Mine Stopes Research Articles

Prediction of Stope Stability Using Variable Weight and Unascertained Measurement Technique

A new model is established to analyze mining stope stability, using variable weight theory to calculate the index weight for each factor in different stopes and unascertained measure evaluation technique to predict the risk grade of stope stability. In this model, an evaluation index system by virtue of the 7 most important factors is established, including rock saturated uniaxial compressive strength, rock quality designation, rock joint and fissure, stope span, condition of pillar, groundwater seepage volume, and rate of supporting pit roof. And each index is divided into 5 grades by assignment value and the classification method of standardization. Accordingly, the analysis result is also classified into 5 risk grades. This model is used for the 6 main stopes from the -270 m section in Xin-Qiao Mine, China. The results, giving risk grade for each stope and guiding the use of corresponding measures, avoided the problem of state out of balance caused by conventional invariable weight theory models and have ensured no accident occurred in mining production in recent years. This model can be used in other mines widely, by assigning values for the 7 factors on basis of current in situ cases.

Evaluation of the use of sublevel open stoping in the mining of moderately dipping medium-thick orebodies

The flow of blasted ore during mining of moderately dipping medium-thick orebodies is a challenge. Selecting a suitable mining system for such ore bodies is difficult. This paper proposes a diamond layout sublevel open stoping system using fan blastholes with backfilling to mine such orebodies. To evaluate the performance of system the relationships between ore recovery and stope footwall dip angle, footwall surface roughness, drawpoint spacing and production blast ring burden were investigated. An ore recovery data set from 81 laboratory physical model experiments was established from combinations of the listed factors. Various modules in a back propagation neural network structure were compared, and an optimal network structure identified. An ore recovery backpropagation neural network (BPNN) forecast model was developed. Using the model and sensitivity analysis of the factors affecting the proposed open stope mining system, the significance of each factor on ore recovery was studied. The study results were applied to a case study at the Shandong Gold Group Jiaojia Gold Mine. The results showed that the application of a BPNN and sensitivity analysis models for ore recovery prediction in the proposed mining system and field experimental results confirm that the suggested mining method is feasible.

A Three‐Dimensional Nonlinear Dynamic Numerical Optimization of the Risks of Stope Blasting Based on FOA‐GRNN

The fruit fly optimization algorithm‐general regression neural network (FOA‐GRNN) coupled model and the Finite Element Method‐Smoothed Particle Hydrodynamics (FEM‐SPH) numerical calculation method are comprehensively used. The control problem of blasting vibration in the process of mining hidden resources under complex environmental conditions has been studied. Taking a lead‐zinc mine as the engineering background, the development of hidden resources in the collapse area due to unreasonable mining was studied. Based on the establishment of the first mining stope and its mining method in this area, biosimulation and generalized neural networks were introduced to solve this problem, the coupling of blasting parameters was analyzed, and the 3D nonlinear dynamic coupling model was constructed for numerical simulation. The results show that the blasting parameters of deep‐hole mining were optimized, including the values of six output quantities: hole distance, row spacing, side hole distance, explosive unit consumption, minimum resistance line, and interval ratio (the Root Mean Squared Error value is only 0.051). The error between the network optimization parameters and the empirically obtained values was controlled to within 0.05; five possible edge‐hole charge structures were designed (the interval ratio is 0.696), and the vibration velocity peak and pressure peak variations with time after detonation are reflected by the simulation results. The dynamic evolution law of the rock mass velocity vector and the damage of the rock damage was revealed. According to the analysis in this paper, the smallest and optimal edge‐hole charge structure of the surrounding rock was obtained.

Experimental Tests on a Small-Scale Model of a Mine Stope to Study the Behavior of Waste Rock Barricades during Backfilling

This paper presents a reduced-scale physical model of a mine stope used to reproduce the underground stope backfilling practiced in some Canadian mines. The objective is to study the geomechanical behavior of the waste rock barricades in interaction with the mine backfill. The instrumentations, along with visual observations and preliminary results, are presented. The main results demonstrated that: (i) the stability of the barricade depends on its physical properties (e.g., size, location, particles gradation and compaction) and the frictional behavior at the barricade/drift walls interface, and (ii) for two backfill formulations, cemented and uncemented, prepared with 70% of solid mass concentration, the volumetric strain due to self-weight consolidation of the backfilled room was higher for uncemented backfill (16%) than for the cemented one (4.5%). In addition, the results highlighted the importance of using shotcrete around the downstream face of the barricade, mostly at the top, to close the gaps and bind the barricade particles, which improves its stability.

Обоснование возможности размещения радиоактивных отходов 2-го и 3-го классов в подземном пространстве урановых рудников

Intensive development of the nuclear power generation industry creates the issue of radioactive waste disposal (RAW), which has a negative impact on the environment. Development of uranium deposits using underground mines produces openings, e.g. workings and stopes that can be used as reservoirs for RAW storage. This requires a geomechanical assessment of the condition of mine workings and stopes, evaluation of their total volume, compliance with the requirements for the nuclear waste disposal sites, necessary preparation, as well as evaluation of the limits of existing mining technologies and equipment.

Study on attenuation coefficient characteristics of the in-seam seismic wave in fault and collapse column

Various types of geological structures exist in the working face of coal mine stope. Failure to identify the structural development in advance could defer the timely implementation of reasonable management measures, which may eventually affect production safety and connectivity. As a matter of fact, fine detection and interpretation problems of in-seam seismic wave caused by different types of geological anomalies such as faults and collapse columns can exist simultaneously in the working face of mining. In view of these problems, forward modeling research of three-dimensional seismic wave fields on geological models with fault and collapse column are carried out in this study. Meanwhile, in combination with the imaging results of in-seam seismic wave attenuation coefficient of the exposed fault and collapse column, the characteristics of in-seam seismic wave were analyzed. Following comparative analysis, we found the attenuation coefficient anomaly of the fault is generally banded and weakens at both ends of the fault. The attenuation coefficient of the collapse column presents as an irregular ellipse. The energy of the smaller collapse column has a relatively small attenuation, while the energy of the larger collapse column shows a significantly obvious attenuation.

Study on the maximum pressure-causing stratum in longwall mining stope and its mechanics analysis

Based on the movement model of overburden in longwall mining, a 12-parameter model of stope overburden pressure considering the physical and mechanical parameters of the strata and structural parameters of the stope is established, which can be used to calculate the abutment pressure of each roof to the working face. The maximum pressure-causing stratum is proposed, and the determination of the maximum pressure-causing stratum and the quantitative analysis on the factors influencing the maximum pressure-causing stratum are given. Finally, maximum pressure-causing stratum analysis was carried out under the geological conditions of the Tongxin coal mine. It is found that the stratum horizon has a great influence on the determination of the maximum pressure-causing stratum. The lower the stratum horizon and the greater the bulk density and thickness, the more likely a stratum is to be the maximum pressure-causing stratum. Other parameters need to be combined under certain conditions to determine the maximum pressure-causing stratum. In addition, the structure of the stope overburden also has a great influence on the abutment pressure of the working face. The roof near the working face and the key strata plays significant pressurisation roles in the structure of the stope overburden, even far exceeding the pressure of their self-weight on the working face. The research results can be used to calculate the abutment pressure of the working face, to determine the maximum pressure-causing stratum, to select the measurement stratum and to prevent and control mine disasters.

Factors Influencing Ore Recovery and Unplanned Dilution in Sublevel Open Stopes. Case study of Shaft No.4 at Konkola Mine, Zambia

Konkola Copper Mine’s Number 4 Shaft is a trackless underground mine applying sublevel open stoping (SLOS) mining method. Number 4 shaft wants to increase ore production from 1 million metric tonnes per annum to 3 million metric tonnes per annum in the next 5 years but ore recovery is 70% or less and dilution is 20% or more. In order to achieve the desired annual target of 3 million metric tonnes ore recovery should be increased from70% to (≥85%) and dilution should be reduced from 20% to (≤10%). Despite being one of the most used underground mining methods, the current SLOS has a challenge of high unplanned dilution. This paper reviews and evaluates parameters that influence recovery and unplanned dilution in sublevel open stopes and applies numerical modelling using PHASE2 software to establish the influence of stress environment on unplanned dilution at the mine. The input parameters for numerical modelling were: Uniaxial Compressive strength (UCS=170MPa), Geological Strength Index (GSI) =55, Young’s Modulus (E) =26000MPa, Hoek-Brown constant (s) =0.0067, Hoek-Brown constant (mi) =20 and Poisson ratio (v) =0.2 major principal stress (σ1) 39MPa, intermediate stress (σ2= 18MPa) and the minor principal stress (σ3= 15MPa). Results obtained from review of mine production records indicate that the main factors that influence unplanned dilution at Number 4 shaft are: poor ground conditions, lack of compliance to recommended stope designs, poor drilling and blasting practices, presence of geological discontinuities, adopted mining sequence of extracting high ore grade first that leads to creation of high stress blocks within the orebody and delayed mucking practice. Results obtained from PHASE 2D model indicate that total displacement of 90mm is recorded in the hangingwall hence influencing stope wall instability that leads to increased unplanned dilution. After stope extraction, it was observed that 60MPa of induced stress developed at the top right corner and 45-50 MPa at the crown pillar and right bottom corner of the stope.

Numerical Simulation of Fluid-Solid Coupling in Surrounding Rock for River Stope Mining

Mining disturbance will induce further weakening of faults and rock bridges, improve rock mass permeability and, in serious cases, conduct surface rivers to cause disasters. A numerical calculation model of river-fault in the mining area is established. Based on the fluid-solid coupling theory of rock mass, the influence of mining disturbance on the development and evolution process of rock bridge rupture and river-fault-stope potential seepage channel is simulated and calculated. Research studies show that under the disturbance of ore body mining, it is possible to form a channel from the river to fault to seepage and drainage in the stope. The disturbance of ore body mining has no great adverse effect on the stability of the rock mass at the top of F2 fault. The rock mass damage caused by mining is only distributed in local areas, and the rock bridge between the river, fault, and stope is not completely connected. The fracture of mining rock mass leads to the increase in permeability of rock mass, and seepage tends to spread in the direction of the fault, but there is no obvious through drainage channel from surface water to the stope. The results of research provide technical guidance for the mine to use the filling mining method after the river does not change the road safety and reliability certification and can also provide reference for similar mines.

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

SummaryMining 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.

Numerical and experimental study of transient conjugate heat transfer in helical closed‐loop geothermal heat exchangers for application of thermal energy storage in backfilled mine stopes

The geothermal potential available from deep underground mines has yet to be utilized. However, stope-coupled heat exchangers (SCHE) are aiming to take advantage of the unused low-grade geothermal energy. Backfilled stopes provide a unique opportunity to install nonlinear heat exchangers, as the geometry is not limited to the shape of a borehole. Helical pipes deliver superior fluid mixing and heat exchange compared to straight pipes, due to the effect of the secondary flow within the helical pipe. The helical closed-loop geothermal heat exchanger enables the backfilled stopes of the mine to be repurposed as thermal energy storage units. This article delves into the experimental results from a unique state-of-the-art laboratory scale helical closed-loop heat exchanger with varying thermophysical parameters. Additionally, a novel conjugate numerical model is developed and its results are validated against the base case of the experimental studies. Additionally, the numerical model is validated in a spatial-temporal sense with thermocouple data from the experimental rig. The numerical model is also applied to a helical SCHE situated within a backfilled stope for the first time. The results of the numerical model suggest that the pumping rate through the SCHE has a significant effect on the heat exchange rate and the overall energy transfer between the SCHE and the backfill. Additionally, the temperature contours from the numerical model suggest that a decreased pitch/helical diameter will increase the storage capacity of the helical SCHE. Overall, an average of 2.5 MW can be stored over the first 4 days of geothermal charging with the investigated full-scale SCHE, boasting a pseudo-steady-state storage rate of 1.7 MW.

Study on Stability Analysis and Control Technology of Floor Rock Roadway in Dynamic Pressure Stope

Taking the floor rock roadway of 10414 working face of Yangliu Coal Mine in Huaibei as the engineering technology background, this paper uses theoretical analysis and numerical simulation technology to analyze the stability of floor rock roadway caused by stope mining. According to the dynamic pressure of stope, the support stage is divided into three stages: timely support scheme after excavation, pre-mining reinforcement support stage and post-mining repair support stage, and corresponding suggestions are put forward. Support scheme, through field practice, the overall maintenance of roadway affected by dynamic pressure is in good condition, the deformation of roof, floor and both sides are within the controllable range, and the roadway section can meet the requirements of normal use.

Long-term mechanical behavior and characteristics of cemented tailings backfill through impact loading

Cemented tailings backfill (CTB) structures are important components of underground mine stopes. It is important to investigate the characteristics and dynamic behavior of CTB materials because they are susceptible to disturbance by dynamic loading, such as excavation and blasting. In this study, the authors present the results of a series of Split-Hopkinson pressure bar (SHPB) single and cyclic impact loading tests on CTB specimens to investigate the long-term dynamic mechanical properties of CTB. The stress-strain relationship, dynamic strength, and dynamic failure characteristics of CTB specimens are analyzed and discussed to provide valuable conclusions that will improve our knowledge of CTB long-term mechanical behavior and characteristics. For instance, the dynamic peak stress under cyclic impact loading is approximately twice that under single impact loading, and the CTB specimens are less prone to fracture when cyclically loaded. These findings and conclusions can provide a new set of references for the stability analysis of CTB materials and help guide mine designers in reducing the amount of binding agents and the associated mining cost.

Experimental study on the strength of soil-cement with additions of mineral powder and ferronickel slag powder

With the rapid development of soil-cement application technology, soil-cement is widely applied in mine development, such as mine road construction, pit repair, stope reinforcement and mine backfill, etc. In this paper, ferronickel slag powder and mineral powder are applied in soil-cement to study the impact of their content on the strength performance of soil-cement. The results show that the addition of ferronickel slag powder has a greater impact on the strength of soil-cement at the early age. However, with the increase of age, the strength decrease rate of soil-cement with ferronickel slag powder reduces. When ferronickel slag powder and granulated blast furnace slag are mixed, the performance of soil-cement at the early age is better than that with ferronickel slag powder alone. The optimal combination is that ferronickel slag powder accounts for 20%, among which the mineral powder replaces 30% of the ferronickel slag powder mass.

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.

Numerical simulation study on the width of coal pillar in dynamic pressure roadway

The deep coal mine roadway is easy to deform and destroy under the high ground stress. At the same time, it is disturbed by the mining stress of the adjacent working face. At present, the scope and size of the influence of stope mining are mainly studied at home and abroad. However, there is not enough understanding of the propagation law of the working face support pressure and the surrounding rock control of the deep well dynamic pressure roadway, and there is no in-depth study of the influence of the pillar width on the stability of the roadway. Therefore, this paper comprehensively uses the methods of field investigation and FLAC3D numerical simulation to study the deformation and stress distribution of surrounding rock under the influence of mining. By using FLAC3D numerical simulation software, this paper studies the distribution of surrounding rock stress and the law of surrounding rock deformation under different pillar width in the mining process of adjacent working faces. Studying conclude that when the pillar width is 80m, the roadway is less affected by mining.

Assessment of expansion and strength properties of sulfidic cemented paste backfill cored from deep underground stopes

The expansion and strength of cemented paste backfill (CPB), especially when prepared from sulfide mill tailings, are valuable properties for the estimation of design parameters for underground stope filling. These properties are particularly important for deep mining. In this paper, the free expansion ratio of CPB specimens containing sulfides was investigated using an invented apparatus called the free expansion measuring instrument. Moreover, the unconfined compressive strength (UCS) of backfill materials cored from the deep stope was studied. In the laboratory, the filling specimens continued to expand, and substantial cracks were observed at 28 days. Moisture and other reactants entered the samples through the cracks, and the specimens continuously expanded until collapse. In the deep mining stope, the strength of the backfill body in the same horizontal plane presents a wave-type change along the flow direction of the paste (or y-direction) and a hammock-shaped change along the x-direction (or crossing the y-direction). In the deep mining stope, due to the wall convergence effect of the deep surrounding rock and the expansion effect of the filling body, the filling material underwent a consolidation process. The backfill material after consolidation had a finer pore mechanism and a more compact microstructure based on the results of scanning electron microscopy. Therefore, the strength of the backfill near the surrounding rock was higher than that in the central area. The mechanical properties of the CPB mass differ at different locations along the same height in the stope, and the expansion of the sulfidic cemented paste and the convergence of the rock wall play reinforcing roles.

The identification and mitigation of geohazards using shallow airborne engineering geophysics and land-based geophysics for brown- and greenfield road investigations

South Africa is a mineral-rich country with a diverse geology and a long history of mining. The rich history of mining activities includes the extraction of coal from the Ecca Group Sediments of the Karoo Supergroup (250 Ma), gold and uranium from the Witwatersrand Supergroup (2900 Ma), as well as platinum, uranium, tin and lead from the layered Bushveld Igneous Complex (BIC) (2150 Ma). The extraction of gold, copper, tin, lead and rare earth minerals also took place in the Archean rocks of Swazium age (3500–3000 Ma). The historical mining records have either not been accurately recorded or have been lost over time. This has resulted in significant geohazard risk during infrastructure development, especially in and around historical mining towns, such as Johannesburg and Ermelo. These geohazard risks require careful appraisal and quantification prior to any infrastructure design or construction. This case study aims to set out the development aspects of the Multi-Faceted Geophysical Modelling Systems approach, which was used by the South African National Roads Agency SOC Ltd (SANRAL) during an investigation of undermined ground for the historical coal-mining town of Ermelo in South Africa. The N11/N2 ring road was planned to go around Ermelo to ensure mobility between major routes, whilst still maintaining town access. The systems approach used a combination of airborne geophysics (Versatile Time Domain Electromagnetic System (VTEM TM ) and magnetics), generally used in mining exploration, land-based and borehole geophysics, borehole water testing, and ground-truthing. The approach was continuous and iterative, building on the data at hand and reducing unnecessary investigations while eliminating the possibility of anomalies being missed, as in the case of conventional discrete drilling. The investigation ensured that 100% of the route was comprehensively investigated with a high confidence in the geological and geophysical data, and concomitant mitigation of infrastructure risk. The Multi-Faceted Geophysical Modelling Systems approach was successfully used to identify a previously unknown 1 × 1 m mining stope cavity at 90 m depth and a 3 × 5 m access tunnel at 24 m depth in a timely and cost-effective manner. Seven reverse-circulation percussion boreholes confirmed the structural integrity of these underground cavities, as well as the structural geology along the centreline. Based on the great success achieved in identifying shallow anomalies, this Multi-Faceted Geophysical Modelling Systems approach is now being considered for field trails on the dolomitic formations and the Wild Coast greenfields road project where there are large historical slumps and many fault lines. Thematic collection: This article is part of the Ground-related risk to transportation infrastructure collection available at https://www.lyellcollection.org/cc/Ground-related-risk-to-transportation-infrastructure

PTFI Big Gossan Mine - Ventilation Design to Support the New Stope Sequence Strategy

Big Gossan (BG) mine is an open stope mine operated by PT Freeport Indonesia(PTFI). This mine started its development in 2006. Currently, the mine consists of 9 active levels, each level is designed with about 1 km footwall drift East-West. The production initiated in 2009, but the mine was temporarily shut down due to a company decision. Lately the mine has been re-activated since 2017 and will be pushed into its peak production in 2019, with 7000 tpd production rate. In order to meet with the production goal, 5 levels consisting of 34 at least production stopes are required on a yearly basis. The other strategy to meet the production goal is an improvement of stopes sequencing. Big Gossan Mine is ventilated by two parallel 1600kW exhaust Mixed-Flow fans.This paper presents the ventilation plan and design to support the improved stope sequence until peak production, include the analysis of ventilation design criteria, ventilation network modeling, infrastructure required, possibility of main fans upgrade and other ventilation open stope mine challenges.

Role of kisspeptin and its therapeutic potential in fetoplacental dysfunction of hypothyroid rats

In order to overcome the limitation that rock mass instability warnings are caused by a lack of deep consideration of the inherent mechanism of disaster formation, early warning signs of rock mass instability were detected and multi-field coupling was analyzed. A multi-field coupling model of a damaged rock mass was established. The relationship between microseismic activity parameters and rock mass stability was analyzed, and a multi-parameter early warning index system was established and its solution program was compiled. Based on the D−S data fusion theory, an early warning model of rock mass instability combining multi-field coupling analysis and microseismic monitoring was constructed. Taking an underground mine stope as an object, the multi-field coupling model and its solution program were used to analyze mining response characteristics. The seismic field data were used to verify the accuracy of the multi-field coupling analysis. The early warning model was used to predict the instability of stope rock mass, and the early warning result is consistent with a real-world scenario.