改进的节理岩体变形模量经验确定方法及其工程应用

在节理岩体工程的数值计算及稳定性评价中,变形特征参数的选择至关重要。在原位试验受到各种条件无法进行时,经验确定方法不失为一种好的选择。本文在大量收集目前国内外节理岩体变形模量经验确定方法的基础之上,提出了改进的节理岩体变形模量经验确定方法,即“尺寸效应折减”与“节理特征折减”的二次折减法,并应用3个坝址与水电站的节理岩体工程实例进行分析验证,得出了一些有益的结论。     

基于TCK模型的非贯通节理岩体动态损伤本构模型

提出在岩体动态损伤本构模型中应同时考虑宏、细观缺陷;基于能量原理和断裂力学理论推导得出了同时考虑节理几何及力学特征的宏观损伤变量(张量)的计算公式;基于综合考虑宏、细观缺陷的复合损伤变量(张量)及完整岩石动态损伤Taylor-Chen-Kuszmaul(TCK)模型,建立了相应的单轴压缩下节理岩体动态损伤本构模型;利用该模型讨论了节理内摩擦角及节理长度对岩体动态力学特性的影响规律。研究表明,试件动态峰值强度随着节理内摩擦角的增大而增大,随着节理长度的增加而减小。     

深部节理岩体塑性损伤耦合微面模型

采用微面模型理论和损伤力学方法,建立了节理岩体的弹塑性损伤耦合微面模型. 在节理岩体的微面上,将岩体视为由节理面与岩石组成的二元介质,以节理连通率作为岩体沿该方向的面积损伤变量,考虑微面法向拉应力和压应力下的不同塑性变形和损伤耦合作用机制,基于塑性理论建立了节理岩体的微面塑性损伤增量本构关系. 采用微面物理量与宏观物理量的几何约束模型,根据微面方向积分导出了节理岩体的宏观弹塑性增量本构关系. 编制了节理岩体微面模型的MARC有限元子程序,对节理岩体的单轴拉伸、压缩试验和泥浆压力作用下的井壁稳定问题进行了数值模拟研究. 数值计算结果表明,该模型能很好地揭示载荷作用下节理岩体的各向异性非弹性变形和次生节理演化过程.      

Particle flow study on strength and meso-mechanism of Brazilian splitting test for jointed rock mass

A discrete element method （DEM） called particle flow code （PFC2D） was used to construct a model for Brazilian disc splitting test in the present study. Based on the experimental results of intact Brazilian disc of rock-like material, a set of micro-parameters in PFC2D that reflected the macro-mechanical behavior of rock-like materials were obtained. And then PFC2D was used to simulate Brazilian splitting test for jointed rock mass specimens and specimen containing a central straight notch. The effect of joint angle and notch angle on the tensile strength and failure mode of jointed rock specimens was detailed analyzed. In order to reveal the meso-mechanical mechanism of crack coalescence, displacement trend lines were applied to analyze the displacement evolution during the crack initiation and propagation. The investigated conclusions can be described as follows. （1） The tensile strength of jointed rock mass disc specimen is dependent to the joint angle. As the joint angle increases, the tensile strength of jointed rock specimen takes on a nonlinear variance. （2） The tensile strength of jointed rock mass disc specimen containing a central straight notch distributes as a function of both joint angle and notch angle. （3） Three major failure modes, i.e., pure tensile failure, shear failure and mixed tension and shear failure mode are observed in jointed rock mass disc specimens under Brazilian test. （4） The notch angle roles on crack initiation and and joint angle play important propagation characteristics of jointed rock mass disc specimen containing a central straight notch under Brazilian test.     

三维加锚弹塑性损务模型在溪洛渡地下厂房工程中的应用

本文根据断续裂隙岩体的损伤机制,建立了三维弹塑性损伤本构模型反映裂隙岩体的损伤变形特性。考虑断续裂隙岩体的岩锚支护效应,建立了空间损伤锚柱单元模型模拟锚杆的支护效果。最后将建立的模型应用于溪洛渡水电站地下厂房,进行了洞室群开挖弹塑性损伤及岩锚支护三维非线性有限元计算,获得了一些有益的工程结论。     

DEM analysis of the effect of joint geometry on the shear behavior of rocks

In order to comprehensively investigate the effect of different joint geometries on the shear behavior of rocks, the Distinct Element Method (DEM) was utilized with a new bond contact model. A series of direct shear tests on coplanar and non-coplanar jointed rocks was simulated using the PFC2D software, which incorporates our bond contact model. Both coplanar jointed rocks with different joint persistence and non-coplanar ones with different joint inclinations were simulated and investigated numerically. The numerical results were compared and discussed with relevant laboratory tests as well as some reported numerical works. The results show that for coplanar jointed rocks, the peak shear stress decreases nonlinearly with the joint persistence, and the failure process can be divided into four stages: elastic shearing phase, crack propagation, failure of rock bridges, and residual phase. For non-coplanar jointed rocks, as the absolute value of the inclination angle of the rock joints increases, its shear strength increases, changing the failure patterns and the length of new fractures between existing cracks. When the absolute value increases from 15° to 30°, the average shear capacity increases the most as 39%, while the shear capacity increases the least as 2.9% when the absolute value changes from 45° to 60°. There is a good consistency of the failure patterns obtained from experiments and numerical tests. All these demonstrate that the DEM can be further applied to rock mechanics and practical rock engineering with confidence in the future.     

基于六参数非均匀密度函数的伊万模型研究

伊万模型(Iwan model) 常用于描述连接的能量耗散和阻尼特性,来研究连接结构的非线性静动力学行为.本文提出了一个含截断幂律分布和双脉冲的非均匀密度函数的六参数伊万模型, 推导出六参数伊万模型的骨线方程,微、宏观滑移情况下的卸载方程和能量耗散的解析表达式,并讨论了模型参数对能量耗散的影响. 与已有的伊万模型相比,六参数伊万模型能够更好地描述连接结构的实验现象.      

STRENGTH PROPERTIES OF JOINTED ROCK MASSES BASED ON THE HOMOGENIZATION METHOD

This paper aims to determine the strength properties of jointed rock masses by means of the homogenization method.To reflect the microstructure of jointed rock masses,a representative element volume (R...     

裂隙岩体局部化破坏分析的多重势面分岔模型

采用多重势面弹塑性分岔理论对裂隙岩体的局部化破坏进行计算模拟．基于多重势面弹塑性理论分析局部化问题，构造了适用于裂隙岩体破坏的多重势面不连续分岔模型，并使用数值方法求解局部化方阶在有限元方法的基础上，使用该模型计算裂隙岩体的局部化破坏条带．算例分析表明这一模型用于分析裂隙岩体的局部化破坏是有效的．     

爆破开挖扰动下锚固节理岩质边坡位移突变特征与能量机理

针对白鹤滩水电站左岸坝基河谷底部边坡岩体爆破开挖,采用现场岩体位移监测、锚索轴力监测及数值模拟的手段,研究了爆破开挖扰动下锚固节理岩质边坡的位移突变特征及其能量机理。研究结果表明:对于深切河谷底部高地应力边坡岩体爆破开挖,爆炸荷载挤压及地应力作用下,岩体所积聚的应变能快速释放,导致了节理岩质边坡的位移突变,突变位移包括节理张开位移和岩体回弹位移两部分;地应力水平越高、岩体弹性模量越低,总的突变位移量越大;预应力锚索主要通过抑制节理张开位移来控制边坡岩体的位移突变,锚索预应力等级越高,其吸能和释能速率越高,对节理岩体位移突变的控制效果越好,当锚索的预应力等级高到一定程度后,节理岩体的突变位移不再随锚索预应力等级的升高而显著减小。     

层状岩体的Cosserat介质均匀化

将层状岩体视为由Cosserat介质组成的复合体,对其进行均匀化等效,在MATLAB平台上进行有限元编程,得到新等效本构关系。不仅能反映层状岩体的弯曲特性,而且可以对节理岩体的力学性能进行宏观和细观描述。通过对洞室算例进行显式节理模型、横观各向同性模型以及均匀化Cosserat等效模型三种方法的数值计算比较,证明理论分析与计算方法可行有效。     

Upper and lower bounds for constitutive relation of crack-weakened rock masses under dynamic compressive loads

A micro-mechanics-based model is proposed to investigate the rate-dependent constitutive relation for crack-weakened rock masses subjected to dynamic compressive loads. The present micro-mechanical model reveals that the nucleation, growth and coalescence of sliding cracks dominate the failure and macroscopic properties of crack-weakened rock masses subjected to dynamic compressive loads. The interactions among multiple parallel sliding cracks in crack-weakened rock masses subjected to dynamic compressive loads are examined asymptotically in an explicit and quantitative manner in order to reveal fully their so-called shielding and magnification effects on the stress–strain relation. Based on the micro-mechanical framework and the asymptotic analysis, analytical upper and lower bounds are proposed for the rate-relation for rock masses containing multiple rows of echelon cracks subjected to dynamic compressive loads. The factors that affect the rate-dependent properties of crack-weakened rock masses have been analyzed. The strain energy density factor approach, which is related to crack growth velocity and dynamic fracture toughness of rock material, is employed in the analysis. The rate-dependent constitutive relation of crack-weakened rock masses is derived from micro-mechanical framework and the asymptotic analysis. The closed-form explicit expression for the rate-dependent constitutive relation of rock masses containing echelon cracks subjected to dynamic compressive loads is obtained. Finally, the present model is used to analyze the complete stress–strain relation and strength for jointed rock masses at shiplock slope of the Three Gorges Dam.     

节理玄武岩体变形模量的尺寸效应和各向异性

目前系统研究柱状节理玄武岩工程力学特性的成果仅见于美国汉佛德玄武岩核废料埋藏工程和中国西南白鹤滩水电工程。列举了国内外相似工程柱状节理玄武岩的原位试验成果,分析了我国不规则柱状节理玄武岩体的柱体偏转特性和多级结构面发育特征,采用可变形离散元法建立了柱状节理玄武岩体的三维离散元数值模型,通过数值模拟不同尺寸的承压板试验,探讨了尺寸效应和各向异性对试验成果的影响。数值分析表明：承压板的尺寸效应是产生柱状节理岩体水平和铅直原位试验各向异性的主要原因,随着承压板直径的增大,各向异性效应减小,当承压板直径大于6m后,柱状节理玄武岩体可视为各向同性体,研究成果对利用和改造柱状节理岩体具有较好的工程意义。     

Study on stress wave propagation in fractured rocks with fractal joint surfaces

This paper presents the experimental and theoretical investigation of property of stress wave propagation in jointed rocks by means of SHPB technique and fractal geometry method. Our aim focuses on the influence of the rough joint surface configuration on stress wave propagation. The comparison of behavior of reflection and transmission waves, deformation and energy dissipation of a rough joint surface characterized by its fractal feature with that of a smooth plane joint has been carried out. It has shown that the rough joint surface distinctly affects the stress wave propagation and energy dissipation in the jointed rocks. The rougher the joint surface was, the more permanent deformation occurred and the more attenuation stress wave took place as well. A nonlinear relationship between the normalized energy dissipation ratio W_J/W_I of the jointed rock and the joint roughness in terms of the fractal dimension has been formulated. It seems that the ratio W_J/W_I, presenting how much energy has been dissipated in the joint, nonlinearly increased with the increment of the fractal dimension D of the jointed surface. The ratio W_J/W_I of a roughly jointed rock, however, tends to be the same as that of a smoothly jointed rock if the fractal dimension is less than a critical value D_c = 2.20. The energy dissipation ratio at the critical point D_c seem to be a constant, not dependent of rock type but fractal joint configuration.     

基于时域自适应算法的单向粘弹性节理岩体的等效分析

在粘弹性节理岩体的数值仿真中,必需合理地计及节理的影响.若将节理与岩体作为独立的材料组分考虑,在节理密集的情况下,时空两方面的计算开销可能是很难承受的.本文通过时域展开技术与一个简单的等效假定,得到了递推格式的粘弹性单向节理岩体的等效本构关系,及等效场的递推求解格式,并由此数值模拟了一个粘弹性节理岩体中的洞室,计算结果与考虑独立组分的ANSYS粘弹性分析进行了比较,二者的计算平均误差约为11.03%,但前者的计算效率为后者16.81倍.本文工作有可能为粘弹性节理岩体的数值模拟提供一条新的途径.     

刚性元方法和块状岩体稳定性分析

本文提出的刚性元方法是一种数值分析方法,它将变形体离散为一些刚性块体(剐性元)和块体之间的可变形薄层(节理元)的组合体,在各种载荷条件下求出块体的运动以及薄层的变形和应力分布。本文联合岩石系统的失稳准则来使用刚性元方法,成功地研究了块状岩体的稳定性问题。计算实例表明,本文提出的方法可以正确地反映块状岩体的失稳机制,是一种合理和可行的岩体稳定性分析手段。     

节理岩体中地下洞室超挖预测

本文着重于岩体中洞室超挖-不稳定楔形体的预测。首先,论述洞室超挖的基本概念、主要原因及评价方法;其次分析和比较目前现有的针对洞室超挖的计算软件及其特征;然后介绍本文作者的计算软件;最后,简单介绍一个计算实例,即从野外地质调查着手,应用数理统计理论评价构成不稳定楔形体的主要地质参数及其模型,推导岩体中洞室超挖预测的一般公式;最后评价构成不稳定楔形体主要地质参数中的主要因素及次要因素,为节理岩体洞室防止超挖及其处理提供依据。     

综合考虑宏细观缺陷的岩体动态损伤本构模型

针对节理岩体同时含有节理、裂隙等宏观缺陷及微裂隙、微孔洞等细观缺陷的客观事实, 提出了在节理岩体动态损伤本构模型中应同时考虑宏细观缺陷的观点。为此, 首先对基于细观动态断裂机理的经典岩石动态损伤本构模型—TCK(Taylor-Chen-Kuszmaul)模型进行了阐述, 其次基于Lemaitre等效应变假设推导了综合考虑宏细观缺陷的复合损伤变量(张量), 进而在此基础上建立了相应的节理岩体动态损伤本构模型, 并利用该模型讨论了载荷应变率及节理条数对岩体动态力学特性的影响规律。结果表明, 在不同载荷应变率下试件在变形初始阶段是重合的, 而后随着应变的增加, 试件峰值强度、峰值应变及总应变均随载荷应变率的增加而增加; 随着节理条数的增加, 试件峰值强度逐渐降低, 但降低趋势逐渐变缓并趋于某一定值。上述研究结论与目前的理论及实验研究结果的基本规律是一致的, 说明了本模型的合理性。     

Statistical Scaling of Geometric Characteristics in Millimeter Scale Natural Porous Media

We analyze statistical scaling of structural attributes of two millimeter scale rock samples, Estaillades limestone and Bentheimer sandstone. The two samples have different connected porosities and pore structures. The pore-space geometry of each sample is reconstructed via X-ray micro-tomography at micrometer resolution. Directional distributions of porosity and specific surface area (SSA), which are key Minkowski functionals (geometric observables) employed to describe the pore-space structure, are calculated from the images, and scaling of associated order- $q$ sample structure functions of absolute incremental values is analyzed. Increments of porosity and SSA tend to be statistically dependent and persistent (tendency for large and small values to alternate mildly) in space. Structure functions scale as powers $\xi (q)$ of directional separation distance or lag, $s$ , over an intermediate range of $s$ , displaying breakdown in power law scaling at large and small lags. Powers $\xi \!\!\left( q \right) $ of porosity and SSA inferred from moment and extended self-similarity (ESS) analyses of limestone and sandstone data tend to be quasi-linear and nonlinear (concave) in $q$ , respectively. We observe an anisotropic behavior for $\xi (q)$ , which appears to be mild for the porosity of the sandstone sample while it is marked for both porosity and SSA of the limestone rock sample. The documented nonlinear scaling behavior is amenable to analysis by viewing the variables as samples from sub-Gaussian random fields subordinated to truncated fractional Brownian motion or fractional Gaussian noise.