Arching in Inclined and Vertical Mine Stopes

Hydraulic fills are one of the most common backfills used by mining industries to backfill the stopes (voids) created after extracting the ore. It is important to estimate the stresses within to the stope to design the drainage and barricades. Most of the existing analytical models for the estimation of stresses within the stopes consider flat rectangular elements to include the effects of arching, although a continuous compression catenary arch of principal stresses using intersections of shear lines is the reality in field situations. In this paper, a circular compression arch of principal stresses has therefore been used to derive a general expression for stress within the inclined stopes. The results have been compared with the existing analytical and numerical models for vertical stopes as well as inclined stopes. A methodology has been presented to determine the vertical stress variation along the width of stope at different depths. The variation of stresses along the width of stope is also presented graphically.     

Blast Damage and Blast Dilution Control: The Application of Bulk Emulsion Systems at the WMC St Ives Junction Mine

The application of modern bulk emulsion explosive systems at an underground gold mine resulted in a 57% improvement in gold dilution. While this improvement is impressive and could be expected to be achieved at other sites, the work required to assess and demonstrate the benefits is painstaking. Forty-eight rings involving a total of approximately 50 000 tonnes of ore were monitored using various modern surveying instruments over a 6-month period. The geometric data included blasthole locations and deviation, and the cavity monitoring of stopes. Implementation of a bulk emulsion system not only provided logistical benefits but it also has the desirable explosive properties associated with reducing the effects of blast damage and blast dilution.     

Numerical modelling of staged stope extraction in a tabular steeply dipping deposit

Stope stability is a key factor for the success of a mining operation. To optimise ore productivity while maintaining stope stability, the mining block/stope must be extracted in stages. Ore dilution will occur if the stope is not properly excavated/blasted. This study examines stope stability during mining in three stages, where the height of each stage stope is 10 m. The paper also presents simulation analysis of a typical steeply dipping tabular orebody at 1200 m depth below the surface, which is common in many Canadian underground hard rock mines. Numerical modelling analysis was conducted using the finite element program, RS^2D, where the non-linear elasto-plastic Mohr-Coulomb failure criterion was adopted. The rock reinforcement system (i.e. cable bolts) was modelled/installed in the stope footwall after each mining stage to strengthen access drifts and stabilise the rock mass around the stope that was disturbed by mining activity. Results are discussed in terms of depth of failure zones, total deformation and axial forces in cable bolts with respect to mining stage.     

深部变面长采场顶板破断演化的力学机制分析

不规则煤层开采容易引发顶板应力集中、矿压显现异常等问题,为探究变面长采场顶板破断规律与结构演化特征,针对工作面斜长由小变大的突变型采场不同开采阶段的几何特征与力学成因,运用小挠度薄板弯曲理论依次建立并解析4种边界条件的顶板结构模型。根据变面长采场顶板矿压分区显现特征,采用MATLAB与FLAC^3D数值模拟方法分析顶板破断规律与宏观力学响应。通过系统分析与总结归纳,构建了变长工作面“三场三区三结构”的覆岩结构传递演化模式,提出了“两场两规律”的顶板分区破断效应。并通过典型工程案例的矿压实测进行应用验证。结果表明：变面长采场分为小面采场、变面采场和大面采场,小面采场顶板为缓压型结构,发生的是传统“O-X”形破断;变面采场顶板为突变型结构,顶板断裂产生的延长形与漂移形“O-X”破断裂隙与大面采场增压型结构顶板的裂纹发育特征较为相似,故将二者整合为全大面采场;全大面采场顶板发生的是“X-O”形破断,裂纹继续发展产生延长形破断,形成“两场两规律”的顶板破断理论。研究结论为探明变面长采场的覆岩运移本质,加强深部复杂煤层赋存条件下的顶板灾害防控提供了重要依据。     

Fracturing around a preconditioned deep level gold mine stope

The mining faces of the highly stressed tabular stopes in South Africa's deep level gold mines are prone to a type of rock burst termed a face-burst. As a means of ameliorating these face-burst conditions, a destressing technique termed preconditioning has been employed. Part of the studies into the quantification of the effects and mechanisms of preconditioning was a detailed investigation of the fracture pattern around unpreconditioned and preconditioned stopes. Techniques included mapping of the fractures exposed in the mined areas of the stope, measurement of profiles of the stope hangingwall and the use of Ground Penetrating Radar (GPR). These studies indicate that preconditioning does not produce new sets of fractures and stress redistribution ahead of the face occurs by re-activation of specific pre-existing fractures, thereby reducing the potential for face-bursting.     

Applications of numerical modelling in underground mining and construction

Numerical modelling has been used to investigate a variety of problems in underground mining and tunnelling: subsidence induced by longwall coal mining; stresses generated when an open stope is filled cemented backfill and the stability of exposures created during subsequent mining of adjacent stopes; the interaction of two tunnels; and the effects of under-mining a pre-existing tunnel and shaft. In each case, results from nonlinear stress analyses can be used to guide the design of excavations and rock support mechanisms.     

Mining Method Selection and Optimization for Hanging-Wall Ore-Body at Yanqianshan Iron Mine,China

In order to smooth ore production during the transition from open pit to underground mining at Yanqianshan Iron Mine, China, it is necessary to select an appropriate mining method to operate simultaneously open-pit mining and underground mining for inner-slope (hanging-wall) ore-body. Based on practical geologic setting of the hanging-wall ore-body, a comprehensive evaluation model for selecting the underground mining method to extract handing-wall ore-body was proposed, which is constituted by 3 sub-systems of safety factors, production factors and technical–economic factors. This evaluation model could be analyzed by the mutation progression method, which based on catastrophe theory and fuzzy mathematics. In addition, the FLAC^3D is employed to simulate the mining process of hanging-wall ore-body, and finally the optimal mining scheme is determined. By using mutation progression analysis and numerical modeling, some useful conclusions for hanging-wall ore-body mining have been drawn, which will be beneficial to mining safety during transitional period from open-pit to underground mining.     

金川矿区深部高应力矿床开采关键技术研究与发展

金川矿区是我国唯一一座大型有色矿产资源生产基地。该矿体埋藏深、地应力高和围岩破碎所固有的不利条件,使得矿床在开采过程中面临极大困难。随着开采的延深,开采面积扩大,采场地压显现日趋剧烈,揭示和研究深埋、大面积采场的地压显现规律以及控制技术,是该类难采矿床安全、高效开采的关键。金川矿区自建矿30多年来,开展了大量的地压规律与控制技术的研究,积累了丰富的工程经验,解决了生产中的难题,使得矿山一期工程得以顺利实施。然而,随着二期工程的进展,尤其多中段开采水平矿柱日趋变薄的开采条件下,采场地压活动极为剧烈,巷道变形难以控制,并潜在着采场突变失稳的风险。本文在总结国内外难采矿床采场地压规律和控制技术研究的基础上,深入论述了金川1#矿体开采存在的问题、潜在的风险以及需要解决的关键技术难题。并明确了数值分析、现场监测与工程经验集于一体的动态反馈系统工程方法,是解决复杂采矿工程的必由之路。     

采场结构体回采可移动性分析

采场范围内存在的结构体严重影响地下矿山安全生产,分析不同回采顺序下采场结构体可移动性具有重要意义。以块体理论为基础,结合空场法开采的采场空间属性,分析了结构体在采场内的一般嵌套模式。运用GeneralBlock程序建立了采场结构体模型,对采场内结构体的类型、体积和位置等元素进行了解构。利用矢量方法分析了不同回采顺序下采场结构体可移动性,并利用力学方法分析了考虑岩桥破坏时的矢量不可动结构体的回采移动性,推导了结构体破坏岩桥移动的条件公式。以铜坑矿锌多金属矿体1#矿块采场为样本,进行了回采可移动性实例分析,结果表明：一端至另一端后退回采时,4个结构体滑动;中间至两端后退回采时,7个结构体滑动,1个结构体破坏岩桥后滑动;上向水平分层回采时,4个结构体滑动,2个结构体掉落。研究成果可为地下矿山裂隙矿岩空场法回采顺序的合理选择及采场安全管理提供技术指导。     

地下与露天复合采动影响下边坡岩体稳定性评价方法的研究

矿产资源的开采, 有些是按地下与露天复合开采方式进行。依据采区的空间对应关系, 两种采动影响域中的一部分相互重叠, 导致采动效应相互作用和相互叠加, 从而组成一个复合动态系统, 因此边坡岩体变形机理更加复杂, 与单一露天开采相比有较大的差异;然而, 过去在处理此类问题时近似地应用单一露天采动影响下的分析方法, 结果与实际情况存在一定差异;本文在理论分析的基础上, 推导出边坡稳定性的评价方法, 为此类矿山后续采矿设计及安全生产提供科学依据。     

USING DYNAMIC PHOTOELASTICITY TO EVALUATE THE INFLUENCE OF PARTING PLANES ON STRESS WAVES INTERACTING WITH STOPES

Dynamic photoelasticity is used as a means for visualizing the complex interaction process between elastic waves and geometrical discontinuities. The photoelastic experiments are back-analysed by the dynamic finite difference program WAVE, and the code is assessed in terms of its accuracy and modelling capabilities. Three model geometries are investigated: (i) a stope situated within a homogeneous medium; (ii) a stope surrounded by softened material, the interface between the softened and bulk material being bonded and (iii) a stope situated within softened material, with a non-cohesive material interface. Prominent waves resulting from the diffraction, refraction and reflection of incident waves, as well as normalized dynamic stress intensification factors at the stope face, stope back area and along the hanging-wall skin are analysed in this study. The parting planes are found to reflect a portion of the incident energy and thus shield the stope. However, a non-cohesive parting plane traps energy within the hanging-wall beam, and any shielding benefits are negated. WAVE has been proven to model accurately the diffraction, refraction and reflection of stress waves in a homogeneous medium and the interaction with cohesive and non-cohesive interfaces separating two material types.     

陕西铜峪铜矿床地质特征及非常规采矿方法的探索与实践

：铜峪铜矿床是火山岩磁黄铁矿黄铁矿型铜矿床,矿体多,矿床规模小,品位低;矿体厚度变化大,矿体与围岩属渐变过渡关系,采矿极易贫化.采用非常规开采,即开拓（直接沿矿体拉底、切割）—形成矿房—在矿房内按一定间距拉槽—最后在矿体下盘施工运输坑道—再按常规开采,有效降低了贫化率,提高了矿山的经济效益.     

Geotechnical properties of cemented paste backfill from Cannington Mine,Australia

Paste fill is the newest form of backfill material in the spectrum available to international mines and is made from full mill tailings. Tailings have an effective grain size of approximately 5 μm and are combined with a small portion of binder and water to make paste. It is deposited into the voids created by mining which are referred to as stopes. The empty voids are approximated as vertical rectangular prisms, with plan dimensions of 15–40 m and heights of 100 m or more. Backfilling of mined stopes provide an increased level of local and regional stability to the ore body, as well as providing a suitable and economic dump of mining related waste. Paste is a relatively new technology in the mining industry and a review of the physical properties and mechanical fill behaviour was considered pertinent.     

Dynamic Modelling of Fault Slip Induced by Stress Waves due to Stope Production Blasts

Seismic events can take place due to the interaction of stress waves induced by stope production blasts with faults located in close proximity to stopes. The occurrence of such seismic events needs to be controlled to ensure the safety of the mine operators and the underground mine workings. This paper presents the results of a dynamic numerical modelling study of fault slip induced by stress waves resulting from stope production blasts. First, the calibration of a numerical model having a single blast hole is performed using a charge weight scaling law to determine blast pressure and damping coefficient of the rockmass. Subsequently, a numerical model of a typical Canadian metal mine encompassing a fault parallel to a tabular ore deposit is constructed, and the simulation of stope extraction sequence is carried out with static analyses until the fault exhibits slip burst conditions. At that point, the dynamic analysis begins by applying the calibrated blast pressure to the stope wall in the form of velocities generated by the blast holes. It is shown from the results obtained from the dynamic analysis that the stress waves reflected on the fault create a drop of normal stresses acting on the fault, which produces a reduction in shear stresses while resulting in fault slip. The influence of blast sequences on the behaviour of the fault is also examined assuming several types of blast sequences. Comparison of the blast sequence simulation results indicates that performing simultaneous blasts symmetrically induces the same level of seismic events as separate blasts, although seismic energy is more rapidly released when blasts are performed symmetrically. On the other hand when nine blast holes are blasted simultaneously, a large seismic event is induced, compared to the other two blasts. It is concluded that the separate blasts might be employed under the adopted geological conditions. The developed methodology and procedure to arrive at an ideal blast sequence can be applied to other mines where faults are found in the vicinity of stopes.     

A three-dimensional analytical solution to the arching effect in inclined backfilled stopes

The stress state in backfilled mine stopes is an important issue to assess the behavior of the interaction between the backfill and the surroundings or barricades. Most previous arching analyses have considered only the vertical backfilled stopes in both 3D and 2D conditions, and the 3D stress distribution that results from the arching effect in inclined mine stopes remains unclear. In this paper, based on the limit equilibrium theory, a 3D stress solution that is applicable to vertical and inclined backfilled stopes is proposed to further examine the arching effect. The solution is validated against an available centrifuge model by changing the inclination of the model. The proposed analytical solution is consistent with the numerical simulations, and it is suggested that neglecting the wall inclination causes one to underestimate the arching phenomenon. In other words, the vertical stresses at the bottom of the stope can decrease when the wall inclination is considered. Hence, when the stope is assumed in plain strain conditions, both the vertical and horizontal stresses exerted on the barricades are overestimated.     

采场内结构体解算及其稳定性计算

采场内结构体的存在对矿块安全回采影响较大,开展其解算方法与稳定性计算方法研究具有重要意义。应用一般块体理论,以采场四周的开拓巷道结构面调查数据为基础,运用GeneralBlock程序初步解算出采场内结构体,分析结构体的真实性,制定真实性分级表。结合3DMine软件,用定义包裹长方体的方法准确刻划结构体的位置,建立简单材料力学模型,计算出固定结构体的最小固定面面积。对于解算出的结构体,在块体可移动性定理和稳定性原理的基础上,运用材料力学、集合等方法,分析矿块回采过程中结构体可移动性,计算结构体稳定性系数。研究成果成功解算出采场内结构体并进行了稳定性分析,对于裂隙岩体加固与采矿工艺优化具有较好的指导意义。     

Optimization Methods of Blasting Parameters of Large Cross-Section Tunnel in Horizontal Layered Rock Mass

For large cross-section tunnel in horizontal layered rock mass, blasting excavation often causes serious overbreak and underbreak. In this study, blasting excavation tests of tunnel upper face were conducted, blast-induced excavation damage and the influence mechanisms of weak beddings and joints were analyzed based on the Panlongshan tunnel. In order to achieve fine excavation, the cut mode of “center holes and four-wedge cutting holes”, the blasthole pattern of “empty holes, long holes, short holes and additional relief holes”, the maximum single-hole charge and the air-deck charge structure were proposed. Compared with the damage characteristics, overbreak and underbreak, and deformations of surrounding rock before and after optimization, the latter was better in tunnel contour formation and surrounding rock stability. The results show that after optimization, the large-area separation of vault rock mass is solved, the step-like overbreak of spandrel rock mass is reduced and the large-size rock block and underbreak are avoided. The maximum linear overbreak of vault, spandrel, and haunch surrounding rock is decreased by 42.3%, 53.7% and 45.1%, respectively. The underbreak at the bottom of the upper face is reduced from ??111.5 to ??16.5 cm. The average overbreak area is decreased by 61.1%. The surrounding rock displacement after optimization finally converges to the smaller value. The arch crown settlement and the horizontal convergence of haunch are reduced by about 21.6% and 18.3%, respectively. Furthermore, from the completion of blasting excavation to the stabilization of surrounding rock, it takes less time by using the optimized blasting scheme.

     

柿竹园多金属矿床开采方案确定的数值模拟研究

针对柿竹园多金属矿,在形成200万方大空区,部分矿柱跨塌,最大顶板连续暴露面积达8000 2,且不能采用充填法的情况下,如何立足矿山实际情况,合理规划矿产资源的整体开发,确保矿山企业的可持续发展问题,对该矿床的各种可能的开采方案进行了弹塑性有限元、离散元数值模拟研究,模拟研究的结果,对开采方案的确定具有积极的指导意义.     

A solution to estimate the total and effective stresses in backfilled stopes with an impervious base during the filling operation of cohesionless backfill

Mining backfill is commonly used in underground mines. A critical concern of this practice is to evaluate the pressures and total stresses in backfilled stopes to ensure a safe and economic design of barricades, constructed to retain the backfill. When a slurried backfill is placed in a mine stope, excess pore water pressure (PWP) can instantaneously generate and progressively dissipate. The dissipation of the excess PWP and consolidation lead to the development of effective stresses, which in turn lead to an arching effect in the backfilled stope. Until now, arching effect has been largely considered for stress estimation in dry or submerged backfill. The former corresponds to the final state at the end process of the drainage and consolidation of the backfill with a pervious while the latter with an impervious barricade. However, previous studies have shown that the most critical moment for the stability of barricades is during the stope filling. Therefore, the design of barricades requires a proper estimation of the pressure and total stresses during the filling operation. This in turn needs joint consideration of the arching effect and consolidation of the backfill. In this paper, a new solution is developed to evaluate the pressures and stresses in backfilled stopes during the filling operation of cohesionless backfill by considering the self-weight consolidation and arching effect. The proposed solution is validated by numerical modeling with Plaxis2D. It can thus be used to evaluate the pressures and stresses in backfilled stopes during the stope filling with an impervious barricade.     

Open Stope Stability Using 3D Joint Networks

Summary The most popular exploitation method used in Canadian hard rock mines is open stope mining. Geomechanical design of open stopes relies on a range of analytical, numerical and empirical tools. This paper presents an engineering approach for the analysis and the design of reinforcement for open stopes in jointed rock. The proposed methodology, illustrated by three case studies, relies on developing 3D joint network models from field data. The 3D joint networks have been successfully linked to a 3D limit equilibrium software package. The models account for the finite length of joints as well as the influence of random joints. The integrated approach facilitates comparative analyses of different reinforcement strategies under different degrees of jointing in the hard rock environment. Received February 23, 2001; accepted October 11, 2002; Published online January 21, 2003 Acknowledgments The financial support of the National Science and Engineering Council of Canada and the Institut de Recherche en Santé et Sécurité au Travail of Quebec and Noranda Inc. is greatly appreciated. Authors' address: Prof. John Hadjigeorgiou, Université Laval, Department of Mining, Metallurgy and Materials Engineering, G1K 7P4 Quebec City, Quebec, Canada; e-mail: john.hadjigeorgiou@gmn.ulaval.ca