Rock burst laws in deep mines based on combined model of membership function and dominance-based rough set

Rock bursts are spontaneous, violent fracture of rock that can occur in deep mines, and the likelihood of rock bursts occurring increases as depth of the mine increases. Rock bursts are also affected by the compressive strength, tensile strength, tangential strength, elastic energy index, etc. of rock, and the relationship between these factors and rock bursts in deep mines is difficult to analyze from quantitative point. Typical rock burst instances as a sample set were collected, and membership function was introduced to process the discrete values of these factors with the discrete factors as condition attributes and rock burst situations as decision attributes. Dominance-based rough set theory was used to generate preference rules of rock burst, and eventually rock burst laws analysis in deep mines with preference relation was taken. The results show that this model for rock burst laws analysis in deep mines is more reasonable and feasible, and the prediction results are more scientific.     

煤岩动力灾害的弱化控制机理及其实践

煤岩动力灾害的实质是能量积聚与耗散的自组织临界过程，当煤岩体中所积聚的弹性能达到其极限冲击能时，就会发生冲击矿压．实验室研究发现，弹脆性煤体是能量积聚与耗散的主体，顶板关键层（坚硬厚层砂岩顶板）的运移则会导致能量积聚与耗散，加速失去动态平衡．以煤岩冲击倾向性与顶板强度及厚度的关系为基础，依据能量积聚与耗散理论，提出了煤岩动力灾害的强度弱化机理，即通过钻孔卸压与深孔卸压爆破来弱化煤岩体的强度，降低煤岩体的聚能能力，释放煤岩体中所积聚的大量弹性能，使得煤岩体中所积聚的弹性能达不到最小冲击能，同时利用电磁辐射监测仪来检验煤岩体强度弱化治理的效果，以达到消除或降低冲击危险的目的．通过在三河尖煤矿9202高冲击危险工作面的生产实践，充分证明了这种技术的有效性．     

基于改进熵权-突变级数法的岩爆等级评判

为能够准确预测岩爆等级,从岩性、应力、围岩三方面选取岩爆发生的五个因素作为预测评价指标,通过改进后的熵权公式来计算评价指标的重要程度;结合突变级数法中多维的印第安人茅舍模型对无量纲处理后的岩爆样本数据进行归一化计算得到突变级数值,并划分岩爆等级区间。最后将此方法应用在江边水电站隧道岩爆预测中。结果表明:利用该方法评判岩爆等级,模型维数较多,评判结果客观、准确,和实际工程情况一致,与其他方面相比具有一定优势。     

直剪作用下不共面断续节理岩桥 破断试验与数值研究

在伺服控制剪切加载系统下对不共面类岩石断续节理试件进行正向、反向直剪试验,研究直剪下不共面断续节理的岩桥破断机理和剪切规律,试验研究发现,直剪作用下不共面断续节理岩桥破坏过程具有明显的阶段性,经历线弹性阶段、裂纹起裂扩展阶段、岩桥断裂贯通阶段、剪切面爬坡咬合阶段和残余摩擦阶段5个阶段,正向剪切下岩桥呈齿形破断面,反向剪切作用下岩桥产生沿直剪方向贯通的带形破断面,与正向剪切相比,反向剪切下节理的初裂抗剪强度和峰值抗剪强度较大,裂纹倾角、法向应力和相邻节理搭接比例是影响试件初裂抗剪强度和峰值抗剪强度的主要因素。采用FLAC3D对正向、反向直剪作用下不共面断续节理的岩桥破断、剪切破断面的形成过程进行数值试验,数值试验结果和类岩石直剪试件的试验结果基本吻合,数值试验揭示了直剪作用下不共面断续节理岩桥的拉裂破坏和破断面的剪切屈服机理。     

Numerical Simulation of Rock Burst in Circular Tunnels Under Unloading Conditions

Rock burst in a circular tunnel under high in-situ stress conditions was investigated with a numerical method coupled the rock failure process theory (RFPA) and discontinuous deformation theory (DDA).Some numerical tests were carraied out to investigate the failuer patterns of circular tunnel under unloading conditions.Compared the results under loading conditions, the shapes of failure zones are more regular under the unloading conditions.The failure patterns in the same type of rock mass are clearly different because of non-homogeneity of the rock material.The extension of cracks shows some predictability with an increasing of in-situ stress.When the homogeneity index of rocks (m) is either relatively high or low and lateral pressure coefficients (λ) is high, the number of regular shear slide cracks decreases and the probability of a rock burst also becomes lower.Our numerical simulation results show that the stability of surface rock and the natural bedding stratification of rock material greatly affect rock bursts.Installing bolts with due diligence and suitably can effectively prevent rock bursts.However, it is not effective to control rock bursts by releasing the strain energy with normal pre-boreholes.     

Failure mechanism and stability control of a large section of very soft roadway surrounding rock shear slip

The measured data and simulation test phenomenon of surrounding rock deformation and failure at the project site indicate that shear failure which firstly occurs in surrounding rock, block slip and second shear failure are the root cause of deformation and damage of supporting structure of the surrounding rock at a large scale. We derived limit load of surrounding rock shear slip failure and reasonable support resistance of given load by means of shear slip line field theory, discussed the main factors which influence the limit load of surrounding rock. Shear slip line field and limit load of circular tunnel surrounding rock were obtained by means of physical simulation test, which agreed well with the theoretical analysis results. Based on the theoretical analysis and physical simulation test, the cause deformation and failure at large scale of Xinshanghai No. 1 coal mine big section ingate was analyzed, and the shear failure resistance and block slip in surrounding rock were proposed as the core technical supporting ideas. Proper range of supporting resistance which came from calculation was suggested. The support scheme which is mainly composed of large grouting anchor, sprayed anchor net support technique and full-face grille concrete finally ended the dilemma of repeated failure and mending of ingate and created critical conditions for smooth production in the coal mine.     

Macro and meso characteristics evolution on shear behavior of rock joints

Direct shear tests were conducted on the rock joints under constant normal load(CNL), while the acoustic emission(AE) signals generated during shear tests were monitored with PAC Micro-II system. Before and after shearing, the surfaces of rock joints were measured by the Talysurf CLI 2000. By correlating the AE events with the shear stress-shear displacement curve, one can observe four periods of the whole course of shearing of rock joints. By the contrast of AE location and actual damage zone, it is elucidated that the AE event is related to the morphology of the joint. With the increase of shearing times, the shear behavior of rock joints gradually presents from the response of brittle behavior to that of ductile behavior. By combining the results of topography measurement, four morphological parameters of joint surface, S p(the maximum height of joint surface), N(number of islands), A(projection area) and V(volume of joint) were introduced, which decrease with shearing. Both the joint roughness coefficient(JRC) and joint matching coefficient(JMC) drop with shearing, and the shear strength of rock joints can be predicted by the JRC-JMC model. It establishes the relationship between micro-topography and macroscopic strength, which have the same change rule with shearing.     

Quantitative calculation for the dissipated energy of fault rock burst based on gradient-dependent plasticity

The capacity of energy absorption by fault bands after rock burst was calculated quantitatively according to shear stressshear deformation curves considering the interactions and interplaying among microstructures due to the heterogeneity of strain softening rock materials. The post~peak stiffness of rock specimens subjected to direct shear was derived strictly based on gradientdependent plasticity, which can not be obtained from the classical elastoplastic theory. Analytical solutions for the dissipated energy of rock burst were proposed whether the slope of the post-peak shear stress-shear deformation curve is positive or not. The analytical solutions show that shear stress level, confining pressure, shear strength, brittleness, strain rate and heterogeneity of rock materials have important influence on the dissipated energy. The larger value of the dissipated energy means that the capacity of energy dissipation in the form of shear bands is superior and a lower magnitude of rock burst is expected under the condition of the same work done by external shear force. The possibility of rock burst is reduced for a lower softening modulus or a larger thickness of shear bands.     

岩溶地区隧道设计探讨

可溶岩分布面积约占我国国土面积的三分之一,大量隧道的修建使得越来越多的隧道需穿过可溶岩地带。然而可溶岩往往伴随着岩溶洞穴、地下暗河、破碎带等复杂地质构造,这无形中给隧道的修建带来极大的困难。隧道设计,围岩分级是关键,围岩级别的确定离不开超前地质预报。有鉴于此,重点分析了隧道超前地质预报和围岩分级,同时论述了隧道选线和隧道支护等方面,旨在与各位同行交流探讨,共同推进岩溶隧道设计技术的发展,降低甚至避免岩溶对隧道修建的影响。     

煤体剪切破坏过程电磁辐射与声发射研究

用剪切实验台和电磁辐射、声发射接收系统对煤体剪切破坏的电磁辐射、声发射特征进行了研究 .结果表明 ,煤体剪切破坏过程中电磁辐射和声发射有两种类型 :一种是在加载初期出现较高的强度 ,加载中间阶段有较为平静的区域 ,主破坏发生前又逐渐增强 ,破坏时出现较高的强度 ,破坏后逐渐减弱 ;另一种是随应力增大电磁辐射和声发射持续增强直至破坏 ,破坏后减小 .试验结果与预测冲击矿压、煤与瓦斯突出等动力灾害的现场测试结果吻合 .     

岩石材料动态断裂韧性的实验研究

为了研究岩石类材料的动态力学性能及动态破坏机理,防止出现岩石爆裂造成灾难性破坏,根据中心裂纹圆盘试件断裂韧性测试方法和分离式霍普金森压杆的基本原理,在SHPB装置上测试了花岗岩的动态断裂韧性。对测试结果按照SHPB基本原理进行处理,以试件两端平均载荷带入准静态公式得到动态断裂韧性。处理结果表明,用试件两端平均载荷获得岩石动态断裂韧性的实验方法有效的;花岗岩的动态断裂韧性具有加载速率相关性,随着加载速率的增加断裂韧性增大。     

岩石节理剪切强度研究

利用断裂力学理论分析了纯剪切应力状态和双向压应力状态作用下节理模型的断裂机制。在已有的数值模拟和实验基础上,通过引入分形维数,推导了粗糙节理的摩尔-库仑剪切强度的改进公式。该公式的分析结果显示,节理尺度相对于岩体尺寸越大,节理的抗剪强度就越低,并且节理的抗剪切强度与分形维数的关系是一种非线性增长关系。     

Focal mechanism caused by fracture or burst of a coal pillar

As a regional, real-time and dynamic method, microseismic monitoring technology is quite an appropriate technology for forecasting geological hazards, such as rock bursts, mine tremors, coal and gas outbursts and can even be used to prevent or at least reduce these disasters. The study of the focal mechanisms of different seismic sources is the prerequisite and basis for forecasting rock burst by microseismic monitoring technology. Based on the analysis on the mechanism and fracture course of coal pillars where rock bursts occur mostly, the equivalent point source model of the seismicity caused by a coal pillar was created. Given the model, the seismic displacement equation of a coal pillar was analyzed and the seismic mechanism was pointed out by seismic wave theory. The course of the fracture of the coal pillar was simulated closely in the laboratory and the equivalent microseismic signals of the fractures of the coal pillar were acquired using a TDS-6 experimental system. The results show that, by the pressure and friction of a medium near the seismic source, both a compression wave and a shear wave will be emitted and shear fracture will be induced at the moment of breakage. The results can be used to provide an academic basis to forecast and prevent rock bursts or tremors in a coal pillar.     

A five-parameter constitutive model for hysteresis shearing and energy dissipation of rock joints

Rock joints exhibit hysteresis shearing behavior and produce energy dissipation under shear cyclic loads, which however cannot be accurately depicted by existing constitutive models. This paper establishes a constitutive model for hysteresis shearing and associated energy dissipation of rock joints. Analytical expressions of the model during cyclic shearing processes are derived. Derivation of the model indicates no energy dissipation in the elastic stage. When the shear load exceeds elastic boundary, nonlinear energy dissipation takes place. Validations with experiments show that the proposed model provides good conformities with direct shear curves and hysteresis loops, and can predict the energy dissipation characteristics of rock joints under different working conditions. Compared to the constitutive models using Weibull’s distribution, the proposed one is smooth at the elastic boundary and can accurately capture the maximum shear stress. Unlike the existing incremental-type models, the proposed one provides clear and direct analytical expressions for both shear stress and energy dissipation during the whole displacement domain, which is more convenient in application.     

Determination of ejection velocity of rock fragments during rock burst in consideration of damage

The ejection velocity of rock fragments during rock burst, one of the important indexes representing the rock burst strength, is used most conveniently in the supporting design of tunnel with rock burst tendency and is often determined by means of observation devices. In order to calculate the average ejection velocity of rock fragments theoretically, the energy of rock burst was divided into damage consuming energy and kinetic energy gained by unit volume of rock firstly, and then the rock burst kinetic proportional coefficient η was brought up which could be determined according to the rock-burst damage energy index WD, at last the expression of the average ejection velocity of rock fragments during rock burst was obtained and one deep level underground tunnel was researched using the mentioned method. The results show that the calculation method is valid with or without considering the tectonic stress of tunnels, and that the method can be a reference for supporting design of deep mining.     

岩石动静态参数间关系的研究

岩石由矿物颗粒组成,内部存在弱面、裂隙等结构,并非线弹性材料,动静态参数之间并没有确定的力学关系.含有大量裂隙的砂岩、煤等软弱岩石,动态模量大于平均模量;大理岩的动态模量大于变形模量,但与平均模量的关系较为复杂;火成岩及其变质岩,动态模量可以小于变形模量.动态泊松比对波速极端敏感,与静态参数没有明确的关系.现场取回岩块已经卸载、脱水,岩样加工也会对材料产生损伤,内部出现张开裂隙,超声波速度降低.如某大理岩矿岩墙端头所测纵波速度的平均值就大于室内岩样纵波速度的最大值,因而以岩体与岩样纵波速度的比值评价岩体完整性将偏于不安全.     

受载煤体变形破裂表面电位效应及其机理的研究

矿井煤岩动力灾害如煤与瓦斯突出、冲击地压等是井下煤岩体在地应力作用下快速断裂破坏而引起的,在这些过程中会伴随有多种地球物理信号产生,对煤岩灾变伴生地球物理信号特征规律的研究,对于预测矿山灾害危险,保障矿山安全,具有重要的理论意义和实际应用价值.本文对受载煤体表面电位效应、规律、影响因素及其产生机理等方面进行了系统的研究.全文的主要成果及创新点如下:1)揭示了煤体在单轴压缩、拉伸、三点弯曲等不同加载方式下的表面电位特征及规律,发现煤体在不同受载破坏条件下都能够产生表面电位,并且表面电位与载荷及载荷变化率有较好的相关性,二者之间的相关系数在0.6～0.9以上;研究表明受载破坏煤体的内部电位与表面电位变化趋势基本一致,煤体内部电位在试件无宏观破裂时对载荷变化的反映比表面电位更显著和敏感.2)深入研究了不同因素(煤体电性参数、加载速率、水分等)对煤体表面电位的影响.结果表明:a.煤体受载时电阻率减小,电场在煤体中的损耗增加,对表面电位有削弱作用;b.煤体表面电位的产生与加载速率(即煤体结构损伤速率)有着直接的关系,加载速率越大,表面电位信号则越强;c.煤体中水分对表面电位有较大的影响,在较低应力水平(7%～21%σmax)下就会出现表面电位的峰值.3)对表面电位信号进行了R/S统计分析,其Hurst指数均大于0.5,煤体破坏过程中产生的表面电位信号与时间(载荷)之间呈现正相关性,即随煤体破坏电位信号在时间上呈增强趋势.4)受载煤体表面的应变场分布具有非均匀性和各向异性特征,煤体表面的电位场分布随加载过程而不断变化;表面电位集中点的连线与试样破裂面位置吻合较好,破坏时刻高电位点与低电位点以破裂面基本对称.5)煤体破裂是其中缺陷、裂隙在应力作用下分叉扩展、汇合、贯通的结果,煤体受载过程中裂隙面的摩擦起电作用、新生裂隙扩展壁面电荷分离等产生的自由电子为表面电位提供电荷源;基于损伤力学、电磁动力学等理论建立了有限边界煤体表面电位的统计损伤计算模型U(P)σ,并且建立了煤体破坏自由电荷累积与煤体本构关系之间的联系.6)现场测试结果表明:表面电位在时间上与周期来压同步,在空间上与工作面前方煤体应力场分布基本一致并随工作面推进同步前移;煤体表面电位对采掘空间电磁噪音的抗干扰能力较强,而煤层注水对其影响较大,现场测试中应避开.对表面电位的深入研究可望为评定矿山煤体应力状态及其稳定性、监测预报煤岩动力灾害提供一种新的方法和手段.     

裂隙岩体中隧道开挖流固耦合模型及开挖诱发损伤分析

裂隙岩体中隧道开挖会诱发强烈的流固耦合效应,从而引发显著的岩体损伤和水压力扰动,针对该问题,首先建立了一种计算裂隙岩体中隧道开挖和后续排水诱发损伤和裂隙变形的流固耦合模型,然后对不同参数化裂隙网络进行了模拟,最后针对模拟结果给出了实例分析。研究结果表明:所建模型可有效模拟含裂隙网络的岩体中隧道开挖和后续排水降压过程以及岩体损伤发展、裂隙变形和地下水渗流过程;岩体裂隙网络显著影响应力分布的均匀性,隧道开挖和地下水渗流的耦合作用造成隧道周围极易出现高应力区,且局部应力、裂隙变形和水压力之间呈现出显著相关性;不同裂隙网络的分布特征在隧道开挖诱发损伤发展中起到主导作用,进而影响隧道开挖扰动区和损伤区的形成与发展程度。     

Numerical analysis of tunnel reinforcing influences on failure process of surrounding rock under explosive stress waves

Based on mesoscopic damage mechanics, numerical code RFPA2D （dynamic edition） was developed to analyze the influence of tunnel reinforcing on failure process of surrounding rock under explosive stress waves. The results show that the propagation phenomenon of stress wave in the surrounding rock of tunnel and the failure process of surrounding rock under explosive stress waves are reproduced realistically by using numerical code RFPA2O; from the failure process of surrounding rock, the place at which surrounding rock fractures is transferred because of tunnel reinforcing, and the rockfall and collapse caused by failure of surrounding rock are restrained by tunnel reinforcing; furthermore, the absolute values of peak values of major principal stress, and the minimal principal stress and shear stress at center point of tunnel roof are reduced because of tunnel reinforcing, and the displacement at center point of runnel roof is reduced as well, consequently the stability of tunnel increases.     

Dynamic Mechanical Behavior and Adiabatic Shear Bands of Ultrafine Grained Pure Zirconium

Dynamic compression tests were carried out to investigate dynamic mechanical behavior and adiabatic shear bands in ultrafine grained(UFG) pure zirconium prepared by equal channel angular pressing(ECAP) and rotary swaying. The cylindrical specimens were deformed dynamically on the split Hopkinson pressure bar(SHPB) at different strain rates of 800 to 4 000s~(-1) at room temperature. The temperature distribution of the shear bands was estimated on the basis of temperature rise of uniform plastic deformation stage and thermal diffusion effect. The results show that the true stress-true strain curves of UFG pure zirconium are concave upward trend of strain in range of 0.02-0.16 due to the effects of strain hardening, strain rate hardening and thermal softening. The formation of the adiabatic shear bands is the main reason of UFG pure zirconium failure. A large number of micro-voids are observed in the adiabatic shear bands, and the macroscopic cracks develop from the micro-voids coalescence. The fracture surface of UFG pure zirconium exhibits quasi cleavage fracture with the characteristic features of shear dimples and river pattern. The highest temperature within the shear bands of UFG pure zirconium is about 592 K.