Fracture behaviors of columnar jointed rock mass using interface mechanics theorem

For a special geological structure of columnar jointed rock mass(CJRM),its mechanical properties are strongly affected by the columnar joints.To describe the fracture behaviors of CJRM using the basic theories of interface mechanics for composite materials,the interface stresses of the vertical and horizontal joints,which are the two primary joints in the CJRM under triaxial compression,are studied,and their mathematical expressions are derived based on the superposition principle.Based on the obtained interface stresses of the vertical and horizontal joints in the CJRM,the crack initiation of the joint interface in the CJRM is studied using the maximum circumferential stress theory in fracture mechanics.Moreover,based on this investigation,the fracture behaviors of CJRM are analyzed.According to the results of similar material physical model tests for the CJRM,the theoretical study is verified.Finally,the influence of the mechanical parameters of the CJRM on the joint interface stress is discussed comprehensively.

Coordination and evolution mechanism of fractal crack network in mining rock mass destruction

Based on the natural characters of stratum, complicated geological mining conditions and the essence of mining rock mass destruction, the complexity of rock mass destruction caused by miningw as analyzed. The inner link between rock mass destruction phenomena caused by mining and nonlinear science was revealed. There are numerous cracks in natural rock mass. The cracks’ distribution is irregular and is of statistical fractal structure. Self-organizational nonlinear evolution of the inner structure flaws leads to the rock mass destruction with external force. The evolution includes single fault’s fractal development, formation and evolution of fractal crack network and coordination of fractal crack network, etc. The law of fractal crack network’s evolution was introduced, at the same time, the coordination of fractal crack network was analyzed. Finally, based on coordination the principal equation of mining-caused subsidence of structural rock mass was established and its steady-state solution and unsteady-state solution were found.

A new estimation method and an anisotropy index for the deformation modulus of jointed rock masses

The deformation modulus of a rock mass is an important parameter to describe its mechanical behavior.In this study,an analytical method is developed to determine the deformation modulus of jointed rock masses,which considers the mechanical properties of intact rocks and joints based on the superposition principle.Due to incorporating the variations in the orientations and sizes of joint sets,the proposed method is applicable to the rock mass with persistent and parallel joints as well as that with nonpersistent and nonparallel joints.In addition,an anisotropy index AIdmfor the deformation modulus is defined to quantitatively describe the anisotropy of rock masses.The range of AIdmis from 0 to 1,and the more anisotropic the rock mass is,the larger the value of AIdmwill be.To evaluate the proposed method,20 groups of numerical experiments are conducted with the universal distinct element code(UDEC).For each experimental group,the deformation modulus in 24 directions are obtained by UDEC(numerical value)and the proposed method(predicted value),and then the mean error rates are calculated.Note that the mean error rate is the mean value of the error rates of the deformation modulus in 24 directions,where for each direction,the error rate is equal to the ratio of numerical value minus predicted value to the numerical value.The results show that(i)for different experimental groups,the mean error rates vary between 5.06%and 22.03%;(ii)the error rates for the discrete fracture networks(DFNs)with two sets of joints are at the same level as those with one set of joints;and(iii)therefore,the proposed method for estimating the deformation modulus of jointed rock masses is valid.

Determination of geological strength index of jointed rock mass based on image processing

The geological strength index(GSI) system,widely used for the design and practice of mining process,is a unique rock mass classification system related to the rock mass strength and deformation parameters based on the generalized Hoek-Brown and Mohr-Coulomb failure criteria.The GSI can be estimated using standard chart and field observations of rock mass blockiness and discontinuity surface conditions.The GSI value gives a numerical representation of the overall geotechnical quality of the rock mass.In this study,we propose a method to determine the GSI quantitatively using photographic images of in situ jointed rock mass with image processing technology,fractal theory and artificial neural network(ANN).We employ the GSI system to characterize the jointed rock mass around the working in a coal mine.The relative error between the proposed value and the given value in the GSI chart is less than 3.6%.

Experimental study on acoustic emission characteristics of jointed rock mass by double disc cutter

The characteristics of joints are crucial factors which influence the penetration efficiency of tunnel boring machine(TBM).Based on the theoretical study,numerical simulation and experimental research,many researchers have studied the interaction between TBM disc cutters and jointed rock mass.However,in most of these works,the effect of joint on rock fragmentation by double disc cutter has been scarcely investigated.Thus,the effects of joint orientation and joint space on rock fragmentation by double disc cutter are highlighted in this study.During the test,jointed concrete specimens are adopted to simulate jointed rock mass.Improved RYL-600rock shear rheological instrument was employed during the indentation process under disc cutters,and acoustic emission location system was used to analyze the rock damage and physical deterioration.The results show that there are four failure modes and three modes of crack initiation and propagation in jointed rock mass.It is concluded that the existing joint planes have obviously restrained the crack initiation and propagation during the rock fragmentation process.The results also indicate that samples are damaged most seriously when joint orientation equals60°,which is proved to be the optimum joint orientation in TBM penetration.

Development of an improved three-dimensional rough discrete fracture network model:Method and application

Structure plane is one of the important factors affecting the stability and failure mode of rock mass engineering.Rock mass structure characterization is the basic work of rock mechanics research and the important content of numerical simulation.A new 3-dimensional rough discrete fracture network(RDFN3D)model and its modeling method based on the Weierstrass-Mandelbrot(W-M)function were presented in this paper.The RDFN3D model,which improves and unifies the modelling methods for the complex structural planes,has been realized.The influence of fractal dimension,amplitude,and surface precision on the modeling parameters of RDFN3D was discussed.The reasonable W-M parameters suitable for the roughness coefficient of JRC were proposed,and the relationship between the mathematical model and the joint characterization was established.The RDFN3D together with the smooth 3-dimensional discrete fracture network(DFN3D)models were successfully exported to the drawing exchange format,which will provide a wide application in numerous numerical simulation codes including both the continuous and discontinuous methods.The numerical models were discussed using the COMSOL Multiphysics code and the 3-dimensional particle flow code,respectively.The reliability of the RDFN3D model was preliminarily discussed and analyzed.The roughness and spatial connectivity of the fracture networks have a dominant effect on the fluid flow patterns.The research results can provide a new geological model and analysis model for numerical simulation and engineering analysis of jointed rock mass.

Equivalent elastic compliance tensor for rock mass with multiple persistent joint sets:Exact derivation via modified crack tensor

Discontinuities constitute an integral part of rock mass and inherently affect its anisotropic deformation behavior.This work focuses on the equivalent elastic deformation of rock mass with multiple persistent joint sets.A new method based on the space geometric and mechanical properties of the modified crack tensor is proposed,providing an analytical solution for the equivalent elastic compliance tensor of rock mass.A series of experiments validate the capability of the compliance tensor to accurately represent the deformation of rock mass with multiple persistent joint sets,based on conditions set by the basic hypothesis.The spatially varying rules of the equivalent elastic parameters of rock mass with a single joint set are analyzed to reveal the universal law of the stratified rock mass.

基于AttentionR2U-net的岩石(体)关键节理智能识别与参数提取

针对岩石(体)表面复杂节理网中关键节理的智能识别与参数提取问题,提出一种基于AttentionR2U-net网络与节理几何特征模型耦合识别的方法.在R2U-net网络的基础上引入注意门(attentiongate)改进网络,通过定性与定量的方法对边坡节理图像和混凝土、龟裂土、常见脆性岩石裂隙图像的识别结果分别作准确性及泛化能力检验;利用AttentionR2U-net网络耦合节理几何特征的方法识别关键节理,提取原始节理和关键节理的几何参数并对其迹长、面积及倾角作差异性分析.研究结果表明:针对岩石(体)节理识别,本文算法的Dice相似系数从U-net网络的0.965提升至0.990,且明显优于传统算法,故本文算法在岩石(体)节理识别上具有更强的可靠性与优越性;针对混凝土、龟裂土和大理岩、花岗岩、砂岩等脆性岩石裂隙的识别,本文算法的Dice相似系数均在0.953以上,故本文算法具有较强的泛化能力.与原始节理网络相比,关键节理网络优势迹长由0.732m显著增大至1.835m,节理倾角分布形式和优势倾角组均不变,优势迹长和倾角的节理占比均显著增大.

单节理深埋隧洞开挖瞬态卸荷响应机理数值模拟研究

采用颗粒流数值模拟重现深埋单节理隧洞瞬态卸荷过程,从应力状态、变形特征、裂纹扩展等多角度探析节理特征对双江口水电站进厂交通洞瞬态卸荷效应的影响,研究表明:节理对深埋隧洞瞬态卸荷的应力调整过程有着重要的影响,应力集中区将由硐室底角、拱顶转移至节理尖端。随着节理长度的增加,节理尖端应力集中区域离自由面距离逐渐增大,围岩损伤区逐步向岩体深部发生迁移。不同节理角度下,微裂纹数目差异性显著,其中60°和30°节理围岩中的微裂纹数量较多;此外,压剪裂纹所占比例随着节理角度的增大呈现先增大后减小的变化趋势,45°时达最大。研究成果对水工隧洞开挖卸荷作用下围岩破坏机制认识和评价具有指导意义。

基于掌子面三维几何图像计算J_(v)值的方法研究

为解决传统人工素描的诸多弊端,提出在掌子面三维几何图像的基础上提取掌子面围岩结构面特征。使用相机和激光雷达采集掌子面围岩数据,建立隧道掌子面三维实景模型;基于围岩结构面法向量的差异,在三维模型上对围岩结构面进行识别;采用卷积神经网络算法训练软件基于地质工程师地质素描识别围岩节理迹线;将三维模型识别结果与图像识别训练进行结合判识,实现掌子面围岩节理迹线的自动识别;基于自动识别结果得到掌子面围岩的岩体体积节理数J_(v),从而实现对围岩完整程度的判识。将该方法应用于池黄铁路黄坑隧道和岭上村隧道进行掌子面围岩完整度分析,结果表明:该方法可获取高精度的掌子面三维模型,能够对隧道掌子面围岩的完整度进行快速、准确的判识,实现隧道地质信息编录。

岩体裂隙网络渗流模型及隧道掌子面渗流预测研究

【目的】岩体的裂隙特征直接影响其渗流特性,随着隧道工程中与岩体裂隙渗流有关的突涌水问题日益突显,为提高隧道建设与维护的安全性及稳定性,建立一套隧道掌子面岩体裂隙渗流量的预测计算程序。【方法】基于MATLAB平台,利用Monte-Carlo随机模拟方法编制岩体裂隙二维网络模型生成程序及稳定渗流数值计算程序,研究了裂隙岩体表征单元体积(REV)的尺寸效应及渗透张量的确定方法。将该程序应用于某地铁隧道,在现场调查及裂隙参数统计的基础上,对隧道掌子面裂隙岩体稳定渗流量和渗透系数进行预测。【结果】结果显示:(1)掌子面岩体裂隙方向角服从正态分布,迹长及间距服从负指数分布;(2)裂隙岩体表征单元体(REV)的最佳尺寸为裂隙迹长均值的14倍;(3)计算了裂隙岩体的渗透系数椭圆、渗透张量及渗透主轴,分析结果表明该隧道掌子面裂隙岩体具有强烈的渗透各向异性特征。【结论】结果表明:岩体裂隙的网络模型对于隧道工程岩体的水力学问题研究有不可替代的作用。所编程序可以预测隧道开挖过程中掌子面的渗流量和渗透主方向,为采取经济、合理的地下水控制措施提供依据。

破裂过程模拟的可变形圆化多边形离散单元法

为研究工程中岩体内部裂纹的萌生、拓展和贯通机制,模拟其破裂时接触碰撞的全过程,提出可变形圆化多边形离散单元法。该方法将有限单元法与圆化多边形离散单元法进行耦合,采用圆化多边形离散单元法计算非连续岩体间的相互接触作用,连续体内部的应力应变状态则通过有限单元法进行分析。为准确模拟裂纹演化过程,在有限单元间插入节理单元,采用虚拟裂缝模型和具有拉伸截断的摩尔-库仑准则描述节理单元在拉伸、剪切等不同破坏模式下的力学状态。最后模拟巴西圆盘开裂、单切口弯梁开裂及块体冲击破坏试验。研究结果表明:所提出方法能准确模拟岩体从连续体变化为非连续体的破裂过程。

基于裂隙网络有限元的破碎岩体边坡变形破坏演化规律

针对节理裂隙在降雨入渗、人工活动等作用下持续劣化引发边坡变形破坏问题,以广西在建的天峨—巴马高速公路沿线某破碎岩体边坡为依托,采用裂隙单元和实体单元相结合的方式对破碎裂隙岩体进行建模,模拟了该边坡在节理裂隙持续劣化影响下的变形和破坏过程,分析了破碎岩体边坡的整体和局部变形、破坏的发展规律。

基于3D打印的类节理岩体模型及力学特性

节理裂隙构造分布对岩体变形与破坏特性具有关键控制作用,厘清节理构造及岩体力学特性对于指导工程稳定性具有重要意义。3D打印技术在岩石力学方面的应用为节理岩体力学特性研究提供了有效手段。基于3D打印技术提出一种节理岩体制备方法,开展单轴压缩测试分别分析了实心试样、RDFN模型和DFN试样的变形特性及破裂模式,讨论了透明硬水晶与PLA材料在预制节理岩体力学特性分析的适用性,对比了冷冻处理下透明硬水晶材料的力学变化。研究发现:基于PLA树脂的3D打印材料在单轴压缩条件下发生了膨胀扩容,并呈现显著的塑性变形特征,与岩石的力学性质有较大差异;硬水晶材料的破坏模式为明显的“X”共轭剪切变形破坏特征,峰前应力-应变曲线特征与岩石接近,含裂隙试样的表现为沿近似45°斜面的压剪破坏;裂隙网络的存在会显著降低类岩体模型的抗压强度,粗糙RDFN的类节理岩体模型强度高于直线型DFN类节理岩体模型,试样发生斜截面剪切破坏时,节理模型增强了裂隙系统的锁固效应;类节理岩体表现出一定的尺寸效应,并受PLA材料高塑性特性影响;承压强度实心试件总体来说最强,RDFN模型次之,DFN模型最小,3类模型强度存在一定的尺寸效应特征。冷冻处理后,实心水晶模型试样的峰值强度降低约56.57%并呈现一定脆性特征,含节理模型的破坏模式为单斜面剪切破坏,开挖含孔洞裂隙体产生劈裂破坏,顶部及底部产生微裂纹,表现出与岩体相近的结构控制型破坏模式,表明开展冷冻条件下的类节理岩体模型处理可以用来开展节理岩体力学特性研究。

分段黏结非连续变形分析方法及其在砂岩破裂分析中的应用

深部采煤面临高地温、高地压、高岩溶水压及开采扰动的综合影响,岩石的非连续变形及破裂行为也比浅部更为复杂,开发模拟岩石破裂行为的数值计算方法,进行从实验室尺度到工程现场尺度的分析是研究岩石破裂相关灾害规律和机理的重要手段。非连续变形分析方法 (Discontinuous Deformation Analysis,DDA)在接触理论、块体积分、计算收敛中具有严格的数学基础,采用子块体剖分和黏结处理的DDA模型可以有效模拟岩石及裂隙岩体从连续弹性变形到渐进断裂和完全破断的全过程。基于边-边黏结效应分段线性表征的朴素思想,提出分段式边-边黏结模型,将线性及非线性黏结本构关系通过分段中心点处的成对罚弹簧进行等效表征,嵌入三角形剖分的非连续变形分析求解框架内,实现模拟岩石断裂的优化DDA模型。通过简支梁中心受压、单轴压缩、巴西劈裂案例的变形、应力结果分析,验证了优化模型的准确性,获得了边-边黏结模型中分段数目、黏结刚度比、切向法向刚度比等参数的合理取值范围;通过完整及带孔洞的砂岩试样的单轴压缩试验,阐明了块体弹性模量、泊松比等变形参数及黏结单元抗拉强度、黏聚力、内摩擦角等强度参数的赋值方法,验证了优化模型在应力-应变曲线,裂纹起裂位置捕获的准确性;通过含单裂隙及组合裂隙的砂岩巴西圆盘劈裂试验的分析,验证了优化模型在裂纹起裂、裂纹扩展、多裂纹交汇等复杂裂隙扩展问题中的适用性;采用分段式边-边黏结的优化模型可推广用于包含复杂裂隙网络的岩体破坏规律和机理的分析。

不同加载速率下X型节理间相互干涉对岩体力学特性影响

X型节理岩体广泛分布于自然界,准确认识不同加载速率下X型节理岩体破裂失效机制对相关岩体工程的科学评价至关重要。文中通过制作X型节理岩体相似材料试件,改变主次相交节理的几何特征及加载速率,采用DIC技术实时监测主次节理尖端扩展,研究X型节理间相互干涉对岩体力学特性的影响规律。结果表明,不同加载速率下X型节理间的干涉效应对弹性变形阶段及屈服阶段的力学特性具有显著影响。对于含45°主节理的同倾向X型节理岩体,随着次节理倾角的增大,岩体起裂强度先减小后增大;而对于反倾向X型节理岩体,随着次节理倾角的增大,岩体起裂强度先增大后减小,且β=120°时干涉效应最强,其加载速率效应也先增大后减小。

3D打印技术在岩体模型试验中的应用探讨

3D打印技术因具有易成型、可复制、可定制的特点,被广泛应用于各个领域。本文从3D打印成型原理出发,介绍可应用于岩体模型试验的2种打印技术及打印材料的性质;以含结构面网络的岩体试件制作方法、模型相似条件与试验步骤等为基础,探讨3D打印技术应用于岩体模型试验的可行性和路径,可以为该类模型试验提供一定的借鉴和参考。

含交叉裂隙节理岩体单轴压缩破坏机制研究

对含交叉裂隙相似材料试件进行单轴压缩试验,用Abaqus对含交叉裂隙节理岩体进行应力分析,研究了含交叉裂隙节理岩体单轴压缩下的破坏机制。结果表明:交叉裂隙的主裂隙与加载方向呈30°、45°时,主裂隙是裂隙扩展及破坏的控制裂隙,此时含交叉裂隙岩体强度高于含单向裂隙岩体,是由于主裂隙裂尖最大环向应力σθmax低于单向裂隙;主裂隙与加载方向呈0°或90°时,次裂隙是控制裂隙;主裂隙与加载方向呈0°时,大部分次裂隙裂尖σθmax及裂尖最大应力强度因子KⅡmax高于单向裂隙,因此,此时大部分含交叉裂隙岩体强度低于含单向裂隙岩体;在主裂隙与加载方向呈90°工况组中,主、次裂隙夹角为45°时,次裂隙裂尖KⅡmax最大,所以此工况组中此时强度最低。

节理几何特征对预裂爆破效果影响的数值模拟

运用有限元软件AUTODYN 2D计算爆炸荷载与离散元软件UDEC模拟节理岩体相结合的方法研究了节理几何特征对预裂爆破的影响。通过计算可知,预裂爆破时炮孔间的节理组对预裂成缝的影响明显,当节理法线与炮孔连线夹角在一定范围内时,预裂缝沿炮孔连线方向的平直程度随节理与炮孔连线夹角的增大而逐渐趋于平直,其中当节理组与炮孔连线夹角为90°时成缝效果最好,裂缝与炮孔连线基本重合,与理论分析较一致;节理间距对预裂爆破有较大影响,相同条件下节理间距越小,越难形成连通裂缝,减小炮孔间距有利于小节理间距情况下的预裂缝贯通。

露天矿节理岩体边坡稳定性研究

针对眼前山露天矿南帮节理岩体边坡的结构特征,通过现场节理调查及统计分析,采用Monte-Carlo随机模拟方法,进行了节理三维网络的计算机模拟,研究确定了南帮边坡的节理岩体强度和破坏模式。通过滑动面自动搜索及FLAC数值模拟,系统地计算分析了南帮节理岩体边坡现执行开采和调整方案随采场逐渐下延的稳定状况,指出将三并段边坡的台阶坡面角由65°调整为60°可以从根本上改善眼前山露天矿南帮边坡的稳定状况,在矿山服务年限内满足开采的稳定性要求。