粘土岩饱和–非饱和渗流应力耦合模型及数值模拟研究

岩体中饱和–非饱和渗流、应力耦合行为对工程岩体的强度和稳定性有十分重要的影响。基于粘土岩实验室非饱和渗流试验的结果,将考虑塑性应变硬化的非饱和渗流、应力耦合模型、Hoek-Brown非饱和渗流、应力耦合模型应用于模拟某粘土岩竖井,研究其在开挖、通风、衬砌支护及长期运营期围岩内渗流从初始饱和→非饱和→近饱和的过程,以及竖井的非饱和流动区域大小对水力学参数(Biot固结系数、饱和度与毛细孔隙压力、水相的相对渗透系数与饱和度)的敏感性。结果表明:水力学参数对非饱和渗流的影响区域非常显著,尤其是水相的相对渗透系数与饱和度的关系。力学模型的差异对非饱和区的影响几乎可以忽略不计。     

粘土岩非饱和渗流模型在地下水运移过程中的数值模拟

根据实验室粘土岩非饱和渗流实验的结果,将考虑塑性应变硬化、Hoek-Brown和Mohr-Coulomb 3种非饱和渗流应力耦合模型应用于模拟某粘土岩竖井,研究了粘土岩在开挖、通风、衬砌支护及长期运营期,围岩内渗流从初始饱和→非饱和→近饱和的过程以及地应力和水力学参数(Biot系数、饱和度与毛细孔隙水压力关系、水相的相对渗透系数与饱和度关系)对围岩内的非饱和流动区域大小的影响.计算结果表明,水力学参数对非饱和渗流的影响区域非常显著,尤其是对水相的相对渗透系数与饱和度的关系的影响.     

粘土岩饱和-非饱和渗流机理研究

非饱和渗流、应力耦合行为是影响粘土类工程岩体的强度和稳定性的重要因素。基于粘土岩实验室非饱和渗流试验的结果，应用塑性应变硬化的非饱和渗流、应力耦合模型，研究在隧道开挖、混凝土衬砌支护和通风的过程中围岩干缩和膨胀的力学机理，得到了围岩内渗流的初始饱和一非饱和一近饱和过程，研究成果对解释工程现场的泥化、崩解机理具有重要的理论和实践意义。     

考虑非饱和渗流过程的岩体变形规律分析

蓄水初期谷幅变形异常是我国特高拱坝面临的新问题,考虑岩体从非饱渗流和到饱和渗流转变过程中的变形机制亟待研究。基于岩体从非饱和渗流到饱和渗流的过渡过程,推导岩体在非饱和渗流–应力耦合作用下的控制方程,建立非饱和岩体水力耦合模型,并应用于圆柱试件和边坡入渗过程的变形分析。结果表明:岩体从非饱渗流和到饱和渗流转变过程中,饱和度的改变是引起岩体变形的重要因素之一。研究成果对揭示特高拱坝蓄水初期坝体及山体异常变形机制具有重要的指导意义。     

灰岩单裂隙非饱和渗流–应力耦合特性试验研究

为研究不同应力条件下岩体裂隙非饱和渗流特性及其影响因素,基于自主研发的岩体裂隙非饱和渗流试验系统,对4组灰岩裂隙试样开展变饱和度和不同围压条件下的渗透试验。试验结果表明：(1)随着围压的增加,裂隙进气值增大,非饱和渗透系数–毛细压力关系曲线下降斜率及幅度均减小,在相同毛细压力下,高围压对应的裂隙非饱和渗透系数要高于低围压的情况;(2)通过对比毛细压力、围压这2个因素对非饱和渗透系数的影响发现,随着毛细压力的增加,围压对非饱和渗透系数的影响降低;同样,随着围压的增加,毛细压力对非饱和渗透系数的影响降低;(3)随着粗糙度的增大,裂隙饱和渗透系数降低,残余饱和度有小幅增长;(4)基于不同围压和毛细压力下的裂隙非饱和渗流试验数据,对裂隙非饱和渗透系数与毛细压力和围压的关系式进行拟合,从拟合曲面与试验实测数据的对比来看,拟合关系式可以较为准确地描述试验测得的裂隙非饱和渗透系数随毛细压力和围压的变化。本文对变应力条件下裂隙非饱和渗流过程及规律的研究成果可为降雨入渗条件下的工程岩体稳定分析提供依据。     

裂隙岩体非饱和水力应力耦合的不连续介质模型研究

目前对于裂隙岩体饱和水力应力耦合的研究取得了一些进展,但在很多工程领域不能简单地采用饱和渗流分析,而是要考虑岩体饱和-非饱和渗流、应力耦合作用对工程岩体的强度和稳定性的重要影响.因此在总结众多学者对裂隙岩体水力耦合研究成果的基础上,根据DDA力学计算和非饱和渗流计算原理,提出了基于非连续介质方法的--DDA方法的非饱和水力应力耦合模型;并给出了降雨入渗工况下的边坡水力耦合算例.计算结果表明,边坡稳定性随着降雨入渗时间的增加而减小,降雨强度越大,边坡稳定系数的降幅越大;考虑水力耦合时的边坡稳定性要小于不考虑水力耦合时的边坡稳定性,且在同一时刻,若降雨强度越大,考虑水力耦合与不考虑水力耦合的稳定系数差值越大.仿真试验和工程应用表明其计算成果是符合实践规律的,由此说明了所提出的水力耦合模型能正确反映裂隙岩体的水力学特性,验证了该模型是可行有效的,可付诸于实践.     

考虑变形效应的非饱和土相对渗透系数模型

 相对渗透系数是土体非饱和渗流分析的重要参数,Mualem统计模型在土体相对渗透系数预测中得到广泛应用。然而,Mualem统计模型假定土体具有刚性的孔隙结构,因而无法反映变形对非饱和渗透系数的影响。笔者最近提出的变形土土水特征曲线模型为基础,建立考虑变形效应的非饱和土相对渗透系数的修正Mualem统计模型。修正模型引入某一饱和度条件下被水充满的平均孔隙半径这一参量,来反映有效饱和度及土体变形过程中孔隙形态变化对其非饱和渗透特性的影响。采用4种不同类型土体的非饱和渗透试验数据对修正模型进行验证。结果表明,修正模型给出的相对渗透系数预测值与实测值的均根误差相比Mualem统计模型减小27%,说明修正模型对于变形条件下土体的相对渗透系数具有更强的预测能力。研究成果为非饱和土渗流规律以及水–力耦合数值模拟等研究提供了更为可靠的理论模型。     

岩体结构类型与水力学模型

 岩体水力学是一门研究岩体内一定温度条件下渗透力与应力相互作用关系及其耦合作用对岩体及岩体工程稳定性影响的交叉学科。为了准确描述岩体的水力学问题, 定义了有关名词。依据岩体的水力学特征, 把岩体的结构分为五类, 即: 准孔隙连续介质、裂隙网络介质、双重介质、岩溶管道网络介质以及岩溶溶隙- 管道介质。以岩体结构类型、达西定律、立方定律等为基础, 推导了在变温度和变应力条件下的孔隙型、裂隙型及管道型岩体的渗透定理, 并将岩体渗流场、温度场与应力场耦合模型分为两大类, 即: 集中参数型模型和分布参数型模型。     

岩体应力与渗流的耦合及其工程应用

岩体中应力与渗流的耦合对于工程应用十分重要。应用孔隙弹性力学理论，研究裂隙岩体与多孔介质岩体的应力变化引起的渗透性变化。推导出应力与渗透系数的关系式，得出由于多孔介质含水层疏水及应力变化造成的地表下沉计算公式。基于孔隙弹性理论，开发用于耦合应力与渗流的有限元计算软件。采用有限元方法耦合应力与渗流的关系，模拟不同采宽条件下采煤工作面的采动影响特征，得出工作面围岩渗透性变化、覆岩破坏高度、地表下沉与工作面几何参数的关系，这对于类似条件下的煤矿开采与设计有指导意义。     

不连续面对饱和-非饱和介质热-水-应力耦合影响的二维有限元分析

从建立应力平衡方程、水连续性方程、能量守恒方程入手，利用Galerkin方法，对于岩体和不连续面分别采用等参数单元和具有相同厚度的四节点节理单元，将各控制方程分别在空间域和时间域进行离散，建立了用于分析存在不连续面的饱和-非饱和介质中的热-水-应力耦合弹塑性问题的有限元模型，并开发了相应的计算程序。通过假定的有、无节理的核废料地下处置算例，表现了由于存在渗透系数很大的不连续面，推迟了缓冲材料达到饱和的时间，并对岩体中的位移场、应力场和渗流场产生很大的影响。     

A thermo-hydro-mechano-chemical formulation for modeling water transport around a ventilated tunnel in an argillaceous rock

Argillaceous rocks are being considered as potential host rocks for deep geological disposal. For the research work in DECOVALEX-2011, 5 participant research teams performed simulations of a laboratory drying test and a ventilation experiment for Mont Terri underground laboratory built in argillaceous rock formation. Our study starts with establishing a coupled thermo-hydro-mechano-chemical (THMC) processes model to simulate water transport in rock around the ventilated tunnel. Especially in this THMC formulation, a three-phase and two-constituent hydraulic model is introduced to simulate the processes which occur during tunnel ventilation, including desaturation/resaturation in the rock, phase change and air/rock interface, and to explore the Opalinus clay parameter set. It can be found that water content evolution is very sensitive to intrinsic permeability, relative permeability and capillary pressure in clay rock. Water loss from surrounding rock is sensitive to the change of permeability in clay which is induced by excavation damaged zone. Chemical solute transport in the rock near ventilation experiment tunnel is simulated based on the coupled THMC formulation. It can be estimated that chemical osmotic flow has little significance on water flow modeling. Comparisons between simulation results from 5 teams and experimental observations show good agreement. It increases the confidence in modeling and indicates that it is a good start for fully THMC understanding of the moisture transportation and mechanical behavior in argillaceous rock.     

Excavation-induced hydraulic conductivity reduction around a tunnel – Part 1: Guideline for estimate of ground water inflow rate

Field observations indicate that current engineering practice does not consistently estimate ground water flows into unlined rock excavated tunnels due to various factors that analytical solutions do not take into account. These factors include significant geological features, groundwater drawdown, inadequate estimates of hydraulic conductivity from packer tests, and stress-induced rock-mass permeability reduction in the vicinity of tunnel (lining-like zone). A key variable that is not properly accommodated in current practice, is the hydro-mechanical interaction within the joints in the surrounding rock mass. The significance of this variable is discussed in the 1st part of the paper which presents an analytical solution assessing ground water inflow rate into a tunnel using a mathematical derivation that takes into account the excavation-induced rock permeability reduction in the vicinity of a tunnel based on hydro-mechanical coupling effect. In the 2nd part of the paper, results from numerical analysis are presented to verify the proposed analytical solution for estimating ground water inflow rate into a tunnel. Further studies are currently underway to identify other key variables and their impact on the behavior of unlined tunnels and hydrological flow regime in the surrounding fractured rock mass using a distinct element method program which can fully consider hydro-mechanical coupled behavior of joints.     

三维复杂裂隙岩体渗流传热耦合的数值研究

将复杂裂隙岩体视为由离散裂隙网络和岩石基质两部分组成,采用四面体单元离散岩石基质,无厚度三角形单元离散复杂三维离散裂隙网络,考虑温度对流体密度和动力粘度的影响,建立了描述三维裂隙网络的裂隙岩体渗流-传热耦合模型。通过与二维单裂隙渗流-传热耦合问题的解析解对比,验证了该模型的可靠性。随后,利用该模型对复杂三维随机裂隙岩体的渗流-传热耦合过程进行了研究,研究发现:裂隙网络是主要的导水通道,在贯通裂隙簇中出现了明显的优势流,大量的流体在流经基岩的途中与会周围的高温岩体进行热量交换,导致在裂隙网络贯通区域的岩体首先温度下降,形成一条低温带,然后由于岩体的热传导作用,低温带再向四周进行扩散。     

裂隙岩体非饱和渗流本构关系

基于连续介质的方法，通过裂隙非饱和渗流的二维数值模拟，对裂隙岩体非饱和渗流中应用Van Genuchten(VG)模型和Brooks-Corey(BC)模型进行评价并建立了改进的本构关系。VG模型虽然可以与持水曲线匹配得很好，但是VG模型和BC模型都对相对渗透率估计过低。模拟结果表明：改进的BC相对渗透率-饱和度的关系和VG毛管压力-饱和度的关系结合，可以较好地描述非饱和渗流的本构关系。     

Some aspects of unsaturated flow in jointed rock

The applicability of Darcy's Law to two-phase flow has been discussed. Specialised triaxial equipment has been employed to separately inject two pore fluid components (air and water) into fractured rock specimens, so that two-phase flow behaviour can be studied at high axial and confining stresses. Improvements to recently developed two-phase high-pressure triaxial apparatus have enabled the authors to continue their study of air–water (i.e. unsaturated) flow in intact and fractured rock specimens under a wide range of stress conditions, similar to those encountered in underground mining operations. In this paper, a simplified stratified two-phase flow model is also presented that satisfactorily predicts flow behaviour in an inclined rock fracture over a range of linear laminar flow for particular capillary pressure relationships. The mathematical model is based upon the principles of conservation of mass and momentum, and relates the fracture aperture (e_t) to phase permeability (k_i) using Poiseuille's law and the proposed ‘phase height’, h_i(t), for water and air phases. The experimental approach used to verify the model predictions is described and the predicted results compared with the measurements. The experimental data confirmed the relationship between relative permeability and flow rate, with respect to two-phase flow conditions.     

非饱和岩石温度-渗流-应力耦合模型研究

以研究岩石孔隙比和含水量两个基本量为出发点,考虑温度对渗流黏滞系数和孔隙比的影响、温度梯度引起的流体流动以及流体流动引起的热对流的影响,应用修正的Darcy定律、Fourier定律等,推导出非饱和岩石在温度–渗流–应力耦合作用下的平衡方程、流体物质守恒方程、气体质量守恒方程和能量方程。并将建立的多场耦合力学模型应用于一泥岩竖井的开挖、支护过程,重点分析围岩和衬砌内温度场、渗流场的变化规律,以及泥岩竖井在开挖、支护和运行过程中饱和度的变化规律。研究成果对我国地下石油、核废料储存以及高寒地区的隧道工程设计与施工具有重要的指导意义。     

Coupled hydro-mechanical effect of a fractured rock mass under high water pressure

To explore the variation of permeability and deformation behaviors of a fractured rock mass in high water pressure,a high pressure permeability test(HPPT),including measuring sensors of pore water pressure and displacement of the rock mass,was designed according to the hydrogeological condition of Heimifeng pumped storage power station.With the assumption of radial water flow pattern in the rock mass during the HPPT,a theoretical formula was presented to estimate the coefficient of permeability of the rock mass using water pressures in injection and measuring boreholes.The variation in permeability of the rock mass with the injected water pressure was studied according to the suggested formula.By fitting the relationship between the coefficient of permeability and the injected water pressure,a mathematical expression was obtained and used in the numerical simulations.For a better understanding of the relationship between the pore water pressure and the displacement of the rock mass,a 3D numerical method based on a coupled hydro-mechanical theory was employed to simulate the response of the rock mass during the test.By comparison of the calculated and measured data of pore water pressure and displacement,the deformation behaviors of the rock mass were analyzed.It is shown that the variation of displacement in the fractured rock mass is caused by water flow passing through it under high water pressure,and the rock deformation during the test could be calculated by using the coupled hydro-mechanical model.     

单裂隙水流对岩体裂隙法向刚度的影响研究

岩体边坡工程与地下工程稳定性主要依赖岩体中的节理、裂隙、软弱夹层等结构面的力学性态。基于岩体低渗透性与结构面导水性,采用广义双重介质模型,对孔隙空间建立非饱和渗流HM耦合方程。对饱水/干燥裂隙空间建立裂隙受压体积变化的HM耦合方程。通过考虑孔隙和裂隙界面处压力连续,实现两处模型在应力边界上的耦合。对开口裂隙、封闭裂隙、半开半闭裂隙岩体的非饱和渗流过程进行了数值模拟计算。由计算结果得知:裂隙的闭合程度影响裂隙水向孔隙消散,从而影响裂隙刚度;在正应力作用下,裂隙受压逐渐分段闭合,由于裂隙的不同位置具有不同的刚度特征,整条裂隙不具同步性,甚至由于裂隙面性质不同,刚度变化甚至出现反复性。     

深部巷道底板岩体渗透性高压压水试验研究

岩体渗透性是反映岩体水力学特征的重要参数,为探究深部岩体的渗透性,采用钻孔高压压水试验手段,对东滩煤矿深部巷道底板四段岩体进行了现场原位压水试验,获得了大量实测数据。试验和数据分析结果表明：岩体在压水过程中经历了“隔水-导渗-稳渗”的过程,随着压水的进行,岩体的渗透性不断增强。东滩煤矿深部底板的厚层泥岩具有低阻弱渗的特点,厚层砂岩和互层具有高阻弱渗的特点,四段岩体原始状态下渗透性均较差。注水压力与流量关系曲线具有很好的指数关系,除厚层砂岩外,厚层泥岩和互层的注水压力-流量关系具有明显的分段性。岩体等效裂隙宽度随着注水压力的增大具有较好的指数关系且具有明显的分段性,即可分为突变点前的稳定阶段和突变点后的突增阶段。可通过裂隙宽度变化量是否大于0来判断岩体内是否发生明显渗流。研究结果有助于加强对深部岩体在水压作用渗透性变化的认识,为深部煤层的安全开采提供重要的参考依据。