Pillar failure by axial splitting in brittle rocks

An analytical approximate elastic model is presented of the pillar failure mechanism in the case of multiple underground openings in brittle rocks by parallel equidistant vertical splitting cracks forming slabs, which are assumed to buckle. The failure region is considered to be elliptical in shape with the major axis growing as failure proceeds parallel to the minimum applied principal stress. A modified solution for the potential energy loss due to the presence of an elliptical hole in an infinite elastic space was derived in order to account for multiple openings. This solution, which yields the failure initiation stress and the crack spacing, was achieved by inserting configuration correction factors estimated by considering certain limiting conditions. In order to obtain simple approximate formulae and after considering the blast damage effect, equivalent effective circular holes are assumed for the case of square openings and elliptical holes for the case of rectangular openings. Next, the stable mode of pillar failure was formulated based on the observation that the weak inclusion of the axially split rock mass reduces the stresses for some distance inside the pillar. The stable model was obtained first by computing the elastic stresses outside the failure zone using a circular approximation and then applying a stability criterion based on Huber's classical fracture hypothesis. Comparison of the theoretical results with field data concerning a bauxite mine using room and pillar have indicated reasonable agreement. Furthermore, the scale effect exhibited by the strength and the axial splitting crack spacing was predicted sufficiently well by the above model.     

露天矿边坡岩石剪切力学特性与破裂特征研究

通过对新疆地区某露天矿不同岩石开展一系列不同法向应力条件下的直剪试验,结合数字照相监测与电镜扫描技术对不同岩石不同法向应力条件下剪切力学特性与宏细观破裂特征展开深入研究.结果表明:Group 1,3两组岩石应力-应变曲线变化平缓,在低法向应力条件下(1,2 MPa)裂隙倾角分布较广,产生了较为复杂的裂隙面,且细观形貌以...     

Impulsive liquid-gas fracture of brittle and ductile rocks and ways of improving the process

Conclusions 1. Other conditions being equal, an increase in the strength and fracture toughness of rock reduces mean crack velocity in impulsive hydraulic fracture and the final dimensions of the cracks within the loading-rate range 0.5·10⁹≤ ≤5·10⁹ Pa/sec. 2. Since the drag coefficient of fluid in a crack is determined by the roughness of the crack’s walls, other conditions being equal, the greatest effect from impulsive fracture should be seen in rocks with fine and cryptocrystalline structures. 3. If the coefficient that characterizes the degree to which a well is filled by combustible material is increased in value from 0.62 to 0.75, the dize of the disk-shaped tensile ruptures formed in ductile rocks increases 60–70%. 4. The main parameters characterizing the impulsive fracture of a productive bed (crack depth and width) depend more on the thermodynamic characteristics of the pressure generator in the well (injection time and pressure) than on the viscosity of the injected fluid. 5. A technology involving interval-by-interval impulsive fracture by sectional shaped charges of high explosives is recommended for strong brittle rocks of moderate and high density. Institute of Geophysics, National Academy of Sciences of the Ukraine (Kiev). Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 4, pp. 50–58, July–August, 1997.     

Support vector machine regression analysis of LHD failures

Load-haul-dump (LHD) machines are the main material handling equipment in underground mines. Reliability analysis of the machine, in the form of forecasting the time between failures (TBFs), is a reliability index for scheduling, preventive maintenance. Support vector regression (SVR) was employed for reliability analysis of an LHD unit. The LHD’s engine was detected as the most critical system by a Pareto analysis. TBFs of 32 failures were obtained. Twenty-five records were used for SVR modelling and the remaining for testing. Mean absolute percentage error value of less than 2% was achieved, which demonstrated the applicability of SVR.     

Crack analysis of pre-cracked brittle specimens under biaxial compression

Crack propagation process in rock like specimens has been studied experimentally and numerically considering both; a single crack and double cracks in the center of specimens. The rock-like specimens are specially prepared from Portland Pozzolana Cement (PPC), fine sands and water. These precracked cylindrical specimens are experimentally tested under compressive loading. Effect of confining pressure on the crack propagation path of specimens with single crack is explained first. In these experiments, it has been observed that the crack propagation path is diverted from its rout due to lateral confinement compared to that of the uniaxially loaded pre-cracked experiments. The same experiments are numerically simulated by an indirect boundary element method using higher order displacement discontinuity elements. Effect of lateral stress on the crack propagation of specimens containing single and double cracks have been studied and compared with the experimental results showing a good agreement between them. Effect of confinement on the cracks coalescence in the specimens containing two cracks is also investigated. It has been observed that wing cracks are produced at the first stage of compression and start their propagation toward the direction of uniaxial compressive loading in the absence of confinement. In the presence of confining pressure the propagating wings are diverted related to the uniaxially loaded cracks and showing a mixed mode crack propagation phenomenon due to both induced tension and shear. It is also observed that the crack coalescence path is affected a little bit (due to confinement) compared to that of wing cracks.     

爆破岩体边坡稳定性分析

通过对岩体边坡产状与结构面产状关系的变化分析,表明爆破后的边坡的稳定性随地形的变化而不断变化。文中讨论了岩体结构面的走向、倾向、倾角与边坡稳定性之间的相互关系,最后对爆破施工与地质条件的关系作进一步阐述。     

考虑初始空隙闭合及其影响的脆性岩石变形破坏全过程模拟

岩石材料本构模型是进行岩体工程设计与分析的基础。为了建立能够准确反映脆性岩石变形破坏全过程模拟方法,针对当前统计损伤本构模型难以很好地反映脆性岩石峰前变形力学性质的局限性,进行了深入分析。首先,在脆性岩石变形力学特征分析基础上考虑初始空隙闭合及其影响,并由此将其分为两类:第1类初始空隙和第2类初始空隙,其中,第1类初始空隙仅能够在静水压力状态下发生闭合,其闭合程度对脆性岩石弹性模量变化特征产生影响,且其未闭合部分引起脆性岩石具有初始损伤;第2类初始空隙能够在任意应力状态下发生闭合,且能够在脆性岩石初始宏观变形阶段完全发生闭合,其闭合程度对脆性岩石初始压密变形阶段与初始宏观非线性变形曲率均产生影响。其次,脆性岩石被抽象为由裂隙材料和骨架材料两部分组成并基于材料变形力学分析方法建立脆性岩石变形分析方法,然后基于瞬时应变和统计损伤理论分别建立裂隙材料变形分析方法和骨架材料变形分析方法,进而建立考虑初始空隙闭合及其影响的脆性岩石本构模型,并给出了模型参数的确定方法。最后,将该模型及同类型模型理论曲线分别与试验曲线进行比较分析,并在此基础上探讨初始空隙闭合对脆性岩石损伤和附加损伤演化规律产生的影...     

分形理论在边坡稳定性分析中的应用

边坡稳定性分析一直以来是边坡工程研究的核心,文中根据露天边坡中局部信息与整体信息的自相似性,小尺度下测得的信息与大尺度下测得的信息自相似性,由此构造模型,挖掘原始信息中不能反应的更多信息,由前者来预测后者,为边坡稳定性分析提供更多的信息、参数和依据,从而为边坡稳定性判别的进一步研究提供了可靠的数据依据和研究价值。     

RFPA-SRM在边坡稳定性分析中的应用研究

结合扎泥河露天矿工程实际,基于强度折减法,应用RFPA-SRM模拟了边坡岩体的变形破坏过程,计算了稳定性。通过分析数值模拟结果,研究了边坡岩体的变性特征及滑坡模式。为提出合理的滑坡防治措施提供科学依据。     

扎哈淖尔露天矿南帮边坡稳定性分析

为保证扎哈淖尔露天矿南帮边坡采剥过程的安全,对南帮边坡稳定性进行研究,通过分析弱层和水对南帮边坡稳定性的影响,提出采用压脚和筑排水沟等治理方案来提高南帮边坡的稳定性。     

强度折减法在顺层边坡稳定性分析中的应用

以有限元解的不收敛确定强度储备安全系数,并由水平方向位移突变和等效塑性应变云图辅助验证,提高边坡稳定性分析的准确性。将基于ANSYS软件的强度折减法所得强度储备安全系数转换为摩尔-库仑匹配D-P准则(非关联)条件下的安全系数,与传统工程实践中采用的安全系数接轨。并确定潜在剪出口位置和滑动面滑动次序,为边坡治理方案的制定提供参考。     

京珠高速公路耒阳段滑坡稳定性分析

介绍了一种常用的詹布(Janbu)法，该方法考虑了地下水、水平荷载(如地震荷载)、滑面的不连续性、土体性质的不均匀性等因素的影响．并根据该方法编制出程序。对京珠高速公路耒阳段滑坡采用詹布法进行分析．并将计算和勘测设计结果进行比较。     

离心加载法在边坡稳定性分析中的应用

基于离心加载法的原理,应用RFPA-Centrifuge软件对某露天矿边坡的变形及破坏过程进行了数值试验研究,再现了边坡失稳的动态过程。根据数值试验所得出的模拟结果,分析得出了该边坡最危险滑动面的形成机制,为边坡失稳的预测及防治提供科学依据。