【作者】 王刚；

【导师】 李术才； 蒋宇静；

【作者基本信息】 山东大学 ， 工程力学， 2008， 博士

【摘要】 在核废料储存、地下洞室群、隧道、石油、采矿、水利、边坡等各种岩体工程和环境工程中经常会遇到复杂的节理岩体。渗透特性和锚固性质是节理岩体的重要性质,往往直接或间接地决定着岩体工程的设计、施工、稳定性评价等。渗流场与应力场的耦合性质是岩体力学的重要特性。裂隙是节理岩体渗流的基本元素,为研究岩石水力学性质,合理预测工程岩体中复杂的渗流状态,应首先对单一裂隙水力特性进行研究。外力引起裂隙变形,改变了裂隙渗流速率,进而引起的孔隙应力变化,孔隙应力变化又会影响裂隙变形。通常节理裂隙作用力包括正应力、剪切应力和流体压力;根据作用力大小和方向不同,依据节理表面几何性质、变形性质及岩石材料的强度,裂隙将产生相应的变形;对于粗糙面节理,节理变形也会影响节理开度及其渗流性质。近年来,所谓的剪切渗流耦合试验引起广泛的研究兴趣。然而,由于断裂节理表面粗糙度定量表述的困难,以及剪切渗流耦合试验中所需柔性边界条件的限制,剪切渗流耦合试验中变形和渗流机制还不能充分地理解和描述。而且,以往的研究中,大多数直接剪切实验都采用在剪切过程中保持垂直应力不变(CNL)的边界条件,这类剪切实验只能模拟作用于结构面的垂直应力(自重)不变的未支护的边坡问题。但是,在大深度地下岩体结构工程问题中,岩石节理发生的表面变形和表面损伤的剪胀,会引起围压的变化。同时,围压的影响会引起节理的垂直应力变化。为解决大深度地下岩体结构工程的节理问题,从80年代开始,保持垂直刚度不变(CNS)的剪切实验装置得到了开发应用。基于上述问题,本文的研究采用自动化数控技术及虚拟仪器,开发了一套具有电液伺服微机控制系统的新型数控直接剪切实验机。这种数控剪切实验机用数控系统代替弹簧模拟节理周围围岩的变形刚度特性,克服了以往剪切实验机的上述缺点,能适应围压影响下的节理变形特点。应用该试验设备及其控制系统,采用适当的柔性边界条件,在恒定法向荷载(CNL)和恒定法向刚度(CNS)边界条件下进行剪切渗流耦合试验。试验中,分别取3组人工断裂试件;然后,以三组节理试件为原型,分别复制出5组透明石膏材料的断裂节理时间进行节理的剪切渗流耦合试验,并对5组断裂节理试件进行剪切渗流耦合试验。在剪切渗流耦合试验前,首先对试件进行循环加卸载试验,以便使试件最大可能的闭合。据此应用第4个循环的加卸载试验结果,来计算在法向荷载下断裂节理的力学梯度,这样能得到合理的法向应力和法向位移曲线。在所有的试验当中,流动方向平行于剪切方向,属于低围压下粗糙自然断裂节理内的流体流动,可适用于立方准则。在渗透率计算中,通过降低与剪切位移相应的水力梯度来消除这种断裂节理试件的上下2部分的接触长度(即有效剪切长度)减小带来的影响。在试验剪切过程中,应用数码摄像机记录着色水在节理内的流动过程和状态。在断裂节理的剪切渗流耦合试验研究中,法向应力和法向刚度是通常的边界条件,和剪切位移一起,被用来分析剪切行为和法向行为的耦合性质,或者解释发生在自然岩体内的剪切过程。立方准则能适用于大多数岩石断裂节理。试验结果发现:在试验剪切过程中随着剪切位移的发生,剪切应力明显呈现三阶段的变化,而渗透性呈现两阶段的变化趋势。剪切过程中的透过率变化亦表现出两阶段的变化性质。在第Ⅰ阶段透过率升高的比较快,直到一个拐点值,之后,其升高的速率趋于0,即第Ⅱ阶段。在剪切开始的时候,负膨胀可能使第Ⅰ阶段的透过率偏离立方体准则。在该研究中应用的断裂试件具有良好的匹配性能,负膨胀的产生是由于剪切试验前作用在试件上的法向荷载引起的固结压实和收缩。在本次试验中,这是一个短暂的现象,在这个过程中透过率的值比较低。在第Ⅱ阶段,较粗糙的节理比平坦节理有更大的透过率,且第Ⅰ阶段的极限值来的比较早。较高的法向应力和法向刚度将约束抑制剪切过程中的断裂膨胀,因此会降低第Ⅱ阶段的透过率值。随剪切位移增大,因剪胀作用,裂隙开度和水力传导系数均显著增大。剪切位移由零增加到8-12mm时,受剪胀作用影响,裂隙开度和水力传导系数达到最大值,而后随剪切位移的增加水力开度值基本持平。而且由实验结果可知,节理面剪切位移引起节理面剪切应力和渗透系数极大改变,特别是渗透性变化,节理面的微小剪切位移也可能引起渗透性数量级上的改变。根据适用于描述断裂节理内的流体流动Reynolds方程以及相应的边界条件,采用有限单元处理方法,应用有限元数值模拟技术模拟在法向荷载作用下剪切过程中断裂节理试件内的流体流动,着重分析接触面面积的变化,剪切过程中开度和渗透性变化。从与室内试验结果对比看,数值模拟结果和实验结果比较一致。另一方面,岩体中节理裂隙的存在严重削弱了岩体强度,降低了岩体的弹性模量;而且,岩体中存在的结构面在外部荷载作用下往往更容易发生错动和离层等变形。为限制裂隙及岩石变形提高岩体强度和工程结构稳定性,岩体工程需要采取适当的加固措施。作为岩体支护的主要手段之一,锚杆已广泛应用于各种岩土工程中。在工程实践中,锚杆和岩体联合作用,其加固效果往往十分明显。一些商业计算软件还不能有效反映锚杆对岩体结构巨大的支护作用,不能对这种加固效果进行准确的定量分析和评价。研究发现:在节理岩体中,节理面和锚杆相互作用,节理面对锚杆产生剪切作用,锚杆同时限制了节理面变形;致使锚杆在节理面附近发生明显弯折和变位,锚杆的变形往往远大于岩体的变形。论文对锚杆与节理面的相互作用机制及锚杆-节理系统进行了详细的分析研究,提出了相应的理论分析公式和计算方法。而且,当节理发育,锚杆数量众多时,我们既不可能用节理单元或杆单元逐一模拟如此众多的节理裂隙和锚杆,也不能略去由于这些节理裂隙的存在而使岩体具有各向异性和强度弱化的特性及锚杆的加固作用,因此需要寻找一种较为科学合理的适合加锚裂隙岩体特点的计算模型。在前面研究的基础上,采用损伤力学的方法研究节理面及锚杆在节理面附近的能量变化;根据Betti能量互易定理,求得加锚节理岩体的本构关系;应用损伤和弹塑性的半解耦方法对本构关系进行有限元程序化。将研究成果应用于地下洞室群的开挖支护的计算中,并分别与一般弹塑性计算结果和监测结果进行了对比分析。由研究结果司以得出结论。应用加锚断续节理岩体断裂损伤模型模拟锚杆的支护效应,通过分析锚杆与围岩的联合作用,有效地限制了围岩变形,改善了围岩的应力状态;而且锚杆嵌入岩体后,能承担一部分原来由围岩所承担的荷载,有效地阻止了洞周围岩破损区的发展演化,从而增强了围岩的稳定性。相比于普通的弹塑性模型,加锚断续节理岩体断裂损伤模型考虑了岩体中节理裂隙对洞室围岩稳定性的影响,以及锚杆针对节理裂隙的加固作用,因而能更好地反映裂隙岩体洞室围岩稳定性特征。根据位移的数值计算值与监测值比较后可以发现:监测点的数值计算位移值与监测值吻合良好,说明加锚断续节理岩体断裂损伤模型能够很好的反映加锚断续节理岩体洞室围岩的变形破损特征。在洞室开挖过程中,洞室拱顶处的位移在一定范围内逐步向上回弹,随着开挖的进行,位移回弹的速度减小。这是由于水平方向的地应力比竖直方向的地应力要大所致。这种规律也符合高地应力情况下的洞室开挖的位移变化规律。岩石遇水强度降低一直是困扰着地下工程围岩稳定性的一大难题。在前面研究基础上,结合固体力学中自洽理论、应变能等效原理,推导得到在压剪和拉剪应力状态下加锚节理岩体等效计算模型。并将其应用于象山港海底隧道的稳定性分析中。更多还原

【Abstract】 The presence of discontinuities significantly affects the strength, deformability and permeability of rock masses. Many failures of underground caverns during excavation and in operation are reported to closely relate to the occurrence nearby. Examples of such works are repositories for radioactive waste, dam foundations, excavation of tunnels and caverns, geothermal energy plants, oil and gas production, etc.The performance and safety of underground facilities mostly depend on the knowledge of permeability of rock masses, which varies with in situ and disturbed stresses around the repositories and the hydro-mechanical behaviors of rock fractures. The first step in understanding the rock mass conductivity is the analysis of single rock joint conductivity. When rock fractures experience a relative displacement process, the void spaces between their opposite surfaces, namely their apertures, may increase (dilation) with relative shear or decrease (closure) with normal loads, respectively. By coupling the mechanical aperture changes to the hydraulic aperture changes, a hydro-mechanical coupling is achieved. Most research concerning hydro-mechanical coupling in rock joints has been focused on the connection between normal loading and unloading and their effect on joint conductivity. The fact that shearing of rock joints can give an increasing or decrease of joint conductivity was highlighted in recent years. The studies considering both normal and shear stresses on fractures with fluid flow, the so-called coupled shear-flow tests, have attracted much attention.In laboratory shear testing for single rock joint, the constant normal loading (CNL) condition corresponds to the cases such as non-reinforced rock slopes, in concept. For deep underground opening or rock anchor-reinforced slopes, more representative behavior of rock fractures would correspond to a boundary condition of constant normal stiffness (CNS). Laboratory testing of rock fractures involve a number technical issues that may have significant impacts on the reliability and applicability of the testing results, chiefly 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 the present 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) boundary conditions. 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 coupled tests were carried out on three kinds of created rock fracture specimens to evaluate the influence of morphological properties of rock fractures on their hydro-mechanical behaviour. Some significative conclusions are drawed. During shearing, CCD camera is used to visualize the flow state of dyeing water in the rock joint. Numerical models using the measured topographical data of fracture surfaces were conducted to simulate the change of void spaces and fluid flow during shearing.The hydraulic conductivity and mechanical behavior of the joint depend on its surface morphology as well as aperture distribution. If the joints are rough, deformations will also change the joint aperture and fluid flow. The joint roughness governs the mechanical response of rock discontinuities, either in terms of stresses or displacements, as well as its hydro-mechanical behavior. Indeed, an increased (or decreased) void space due to dilation (or contraction) will lead to an augmentation (or reduction) of the hydraulic conductivity. The roughness evolves significantly during a shear test and the interface asperity degradation has a significant impact on the hydro-mechanical response and on the alteration in hydraulic conductivity. If the fracture conductivity increases when rock wall asperities are worn off, it can also decrease when sheared rock particles close the flow path, which is known as the gouge material effect.Many efforts have also been made to visualize the fluid flow in rock fractures using different visualization technique. It was found that fluid flows in rock fractures through connected and tortuous channels that bypass the contacts areas. Flow simulations in rough fractures are often performed considering effects of only normal stress or shear displacements without normal stress or with only very small normal stresses. The Reynolds equation is commonly applied to simulate such tests for simplicity. How to measure or calculate the fracture aperture under different normal stresses and shear displacements during the coupled stress-flow tests and numerical simulations are the most essential points to understand the process, interpret the testing and simulation results and quantify the hydraulic properties. In this study, a series of laboratory coupled shear-flow tests for fracture replicas under normal stresses was performed with visualization of fluid flow using a newly developed coupled shear-flow-tracer testing equipment and these laboratory tests were simulated by using FEM, considering evolutions of aperture and transmissivity with large shear displacements. The distributions of fracture aperture and its evolution during shearing and the flow rate were calculated from the initial aperture and shear dilations and compared with results measured in the laboratory coupled shear-flow-tracer tests using transparent fracture replicas and a CCD camera that provides continuous images of contact area and flow path evolution in real-time of the shearing tests, with reasonable agreements for the validation of the numerical model. The contact areas in the fractures were treated correctly with zero aperture values with a special algorism so that more realistic flow velocity fields and potential particle paths were captured, which is important for continued works on more realistic simulations of particle transport to be reported separately later.In other ways, as a flexible method, rock bolts have been widely used for rock reinforcement in civil and mining engineering for a long time. Bolts reinforce rock masses through restraining the deformation within the rock masses. Much field monitoring work carried out on the rock bolts installed in various rock types has shown that bolt reinforce has an huge effect on the rock masses deformation and the stability of underground structure. However, the interaction mechanism of the rock bolt and the rock mass, especially the jointed rock mass, is not well understood. In order to improve bolting design, it is necessary to have a good understanding of the behavior of rock bolts in deformed jointed rock masses.The design of bolts for stabilizing jointed rocks has been largely based on the tensile strength of the steel bars. The lateral shearing action of bolts is usually not taken into account in the design. It has been observed that the localized lateral deformation of bolt at its intersection with a rock joint is usually large. These investigations helped us to understand the tensile-shearing behavior of rock bolts qualitatively and quantitatively. This paper proposes the theoretical expressions of global resistance of bolted rock joints under the tensile-shearing or compression-shearing loads. The computational method of Finite Element Method for bolted rock joint is brought forward.Establishment of an analysis method for rock masses containing discontinuities and bolt reinforce is one of the most important issues in rock mechanics. The presence of discontinuities and bolts makes the mechanical behavior of the rock mass and underground structure complicated. It is well known that the existence and behavior of joints in a rock mass governs the mechanical behaviors of the jointed rock mass, and the bolt reinforce restrains the damage of joints to the rock mass and improves the stability of the underground structure. The number of joints and bolts is, however, so large that dealing with each joint and bolt individually is nearly impossible. Thus, the bolted jointed rock mass needs to be replaced with an equivalent continuum to conduct analysis that reflects the behavior of the joints. The adjacent rock mass of underground caverns is mainly under the state of tension-shearing stress and compression-shearing stress.According to the theories of damage mechanics, the constitutive model and fracture damage mechanism of jointed rockmass are systematically studied under the state of complex stresses. Firstly, with the equivalent strain energy, the constitutive relation of anchored jointed rockmass is derived under compression-shearing stresses. The constitutive relation under tension-shearing is also developed according to the theory of self-consistence. Based on the above constitutive models, the three-dimensional finite element procedures, considering the coupling of damage and elasto-plastic deformation by dint of the half solution coupling method, have been developed to model the ground movements that occur when underground power-houses of Pumped-storage Power Station are installed in jointed rockmass. Some useful conclusions are obtained and they have great significances to the project.更多还原