岩石弹脆性分维损伤本构模型

本文定义岩石构元中破裂面的分维值为各向同性损伤变量,而各个方向上裂纹面的累加量定义为各向异性损伤变量,并根据裂纹发育特征提出了损伤变量演化方程,从而建立起岩石脆性变形破坏过程的分维损伤本构模型。最后,利用该模型对大理岩单轴压缩应力应变曲线进行了模拟,结果说明本文提出的模型是较为合理的。     

Numerical simulation of the fracture process in cutting heterogeneous brittle material

The process of cutting homogeneous soft material has been investigated extensively. However, there are not so many studies on cutting heterogeneous brittle material. In this paper, R‐T^2D (Rock and Tool interaction), based on the rock failure process analysis model, is developed to simulate the fracture process in cutting heterogeneous brittle material. The simulated results reproduce the process involved in the fragmentation of rock or rock‐like material under mechanical tools: the build‐up of the stress field, the formation of the crushed zone, surface chipping, and the formation of the crater and subsurface cracks. Due to the inclusion of heterogeneity in the model, some new features in cutting brittle material are revealed. Firstly, macroscopic cracks sprout at the two edges of the cutter in a tensile mode. Then with the tensile cracks releasing the confining pressure, the rock in the initially high confining pressure zone is compressed into failure and the crushed zone gradually comes into being. The cracked zone near the crushed zone is always available, which makes the boundary of the crushed zone vague. Some cracks propagate to form chipping cracks and some dip into the rock to form subsurface cracks. The chipping cracks are mainly driven to propagate in a tensile mode or a mixed tensile and shear mode, following curvilinear paths, and finally intersect with the free surface to form chips. According to the simulated results, some qualitative and quantitative analyses are performed. It is found that the back rake angle of the cutter has an important effect on the cutting efficiency. Although the quantitative analysis needs more research work, it is not difficult to see the promise that the numerical method holds. It can be utilized to improve our understanding of tool–rock interaction and rock failure mechanisms under the action of mechanical tools, which, in turn, will be useful in assisting the design of fragmentation equipment and fragmentation operations. Copyright © 2002 John Wiley & Sons, Ltd.     

DEM–SPH simulation of rock blasting

A numerical model is proposed for the simulation of rock blasting. A bonded particle system is utilized to mimic the behavior of rock. The particles interact at the contact points through normal and shear springs to simulate rock elasticity. To withstand the deviatoric stresses, the particles are glued to each other. If the applied force exceeds the contact strength, local failure occurs and microcracks are developed in the synthetic rock. For simulation of gas flow, the smooth particle hydrodynamic method is implemented. The interaction of gas particles with the rock grains is assumed to follow a perfect plastic collision model in which the initial momentum of the colliding particles is preserved. A detailed examination of the interaction of gas with blast hole is investigated. It is shown that the proposed hybrid model is capable of simulating the induced shock waves in the gas together with wave propagation in the rock material. The model successfully mimics crack propagation in rock. In particular, the crushed zone around the borehole, radial cracks, and surface spalling are all captured successfully. The results of numerical analysis suggest that gas–rock interaction can, in fact, generate a few successive compressive waves in the rock specimen, causing further extension of radial cracks with time as the weaker secondary and tertiary waves interact with the crack tips.     

Modeling of Crack Initiation, Propagation and Coalescence in Uniaxial Compression

Summary ?Cracks that initiate from pre-existing discontinuities can link with other cracks or with other discontinuities and produce failure in a rock mass. The Displacement Discontinuity Method (DDM), FROCK, is used in this investigation to model experimental observations on pre-cracked specimens of gypsum. In these experiments two fractures, which were either both open or closed, were placed through the thickness of the specimens, and detailed observations of the cracking process were performed as the specimens were loaded in uniaxial compression. The following aspects are studied for both open and closed fractures: 1) crack initiation stress; 2) direction and propagation of the new cracks; 3) type of coalescence and stress at which it occurs. Modeling is done considering the actual size of the specimens. Relations between the direction of initiation for each type of crack, the orientation of the initial fractures, and the type and coalescence are established. In addition, comparisons between results from experiments and predictions from the model are presented. The numerical results are in agreement with the experiments.     

The stress-strain behaviour of rock material related to fracture under compression

Fracture is the main reason for the non-linear behaviour of hard rocks. The fracture mechanics of rock is studied in this article by analysis of the fracture process under compression. A constitutive model that describes the relationship between the macro deformation of rock and the micro fracture within rock is developed. The propagation of microcracks, the non-linearity of deformation, the loading-and-unloading hysteresis and the variation of the apparent Young's modulus and Poisson's ratio are studied using the developed model. The model simulations demonstrate that: (1) the fracture toughness, initial crack length, crack density, and Young's modulus are four crucially important parameters that affect the deformation behaviour of rock; (2) the elastic parameters (E and v) of the rock matrix should be measured in triaxial tests. If they are measured in uniaxial tests, the upper straight unloading portion of the stress-strain curve is suggested to be used for the purpose, unless the closure effect of open cracks will be included in the estimations. In addition (3), the slope of the reloading stress-strain curve is a measure of the damage in material.     

岩石细观统计渗流模型研究(Ⅰ): 理论模型

渗流模型是岩石流固耦合研究的一个关键问题。岩石在裂纹开始产生至裂纹充分贯通前，其渗透性质受内部孔隙和不断演化的微裂纹的共同控制。目前，岩石的渗流模型一般只是针对单纯的裂隙（或裂隙网络）或孔隙建立的，因此，不能很好地描述岩石裂纹扩展演化过程中的渗透性质和现象。针对这一问题，提出了岩石细观统计渗流模型，该模型将岩石裂纹演化过程中的渗透性视为一个非线性动态过程，同时，考虑了裂纹扩展演化和孔隙渗流的共同作用。因此，该模型可用于分析岩石裂纹扩展过程中的渗透性演化。     

地震岩石物理分析软件系统设计和实现

介绍了岩石物理分析软件系统的总体设计思想和软件实现思路,给出了系统的功能层次结构,做了具体的功能描述.系统采用面向对象设计方法和跨平台Qt开发工具开发,可移植性和扩充性强,具有灵活方便的图形界面和交互功能,是集岩芯实验测试、测井和地震为一体,是理论和实验相结合、方便实用的分析工具.     

Numerical simulation of the rock fragmentation process induced by two drill bits subjected to static and dynamic (impact) loading

Rock fragmentation processes induced by double drill bits subjected to static and dynamic loading are examined by a numerical method. Micro-heterogeneities of the rock are taken into account in this numerical model. For the static case, the simulated results reproduce the progressive process of brittle rock fragmentation during indentation. For the dynamic case, numerical simulations represent radial cracks, incipient chips, pulverized zones, and shell cracks. Comparing the static and dynamic cases, the dynamic loading can lead to rock fragmentation more efficiently. In addition, numerical results indicate that the dynamic pressure (P _max) plays an important role in the failure process of specimens with two indenters. Furthermore, the heterogeneity of the rock can also affect the failure modes of the rock when two indenters are used. Finally, the numerical results demonstrate the effect of the spacing between the indenters on the rock.     

土石混合体二维细观结构模型的建立与数值流形法模拟

为了揭示土石混合体在三轴循环荷载作用下的结构劣化特征和细观损伤演化过程,采用自行设计的工业CT机配套加载装置对块石含量分别为30%,40%和50%和土石混合体试样进行了低围压实时CT扫描力学试验。重点研究了块石含量对宏观应力-应变曲线、滞回环形态、裂纹几何形态参数和剪胀效应的影响。试验结果表明：反复的循环加卸载导致试样的塑性应变逐渐增大,应力滞回环呈现出稀疏-密集-稀疏形态。在相同应力幅值下,土体基质中块石的存在影响滞回环的形态,随着块石含量的增大,滞回环的面积减小,块石含量较高时,土石间咬合作用形成的骨架效应增强,从而土石混合体结构弱化过程中的能量耗散相应减弱。采用图像处理算法对试样在不同加载周数下的块石和裂纹进行了识别、提取和分析,块石含量较高时裂纹的起裂要先于低含石量的试样,不同含石量土石混合体试样在相同加载周数下的损伤程度有所不同,裂纹的面积、长度、平均宽度和分形维数随块石含量的增大而减小。由于土体和块石的高度弹性不匹配,土石混合体试样的应变局部化现象导致试样剪胀行为的差异,裂纹的扩展和宏观破裂面的形成受块石含量影响较大,土石混合体体积剪胀效应随着块石含量的增加而减弱。研究结果有助于深入理解工程扰动作用下土石混合体的损伤劣化机制,可为土石混合体有关的工程建设及防灾减灾提供必要的理论支撑。     

盾构切刀顺次破岩机制的数值模拟研究

在对盾构切刀顺次破岩实际工况提出合理简化的基础上,从岩土细观角度出发,采用颗粒离散元法建立了切刀破岩的二维数值模型,研究了两把盾构切刀顺次作用下的破岩机制和影响因素,并通过试验对切刀破岩过程中切屑堆积现象及破岩力学特性进行了验证。研究表明,刀具尖端的破坏作用最为明显;切削岩石时切削力随着切削行程不断波动,水平切削力大于垂直切削力;不同于单刀切削,切刀顺次作用时前刀刮过的岩面留下了大量残余裂纹,使得后刀所受的切削力减小;从切削性能来看,随着切削深度的增加,岩石破碎块度不断增大,切削力和裂纹数迅速增加,说明切深与切削力密切相关;切削试验观测到了切屑在前刀面堆积和切削力的波动现象,与数值模拟具有较好的一致性。     

Sound level produced during rock drilling vis-à-vis rock properties

The process of drilling, in general, always produces sound. Though sound is used as a diagnostic tool in mechanical industry, its application in predicting rock property is not much explored. In this study, an attempt has been made to estimate rock properties such as uniaxial compressive strength, Schmidt rebound number and Young's modulus using sound level produced during rotary drilling. For this purpose, a computer numerical controlled vertical milling centre was used for drilling holes with drill bit diameters ranging from 6 to 20 mm with a shank length of 40 mm. Fourteen different rock types were tested. The study was carried out to develop the empirical relations using multiple regression analysis between sound level produced during drilling and rock properties considering the effects of drill bit diameter, drill bit speed and drill bit penetration rate. The F-test was used to check the validity of the developed models. The measured rock property values and the values calculated from the developed regression model are fairly close, indicating that the developed models could be efficiently used with acceptable accuracy in prediction of rock properties.     

Micromechanical Model for Simulating the Fracture Process of Rock

Summary A micromechanical model is proposed to study the deformation and failure process of rock based on knowledge of heterogeneity of rock at the mesoscopic level. In this numerical model, the heterogeneity of rock at the mesoscopic level is considered by assuming the material properties in rock conform to the Weibull distribution. Elastic damage mechanics is used to describe the constitutive law of meso-level elements, the finite element method is employed as the basic stress analysis tool and the maximum tensile strain criterion as well as the Mohr-Coulomb criterion is utilized as the damage threshold. A simple method, similar to a smeared crack model, is used for tracing the crack propagation process and interaction of multiple cracks. Based on this model, a numerical simulation program named Rock Failure Process Analysis Code (RFPA) is developed. The influence of parameters that include the Weibull distribution parameters, constitutive parameters of meso-level elements and number of elements in the numerical model, are discussed in detail. It is shown that the homogeneity index is the most important factor to simulate material failure with this model. This model is able to capture the complete mechanical responses of rock, which includes the crack patterns associated with different loading stages and loading conditions, localization of deformation, stress redistribution and failure process. The numerical simulation of rock specimens under a variety of static loading conditions is presented, and the results compare well with experimental results.     

岩石物性与岩体结构物性研究进展

利用地球物理属性定量化研究岩体结构的成果在国内外较少见。由于风化和构造等原因,浅层岩石与一定范围内岩体的地球物理性质有很大的差别。本文从Archie公式出发介绍岩石物性研究现状,在岩体结构和工程物探研究的基础上,除了介绍岩体结构物性的概念和研究现状外,还分析了以岩心为约束条件下电阻率与波速联合的研究现状,初步探索后认为在工程上能用各种地球物理参数帮助精确描述岩体结构,因此岩体结构物性是一个新的研究方向。     

反倾层状岩体斜坡弯曲-拉裂两种失稳破坏之判据探讨

对反倾层状岩体斜坡弯曲-拉裂的失稳破坏判据,已有研究分别基于两种力学模型进行推导,即竖直压杆弹性屈曲稳定和平直梁弯折破坏模型,但对层间错动阻力及挠度产生附加弯矩等因素未加以考虑,不尽合理。在反倾斜坡岩层受力分析基础上,建立考虑了板侧层间错动阻力的下端嵌固、上端自由的斜置等厚弹性悬臂板梁模型,统一地通过瑞利-里兹能量方法,推导了弹性屈曲临界条件和嵌固端弯折破坏临界条件。实例计算及讨论表明,弹性屈曲判据适用于陡立岩层;而中-陡反倾岩层应主要为弯折破坏,但层间的力学性质对弯折临界判据值具有较大影响。     

高瓦斯煤的渗透性试验

煤岩体变形和强度以及流体在多孔隙裂隙煤中的渗流规律,是高瓦斯煤层开采中关注的问题。阐述了高瓦斯煤力学介质属性、微结构模型、渗透特性及其孔裂隙和破碎块度的分形特征;利用电液伺服岩石力学试验系统,以数控瞬态渗透法进行了煤样全应力应变过程的电液伺服试验,研究了全应力应变过程中煤样渗透性的变化特征。试验结果显示:煤样的力学性能与其微结构和微孔隙特征密切相关,渗透率变化与试样内部裂隙发展变化过程密切相关。     

Numerical Analysis of Blast-Induced Stress Waves in a Rock Mass with Anisotropic Continuum Damage Models Part 2: Stochastic Approach

Summary This paper reports the second part of the study carried out by the authors on the underground explosion-induced stress wave propagation and damage in a rock mass. In the accompanying paper reporting the first part of the study, equivalent material properties were used to model the effects of existing cracks and joints in the rock mass. The rock mass and its properties were treated as deterministic. In this paper, existing random cracks and joints are modeled as statistical initial damage of the rock mass. In numerical calculation, an anisotropic continuum damage model including both the statistical anisotropic initial damage and cumulative damage dependent on principal tensile strain and stochastic critical tensile strain is suggested to model rock mass behavior under explosion loads. The statistical estimation of stress wave propagation in the rock mass due to underground explosion is evaluated by Rosenblueth's point estimate method. The suggested models and statistical solution process are also programmed and linked to Autodyn3D as its user's subroutines. Numerical results are compared with the field test data and those presented in the accompanying paper obtained with equivalent material property approach.     

三峡水库碳酸盐岩区岩溶作用与斜坡破坏

三峡库区175 m蓄水以来,巫峡段碳酸盐类岩溶岸坡在周期性水位变动下岩体劣化强烈,新生或加速形成了大量地质灾害。为探讨在周期性水位变动下碳酸盐岩类岸坡的强度弱化规律,文章从岩石(体)物理结构、化学性质、力学性质等方面开展研究,通过在巫峡最具代表性的6处库岸段开展原位岩体回弹强度测试、原位点荷载试验以及室内干湿循环试验、岩石矿物成分分析、岩石表观裂隙扫描等试验,获取水位变动条件下碳酸盐类岩石(体)的强度弱化数据。原位岩体回弹强度测试结果表明,原位岩体单一年度的强度弱化率为0.3%~25.9%,岩体强度弱化主要沿结构面产生;室内干湿循环试验结果表明,在50次干湿循环后,岩石强度弱化率为16.4%~23.9%,变形模量弱化率为17.1%~24.9%;岩石矿物成分分析结果表明,在100次循环后,CaO的溶失量为0.5%~5.6%;岩石表观裂隙扫描结果表明,岩块表面裂纹发育位置发生了水蚀痕迹加重、溶孔变大、裂纹延伸等变形现象。基于干湿循环试验数据,建立岩石强度弱化函数,推导出各点位上的指数函数弱化计算模型。该计算模型可用来预测岩石强度、变形模量与水位循环次数间的数值关系。最后以曲子滩危岩“溃屈”式破坏计算为例,探讨了岩体强度弱化后的灾变效应。研究提出的工作方法和通过试验所得到的数据可为三峡库区岸坡劣化带的防治提供数据和技术支撑。     

Fuzzy-random probabilistic analysis of rock mass responses to explosive loads

This paper addresses the effects of randomness of initial damage in a rock mass and the critical tensile strain of the rock material on its dynamic responses and damage under explosive loads. A fuzzy definition is proposed to describe the fuzzy nature of failure phenomenon in a rock mass. The initial damage of the rock mass is estimated using the longitudinal and transverse elastic wave velocities. By using statistical analysis, the initial damage of the rock mass is found having the Beta distribution. The statistical estimation of a damage state and properties of randomly damaged rock mass are evaluated by the Rosenbluth's point estimate method. In numerical calculation, an isotropic continuum damage model with the initial damage and the cumulative damage dependent on an equivalent tensile strain is suggested to model the rock mass behavior under blast loads. A Beta distribution is proposed to represent the probabilistic distribution of the damage variable of the rock mass under explosive loads. Several types of membership functions are suggested to represent the fuzziness of material failure. Based on the fuzzy–random probabilistic theory, a model including both the effects of randomness and fuzziness is proposed for the failure analysis of rock mass under explosive loads. The suggested models are coded and linked with an available computer program AUTODYN2D through its user's subroutine capacity. The fuzzy failure probability and dynamic responses of the rock mass are calculated. Numerical results are compared with those obtained from independent field tests.     

岩桥直剪细观破坏特征与剪胀效应研究

节理岩体的剪切贯通机制影响着边坡的稳定性。为揭示锁固段型非贯通节理岩体在不同连通率和法向应力下的破坏特征,在室内直剪试验中结合高速摄影与AE特征参数分析其剪切全过程及剪胀效应。结果表明:节理岩体直剪试验中,法向应力的增大及节理连通率的下降会致使峰值剪切应力及峰值剪切位移增大;节理连通率与法向应力对其破坏特征具显著影响,表现为节理连通率较高且法向应力较小时呈直接剪断的特性,节理连通率降低后呈拉剪复合破坏,出现剪胀现象,而法向应力的增大使得剪胀效应呈波动现象;AE特征与岩桥贯通过程一致,事件数峰值随节理连通率的降低及法向应力的增大而增大且位于峰后。试验得到的岩桥细观破坏特征与剪胀效应对研究锁固段型岩质边坡的贯通破坏机制具指导意义。