Evaluation of the effect of geometrical parameters on stope probability of failure in the open stoping method using numerical modeling

Stress-induced failure is among the most common causes of instability in Canadian deep underground mines. Open stoping is the most widely practiced underground excavation method in these mines, and creates large stopes which are subjected to stress-induced failure. The probability of failure(POF)depends on many factors, of which the geometry of an open stope is especially important. In this study,a methodology is proposed to assess the effect of stope geometrical parameters on the POF, using numerical modelling. Different ranges for each input parameter are defined according to previous surveys on open stope geometry in a number of Canadian underground mines. A Monte-Carlo simulation technique is combined with the finite difference code FLAC3D, to generate model realizations containing stopes with different geometrical features. The probability of failure(POF) for different categories of stope geometry, is calculated by considering two modes of failure; relaxation-related gravity driven(tensile)failure and rock mass brittle failure. The individual and interactive effects of stope geometrical parameters on the POF, are analyzed using a general multi-level factorial design. Finally, mathematical optimization techniques are employed to estimate the most stable stope conditions, by determining the optimal ranges for each stope's geometrical parameter.     

井工开采对边坡稳定性影响的有限元分析

边坡下方井工开采是一个露天煤矿普遍存在的问题。本文采用有限元方法针对某一具体实例进行了数值模拟。模拟考虑了岩体力学特性及岩体结构特征,并模拟了井采过程。通过井采前后边坡岩体应力分析、位移分析,对边坡下方井工开采对边坡稳定性影响获得了一些认识。     

大空间建筑环形点式重载作用下深废矿坑岩壁变形稳定性数值分析

近年来,大城市工程建设急速发展,土地资源愈发紧张,一些矿产资源型城市中出现了利用废弃天然矿坑进行地下空间开发的改造项目。以长沙湘江欢乐城项目深废矿坑改造开发工程为背景,针对矿坑边坡稳定性以及受建筑结构点式荷载作用下的岩壁与基础协同作用问题,利用数值分析手段建立三维岩壁-建筑结构相互作用模型。研究岩壁在环形点式受荷条件下的表现,并探究遭遇突发性岩壁变形及承载状态变化后,岩壁与结构的稳定性变化情况。结果表明,在天然状况下废弃矿坑的开采高边坡基本处于稳定状态;而施工扰动和建筑荷载造成的应力变形仅发生于岩壁表面,未达岩体深部;岩壁由于突发灾害产生的局部大变形会严重危及支承其上的基础和结构安全;而在合理的建筑物环形点式基础设计布置情况下,基础结构的偶然失效不会影响岩壁和建筑物的稳定性。     

边坡稳定性有限元分析中确定潜滑面及其安全系数的方法

本文提出了在边坡稳定性的有限元分析中,用模拟边坡垮落过程的方法确定边坡的潜滑面和安全系数。该法反映了边坡的渐过破坏过程和破坏过程中岩体应力场的变化,并把有限单元法和极限平衡法结合起来,既能给出一个总的滑落体和安全系数,又能展示边坡首先破坏的部位。     

Limit analysis for the seismic stability of three-dimensional rock slopes using the generalized Hoek-Brown criterion

The parameters that influence slope stability and their criteria of failure are fairly understood but over-conservative design approaches are often preferred, which can result in excessive overburden removal that may jeopardize profitability in the context of open pit mining. Numerical methods such as finite element and discrete element modelling are instrumental to identify specific zones of stability, but they remain approximate and do not pinpoint the critical factors that influence stability without extensive parametric studies. A large number of degrees of freedom and input parameters may make the outcome of numerical modelling insufficient compared to analytical solutions. Existing analytical approaches have not tackled the stability of slopes using non-linear plasticity criteria and three-dimensional failure mechanisms. This paper bridges this gap by using the yield design theory and the Hoek-Brown criterion. Moreover, the proposed model includes the effect of seismic forces, which are not always taken into account in slope stability analyses. The results are presented in the form of rigorous mathematical expressions and stability charts involving the loading conditions and the rock mass properties emanating from the plasticity criterion.     

岩质高边坡岩体力学参数确定及稳定性研究

以云南某露天矿采场岩质高边坡工程为研究对象,阐述了岩体力学参数在边坡稳定性分析中的重要性,因原位试验对于坚硬岩体或极软岩体的不适用性,对坚硬岩体,以室内试验得出的岩石物理力学参数和岩体质量评价RMR评分值为依据,并综合考虑岩体中节理裂隙、岩体结构、地下水的影响,运用霍克-布朗(Hoek-Brown)强度准则将岩石力学参数进行折减修正后换算成岩体力学参数,并与现场原位试验所得软弱岩体力学参数结果相结合得到最终岩体力学参数.在上述调查、研究基础上,采用有限差分法(FLAC数值分析软件)对现状边坡进行静态的稳定性分析,提出合理的最终边坡角及总台阶高度,保证矿山正常生产和经济效益的提高.     

NMR-based damage characterisation of backfill material in host rock under dynamic loading

It is not uncommon that backfill material used in underground mining being exposed to repetitive dynamic stresses induced by blasting operations or rockburst events. Understanding the strength and fracture evolution of backfilled stopes is critical to maintain the long-term stope stability and ensure safe mining activities. This paper aims to study the damage evolution of the backfill material and its host rock behaviour under three-dimensional(3D) dynamic loading. Using a true-triaxial testing machine, multiple samples of backfill material enclosed by country rock were fabricated and tested under various dynamic loadings with different true-triaxial confining stress conditions. In addition, the nuclear magnetic resonance(NMR) measurement was conducted on the samples before and after exerting static and dynamic loading to obtain their porosity distribution changes. The experiment results suggested that with the increase of the dynamic loading, the porosity of the backfill sample goes through a two-stage process,which shows a slightly linear decrease and then followed by an exponential increase. The research findings can help understand the damage mechanism and fracture development of backfilled stopes and its host rock in deep underground mines, which are constantly subject to the combination of 3D static confining stress and dynamic loading.     

Slope safety control during mining below a landslide

1 Introduction After over 40 years’ mining the East Open Pits of Daye Iron Mine were formally closed in the year 2000[1]. There still remains around 12 million tons of ore beyond the pit limit, which would be mined by underground ways. During the transition period, hanging-wall ores were planned to be mined to maintain the balance of mineral supply, to make full use of open-pit facilities and to avoid unemployment of miners. The four selected mining spots are characterized by high and stee…     

Slope safety control during mining below a landslide

The East Open Pits of Daye Iron Mine were closed in year 2000 and the ore beyond the pit limit was planned to be mined by underground ways. In order to facilitate the smooth transition to underground mining, hanging-wall ores in the old pits were scheduled to be mined. Xiangbishan pit is one of the four mining spots selected. In 1979 when the pit was mined to around 36 m a.s.l., a landside of around 70000 m³ occurred in its North Slope, leading to the closure of the pit. The pit was then backfilled to 60 m a.s.l. to maintain the slope stability. The hanging-wall ore to be mined is just located below the old slide, so whether the slide will be reactivated and how to control its deformation and stability are the key issues concerned. Based on geological investigation and numerical analysis, it was predicted that the slide would be reactivated and a control measure using the intact ore body as a retaining wall was thus suggested. During mining, displacements were monitored to assure safety. By July, 2003, 383000 tons of ore were successfully mined. Though the observed displacement reached 8795 mm, no major failure happened. The final slope is 110 m high with an angle of 70°.     

Determination and stability analysis of ultimate open-pit slope under geomechanical uncertainty

In open-pit mines, pit slope as one of the important parameters affects the mine economy and total minable reserve, and it is also affected by different uncertainties which arising from many sources. One of the most critical sources of uncertainty effects on the pit slope design is rock mass geomechanical properties. By comparing the probability of failure resulted from deterministic procedure and probabilistic one, this paper investigated the effects of aforesaid uncertainties on open-pit slope stability in metal mines. In this way, to reduce the effect of variance, it implemented Latin Hypercube Sampling (LHS) technique. Furthermore, a hypothesis test was exerted to compare the effects on two cases in Middle East. Subsequently, the investigation approved high influence of geomechanical uncertainties on overall pit steepness and stability in both iron and copper mines, though on the first case the effects were just over.     

A new concept of backfill design—Application of wick drains in backfilled stopes

Backfilling represents an environmentally friendly mining waste disposal technique. It is increasingly used in underground mines all over the world. However, its primary purpose remains to improve ground stability and to reduce ore dilution. Previous investigations have shown that fill drainage plays a key role in backfill and barricade design. With a poor drainage system in the backfilled stope, the required dimension of barricade, which is constructed at the base of the stope near the drift entrance, has to be increased. A poor backfill drainage system can also lead to a significant increase in drainage waiting time and further reduction in mining productivity. In this paper, the drainage of conventional backfill design in backfilled stopes is briefly reviewed. For the first time, the application of the wick drain is introduced in the backfill within mine stopes. The drainage improvement from the introduction of the wick drain is illustrated using numerical modeling.     

Probabilistic approach for open pit bench slope stability analysis——A mine case study

The geotechnical slope design of an open pit wall starts at the bench scale configuration. At this scale, the rock slope stability is governed primarily by the geological discontinuities within the rock mass and as a result, structurally-controlled failures(e.g. planar, wedge or toppling) are most likely to occur. The probabilistic approach offers a major advantage over the traditional deterministic method in that it accounts for the different degrees of variability and uncertainty often encountered in rock properties. This paper presents a bench slope stability assessment for an open pit mine in Peru using a probabilistic-based approach by coupling a kinematic analysis based on stereographic projection techniques followed by a kinetic analysis by means of the limit equilibrium method. Finally, these two probabilities are combined to provide an overall measure of the probability of failure(PoF) of the bench slope system. The case study is characterized by significant scatter in the geometrical and mechanical properties of the joints.Extensive surface mapping was conducted at 36 different sites following the ISRM suggested procedures.Several direct shear tests were carried out. It is shown that by combining field and laboratory measurements and engineering judgment, the probability density functions(PDF) of the discontinuity parameters can be obtained. These are then used in a Monte Carlo simulation process to compute both kinematic and kinetic probabilities of failure. The overall probability of failure aims to provide the design engineer with a tool to critically evaluate the bench performance from a geotechnical risk perspective and to provide a basis for future bench design optimization.     

Application of open-pit and underground mining technology for residual coal of end slopes

Given the conditions of residual coal from the boundary of a flat dipping open-pit mine,which uses strip areas mining and inner dumping with slope-covering,we propose an open-pit and underground integrated mining technology for residual coal of end slopes.In the proposal a conveyance road and ventilation conveyance near the slope are built,corresponding to the pit mining area and the surface coal mine dump,as well as an interval haulage tunnel and air-inlet tunnel.The outcome shows that such mining method may reduce the effect to slope stability from underground mining,it does not affect the dumping advance and has a high recovery rate of residual coal resources.The working face is timbered by single hydraulic props,transported by a scraper conveyor and supported by coal walls.This method of mining is one of layered top coal caving,with high resource recovery,low production cost where positive economic benefit can be realized.     

房柱采矿法结构尺寸的模拟研究

本文在前人对有限元研究的基础上,首次将三维空间有限单元法用于分析和研究缓倾斜矿体房柱采矿法的最优采场结构参数.独立地编制了对岩层进行应力和变形分析的三维有限元通用程序,并调试通过.根据对贵州汞矿的实际模拟计算,证明该程序的求解精度满足工程要求,矿山现用采场结构尺寸还存在着很大的潜力,可提高矿房跨度,减小矿柱尺寸,从而降低矿石损失,充分利用地下资源,增加企业经济效益.     

地下厂房洞室围岩稳定的计算问题

本文概括了用有限元计算洞室围岩稳定的若干问题,包括了计算范围、围岩分区、及地应力的输入方式。论述了地下洞室围岩应力的分布规律,其中分析了岩体特性,地应力场特性、洞型、开挖方式对围岩应力场的影响,提出了岩体流变对围岩的影响及采用计算理论的合理性。     

Strategic mining options optimization:Open pit mining,underground mining or both

Near-surface deposits that extend to considerable depths are often amenable to both open pit mining and/or underground mining. This paper investigates the strategy of mining options for an orebody using a Mixed Integer Linear Programming(MILP) optimization framework. The MILP formulation maximizes the Net Present Value(NPV) of the reserve when extracted with(i) open pit mining,(ii) underground mining, and(iii) concurrent open pit and underground mining. Comparatively, implementing open pit mining generates a higher NPV than underground mining. However considering the investment required for these mining options, underground mining generates a better return on investment than open pit mining. Also, in the concurrent open pit and underground mining scenario, the optimizer prefers extracting blocks using open pit mining. Although the underground mine could access ore sooner, the mining cost differential for open pit mining is more than compensated for by the discounting benefits associated with earlier underground mining.     

Characteristics of rockburst and its mining technology in mines

In order to resolve how to mine under the condition of high stress with rockburst, this paper analyzes the law of rockburst, and considers that most of the rockbursts occur in the high stress area of stope. A method of rockburst forecast and its steps are given, and three different stages of rockburst are identified. Furthermore, this paper considers that blasting energy can effectively control rockburst by changing the characteristics of rock mass, which decreases the probability of rockburst happening. According to characteristics of rockburst, two feasible mining techniques under rockburst conditions are put forward, that is stoping-and-filling method, and sublevel caving method of mining without any sills in hanging wall.     

岩层走向对地下洞室围岩稳定的影响

层状岩体沿层面方向和垂直于层面方向的物理力学特性各异,表现出明显的各向异性,其破坏形式也与一般各向同性岩体不同.根据层状岩体的物理力学性质分析了其破坏特性及其迭代计算方法.采用三维非线性弹塑性有限元数值计算方法,从变形、破坏、应力和扰动综合分析了层状岩体中岩层走向对洞室围岩稳定的影响.通过对一工程实例中各种洞室厂房轴线的计算和比较,结合工程经验,得出层状岩体中地下洞室的合理轴线布置方式.分析结果与工程实际相吻合,为工程设计提供了比较可靠的理论依据.     

煤岩体中弹性比能分布的有限元计算分析

冲击地压发生的前提是矿山井巷和采场周围的煤岩体中储存了足够的弹性能．摸清围岩体中弹性能的分布规律是有效地进行冲击地压预测预报的前提，文中探讨了井巷和采场围岩体处于弹塑性变形状态下其弹性比能的计算方法，提出了用有限元法分析计算处于弹塑性变形状态下的煤岩体中弹性比能分布的理论与方法，以及产生冲击地压的弹性能判据．结果表明，蝶层巷道两帮煤体中弹性比能的最大值与采深的平方近似成正比，与其弹性模量近似成反比．对鲁村煤矿2217区段运输平巷的具体条件进行的有限元计算分析表明，该巷道不满足产生冲击地压的条件，与现场实际情况相吻合．     

基于弹塑性有限元的深挖路堑碎裂岩质边坡稳定性分析

西部地区地形地质条件复杂,对于岩体破碎、裂隙发育的边坡,前期地勘和试验工作获取到的信息非常有限,难以确定岩体力学参数统计特征。本文结合边坡施工开挖逐步揭示的工程地质信息,建立切合工程地质特征的三维弹塑性有限元模型,模拟边坡开挖过程对工程岩体岩石力学参数进行反分析,对比开挖过程测斜监测获得的位移变形,获得了接近实际情况的最优计算参数,并利用获得的参数分析边坡的稳定性,预测开挖加固效果。结果表明,采用基于弹塑性有限元的边坡稳定性分析是有效可行的,可以计算得出岩体位移场,应力场的变化特征,揭示边坡开挖变形的内在机制。本研究为复杂地质条件下信息化施工设计提供了一种新方法。