输电线路节理化岩体注浆锚杆基础抗拔力模型试验研究

针对输电线路注浆锚杆基础特点,根据相似理论设计了节理化岩体注浆锚杆基础抗拔模型试验,模型设计中考虑了岩石弹性模量、浆体弹性模量、节理迹长、节理倾角、锚杆埋深5个因素的变化,选择5因素4水平的正交试验方法进行了模型试验研究。结果表明,岩石弹性模量对注浆锚杆基础抗拔力的影响最大,其次为锚杆埋深、节理倾角、浆体弹性模量、节理迹长。试验过程中以剪切破坏和开裂破坏为主,并以此分析了注浆锚杆的传力机制,得出浆体与锚杆和岩体之间的黏结强度是控制试验结果的主要因素,影响着锚杆的极限抗拔力和破坏状态,在施工过程中应注意质量控制。     

Numerical modelling of reinforced jointed rock masses I. Theory

The concept of reinforced multi-laminates has been developed and applied to the analysis of reinforced jointed rock masses. The discontinuities and reinforcements in the rock mass are assumed to occur in regular sets, with relatively close spacing within sets. The constitutive equations are established for an ‘equivalent material’, this being identical in its mechanical response to the reinforced jointed rock mass, consisting of its components, i.e. rock material, sets of discontinuities, and sets of reinforcements with associated sets of interfaces. An elasto-visco/plastic algorithm is used so that each component is described by its elastic, failure and flow properties together with its relative orientation. The constitutive equations for the ‘equivalent material’ can be applied to determine optimal reinforcement arrangements for problems of various levels of complexity. Several practical examples illustrating this are contained in a companion paper.     

Microplane damage model for jointed rock masses

The paper presents a new microplane constitutive model for the inelastic behavior of jointed rock masses that takes into account the mechanical behavior and geometric characteristics of cracks and joints. The basic idea is that the microplane modeling of rock masses under general triaxial loading, including compression, requires the isotropic rock matrix and the joints to be considered as two distinct phases coupled in parallel. A joint continuity factor is defined as a microplane damage variable to represent the stress‐carrying area fraction of the joint phase. Based on the assumption of parallel coupling between the rock joint and the rock matrix, the overall mechanical behavior of the rock is characterized by microplane constitutive laws for the rock matrix and for the rock joints, along with an evolution law for the microplane joint continuity factor. The inelastic response of the rock matrix and the rock joints is controlled on the microplane level by the stress–strain boundaries. Based on the arguments enunciated in developing the new microplane model M7 for concrete, the previously used volumetric–deviatoric splits of the elastic strains and of the tensile boundary are avoided. The boundaries are tensile normal, compressive normal, and shear. The numerical simulations demonstrate satisfactory fits of published triaxial test data on sandstone and on jointed plaster mortar, including quintessential features such as the strain softening and dilatancy under low confining pressure, as well as the brittle–ductile transition under higher confining pressure, and the decrease of jointed rock strength and Young's modulus with an increasing dip angle of the joint. Copyright © 2014 John Wiley & Sons, Ltd.     

节理岩体中隧道开挖与支护的数值模拟

由于节理、断层等不连续面的存在造成岩体变形的不连续性,并且这些不连续面对岩体变形、应力等力学行为造成重要影响。对已有的非连续变形分析程序进行了两点改进,应用改进的程序模拟了节理岩体中隧洞开挖与支护的过程,研究了不同节理倾角岩体的应力分布特性、开挖后隧洞围岩的变形和应力分布规律以及支护后衬砌的变形与应力特点。研究结果表明,节理倾角对节理岩体系统的应力和变形有着直接的影响,并且影响着隧洞开挖后的内空收敛效应;隧洞开挖顺序对围岩的变形和稳定也有重要影响。改进后的非连续变形分析方法和程序可以用来分析复杂节理岩体系统中隧洞的开挖与支护。     

High lateral strain ratio in jointed rock masses

Rock masses encountered in the field are jointed and highly anisotropic. An important manifestation of this characteristic of rock masses is that the blocks, when slipping, separate and create voids in the mass resulting in high lateral strain even under low axial stress. It has been shown in this study that the ratio of lateral to axial strain may be very high, especially, if the joints are critically oriented. The assumption of isotropic linearly elastic material is not applicable in such situations. This observation is based on the outcome of an extensive laboratory testing programme, in which a large number of specimens of a jointed rock mass with various joint configurations were tested under uniaxial loading conditions. The trends of experimental results for both lateral strain ratio and rock mass strength have also been verified through distinct element modelling. The reason for high lateral strains has been attributed to the creation of voids and also to the fact that permanent deformations due to slip commence along rock joints right from the start of loading process. A simple mechanistic model has also been suggested to explain the high values of lateral strain for rough and dilatant rock joints. The lateral strains in such situations are important in the design of rock bolts. An example from a recently completed hydroelectric project has also been discussed where high lateral strain was found to be responsible for excessive wall closure and failure of rock bolts.     

Action of fully-grouted bolts in jointed rock and factors of influence

Summary Bolting has been used in rock engineering for many years, but present knowledge and research experience supply only limited information concerning the action of rock bolts and the determination of the bearing capacity. To improve this unsatisfactory situation a test-based research programm has been carried out at the Rock Mechanics Laboratory of the Swiss Federal Institute of Technology.Based on recent publications treating rock bolting in theory and practice, about 70 laboratory and field tests have been carried out in order to explain the mode of action of fully-bonded, untensioned rock bolts in stratified or jointed rock masses. A three-dimensional model of a laboratory test was implemented using the Finite Element Method, with the aim to check the test observations and to furnish complete information for all stages of the shear tests.Through a systematic variation of the principal bolting parameters, their influence on the increase of the shear resistance of joints has been quantified. Formulae have been developed for the evaluation of the bearing capacity of fullygrouted bolts and for the prediction of the required shear displacements.     

节理岩体应力波反演模型研究

通过分析垂直节理面入射应力波的传播过程,得出节理界面产生的各次回波波形函数表达式,确定波源处的振动组合,从而建立以该振动信号分析为基础的反演节理特征的模型。该模型不仅能反演出节理的一些基本特征,包括：节理的位置、节理内充填物的波阻抗、品质因子、以及节理宽度与波速比值,而且还能反演出节理另一侧岩石的波阻抗,这一成果无疑将扩大应力波在节理岩体测试中的应用范围。     

全长粘结式锚杆加固节理边坡的动静态位移响应

锚杆通常被作为表面粗糙的轴力杆单元进行分析,但在节理边坡加固中,由于节理面的错动,同时考虑锚杆的轴向和横向作用显得更加合理。通过理论分析,建立锚杆三弹簧单元的力学特征模型和变形特征模型,对其受力和变形进行全面分析;运用拉格朗日元数值方法(FLAC3D),建立以理想弹塑性本构Mohr-Coulomb准则为基础的节理边坡模型,应用三弹簧锚杆单元,对其锚固前后的动静态位移响应进行模拟。结果表明：节理面锚固处理后,岩体的刚度得到提高;边坡各部位的位移减小,节理两侧位移的突变值变小;锚杆对节理的上下盘岩体起到有效的拉结作用,抑制了两盘之间的较大变形位移,有利于边坡稳定。     

Shear resistance of en-echelon jointed rock masses in joint direction

Summary A criterion for determining normal stress levels of shear failure of rock masses is developed, then the shear resistance of the rock mass, based upon the geometric model of en-echelon jointed rock masses, can be evaluated for low normal stress levels or high normal stress levels respectively by using the method proposed in this paper. Finally, a procedure generating joint patterns which are described with individual joint geometry parameter or multi-joint geometry parameter is discussed.     

Shear resistance of jointed rock masses and stability calculation of rock slopes

Summary Based on an extension to a model originally proposed by Zhang (1990), a method for estimating the shear strength of a jointed rock mass containing two joint sets is developed. Compared to the original method in which only a single en-echelon joint set was considered, the new method has the following advantages: (1) it allows a much more realistic joint pattern to be incorporated; (2) the effects of joint connectivity and intersection angle between joint sets on shear strength are included. Use of the new method is demonstrated by application to the calculation of the stability of slopes in jointed rock. The importance of joint connectivity, joint persistence and joint set intersection angle on slope stability, as predicted by the model, is revealed.     

Convergence-control approach for rock tunnels reinforced by grouted bolts,using the homogenization concept

The scope of this paper is to introduce a method for the analysis of rock tunnels reinforced by grouted bolts, based on the convergence-control approach. The analytical formulations presented in this paper refers to an elasto-plastic behavior of the rock mass and the latest Hoek and Brown yield criterion (Version 2002). In order to model the reinforced plastic zone, the equivalent material approach was taken into account such that the apparent strength of the rock mass is improved as a consequence of the bolting effect. The general design guides and examples presented are intended to facilitate the comprehension and application of the proposed analytical solution in practice.     

喷锚支护节理岩体的弹性复合单元模型

利用复合单元技术,建立节理岩体喷锚支护的弹性模型。该模型可先不考虑节理、锚杆、喷层等细部结构,生成常规有限元网格,然后根据节理、锚杆、喷层的相关信息,形成复合单元网格信息。该模型可重点考虑锚杆和喷层在节理面上的局部化非线性变形与相互作用关系。算例研究验证了模型的合理性。该复合单元算法同时包含等效模拟和离散模拟的优点,有着较好的应用前景     

节理卸荷岩体非线性本构关系再研究

对地质材料模型、石膏模型、砂浆模型、进行了模型试验,通过对模型试验得出的数据进行分析、拟合,得出初步的节理卸荷岩体的增量本构。针对其不足,从参数选择、物理意义等方面进一步进行修正得出一改进的增量本构关系,并在有限元分析程序ADINA中接入该本构关系,对清江隔河岩电站厂房高边坡三维模型进行有限元分析。     

节理岩体关键块体稳定的概率分析

基于地下岩体受节理面的控制,节理面的几何和力学参数随机分布,从而导致岩体系统具有高度不确定性,提出以关键块体理论为基础,考虑节理几何和力学参数随机性的岩体开挖可靠度分析方法,并给出了块体稳定的总失效概率评价模型。以澳大利亚阿德莱德地区一铜矿地质条件为例,以节理面倾角、倾向、摩擦系数和黏聚力为随机变量,通过Monte Carlo模拟和概率图方法,进行了岩体可靠度和失效概率的计算。最后,采用条件概率的分析方法,计算了单面滑动块体的总失效概率。计算结果表明,块体沿单面滑动并且出现的概率为11.0%,总的失效概率为3.85%,超过一般岩体工程可允许的风险水平,认为该方法可以作为评价块体可靠性的依据。     

Elastic stress and strain in jointed rock masses by means of crack tensor analysis

Summary An elastic stress-strain relation is formulated in terms of crack tensors which makes it possible to take into account explicitly the effect of joints on elastic behavior of rock masses. The present study is to discuss some related topics which may be encountered in its practical application. Two problems are solved by incorporating the elastic stress-strain relation into a program for three-dimensional finite element analyses; i. e., stress concentration by surface loading and displacement by excavation of an intersecting tunnel. Validity of the results is checked by comparing them with a laboratory model test and a field test, with the following conclusions: The overall distribution of stress definitely depends on a joint stiffness ratio (i. e., normal stiffness to shear stiffness). If the ratio is chosen as unity, the stress concentration occurs mainly in the direction parallel to major joints. If the ratio is high, say 10, then the stress concentrates along the perpendicular as well as the parallel directions to major joints. It can be said, on the basis of the fairly good agreement of the calculations using the high stiffness ratio with the field and laboratory measurements, that the elastic solution by crack tensors provides a practical tool for estimating the stress and strain in strongly jointed rock masses.     

Modified predictor-corrector solution approach for efficient discontinuous deformation analysis of jointed rock masses

The high computational costs associated with the implicit formulation of discontinuous deformation analysis (DDA) have been one of the major obstacles for its implementation to engineering problems involving jointed rock masses with large numbers of blocks. In this paper, the Newmark-based predictor-corrector solution (NPC) approach was modified to improve the performance of the original DDA solution module in modeling discontinuous problems. The equation of motion for a discrete block system is first established with emphasis on the consideration of contact constraints. A family of modified Newmark-based predictor-corrector integration (MNPC) scheme is then proposed and implemented into a unified analysis framework. Comparisons are made between the proposed approach and the widely used constant acceleration (CA) integration approach and central difference (CD) approach, regarding the stability and numerical damping features for a single-degree-of-freedom model, where the implications of the proposed approach on open-close iteration are also discussed. The validity of the proposed approach is verified by several benchmarking examples, and it is then applied to two typical problems with different numbers of blocks. The results show that the original CA approach in DDA is efficient for the simulation of quasi-static deformation of jointed rock masses, while the proposed MNPC approach leads to improved computational efficiency for dynamic analysis of large-scale jointed rock masses. The MNPC approach therefore provides an additional option for efficient DDA of jointed rock masses.     

节理岩体的三维阶谱复合单元法初步研究

阐述了节理岩体复合单元法基本原理,引入了阶谱有限单元法中的虚节点和广义节点概念,提出了覆盖虚棱（面）和广义棱（面）的概念,并进一步将虚节点和广义节点分类。在此基础上构造了节理岩体的三维复合单元不同阶次时的位移函数并推导了对应的刚度矩阵。算例表明此法是合理有效的。提出的概念有助于复合单元法和传统有限单元法二者升阶谱的理解与统一实现,并为实现节理岩体三维复合单元法的P型自适应奠定了基础。     

Limits on strength and deformation properties of jointed basaltic rock masses

Summary A study of strength and deformation measurements for basaltic rocks, along with consideration of the influence of fracturing using a rock mass classification system, documents the range of brittle response for basaltic rock masses. Although basalts vary widely in composition and other physical factors, many of the properties of a basaltic rock mass appear to vary within a factor of about 10. Typical values of strength parameters for intact basalt at ambient temperature (20°C) and negligible confining pressure are Young's modulus, 78±19 GPa; Poisson's ratio, 0.25±0.05; tensile strength, –14.5±3.3 MPa; unconfined compressive strength, 266±98 MPa; and conhesion, 66 MPa. Corresponding values for a basaltic rock mass that incorporate the weakening effects of scale are deformation modulus, 10–40 GPa; Poisson's ratio, 0.3; tensile strength, –0.1 to –2.5 MPa; uniaxial compressive strength, 10–90 MPa; and cohesion, 0.6–6 MPa. A measured deformation modulus for ambient pressure in the vertical direction, 20 GPa, is 1.5–3 times larger than that in the horizontal directions, 13.5 and 6.5 GPa, reflecting strength anisotropy due to column or block geometry for one particular basalt. Values of tensile and cohesive strength for the basaltic rock mass are generally one to two orders of magnitude lower than corresponding values for intact basalt. The shear strength of joints appears to vary considerably from flow to flow.     

An anisotropic strength criterion for jointed rock masses and its application in wellbore stability analyses

In this paper, an anisotropic strength criterion is established for jointed rock masses. An orientation distribution function (ODF) of joint connectivity, is introduced to characterize the anisotropic strength of jointed rock masses related to directional distributed joint sets. Coulomb failure condition is formulated for each plane of jointed rock masses by joint connectivity, where the friction coefficient and cohesion of the jointed rock mass are related to those of the intact rock and joint and become orientation dependent. When approximating joint connectivity by its second‐order fabric tensor, an anisotropic strength criterion is derived through an approximate analytical solution to the critical plane problem. To demonstrate the effects of joint distribution on the anisotropic strength of jointed rock masses, the failure envelopes are worked out for different relative orientations of material anisotropy and principal stress axes. The anisotropic strength criterion is also applied to wellbore stability analyses. It is shown that a borehole drilled in the direction of the maximum principal in situ stress is not always the safest due to the anisotropic strength of the jointed rock mass. Copyright © 2007 John Wiley & Sons, Ltd.     

节理岩体地基极限承载力研究

由于节理岩体具有复杂的力学特性,节理岩体地基的极限承载力问题一直都没有很好解决。利用非线性统一强度准则考虑中间主应力影响和岩性、岩体结构特性可以通过参数m,s和σc 来反映的优点,将非连续介质特性的节理岩体等效为连续介质,在确定即时摩擦角后,结合滑移线场理论获得了节理岩体地基极限承载力的封闭形式的理论解,其解考虑了边界条件和基础的几何形状,举例说明了计算裂隙岩体极限承载力的过程和所需的参数。结果表明：节理岩体的材料特性和中间主应力对极限承载力具有重要影响。