岩石节理剪切过程中应力与渗流特性的数值模拟

 岩石节理剪切过程中应力与渗流特性受节理法向条件的影响很大。在岩石节理表面形状三维数值化表达的基础上,首先建立岩石节理剪切过程中力学与渗流的计算模型;接着,应用GIS技术,模拟分析不同法向条件(固定应力、固定刚度)下节理的剪切过程,获得节理剪切过程中应力与渗流特性的变化规律。结果表明,法向应力、裂隙张开度、渗透系数均随着剪切位移的增加而逐渐增加,整个剪切过程渗透系数增加了两个量级左右;而剪应力的变化却受法向条件的影响,剪应力在出现峰值后快速下降,而后固定应力条件下剪应力很快趋于一个稳定的值,而固定刚度条件下剪应力却又缓慢上升。     

岩石裂隙渗流与法向应力耦合的复合单元模型

首先,基于复合单元原理,建立渗流与法向应力耦合分析的复合单元模型,该模型前处理简便快捷,可含有一组或几组有明确定位的裂隙面,且可考虑裂隙面与相邻岩块的流量交换;然后,采用两场交叉迭代算法,对岩石裂隙的渗流场与应力场进行耦合分析。模型中视岩石裂隙为虚拟的＂充填介质＂,采用＂充填模型＂将有充填和无充填的岩石裂隙统一处理,并进行裂隙面开度与其法向有效应力关系的推导。依据的耦合机制为：法向应力的作用导致裂隙面开度的变化,从而引起裂隙面导水系数的改变,以至渗流场的改变,从而反过来影响应力场。算例分析表明法向应力作用会引起裂隙岩体的渗透不均匀性：局部区域的渗透坡降、扬压力和渗透流速显著增大。研究结果表明在裂隙岩体中进行渗流与应力耦合分析的重要性。     

剪切过程中岩石裂隙的渗流与 应力–应变耦合分析

 首先，考虑不同法向应力，建立岩石裂隙剪切应力和剪切变形的关系，其中对裂隙的弹性矩阵进行修正，并用三段函数关系分别描述岩石裂隙剪应力与剪切变形的3个阶段：剪缩阶段，剪胀至峰值阶段以及残余抗剪强度阶段。然后，结合三阶段裂隙剪切变形与其开度的关系，应用复合单元法，建立剪切过程中岩石裂隙渗流与应力–应变的耦合机制，研究裂隙的剪切变形、开度、导水系数、渗流场和应力场的变化与相互关系。算例分析表明：当裂隙中“充填介质”的力学参数保持不变时，通过裂隙的流速也基本保持不变，不随剪切变形以及法向应力的变化而改变，但由于裂隙开度的变化，故通过裂隙的单宽流量也随之改变；法向应力越小，裂隙的剪胀效应越大，且岩石裂隙的剪切变形对通过裂隙的单宽流量的影响也越大。     

爆炸应力波驱动的岩石开裂机制

针对岩石的钻爆法开挖,采用应力强度因子计算公式,分析爆炸应力波随时间、空间的变化规律以及其对岩石开裂过程的影响。研究结果表明,在爆炸应力波的作用下,按照时间顺序,岩石介质中的应力状态将先后处于压剪或拉剪应力状态;在炮孔近区,压剪应力状态对岩石开裂起控制作用;当距炮孔较远时,拉剪应力状态对岩石的开裂起主要作用;随着距离的进一步增大,岩石的开裂主要受拉剪应力状态控制,且以双向受拉的拉剪应力状态为主。尤其是对于强度较低的岩石,双向受拉的拉剪应力状态对开裂区范围的影响不能忽略。     

单裂隙花岗岩在应力–渗流–化学耦合作用下的试验研究

 通过开展单裂隙花岗岩在恒定三轴应力及化学溶液渗透压作用下的试验,对单裂隙岩石在应力–渗流–化学耦合环境下的综合响应机制进行研究。结果表明,单裂隙花岗岩在同时承受三轴压缩荷载及渗透压作用时,其侧向蠕变变形一直以稳定速率增加,显示水对裂隙面的物理软化效果,不同于完整岩石的扩容机制;应力作用下渗流溶液与裂隙表面矿物发生明显的溶解反应,其中反映硅铝酸岩矿物溶解的Al3+及SiO2浓度随时间递增,硅铝摩尔浓度比下降。扫描电镜下观察到长石、石英表面溶蚀孔洞及云母溶解后的不完整解理;随着裂隙接触面上水岩相互作用,水力开度发生变化。酸性溶液渗流情况下的水力开度降低,直至稳定;而蒸馏水渗流情况下的水力开度先增加直至稳定。造成此种不同变化规律是水岩化学反应及水力通道贯通两种因素的相互竞争的结果。对裂隙表面三维激光扫描表明,反应后裂隙面的JRC明显降低,表面趋于平缓化,表明应力作用下的溶解反应优先发展于矿物颗粒接触面。     

多轴应力作用下砂砾岩单裂隙渗流规律试验研究

用劈裂的方法在砂砾岩块上制造裂隙来模拟天然岩体的张性裂隙,在自行研制渗流-多轴应力耦合试验机上开展了一系列单裂隙渗流应力耦合试验,分别研究了垂直于裂隙面加载、平行于裂隙面加载对裂隙渗透能力的影响规律,对单裂隙岩体在多轴应力作用下的渗流规律作了探讨.成果表明,法向应力和侧向应力对裂隙的渗透系数有着明显的影响,共同决定着渗透系数的变化.     

裂隙岩体渗流与三维应力耦合的理论与实验研究

围绕裂隙岩体渗流与应力之间的关系问题,从理论出发,经过合理的建模和严密的推演,得出裂隙岩体渗流与三维应力的耦合方程。该方程经过了大量的三轴实验数据的验证,解决了裂隙岩体受到的侧向应力对其渗流是否有影响这一岩石力学学科中争议很大的问题。指出了裂隙侧向应力引起的裂隙侧向变形是影响裂隙岩体渗流的主要因素,其影响符合负指数规律。同时,还分析了裂隙组的渗流问题。     

基于UDEC平台的裂隙岩体边坡渗流应力耦合分析

根据裂隙岩体边坡渗流的基本特征和基本理论,阐述了离散元软件UDEC渗流—应力耦合的基本计算理论。利用UDEC作为分析平台建立数学模型,在考虑到渗流场与应力场耦合的作用下对裂隙岩体边坡的稳定性进行了全面分析。对边坡的应力、位移、渗流、裂隙分布等方面进行了研究,重点分析了在渗流与应力耦合的作用下边坡的变形破坏规律及自身稳定性。结果表明利用离散元软件UDEC分析流固耦合是一种有效、可行的方法,同时也为裂隙岩体边坡流固耦合方面的研究提供较高的工程应用价值。     

岩石裂隙渗流特性试验研究的新进展

 综述国内外关于岩体裂隙渗流特性的研究成果,并进行相应的分析和讨论。分析表明：试验研究在岩体裂隙渗流特性方面具有不可替代的作用;许多研究者根据试验结果提出相应的经验公式,但关于岩石裂隙渗流应力耦合特性研究的计算公式还没有统一的认识。分析结论也为今后的岩体裂隙渗流特性的试验研究提供了有益的方向。     

剪应力作用下岩体裂隙渗流特性研究

通过对规则、均匀、粗糙裂隙的渗流剪切实验，结合裂隙面受剪时的力学机理，研究了岩体裂隙在剪切荷载作用下的渗流特性，并对裂隙剪缩阶段过流能力的变化进行了探讨。实验结果表明，剪切荷载作用下，裂隙在剪动前渗透性随剪应力的增加而降低，且渗透系数与剪应力有十分明显的线件关系。     

Development of a shear-flow test apparatus and determination of coupled properties for a single rock joint

A new laboratory technique for coupled shear-flow tests of rock joints was developed and used to investigate the coupled effect of joint shear deformation and dilatancy on hydraulic conductivity of rock joints. This technique was used to carry out coupled shear-flow tests with an artificial created granite joint sample under constant normal loads and up to residual shear deformations of 20 mm. The hydraulic conductivity was estimated by using a finite difference method and an approximate equation assuming the cubic law. The shear-flow testing results revealed that the change of hydraulic conductivity is approximately similar to that of the dilatancy of a joint. The hydraulic conductivity increases rapidly, by about 1.2–1.6 orders of magnitude for the first 5 mm of shear displacement. After passing the residual shear stress, the hydraulic conductivity becomes gradually a constant value with increasing shear displacement. On the other hand, the hydraulic conductivity after shearing is about one order of magnitude larger than that prior to shearing. Shear-flow coupling characteristics obtained from these tests have a consistent trend with Barton's model prediction during the initial shear process. However, increasing deviation between measured and predicted hydraulic conductivity of rock joint samples has been observed with increasing shear displacement.     

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。     

Formulation of strain-dependent hydraulic conductivity for a fractured rock mass

By characterizing rock masses as anisotropic continua with one or multiple sets of critically oriented fractures, a methodology is developed in this paper to address the change in hydraulic conductivity resulted from engineering disturbance, material nonlinearity and anisotropy. An equivalent elastic–perfectly plastic constitutive model with non-associated flow rule and mobilized dilatancy is developed to describe the global nonlinear response of the rockmass under complex loading conditions. By separating the deformation of fractures from that of the equivalent medium, a strain-dependent hydraulic conductivity tensor is formulated. This not only considers the normal compressive deformation of the fractures, but also and more importantly, integrates the effect of material nonlinearity and post-peak shear dilatancy. Using this methodology, a closed-form solution is derived to describe the hydraulic behavior of a single fracture during combined normal and shear loading processes. The closed-form solution is validated by an existing coupled shear-flow test under wide ranges of normal and shear loads. Numerical simulations are performed to investigate the changes in hydraulic conductivities of a cubic block of fractured rock mass under triaxial compression and shear loading, as well as a circular underground excavation in a biaxial stress field at the Stripa mine, Sweden. The simulation results agree well with the in-situ experimental observations and an existing elastic strain-dependent analytical solution, respectively. The evaluation results clearly demonstrate that the proposed model is capable of predicting the changes in hydraulic properties of fractured rock masses under loading or excavation.     

岩石节理剪切渗流耦合试验及分析

节理岩体内渗流的发生主要是通过断裂节理网络产生,节理面的几何特性和受力特征决定和影响着节理裂隙的渗透性质,从而极大地影响着水下隧道及地下硐室中的渗流。应用自行研制开发的试验设备(岩石节理单一剪切-渗流试验机(SMT-E-4010)),在恒定法向荷载和恒定法向刚度的边界条件下,对不同接触状态下的岩石断裂节理试件分别进行一系列节理的剪切渗流耦合试验,研究剪切过程中力学性质、水力学性质的变化情况;同时,结合立方准则对试验数据进行分析讨论。试验结果表明:节理力学性质,水力开度和透过率在剪切过程中呈现出两阶段的变化性质。     

Excavation-induced hydraulic conductivity reduction around a tunnel – Part 2: Verification of proposed method using numerical modeling

During tunnel excavation in a jointed rock mass, significant joint closure takes place in the immediate vicinity of tunnel due to joint effective normal stress increase, and the equivalent hydraulic conductivity is largely reduced within a zone approximately one tunnel-radius thick around the tunnel. A significant pressure drop takes place across this zone, and the actual raise of pore-water pressure in the surrounding rock mass is steeper than that estimated from the analytical solution that considers the jointed rock mass around the tunnel as a homogeneous, isotropic medium. This paper presents a numerical modeling of the mechanical and hydraulic behavior of a jointed rock mass around a tunnel and provides estimates of the groundwater inflow rate to be compared to those estimated from generally used analytical solutions. The numerical analysis results presented here verify the validity of the analytical method described in the Part 1 paper for estimating groundwater inflow rate into a tunnel considering excavation-induced hydraulic conductivity reduction.     

Experimental study of the hydro-mechanical behavior of rock joints using a parallel-plate model containing contact areas and artificial fractures

In recent years, geological disposal of radioactive wastes is considered to be the most promising option, which requires the understanding of the coupled mechanical, hydraulic and thermal properties of the host rock masses and rock fractures. The hydro-mechanical behavior and properties of rock fractures are usually determined by laboratory experiments on fracture specimens that serve as the basic building block of the constitutive models of fractured rock masses.Laboratory testing of rock fractures involve a number of technical issues that may have significant impacts on the reliability and applicability of the testing results, chief among them are the quantitative estimation of the evolutions of hydraulic transmissivity fields of fractures during shear under different normal constraint conditions, and the sealing techniques when fluid flow during shear is involved. In this study, a new shear-flow testing apparatus with specially designed fluid sealing techniques for rock fractures were developed, under constant normal load (CNL) or constant normal stiffness (CNS) constraint. The topographical data of all fracture specimens were measured before testing to constitute the geometrical models for simulating the change of mechanical aperture distributions during shearing. A number of shear-flow coupling tests were carried out on three kinds of rock fracture specimens to evaluate the influence of morphological properties of rock fractures on their hydro-mechanical behaviour. Some empirical relations were proposed to evaluate the effects of contact area and surface roughness on the behavior of fluid flow through rock fractures.     

节理起伏角对非贯通节理岩体力学特性的影响

对非贯通节理岩体进行直剪试验,在相同法向应力作用下研究具有不同节理起伏角的非贯通节理岩体的强度特性、变形特征。并采用颗粒流数值模拟软件(PFC 2D)进一步研究非贯通节理岩体的细观扩展机理。两种试验研究表明:(1)非贯通节理岩体的破坏形态受节理起伏角的影响显著,随着节理起伏角增大,岩体的破坏程度逐渐加重,岩体破坏时的张拉裂纹越大,裂纹数目也越多,张拉节理与两节理面之间的夹角将越大,表面破损也越明显;(2)非贯通节理岩体的变形特征受节理起伏角的影响显著,当节理起伏角不同时,非贯通节理岩体的法向变形将不同,随着节理起伏角增大,非贯通节理岩体的峰值切向位移逐渐减小;(3)非贯通节理岩体的强度特性受节理起伏角的影响显著,随节理起伏角的增大,非贯通节理岩体的峰值剪切强度增大,岩体抗剪强度增大。     

不同地应力下爆炸应力波在节理岩体中传播规律模型试验研究

 通过模型试验研究不同地应力下应力波在节理岩体中的传播规律,同时考虑节理数量的影响,并推导地应力作用下应力波在多条非线性节理处的传播方程。首先,通过导爆索产生爆炸应力波,监测不同位置的应力,研究地应力下节理岩体中应力波传播的衰减组成,并分析地应力以及节理数量对应力波衰减的影响,其次,考虑地应力对非线性节理模型的影响,结合时间递归分析法,得出地应力作用下应力波在多条非线性节理处的传播方程,并将计算结果与试验数据进行对比分析。研究结果表明,高地应力下,爆炸应力波在节理岩体中传播时,其衰减主要由岩石材料和节理两部分分别引起的衰减叠加组成,随着地应力增加,节理岩体对应力波的衰减增强,其中岩石材料对应力波的衰减作用加强,而节理引起的衰减减弱。