裂隙岩体高压渗透特性研究

随着越来越多高水头电站、深部地下工程的建设,工程中面临更多渗透失稳风险,必须通过现场试验系统研究裂隙岩体的高压渗透特性和渗透稳定性。通过现场揭示和水-岩相互作用关系,探讨裂隙岩体的高压渗透破坏机制和破坏模式。基于多个高水头电站中的高压压水试验和高压渗透试验成果,研究高水头压力作用下裂隙岩体的水力劈裂、渗透变形、抗冲蚀性能、渗透稳定耐久性等特性。研究成果表明,高压条件下裂隙岩体的渗透特性会发生显著改变,变化规律和特征与所作用的水压力、应力赋存环境和物质填充情况紧密相关。     

应变敏感的裂隙及裂隙岩体水力传导特性研究

通过将岩体单裂隙视为非关联理想弹塑性体，导出单裂隙在压剪荷载作用下，其机械开度和水力传导度的解析模型，并采用已有相关试验研究成果对解析模型进行验证。在此基础上，通过将岩体概化为含一组或多组优势裂隙的等效连续介质，给出一种描述裂隙岩体在复杂加载条件下考虑非线性变形特征及滑动剪胀特性的等效非关联理想弹塑性本构模型。基于该模型，给出裂隙岩体在扰动条件下应变敏感的渗透张量的计算方法，该计算方法不仅考虑裂隙的法向压缩变形，而且反映材料非线性及峰后剪胀效应对裂隙岩体渗透特性的影响。该模型通过引入滑动剪胀角和非关联理想塑性，较为逼真地反映了真实裂隙及裂隙岩体峰后的剪胀特性、变形行为和水力传导度变化特征。通过数值算例，研究了裂隙岩体在力学加载及开挖条件下渗透特性的演化规律。     

高压引水隧洞陡倾角断层岩体高压压水试验研究

结合一抽水蓄能电站高压岔管区高压压水试验,详细介绍了具有陡倾角断层岩体的高压压水试验方法及试验成果。探讨了岩体高压下水力劈裂区扩展的波动理论和渗透破坏特性,明确了岩体与土体渗透破坏形式差异。试验首次对岩体内的渗透压力和变形进行了同步测量,以了解高压条件下岩体的渗透变形特性。在高孔隙压力作用下,岩体的变形发展试验成果表明,岩体应力和稳定性分析过程中孔隙压力的作用不可忽视,因此采用耦合理论对高孔隙压力环境下的工程岩体进行分析有助于降低围岩失效风险。     

高压压水试验的综合探讨

高压压水试验不但能反映裂隙岩体渗透特性,还可以评价各类结构面抵抗水力劈裂破坏的临界压力值大小,为地下工程灌浆处理裂隙岩体时提供依据。本文主要对高压压水试验在深钻孔中的应用做了详细的分析。     

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.     

现场裂隙岩体水力耦合真三轴试验系统研制与应用EI北大核心CSCD

为突破能反映岩体特性、岩体结构、初始应力及应力路径等多因素交互影响的水岩作用机制试验研究瓶颈,研制HMTS–1200型裂隙岩体水力耦合真三轴试验系统。该试验系统由高水压密封试验舱系统、试验荷载加载与反力系统、耐高水压变形测量系统、高精度伺服控制系统等组成。该系统的先进性和创新性如下:(1)采用试样外封闭思想,构造直径为1.6m水压力密封试验舱,模拟裂隙岩体水压力环境,将岩体试样与力学试验装置整体置于试验舱内开展力学试验;(2)试样尺寸310 mm×310 mm×620 mm,试验轴向荷载12 000 kN,侧向荷载3 000kN;(3)实现高水压下岩体变形直接测量,变形传感器耐水压力3 MPa,测试分辨率0.001 mm,线性度小于0.05%。利用该系统开展玄武岩在不同荷载组合下的水力耦合试验。试验结果表明,水压力的力学效应与岩体试样的变形响应与岩体结构特征、初始应力状态和水力变化路径有关。水压力对试样的力学作用主要表现为两种形式的力学作用及其相互耦合,一种是作为附加面力施加于试样表面,压缩岩体;另一种是水渗入裂隙中产生渗透水压力,降低裂隙面的有效应力,引起裂隙剪切错动和岩样膨胀变形。该设备的成功研制可为高坝水库蓄水及运行引起的库岸岩体变形及诱发滑坡等复杂环境裂隙岩体水力耦合问题和工程应用研究提供新的试验手段。     

渗流–应力–化学耦合作用下岩石裂隙渗透特性试验研究

 为研究渗流–应力–化学耦合作用下岩石裂隙渗透特性变化规律,设计3组试验工况,在改变渗透压以及化学溶液的条件下,分别测定每种工况下的渗出水流量、渗出水离子浓度值以及渗出水pH值变化情况,进而得出裂隙渗透特性变化情况。通过处理试验数据,总结分析各因素对裂隙渗透特性的影响,并建立裂隙开度变化率与渗出水中钙离子浓度值之间的关系式。试验结果表明,渗出水流量、裂隙开度总体趋势是随着时间逐渐减小的,最终趋于稳定状态;增大渗透压,稳定状态会被打破,裂隙的流量和开度都会增大,但最终趋于另一个稳定状态;化学溶液对岩体裂隙的侵蚀性大,对岩体渗透性的影响更明显。通过分析和提炼渗出水流量、裂隙开度、渗出水的离子浓度值以及渗出水的pH值等随时间变化的数据,及它们之间的内部关系,在理论上描述岩体裂隙在渗流–应力–化学耦合作用下的渗透特性,进一步揭示渗流–应力–化学耦合作用机制。     

应力对裂隙岩体等效渗透系数影响的离散元分析

 基于现场调查的裂隙网络信息及裂隙网络模拟技术--Monte-Carlo法,采用UDEC中的Fish语言编制裂隙岩体计算模型生成程序DFN-GEN。此程序解决由于裂隙繁多而引起的网格离散困难的问题,可生成大量随机节理,直接进行网络离散,生成裂隙岩体计算模型(DFN),最终用于水力耦合数值计算。结合DECOVALEX国际合作项目TASK C子课题,利用DFN-GEN程序生成裂隙岩体计算模型,研究裂隙岩体水力学特性,探讨应力对裂隙岩体等效渗透系数的影响规律,为研究核废料处置库、坝基、边坡等裂隙岩体工程实践提供方法。     

坝基破碎岩体高压渗透变形原位试验

 为获取向家坝水电站坝基挤压破碎带岩体的渗透变形特性,针对坝基破碎岩体空间分布特点,研究适合于渗透变形试验的现场压水试验系统和压水试验方法,提出坝基岩体渗透变形的原位高压试验方法。本研究最大特点是采用对观测孔内的水质取样分析和钻孔电视录像进行对比分析方法来研究原位渗透变形特征,并提出确定临界水力坡降的基本判据。研究结果表明,所提出的原位渗透变形高压压水试验方法可以较好地反映破碎岩体实际环境状态,原位渗透变形试验获得的临界水力坡降较室内试验成果更真实合理。     

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。     

裂隙岩体渗流场与损伤场的耦合分析

通过引入渗透压力附加柔度张量的概念以及考虑渗透张量的演化行为，详细研究了裂隙岩体渗流与损伤变形的相互作用机理。在此基础上建立了基于两场耦合的裂隙岩体渗流损伤模型。工程算例结果表叫，当存在地下流体流动时，渗流对岩体变形破坏以及损伤变形对岩体渗流场的影响是不可忽略的。     

裂隙岩体精细结构描述及工程特性数值试验

 基于裂隙的空间形态及分布的统计特性,应用裂隙网络随机模拟技术,建立工程裂隙岩体的数字化岩体模型,并编制程序实现自动化建模。利用GeoCAAS程序进行裂隙岩体数值试验研究,发展了研究裂隙岩体的力学和水力学特性以及两者关系的方法。主要探讨裂隙岩体变形模量和渗透系数随裂隙迹长变化而演化的规律,并进一步分析变形模量和渗透系数之间的关系。     

深部隧洞裂隙围岩渗透特性及衬砌外水压力变化规律

高外水压岩是影响隧道开挖过岩围岩稳定及衬砌结构安全的关键因素之一,基于裂隙介质渗流经典理论,给出围岩、衬砌不同渗透系数下的外水压岩解析解,采用数值方法对隧洞二次衬砌后的外水压岩作用特性进行仿真模拟,探讨裂隙围岩岩衬砌渗透系数对渗流场的影响,围岩、衬砌渗透和排水措施岩外水压岩的相关性。研究表明岩体和衬砌渗透系数之比是影响衬砌外水压岩的关键,正确的灌浆、排水设计对外水压岩折减系数影响较大,是减小衬砌外水压岩的有效措施。结论对高压水作用下裂隙岩体渗流及衬砌外水压岩研究具有重要理论意义,对高水压下围岩注浆及衬砌结构材料选型、参数选择等具有重要岩岩实用价值。     

Thermally induced mechanical and permeability changes around a nuclear waste repository—a far-field study based on equivalent properties determined by a discrete approach

A numerical investigation is conducted on the impacts of the thermal loading history on the evolution of mechanical response and permeability field of a fractured rock mass containing a hypothetical nuclear waste repository. The geological data are extracted from the site investigation results at Sellafield, England.A combined methodology of discrete and continuum approaches is presented. The results of a series of simulations based on the DFN–DEM (discrete fracture network–distinct element method) approach provide the mechanical and hydraulic properties of fractured rock masses, and their stress-dependencies. These properties are calculated on a representative scale that depends on fracture network characteristics and constitutive models of intact rock and fractures. In the present study, data indicate that the large scale domain can be divided into four regions with different property sets corresponding to the depth. The results derived by the DFN–DEM approach are then passed on to a large-scale analysis of the far-field problem for the equivalent continuum analysis.The large-scale far-field analysis is conducted using a FEM code, ROCMAS for coupled thermo-mechanical process. The results show that the thermal stresses of fractured rock masses vary significantly with mechanical properties determined at the representative scale. Vertical heaving and horizontal tensile displacement are observed above the repository. Observed stress and displacement fields also shows significant dependency on how the mechanical properties are characterized. The permeability changes induced by the thermal loading show that it generally decreases close to the repository. However, change of permeability is small, i.e., a factor of two, and thermally induced dilation of fracture was not observed. Note that the repository excavation effects were not considered in the study.The work presented in this paper is the result of efforts on a benchmark test (BMT2) within the international co-operative projects DECOVALEX III and BENCHPAR.     

复合温度条件下石灰岩多场耦合裂隙渗透侵蚀试验研究

深部岩石工程处在高应力、高水压力、高地热等复杂地质环境中,这些因素相互作用将对岩石的渗透特性产生重要影响,进而影响深部岩石工程的安全和生产效率。通过开展不同温度(25℃~90℃)条件下的同一块石灰岩裂隙多场耦合渗透特性变化试验,得到了温度因素对石灰岩裂隙渗透特性的影响规律。试验结果表明:在恒定有效压力作用下,升温阶段的初始时刻有一个流量峰值过程,温度恒定时,流量缓慢减小并最终趋于稳定状态;温度升高使得岩石裂隙渗透率单调下降,裂隙开度进一步减小;此外,温度越高,初始阶段裂隙开度闭合速度快,趋于稳定开度值历时越短且最终稳定开度值越小。石灰岩的侵蚀溶解速度随温度的升高而加快,裂隙面溶解出的矿物质增多,因此,渗出液中各离子的浓度随温度的升高变大。     

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。     

裂隙岩体表征方法及岩体水力学特性研究

 岩体中裂隙展布的多样性和随机性是裂隙岩体工程特性研究的关键问题。考虑岩体裂隙几何形态(走向、倾角、迹长、间距、隙宽等)的随机性,利用Monte Carlo模拟技术,编制裂隙网络生成程序RFNM2D和RFNM3D。利用RFNM,不但能够生成可以描述和表征岩体及其裂隙结构信息的虚拟裂隙网络岩体,还能够将生成的裂隙网络岩体进行数值离散化,从而可以直接和多种数值计算方法(有限元法、离散元法等)相结合来解决实际工程问题。因此,RFNM生成的裂隙网络岩体实际上是一种数字随机裂隙岩体模型。基于渗流力学理论,应用有限元方法编制软件GeoCAAS,研究裂隙岩体的水力学特性,探讨裂隙几何形态对渗流性状的影响。     

Seepage–stress coupled analysis on anisotropic characteristics of the fractured rock mass around roadway

Anisotropic properties of the fractured rock masses are investigated considering the coupled effect of the seepage and stress. The equivalent permeability and damage tensor of the fractured rock mass are initially examined using a series of Discrete-Fracture-Network (DFN) models with varied size and orientations from the geological investigation data of the sandstone roadway on the floor of 12# coal seam in Fangezhuang Coal Mine. A seepage–stress cross-coupling anisotropic model considering the coupled effect of the seepage and stress is described and applied to analyze the influence of the principal orientations of the joint sets on the anisotropic properties of the rock mass. It appears that the anisotropic properties of the rock mass have a great influence on the stress distribution, hydraulic conductivity coefficient and damage zone. The model may contribute to a more reasonable explanation on the dominant effect of the joint sets on deformation and failure of rock mass.     

Rôle des fluides dans le comportement hydromécanique des roches fracturées hétérogènes: Caractérisation in situ et modélisation numérique

Hydromechanical coupled processes in a shallow fractured rock mass were investigated in situ through field experiments and numerical simulations. The experimental approach consists of performing simultaneous and multi-frequency measurements of fluid pressures and displacements at different points and on different fracture types within a carbonate reservoir. Two kinds of experiments were conducted at the Coaraze Laboratory Site (France):

1. At the fracture network scale, a global hydraulic loading by groundwater level change shows that the coupling between fluid flow and deformation is simultaneously governed by a dual-permeability hydraulic behaviour and a dual-stiffness mechanical behaviour. The following fluid flow and hydromechanical conceptual scheme was established: first, a transient flow only occurs in faults with high permeability; second, when a steady-state flow is reached in faults, water flows from faults into lower permeability bedding planes. The intact rock matrix is practically impervious but the connectivity between the discontinuities is high. When fluid pressure changes occur within the fracture network, the hydromechanical coupling is direct in the highly permeable faults where a pressure change induces a deformation change. No direct hydromechanical coupling occurs within the lower permeability zones where deformation is not directly correlated with pressure changes. This means that the mechanical deformation of the bedding planes and rock matrix is induced by the fault deformation.
2. At the single fracture scale, the hydromechanical behaviour was evaluated by performing hydraulic pulse injection testing. This test was monitored using high-frequency (f = 120 Hz) hydromechanical measurements conducted with innovative fiber-optic borehole equipment. The hydromechanical response is simultaneously monitored at two measuring points spaced about 1 m apart within the plane of the sub-vertical fracture. Observed fluid pressure versus normal displacement curves shows a characteristic loop-shaped evolution in which the paths for loading (pressure increase) and unloading (pressure decrease) are different. The test was evaluated by coupled hydromechanical modelling using a distinct element technique. By matching the loop behaviour, modelling indicates that the pulse pressure increase portion allows the fracture hydromechanical properties to be determined while the pulse pressure decrease portion is strongly influenced by the hydromechanical effects within the surrounding fractured rock mass. A sensitivity study shows that the key parameters to coupled hydromechanical processes in such fracture systems are the initial hydraulic aperture and normal stiffness of the fracture, the stiffness of the rock matrix and the geometry of the surrounding fracture network.