广义三维Hoek-Brown岩体强度准则的修正及其参数多尺度研究

对广义三维Hoek-Brown(H-B)强度准则的修正及其岩石和岩体参数确定方法、基于颗粒流模型的岩石和岩体细观数值建模方法、宏/细观尺度下修正广义三维Hoek-Brown强度准则参数的多尺度联系等进行了较为系统和深入地研究,主要研究内容和研究成果如下:(1)采用3种不同Lode势函数的替代方法对广义三维H-B强度准则的屈服面进行修正,并对修正后的广义三维H-B强度准则进行了屈服面光滑和全凸性的验证以及强度预测精度的验证和评价。研究结果表明,该修正广义三维H-B强度准则不但拥有较高的强度预测精度,而且较好地解决了广义三维H-B强度准则屈服面的不光滑和非全凸性的问题。(2)运用收集的真三轴试验数据,对修正广义三维H-B强度准则的岩石参数进行了最佳拟合,并借鉴H-B强度准则参数确定方法,提出了适用于修正广义三维H-B强度准则岩石参数mi和岩体参数mb,s,a确定方法。(3)采用细观球形颗粒对岩石进行颗粒流数值建模和试验,研究了球形颗粒的尺寸、尺寸分布、黏结模型、黏结的法向和切向强度、颗粒间摩擦因数等细观参数对修正广义三维H-B强度准则岩石参数mi(mi12)的影响,得出了细观颗粒产生互锁结构的紧密程度是控制整岩石参数mi的关键因素的结论。(4)提出了非球形颗粒间接建模的方法,采用细观非球形颗粒对岩石进行颗粒流数值建模,在细观尺度上构建更加紧密的互锁结构,所建立的岩石数值模型可以反映所有类型的岩石,较好地解决了基于颗粒流模型开展岩石和岩体参数细观研究的难点问题。(5)采用细观非球形颗粒对岩石进行数值建模和试验,研究了非球形颗粒的数量、尺寸、长宽比、形状等细观参数对修正广义三维H-B强度准则岩石参数mi(mi12)的影响,并对2种典型的岩石LDB花岗岩和Carrara大理岩进行了建模和验证。通过建立岩石参数在细观尺度、宏观尺度以及工程尺度的联系,为修正广义三维H-B强度准则提供了多尺度的理论依据。(6)结合"固有型"和"诱导型"各向异性岩石的细观数值建模和试验,对各向异性明显的修正广义三维H-B强度准则完整(I)岩体和块体(B)岩体参数mb,s,a开展了多尺度研究,研究结果表明,采用细观尺度的颗粒流建模不但可以重现宏观尺度的各向异性基本性质,而且可以较精确反映修正广义三维H-B强度准则岩石和岩体参数。(7)结合分形理论和统计数据对不同尺寸的岩石分别进行了数值建模,通过数值试验对岩石尺寸效应进行验证,并对修正广义三维H-B强度准则完整(I)岩体、块体(B)岩体和非常块体(VB)岩体参数mb,s,a开展了尝试性多尺度研究。研究表明,采用细观尺度的颗粒流建模不但可以重现宏观尺度的尺寸效应基本性质,为颗粒流在岩石和岩体力学与工程中的应用开拓广阔的前景,更为重要的是可以为工程中岩石和岩体参数的确定提供更加可靠的依据。     

基于岩体波速的Hoek-Brown准则预测岩体力学参数方法及工程应用

 根据建立的由岩体波速估算地质强度指标GSI和岩体扰动参数D的计算公式,引入Hoek-Brown准则,给出岩体波速预测岩体力学参数方法(简称岩体波速法)。以中缅油气管道(国内段)澜沧江跨域工程边坡岩体力学参数研究为例,并以室内岩石物理力学参数和场区声波测试数据为基础,采用岩体波速法和E. Hoek建议法预测场区的岩体力学参数。结果表明：岩体波速法和E. Hoek建议法所得的结果平均相对误差均较小,两者基本等效,数值模拟结果更进一步验证了工程应用效果的合理性。该方法在试验资料不足的情况下,能为岩体力学参数的快速评价提供一条新途径。     

细观结构的非均质性对花岗岩强度及变形影响的颗粒流模拟

基于等效晶质模型建模方法,利用颗粒流软件PFC2D实现对花岗岩细观结构的重建,开展了一系列不同围压下的花岗岩常规三轴压缩试验研究。揭示了晶体粒径分布所造成的细观结构上的非均质性和Mohr–Coulomb强度准则和Hoek–Brown强度准则中各参数的关系以及对岩石脆性的影响。研究结果表明,非均质性对岩样受压加载情况下的应力–应变曲线具有显著的影响。随着非均质因子增加,岩石由均质变为非均质,弹性模量逐渐减小,泊松比增加。随着非均质性因子的增加,岩石抗压强度减小、内聚力增加、内摩擦角减小。对同一类花岗岩而言,Mohr–Coulomb强度准则和Hoek–Brown强度准则中各参数的取值并非恒定,而是一定程度上依赖于内部的细观结构。当岩石细观结构变化时,两种强度准则中的参数也随之改变。细观结构的非均质性对岩石的脆性指标影响较大,随着非均质性因子的增加,岩石脆性指标减小。     

Hoek-Brown准则的改进及在大光包滑坡滑带碎裂岩体力学强度评价中的应用EI北大核心CSCD

针对目前大光包滑坡滑带碎裂岩体力学强度参数缺乏研究这一问题,提出基于改进后的Hoek-Brown准则获取岩体力学强度参数的新方法。该方法首先通过岩体基本质量指标BQ、岩体结构等级SR、结构面表面等级SCR与结构面条件因子J_c分别对地质强度指标GSI进行量化取值;在此基础上,建立由岩体基本质量指标BQ估算扰动参数D的计算公式;并以现场调查和室内岩石力学试验为基础,将改进后的方法代入Hoek-Brown准则中,对大光包滑坡滑带碎裂岩体的力学强度参数进行评价。与E.Hoek建议法相比,改进后的方法获取的岩体力学参数偏小,更为接近前人研究中的建议值,证明该方法具有一定的合理性。     

裂隙岩体在受荷条件下的声学特性研究

 博士学位论文摘要　自60 年代超声波测试技术应用到岩石工程领域以来, 已经成功地用于岩石、岩体和土体动弹性参数测试、岩体结构分类、参数确定以及岩体质量评价等问题, 因而得到岩土工程界的广泛重视, 并已进行了大量的理论与实验研究。在应用中用声速确定岩体的完整性系数, 作为岩体质量分级的一个重要指标, 已纳入了我国工程岩体分类国家标准; 但目前的研究基本上是沿声速和衰减两个参数而展开的, 对于岩石和岩体的声学特性与应力状态的相关性、对于与应力状态相关联的加载和卸载过程、对于声波信号中的信息如何应用等等, 还是尚未解决的问题, 因而目前的声波测试还难以解决声波与岩石力学特性相关的较复杂问题, 这就阻碍了超声波测试技术在岩土工程领域的更广泛的应用。为此本文重点研究裂隙岩体在受荷条件下的声学特性理论模型, 研究声波信号处理技术的新方法。通过大量的实验验证和对声波波形记录的数值分析, 系统地揭示了微裂隙岩石和裂隙岩体在加卸荷过程中的声学特性。其主要工作如下:(1) 通过分析岩石中裂隙的性态和对岩体中裂隙的界定, 从宏观角度将含裂隙岩石视为连续介质, 推导了超声波在其中传播时的声速及衰减与弹性参数的理论关系; 然后就岩石中裂隙在自由应力状态下对超声波传播的影响进行了详细的分析; 最后运用裂隙的边界元数值分析结果对岩石超声波与应力的相关性进行探讨。(2) 将岩石视为包含随机分布、具有一定开度且无充填物的微裂隙的各向同性体, 运用断裂力学理论推求出岩石在单轴,三轴加、卸荷全过程的本构模型; 运用岩石变形特性、空隙率、等效弹性参数及波速、衰减之间的关系提出等效模型, 建立了岩石在加卸荷过程中声速及衰减与应力的理论关系; 为了检验模型的正确性, 对砂岩、大理岩、花岗岩、灰岩和玄武岩等5 种岩石及石膏模型进行了加卸荷条件下的声波测试实验研究, 其结果与模型预测有较好的一致性。(3) 在对裂隙岩体建立宏观简化模型的基础上, 研究了裂隙岩体的等效弹性参数及其在未受到外部荷作用时的声速和衰减系数; 考虑裂隙闭合效应分析裂隙的变形特性, 并由此建立裂隙岩体在不同受荷条件下的声学特性的理论模型。通过对两种裂隙分布的石膏模型的实验研究, 证实了该理论模型能有效地模拟裂隙岩体的声学特性。(4) 采用小波变换理论对声波信号进行时2频域分析。将声波信号分解成不同频带通道的小波分量, 通过对各小波分量的频域分析, 提出了对应力较敏感的加权波谱参数; 并利用这种处理技术研究了岩石(体) 在受荷条件下波谱参数随应力的变化规律, 并说明以小波分析为基础定义的波谱参数在分析裂隙岩石和岩体的声学特性与应力相关性方面的重要理论意义和应用价值。(5) 运用损伤力学理论研究了岩石的损伤力学特性, 建立了岩石强度与超声波速之间的指数关系式; 并通过对混凝土和重庆砂岩的实验数据的拟合证实了这种指数关系的存在。针对目前在隧道工程中广泛采用的Q 系统围岩分类以及岩石工程中RMR 工程岩体分类, 利用现存的统计结果将岩体的超声波速与岩体质量指数Q、岩体分类指数RMR 及Hoek2Brown 准则联系起来, 建立了用岩体超声波速进行岩体分类以及对岩体强度参数和变形参数的估测方法。通过对三峡工程永久船闸高边坡岩体的应用, 发现由超声波预测的力学参数与直接采用RMR 分类系统和Hoek2Brown 准则估计的岩体力学参数基本吻合。从而表明应用超声波预测岩体力学参数是完全可行的。     

Hoek-Brown准则的改进及在大光包滑坡滑带碎裂岩体力学强度评价中的应用

针对目前大光包滑坡滑带碎裂岩体力学强度参数缺乏研究这一问题,提出基于改进后的Hoek-Brown准则获取岩体力学强度参数的新方法。该方法首先通过岩体基本质量指标BQ、岩体结构等级SR、结构面表面等级SCR与结构面条件因子J_c分别对地质强度指标GSI进行量化取值;在此基础上,建立由岩体基本质量指标BQ估算扰动参数D的计算公式;并以现场调查和室内岩石力学试验为基础,将改进后的方法代入Hoek-Brown准则中,对大光包滑坡滑带碎裂岩体的力学强度参数进行评价。与E.Hoek建议法相比,改进后的方法获取的岩体力学参数偏小,更为接近前人研究中的建议值,证明该方法具有一定的合理性。     

致密砂岩抗剪参数与H-B参数间关系研究

以致密砂岩三轴测试为基础,建立Hoek-Brown(H-B)参数反算模型,应用4种基于不同假设H-B准则方法对岩石抗剪参数进行估值并修正,与Mohr-Coulomb(M-C)准则结果对比。结果表明,修正后两种准则估值结果极为接近。将该方法应用于Shirahama砂岩,评价结果与试验结果较为一致,表明基于反算法建立的H-B参数与岩体抗剪参数间定量关系可信。岩体声学参数与抗剪参数间关系的进一步探索对预测岩体破坏及采矿安全具参考价值。     

具有高次非线性和复杂性功能函数的岩土工程可靠度分析

 应用可靠度计算的改进JC 法, 以岩体Hoek2Brown 强度准则为例, 针对极限状态方程的高次非线性和复杂性,分别采用变量代换法、Monte2Carlo 法、复合函数求导法和引用有理多项式技术计算三维岩体强度准则的可靠指标β。结果表明, 岩土工程可靠度计算中引入有理多项式技术的方法优于其他方法, 而且便于编制通用的可靠度计算程序。     

基于Hoek-Brown准则确定岩石材料强度参数的新方法

对Mohr-Coulomb准则和Hoek-Brown准则关系进行分析,提出基于Hoek-Brown准则的连续非线性黏聚力和内摩擦角计算公式,并对Hoek-Brown参数对强度参数的影响及计算公式的合理性进行讨论。研究表明:参数s较其他参数对内摩擦角φi和黏聚力ic的影响程度小,黏聚力ic随小主应力的增高而增大,内摩擦角φi则随小主应力的增高而减小;采用提出的强度参数计算公式和Hoek等效强度计算公式,对7种具有非线性强度特征的岩块和锦屏二级水电站工程的大理岩岩体的强度参数进行计算,对比分析可见计算公式结果与岩块室内三轴试验和工程岩体现场大剪试验的强度参数试验结果吻合度较高,表明建议的强度参数计算式在估算岩石材料强度参数时具有较高的准确性,对实际工程具有较强的指导作用。     

Hoek-Brown准则的脆性不等式及其对GSI取值的限制

Hoek-Brown准则2018版指出,H-B准则仅适用于岩石脆性破裂,不适用于延性破坏,此论断对地质强度指数GSI的取值构成了物理上的限制,目前尚未得到充分讨论。针对该问题,从H-B准则的脆性破裂假设出发,基于岩石脆–延转换理论,通过推导和计算建立H-B准则的脆性不等式,给出应力强度比对GSI取值的限制条件,探讨不同岩性岩体的GSI取值与埋深的关系,指出不同类型岩体超过极限埋深后将进入延性破坏区,H-B准则也将随之失效。上述研究有助于H-B准则的合理使用,避免岩体参数估计出现较大的偏差。     

Rock mechanics for design of Brisbane tunnels and implications of recent thinking in relation to rock mass strength

This paper explores the potential implications of recent thinking in relation to rock mass strength for future tunnelling projects in Brisbane, Australia, particularly as they are constructed within deep horizons where the in situ stress magnitudes is larger. Rock mass failure mechanisms for the current tunnels in Brisbane are generally discontinuity controlled and the potential for stress-induced failure is relatively rare. For the road tunnels which have been constructed in Brisbane over the last 12 years, the strength of the more massive rock masses for continuum analysis has been estimated by the application of the Hoek-Brown (H-B) failure criterion using the geological strength index (GSI) to determine the H-B parameters m_b, s and a. Over the last few years, alternative approaches to estimating rock mass strength for ‘massive to moderately jointed hard rock masses’ have been proposed by others, which are built on the work completed by E. Hoek and E.T. Brown in this area over their joint careers. This paper explores one of these alternative approaches to estimating rock mass strength for one of the geological units (the Brisbane Tuff), which is often encountered in tunnelling projects in Brisbane. The potential implications of these strength forecasts for future tunnelling projects are discussed along with the additional work which will need to be undertaken to confirm the applicability of such alternative strength criteria for this rock mass.     

The Hoek–Brown failure criterion and GSI – 2018 edition

The Hoek–Brown criterion was introduced in 1980 to provide input for the design of underground excavations in rock. The criterion now incorporates both intact rock and discontinuities, such as joints, characterized by the geological strength index (GSI), into a system designed to estimate the mechanical behaviour of typical rock masses encountered in tunnels, slopes and foundations. The strength and deformation properties of intact rock, derived from laboratory tests, are reduced based on the properties of discontinuities in the rock mass. The nonlinear Hoek–Brown criterion for rock masses is widely accepted and has been applied in many projects around the world. While, in general, it has been found to provide satisfactory estimates, there are several questions on the limits of its applicability and on the inaccuracies related to the quality of the input data. This paper introduces relatively few fundamental changes, but it does discuss many of the issues of utilization and presents case histories to demonstrate practical applications of the criterion and the GSI system.     

Correlation of the Hoek–Brown failure criterion for a sparsely jointed rock mass with an extended plane of weakness theory

An appropriate estimate of rock mass strength is necessary for the design of civil and mining structures built in or on rock. Rock mass is an inhomogeneous and anisotropic material with complex behaviour, which contains random planes of discontinuities that tend to reduce its strength. The direct estimation of this strength is practically unfeasible, due to difficulties in sampling and testing. This has led to the development of empirical failure criteria. These, express the strength of the rock mass in terms of properties of the intact rock and the discontinuities. The Hoek–Brown criterion is the most widely accepted one. However, albeit its use for many years, no experimental in situ validation with the actual rock mass strength has been demonstrated. Therefore, the Hoek–Brown criterion is investigated analytically through an extended plane of weakness theory, already validated with experimental evidence on physical specimens. Various intact rock qualities with blocky and very blocky structure are examined. The results indicate deviations in the rock mass strength predicted by the two approaches, especially when the intact rock strength is low.     

深埋隧洞大理岩卸载路径真三轴强度参数研究

 为研究深埋隧洞围岩卸载路径破坏特性,在现场深埋试验平洞内进行大理岩原位高压真三轴卸载试验,获得大尺度(50 cm×50 cm×100 cm)、高应力( =11.2 MPa)、真三轴( ＞ ＞ )、卸 破坏状态下,能反映深埋隧洞围岩实际应力状态和隧洞开挖应力路径的大理岩全过程应力–应变曲线和三轴强度。在高压卸载路径大理岩原位真三轴试验基础上,引入H-B经验强度准则研究大理岩卸载路径真三轴强度参数。研究成果表明：(1) 对于大理岩卸载真三轴原位试验,按H-B经验强度准则评估卸载路径真三轴强度偏低情况较多,评估经验参数s = 0.003 951 7,mb = 3.414,而由试验成果反算s = 0.095 53,mb = 12.208。(2) 在H-B经验强度准则基础上,按M-C强度准则,评估大理岩卸载真三轴试验强度参数：tan? = 1.39,c = 6.61 MPa,评估未扰动大理岩卸载真三轴强度参数：tan? = 1.60,c = 6.73 MPa,前者可代表卸荷损伤岩体。     

基于GSI系统的岩体变形模量取值及应用

 在分析岩体的变形特性时,岩体变形模量是一个非常重要的参数,一般要通过现场试验来确定。但利用现场试验直接确定岩体变形模量时,具有时间长、代价高以及试验结果可靠性差等缺点。E. Hoek利用地质强度指标GSI,通过大量现场试验数据的分析研究,建立一种新的估算岩体变形模量的公式。分析这种最新计算岩体变形模量的方法,并通过对岩体结构特征和结构面表面特征的定量描述,对GSI系统进行量化取值,特别对岩体体积节理数Jv的取值进行深入分析。最后通过实际工程的运用,研究应用这一方法的具体过程。最后通过与现场试验结果进行对比,分析这一方法的合理性。     

A simple procedure for ground response curve of circular tunnel in elastic-strain softening rock masses

This paper presents a simple procedure for the ground response curve of a circular tunnel excavated in elastic-strain softening rock mass compatible with a linear Mohr–Coulomb or a nonlinear Hoek–Brown yield criterion. The numerical stepwise procedure proposed by Brown et al. [Brown, E.T., Bray, J.W., Ladanyi, B., Hoek, E., (1983). Ground response curves for rock tunnels. J. Geotech. Eng. ASCE 109, 15–39] is modified by including the effects of elastic strain increments and variable dilatancy within the plastic region. The accuracy and practical application of the proposed procedure are shown through some examples. Four different combinations of dilatancy angle and softening parameter are considered to investigate the effects of elastic strain increments and variable dilatancy within the plastic region. The effects of variable dilatancy and peak dilatancy angle on the ground response curve are investigated for tunnels in poor-to-good-quality rock masses. The results show the importance of correctly estimating peak dilatancy angle in elastic-perfectly plastic and elastic-strain softening Hoek–Brown media.     

Evaluation of rock strength criteria for wellbore stability analysis

Polyaxial strength test data of five rocks are used to examine the Mohr–Coulomb, Drucker–Prager, modified Lade, Mogi–Coulomb and three-dimensional (3D) Hoek–Brown criteria regarding their ability, with parameters determined based on the triaxial compression test data, to represent the rock behavior under polyaxial stress states. Then the five strength criteria, with parameters determined based on the triaxial compression test data, are used to analyze wellbore stability of both vertical and inclined boreholes. The results show that the Mohr–Coulomb criterion under-predicts the polyaxial strength and estimates the highest minimum mud pressure required for wellbore stability while the Drucker–Prager criterion over-predicts the polyaxial strength and estimates the lowest minimum mud pressure. The modified Lade, Mogi–Coulomb and 3D Hoek–Brown criteria, with parameters based on triaxial test data, can either over-predict or under-predict the polyaxial strength. The over-prediction of the modified Lade criterion can be very large, and thus it may be unsafe to use it to estimate the minimum mud pressure. Both the over-prediction and under-prediction are relatively small for the 3D Hoek–Brown and Mogi–Coulomb criteria. Therefore, the 3D Hoek–Brown and Mogi–Coulomb criteria are recommended for wellbore stability analysis.     

Mechanical characteristics of the exponential strength criterion under conventional triaxial stresses

The minor principal stress is the key factor influencing the mechanical property of rock, and the strength criterion of conventional triaxial stresses is the basis of any true triaxial criterion. This paper examines the Coulomb criterion, Hoek–Brown criterion, the generalized Hoek–Brown criterion, and the exponential criterion proposed by the author. The procedure to determine the parameters in criteria is studied. Parameters in the generalized Hoek–Brown criterion are sensitive to the power n, thus Coulomb criterion with n=1.0 and the original form of Hoek–Brown criterion with n=0.5, especially that determined by linear regression, are not the best choice for the fitting solution of test data. The exponential criterion determined on the least absolute deviation will approximate a great number of normal test data, and expose the oddity data. It can describe the relation between strength and confining pressure in the entire stress range, with low misfit. The uniaxial compressive strengths predicted by the exponential criterion are nearly the same as the real magnitudes for all rocks. The deviator of strengths under conventional triaxial extension and compression is larger than half of the maximum strength increase from the intermediate principal stress. Therefore, the parameters in the exponential criterion may be completely determined from the strengths under conventional triaxial compression and extension.     

深部岩体强度准则

提出一种新的适用于深部岩体的强度准则,该准则考虑深部岩体的拉伸破坏,同时考虑深部岩体的剪胀和剪缩破坏,其破坏面可以是闭合的也可以是张开的,而且与RMR岩体地质力学分类指标建立联系.深部岩体准则中的参数均有明确的物理意义,可以很容易通过实验确定或通过RMR岩体地质力学分类确定.该准则不仅可考虑所有应力分量对材料破坏的影响,而且可反映深部岩体的受力特点.最后,将新准则与实验结果进行比较,从而验证了新准则的有效性.