成立,对于岩体粗糙裂隙来说,此种状态只会出现在裂隙的局部区域,即局部立方定律;而在裂隙隙宽波动较大的区域,则需准确表述裂隙粗糙对流体流动的影响作用。提出天然粗糙裂隙的多平行板离散等效模型,可以有效地适用局部立方定律,推导粗糙裂隙的隙宽表示和流量计算公式;借助数值软件分析隙宽波动对等效模型单元体内部流体压力的作用规律,并定义一个过量压力降损耗系数,基于该系数对粗糙裂隙的流量计算方法进行修正。     

Interactive roles of geometrical distribution and geomechanical deformation of fracture networks in fluid flow through fractured geological media

In this study,the combined effects of geometrical distribution and geomechanical deformation of fracture networks on fluid flow through fractured geological media are investigated numerically.We consider a finite-sized model domain in which the geometry of fracture systems follows a power-law length scaling.The geomechanical response of the fractured rock is simulated using a hybrid finitediscrete element model,which can capture the deformation of intact rocks,the interaction of matrix blocks,the displacement of discrete fractures and the propagation of new cracks.Under far-field stress loading,the locally variable stress distribution in the fractured rock leads to a stress-dependent variable aperture field controlled by compression-induced closure and shear-induced dilatancy of rough fractures.The equivalent permeability of the deformed fractured rock is calculated by solving for the fracture-matrix flow considering the cubic relationship between fracture aperture and flow rate at each local fracture segment.We report that the geometrical connectivity of fracture networks plays a critical role in the hydromechanical processes in fractured rocks.A well-connected fracture system under a high stress ratio condition exhibits intense frictional sliding and large fracture dilation/opening,leading to greater rock mass permeability.However,a disconnected fracture network accommodates much less fracture shearing and opening,and has much lower bulk permeability.We further propose an analytical solution for the relationship between the equivalent permeability of fractured rocks and the connectivity metric(i.e.percolation parameter) of fracture networks,which yields an excellent match to the numerical results.We infer that fluid flow through a well-connected system is governed by traversing channels(forming an"in parallel" architecture) and thus equivalent permeability is sensitive to stress loading(due to stress-dependent fracture permeability),whilst fluid flow through a disconnected system is more ruled by matrix(linking isolated clusters"in series") and has much less stress dependency.     

裂隙岩体渗流模拟的三维离散裂隙网络数值模型(Ⅱ)：稳定渗流计算

承接上文的工作，给出了三维裂隙网络中稳定渗流的数值解法。每个裂隙被看作一个二维均质各向同性渗流域。数值方法采用边界元法，可以降低问题的维数，并可方便地对裂隙进行自动单元剖分。讨论了渗流问题控制方程基本解的确定，证明了3个常见基本解的等价性。编制了裂隙岩体渗流模拟程序FracFlow，并设计算例校核了程序的正确性。