Stoping Method Research Articles

Joint stochastic optimisation of stope layout, production scheduling and access network

The three main optimisation components of sublevel stoping methods are stope layout, production schedule (or stope sequencing) and access networks. The joint optimisation of these components could further add value to an underground mining project. This potential has not been considered in the literature due to computational difficulties, and the problem was solved sequentially. This paper proposes a new joint optimisation model to integrate these components. In addition, the proposed optimisation model incorporates stochastic simulations to capture uncertainty and variability associated with the grades of the related mineral deposits mined. The optimisation model is based on a two-stage stochastic integer programming (SIP) formulation that maximises the project's net present value (NPV) and minimises the planned dilution. Applying the proposed method at a small copper deposit shows that the SIP outperforms the results obtained from mixed integer programming. For a seven-year mine life, the SIP model generated ∼20% more NPV, demonstrating the importance of developing a joint optimisation formulation and accounting for grade uncertainty and variability.

Damage evolution of rock-encased-backfill structure under stepwise cyclic triaxial loading

Rock-encased-backfill (RB) structures are common in underground mining, for example in the cut-and-fill and stoping methods. To understand the effects of cyclic excavation and blasting activities on the damage of these RB structures, a series of triaxial stepwise-increasing-amplitude cyclic loading experiments was conducted with cylindrical RB specimens (rock on outside, backfill on inside) with different volume fractions of rock (VF = 0.48, 0.61, 0.73, and 0.84), confining pressures (0, 6, 9, and 12 MPa), and cyclic loading rates (200, 300, 400, and 500 N/s). The damage evolution and meso-crack formation during the cyclic tests were analyzed with results from stress-strain hysteresis loops, acoustic emission events, and post-failure X-ray 3D fracture morphology. The results showed significant differences between cyclic and monotonic loadings of RB specimens, particularly with regard to the generation of shear microcracks, the development of stress memory and strain hardening, and the contact forces and associated friction that develops along the rock-backfill interface. One important finding is that as a function of the number of cycles, the elastic strain increases linearly and the dissipated energy increases exponentially. Also, compared with monotonic loading, the cyclic strain hardening characteristics are more sensitive to rising confining pressures during the initial compaction stage. Another finding is that compared with monotonic loading, more shear microcracks are generated during every reloading stage, but these microcracks tend to be dispersed and lessen the likelihood of large shear fracture formation. The transition from elastic to plastic behavior varies depending on the parameters of each test (confinement, volume fraction, and cyclic rate), and an interesting finding was that the transformation to plastic behavior is significantly lower under the conditions of 0.73 rock volume fraction, 400 N/s cyclic loading rate, and 9 MPa confinement. All the findings have important practical implications on the ability of backfill to support underground excavations.

Unplanned dilution back analysis in an underground mine using numerical models

In underground mines, stability problems can cause unplanned dilution, increasing the costs of mining operations, such as loading, transport, crushing and grinding. This is usually dealt with by simply increasing investments with support. However, the design geometry of stopes and drifts also has a great effect on a stope’s stability. The use of empirical stability methods is a very common practice, however because of their few input parameters, it cannot predict the actual performance related to each stope and drift design. This study has as main goals a back analysis of the actual dilution, using the Equivalent Linear Overbreak Slough (ELOS) method and analysis in the drift developments at the hanging wall contact, using numerical models. The case study is an underground hard rock gold mine, with a pillar-less Transversal Stope method. The hanging wall failure was quantified using a database from 19 stopes measured by the Cavity Monitoring System (CMS). Numerical finite elements models (FEM) were used, and 5 primary stopes were selected to calibrate models. The volumes of actual dilution showed a good correlation with the volumes of the relaxation zones produced by the models. Then, new optimized drift geometry layouts at the hanging wall contact were proposed, showing a decrease in 2.35 times in the relaxation zone of the numerical models, therefore justifying the use of these models as a dilution optimization tool. This methodology also proved to be useful in the definition of cable bolt length.

Investigation into near-contour stresses in stoping with backfilling by the polarization-optical method

When mining deposits with room-and-pillar methods with backfilling, available hanging wall rocks and ores of medium or low stability can cause hanging wall rock collapses into stoping areas, thus causing escalation of ore dilution with waste rocks. The research work is aimed at determining areas of maximum stresses and their quantitative characteristics which can cause collapses of hanging wall rocks in the mined-out stope area and developing technological solutions to reduce concentration of stresses. Options of mining stopes located on the hanging wall of the deposit are investigated on polarization-optical models. According to the results of studying polarization-optical models with different designs of stope chains, there are obtained stress fields for each model in the zone of stope influence. The research reveals that when using a stoping method with partial processing of hanging wall rocks in the contact plane with the country rocks, the maximum stresses are much higher than in case of the arched form of the stoping area. On the basis of the obtained research results, it is recommended to carry out chambers with the formation of a vaulted shape of the roof from the hanging side in order to reduce the clogging of the ore.

Investigation and Stability Assessment of Three Sill Pillar Recovery Schemes in a Hard Rock Mine.

In Canada, many mines have adopted the sublevel stoping method, such a blasthole stoping (BHS), to extract steeply deposited minerals. Sill pillars are usually kept in place in this mining method to support the weight of the overburden in underground mining. To prolong the mine’s life, sill pillars will be recovered, and sill pillar recovery could cause failures, fatality, and equipment loss in the stopes. In this paper, three sill pillar recovery schemes—SBS, SS1, and SS2—were proposed and conducted to assess the feasibility of recovering two sill pillars in a hard rock mine by developing a full-sized three-dimensional (3D) analysis model employing the finite element method (FEM). The numerical model was calibrated by comparing the model computed ground settlement with the in situ monitored ground settlement data. The rockburst tendency of the stope accesses caused by the sill pillar recovery was assessed by employing the tangential stress (Ts) criterion and burst potential index (BPI) criterion. All three proposed sill pillar recovery schemes were feasible and safe to recover the sill pillars in this hard rock mine, and the scheme SBS was the optimum one among the three schemes.

Study on Strength Reduction Law and Meso-Crack Evolution of Lower Layered Cemented Tailings Backfill

The green disposal of tailings solid waste is a problem to be solved in mine production. Cemented tailings filling stoping method can realize the dual goals of solid waste resource utilization and mined-out area reduction. However, the volume of the mined-out area of the open-pit method is larger than the filling capacity, resulting in the complex stratification of the underground backfill, and the strength of the backfill cannot meet the requirements. In this paper, according to the delamination situation, the specimens of horizontal and inclination angle layered cemented tailings backfill (LCTB) is made for a uniaxial compression test, and the failure process of delamination backfill is reduced by PFC. The results show that the corresponding reduction factor φ of horizontal LCTB is 0.560–0.932, and the corresponding φ value of inclination angle LCTB is 0.338–0.772. The failure mode of backfill in different layers is mainly manifested as a tensile failure. The PFC numerical simulation results are consistent with laboratory test results, which verifies the correctness of backfill failure. The research results provide a reliable theoretical basis for the strength design of backfill in goaf, which is of great significance for solid waste utilization and environmental protection.

Review on the Development of Mining Method Selection to Identify New Techniques Using a Cascade‐Forward Backpropagation Neural Network

The most crucial event in a mining project is the selection of an appropriate mining method (MMS). Consequently, determining the optimal choice is critical because it impacts most of the other key decisions. This study provides a concise overview of the development of multiple selection methods using a cascade‐forward backpropagation neural network (CFBPNN). Numerous methods of multicriteria decision‐making (MCDM) are discussed and compared herein. The comparison includes several factors, such as applicability, subjectivity, qualitative and quantitative data, sensitivity, and validity. The application of artificial intelligence is presented and discussed using CFBPNN. The Chengchao iron mine was selected for this investigation to pick the optimum mining method. The results revealed that cut and fill stoping is the most appropriate mining method, followed by sublevel and shrinkage stoping methods. The least appropriate method is open‐pit mining, followed by room and pillar and longwall mining methods.

Sublevel stoping with applying artificial hardening stowing pillars for extraction of veins in complicated geotechnical conditions

In the process of underground mining of deep levels rock pressure can appear in any form, creating a serious threat to the lives of miners, disrupting the normal course of mining works and reducing the efficiency of mining production. The solution of the problem of rock pressure control becomes very urgent for underground mines developing vein deposits at a depth of more than 250 m. The aim of the study is the development and justification of mining methods to provide safe and efficient mining of deposits in complicated mining and mechanical conditions. In this paper, the factors of redistribution and dangerous concentration of stresses in the mined ore mass were identified, the methods of rock mass management in complicated geotechnical conditions were studied, and their advantages and disadvantages were revealed. It was determined that the sublevel stoping with the combined use of existing methods of rock pressure control and applying selfpropelled mining machinery is currently one of the most promising method finding widening application scope. In the context of Zarmitan gold ore zone the options of technological schemes of the sublevel stoping method were considered, providing for a combination of different methods of rock pressure control, allowing to minimize the disadvantages of one method through using the advantages of other ones. We proposed sublevel stoping options with artificial polygonal pillars and with artificial columnar pillars, which allowed to reduce ore losses in inter-stope pillars, arch pillars, and secondary dilution. In addition, artificial pillars, taking compressive/tensile stresses, prevent their concentration and create safe conditions for extraction at adjacent and underlying levels.

Analyzing Stability Conditions and Ore Dilution in Open Stope Mining

Ore dilution is a fundamental problem for the production process in underground mining operations. Especially in open stoping methods of underground mining, the continuous estimation, monitoring and treatment of instability issues is considered necessary in order to maintain the consistency of the production process. This paper aims to combine empirical nomograms of stability estimation and numerical approaches and thus link the extensive experiences of the empirical design and the quantitative data derived by numerical analyses. To facilitate this, a large number of different geomechanical conditions were modeled and analyzed in the pursuit of obtaining valid and applicable relationships between the empirical stability graphs’ approaches and the numerical simulation models. The parametric analysis was made to express the stability conditions and the dilution with specific design characteristics, using prevalent stability-graph approaches while the numerical models were tested using the RS2 software package. The obtained results include direct and easy-to-use mathematical expressions that can be applied during the initial design of the stoping process, especially for the case of sidewalls (hanging walls and foot walls). Furthermore, through the research, an initial proposal is made for a dilution-based stability graph that could be utilized for the early identification of dilution.

Empirical approach to ore pass geometry justification in Talnakh mines

Ore mining in the Talnakh and Oktyabrsky fields using stoping methods includes construction and support of many temporal and permanent ore passes for ore haulage by gravity, which is the commonly known effective and cost-saving technology. Despite all benefits, there are some geotechnical complexities. For instance, making ore passes with smaller diameter increases their stability, which allows using them in difficult ground conditions, on the one hand, and, on the other hand, this can lead to frequent ore flow arching phenomena in ore passes and, consequently, to the increase in efforts for their elimination. This paper presents summary recommendations for selecting the cross-section shape and dimension of an ore pass based on global practice. The approach to determining the ore pass diameter with regard to grain sizes and properties of ore flow is substantiated. A series of experiments for determining the physical and mechanical properties (cohesion and internal friction angle) of ore mixture with a given particle size distribution at various degrees of moisture is carried out. Considering the determined properties, the minimum diameter of an ore pass to provide ore flow without formation of cohesive and interlocking arches is calculated. It is found that at the ore pass diameter of 2.4 m and at the maximum lump ore size of 254 mm, the material with natural moisture flows freely without arching in the ore pass.

The stress distribution around the mining excavations under different tectonic loads

The article studies the fatures of stress distribution around the mining excavations under different tectonic loads on the case study of the Zhdanovskoe copper-nickel ore deposit, Murmansk region, Russia. The deposit is located in the Arctic zone on the Russia-Norway state boundary and is excavated by the Severny underground mine using simultaneously the sublevel caving and the open stoping methods. The combination of these mining methods in the same area affects the geomechanical conditions; moreover, the highest level of stresses is identified between the opposing excavation fronts. The deepening of mining increases the geodynamic risks caused by the stress state in the rock mass. In this regard, the study of the Zhdanovskoe deposit rock mass stress state and its transformation due to the mining progress is urgent. To address the issues a numerical geomechanical 3D model was created. To specify the correct boundary conditions, the results of the in-situ measurements were compared to visual observation results. To achieve the most accurate result, the direction and ratio of the tectonic loads were varied and the results were analyzed. The authors have analysed the modelling results in the form of the stresses and deformations distribution in the area around the excavations under different directions of tectonic loads. Based on this analysis, the authors have substantiated a relevant variant of direction of tectonic forces relatively the ore body strike. The results have been applied to forecast the changes in perspective stress-strain state during the mining progress.

STUDY OF THE INFLUENCE OF BACKFILLING ON STABILITY AND LOCATION OF REMAINING STOPES IN SILL PILLAR RECOVERY

To extract steeply dipping orebodies, many mines in Canada have adopted the sublevel stoping method, such as blasthole stoping (BHS) and sublevel longhole retreat (SLR). In such methods, sill pillars are initially kept in place to support the weight of the overburden in underground mining. After the stope mining is complete, the stope voids will be backfilled with cemented rockfill (CRF). The strength of the CRF affects the stability of the adjacent stopes in the sill pillar recovery excavation scheme. Sill pillar recovery may cause prolonged failure, fatality, and equipment loss. Choosing a rational location of the last mined stope in sill pillar recovery can effectively eliminate the possible instability caused by the sill pillar recovery process. This paper uses the Finite Element Method (FEM) to present a comparison of sidewall swellings, floor heaves, and the roof subsidence of the crossing cuts in each stope among different last mined stope location scenarios. At all the 21 location scenarios, most of the roof corner displacements in undercuts are less than 10 cm, while in the overcuts, all the displacements in roof corners are over 10 cm. The values of the floor heave in the overcuts are more than 7 times that in the undercuts. Roofs in both undercuts and overcuts are prone to failures. Floors in the undercuts are more stable than the floors in the overcuts. For the optimum location of the last mined stope in sill pillar recovery, the last mined stope should be at least four-stope-width away from the two sill pillar edges

Improving the Stability of Subsurface Structures in Deep Metal Mines by Stress and Energy Adjustment: A Case Study

In deep hard-rock mines, the failure of subsurface structures (e.g., tunnels, stopes, and shafts) has been a significant problem affecting mining safety due to the high-stress environment. In this paper, the mechanism of structural failure and instability is discussed, and optimized excavation methods are proposed for stress control in deep gold mines. Based on the field observation and investigation of the joints distribution and rock failure modes at 800–1200 m depth of several large gold mines and a typical ultradeep borehole (2017 m depth) in northwest Jiaodong Peninsula, three engineering methods for reducing stress, including the stress transferring by mining optimizations, pressure relief by boreholes, and energy release in advance by optimizations of excavation and support, are analyzed by numerical simulation and field monitoring. Results show that stress reduction by excavation alone is limited and the backfill mining method is more conducive to stress transfer than the opening stope method. Roof contacted backfill can produce an unloading zone around the stope and reduce the stress of the surrounding stope. Relief boreholes can reduce the stress concentration of stopes, but the effect of cutting seams generated by presplitting blasting on pressure relief is not significant. The technology “short excavation and short support” releases less energy. By increasing the bench height and the reasonable timing of support by calculating, the elastic strain energy of rock in the shaft is prereleased, which benefits the long-term stability of the shaft.

Rock pressure control methods based on detected regularities of stress formation in mining structures

Relevance. Subsurface mining at the Gaysky ore mine is intensifying because of the growing need in raw material. It leads to rapid increase in the depth of mining and to problems connected with the stability of mining system constructive elements. The effi ciency of the Gaysky deposit underground development is largely determined by mining system constructive elements stability. Ore cave-in in the chambers of the fi rst and second stages causes the growth of load in the interchamber pillars leading to their collapse, loss of boreholes and development headings. Mining productivity in the chambers of the fi rst, second, etc. stages falls, oversize yield grows, which also impairs the effectiveness of mining. Hanging wall and footwall cave-in in the deposit under consideration may be explained not only by host rock poor stability, but also by the presence of high compressive tectonic stresses, that were determined by the authors. Stress measurements in the rock mass have shown that the east-west stresses have doubled the northsouth stresses and have been 1.5 times as high as the vertical ones. The purpose of the research is to reduce stresses in stopes ore in place when excavating steeply dipping ore bodies using a sublevel stoping method with a hardening backfi ll. Research methodology includes full-scale experimental measurements of the stress state of the rock mass and ore in place at accessible depths and horizons of the deposit. A comprehensive scientifi c research method was used, including the analysis and theoretical generalization of stress distribution regularities in the arrays of the extracted chamber reserves and mathematical modeling of the behavior of the research object; theoretical results were compared with the results of instrumental observations. The analysis of the research results made it possible to establish the stress-strained state behavior in the course of mining. It was revealed that when mining a deposit using sublevel stoping, the most loaded elements are the hanging wall and footwall exposed parts, ceiling, interchamber pillars and bottom. Therefore, it is necessary to take measures to increase ore in place stability in order to guarantee the safety and effi ciency of the mineral extraction technology. Conclusions. Relieve slots method is among the most effective and frequently used active method of rock mass pressure control. The method has come into common use because it is easy to apply. Main labor inputs of a relieve slot creation are only reduced to extra drilling and blasting which do not require additional tunnel driving. The aim of the relieve slot is to create additional free surfaces for deformation, to redistribute rock mass stress-strain state, and remove stress from the protected element of the mining system.

Selection of a strata pressure reduction method to extract deeper level reserves of Mir pipe

The article presents the chronology and stages of mining resumption at Mir pipe. The initiatory steps of the conceptual approach to underground mining of ore reserves at the depth greater than 1500 m are described. The primary measures on catchment of highly mineralized water from Metegero-Ichersky aquifer are identified. The exploratory study results on deeper level mining safety in the future underground mine in terms of the strata pressure reduction are given. The authors in detail discuss two methods of rock mass destressing: destressing drilling and formation of protection layers with different parameters at the depths of 1000 m and greater. Natural stress state of rock mass is modeled in Rocscience RS3 environment. The analyses of the mathematical models of ore and enclosing rock destressing show that the safest and the most effective methods of dеstressing of deeper level rock mass in Mir Mine is creation of a protective separation layer both in ore body and in enclosing rock mass on the both sides of the ore body at a distance of 15 m. Such destressing measures can allow safe mining of ore reserves using the sublevel stoping method with sublevels to 50 m high. The research findings will be used in the front-end engineering as the basis for the further mine planning and design.

Evaluation of Stope Stability in Underground Mine; Hermyingyi (Sn-W Deposit) Mine in Myanmar

The stability of underground excavations has become an important issue in order to extend underground mining operations and extract deeper deposits. The increasing demand for Tin-Tungsten (Sn-W) for industry and its market price has created a motivation for mining companies to extract deep-seated Sn-W ore deposits in Myanmar. Thus, this paper aims to investigate the stability of underground openings, especially, the stope with considering the mining methods. To meet the objective, FLAC3D 5.0 simulation was used for the assessment of stope under different stress ratios, 0.5, 1.0, and 1.5 for two types of underground mines; Open stoping and Cut and Fill stoping. The results show that the risk of instability of stope is high under the stress ratio of K = 0.5 than that of K = 1.0 and K = 1.5 in both mining methods. However, the stability of the stope in open stope method is lower than that of cut-and-fill method obviously. This result shows that the appropriate mining method has to be selected for extraction of Sn-W deposit carefully in terms of the balance of safety and cost.

Extraction of ore reserves from pillars in room-and-pillar mining

The geotechnical situation in mines using the open stoping methods is governed by complex geomechanical behavior of rock mass around rib and level pillars. The impact of rock pressure on underground excavations grows in this case, and dynamic events due rock pressure happen more often. The latter became the reason for implementing this research. In terms of steeply dipping ore bodies, safe mining of earlier left pillars is feasible. The best scenario for pillar extraction, considering their parameters, is caving to open and partly filled with overlying rocks stopes. The geomechanical calculations during justification of mining parameters during extraction of ore reserves from pillars have determined regular patterns in the stress–strain behavior of rocks mass, which contributes to qualitative and quantitative prediction of safe and feasible mining conditions. The zones of instability in structural elements of the geotechnology, including pillars, are detected. The author proposes the order and sequence of pillar caving to open and partly filled stopes at the admissible completeness and quality of extraction.

Quantitative Study on the Contact Force and Force Chain Characteristics of Ore Particle Systems during Ore Drawing from a Single Drawpoint under the Influence of a Flexible Barrier

It is of great significance to carry out quantitative research on the contact force chain characteristics of ore particle systems during ore drawing to reveal the microscopic and mesoscopic characteristics of ore particle systems during implementation of the synchronous filling shrinkage stoping method. Based on the particle discrete element method, combined with the relevant knowledge of contact mechanics and statistical mechanics, microscopic properties of the ore particle system were studied quantitatively. (1) The probability distributions of the normal and tangential contact forces during ore drawing from a single drawpoint under a flexible barrier are similar, and both show exponential decay. (2) In the regions on both sides of the model, the ore particles will not be released because they are far from the drawpoint; there, the coordination number is stable, and the density of contact network is large. In the upper part of the drawpoint, ore particles flow, the coordination number fluctuates violently, and the density of contact network is small. (3) In the initial stage, the stress distribution of the ore particle system is uniform, and the strong force chain does not show obvious directivity. After that, the directions of the strong force chains in the ore particle system are inclined to the vertical direction, and the strong force chains mainly bear the load in the vertical direction. (4) In the initial stage of drawing, the normal contact force is mainly concentrated in the vertical direction. With the progression of drawing, the normal contact force at an angle of 30° to the horizontal direction increases gradually, and the number of the main direction of the average contact force distribution changes from one to three (the vertical direction and the direction with a ±30° angle to the horizontal direction).

Study on the Allowable Exposure Time of Temporary Goaf in the Open Stope and Backfill Mining Method with Large Structure Parameters

Based on the uniaxial rheological experiment data of iron ore rock mass and filling body in large‐scale stope obtained by using the rock servo controlling creep equipment, the characteristics of the creep curve were analyzed. The creep models of iron ore and filling body which can show the attenuation creep of rock were constructed. And a nonlinear creep model was obtained. According to the rheological data of the iron ore and the filling body, the parameters of the new nonlinear creep model were identified to obtain the material parameters of the creep model. Then, the creep model parameters were fitted and reduced to calculate the reasonable exposure time of temporary goaf in the large‐scale stope. The results show that the reasonable exposure time of stope is 520 ～ 650 days, and the reasonable exposure time of filling body is 410 ～ 520 days. The model can well describe the initial attenuation creep stage and steady creep stage in the creep curve, which proves the correctness and rationality of the model. The study provides a reference for mining design and safety production of similar mines with large‐scale stope structure.

硬岩地下开采的一种增值方法: 通过元启发式算法优化平衡矿体走向和开采方向

Underground mines require complex construction activities including the shaft, levels, raises, winzes and ore passes. In an underground mine based on stoping method, orebody part(s) maximizing profit should be determined. This process is called stope layout optimization (SLO) and implemented under site-specific geotechnical, operational and economic constraints. For practical purpose, the design obtained by SLO shows consecutive stopes in one path, which assists in defining the mining direction of these stopes. However, this direction may not accommodate the spatial distribution of the ore grade: if the orebody orientation and mining direction differ, the value of the mining operation may decrease. This paper proposes an approach whereby paths in the SLO are defined as decision variables to avoid the cost of mining in the wrong direction. Furthermore, in the genetic-based formulation, which accounts for orebody uncertainty, a robust cluster average design process is proposed to improve SLO’s performance regarding metal content. A case study in narrow gold vein deposit shows that the profit of an underground mining operation could be underestimated by 25%–48% if the algorithm ignores stope layout orientation.