Pillar Mining Research Articles

Exploration of Limestone Pillar Stability in Multiple-Level Mining Conditions Using Numerical Models.

Pillar stability continues to be a significant concern in multiple-level mining conditions, particularly for deep mines when pillars are not stacked or the thickness of interburden between mining levels is thin. The National Institute for Occupational Safety and Health (NIOSH) is currently conducting research to investigate the stability of pillars in multiple-level limestone mines. In this study, FLAC3D models were created to investigate the effect of interburden thickness, the degree of pillar offset between mining levels, and in situ stress conditions on pillar stability at various depths of cover. The FLAC3D models were validated through in situ monitoring that was conducted at a multiple-level stone mine. The critical interburden thickness required to minimize the interaction between the mining levels on top-level pillar stability was explored, where the top level mine was developed first followed by the bottom level mine. The model results showed that there is an interaction between numerous factors that control the stability of pillars in multiple-level conditions. A combination of these factors may lead to various degrees of pillar instabilities. The highest degree of local pillar instability occurred when pillar overlap ranges between 10 and 70%. On the contrary, the highest degree of stability occurs when the pillars are stacked, the underlying assumption is that the interburden between mining levels is elastic (never fails). Generally, for depths of cover investigated in this study, the stability of top-level pillars shallower than 100 m (328 ft) or with interburden thicknesses greater than 1.33 times the roof span-16 m (52.4 ft) in this study-does not appear significantly impacted by pillar offset. The results of this study improve understanding of multiple-level interactions and advances the ultimate goal of reducing the risk of pillar instability in underground stone mines.

Development of technology for additional extraction of potash ore reserves from previously mined out panels at the depths exceeding 600 metres of the Starobin potash salt deposit

Studied the possibility to extend the life of the Production Unit no. 3 mine of JSC “Belaruskali” through the additional extraction of sylvinite ore reserves left in the previously mined panels of the mine field of the 3rd potash level. It was determined, that during the period from 1971 to 1980 a considerable part of the southern direction of the mine field on the area of more than 5,3 million m2 was mined by the roadways on the layers 2, 2–3, 3 without the mining of the 4th sylvinite layer. The volume of the leftover reserves of minerals in the mined panels makes more than 22 million tons. There is direct access to these panels from the main southern gates. As a study result of geological structure of the mined panels it was determined that under the influence of rock pressure the undermined sylvinite layer no. 4 took the form of a wave-shaped seam with the capacity of about 1 meter which rests on compressed inter-chamber pillars and on compressed rocks of layers 2, 2–3, 3 of destroyed inter-roadway pillars, which fills the space of the roadways. Such geological structure of the seam enables to extract minerals using the technology of selective layer mining by successive top and bottom faces. As a study result of the stability of the mine workings performed along the roadways and inter-chamber pillars under conditions of different roof positioning, it was determined that during the preparation of the faces the most advantageous locations for development workings are the areas previously mined by the room and pillar mining system. In this case, the highest stability of mine workings located in the stopes of the room and pillar mining system will be provided by their roofing location with cut of 0.15 m of the 4th sylvinite layer. When this occurs, their predicted life without repair, even without the use of special protection methods, would be between 3.5 and 8 years. Based on the results of the study, a conclusion was made on the technical possibility and economic feasibility of additional extraction of sylvinite ore reserves left in the western panels of the southern direction of the mine field of the 3rd potash level of the Production Unit no. 3 mine, finished over 40 years ago by the room and pillar mining system using selective layer mining technology by the longwall faces. With minimal capital, organizational and technical expenditures, the extraction of these reserves will allow the company to produce additionally 5.5 million tons of potash fertilizers.

Determining the optimal dimensions of the pillars under static and dynamic loads in room and pillar mines (Case study: Tabas central coal mine)

Determining the optimal dimensions of the pillars under static and dynamic loads in room and pillar mines (Case study: Tabas central coal mine)

Overview of mine rescue approaches for underground coal fires: A South African perspective

Coal is mined by both surface and underground methods and its extraction is normally characterized by numerous hazards that can lead to catastrophic accidents, which result in devastating effects such as injuries or fatalities, damage to mining assets, and destruction of mineral resources. These hazards exist due to the ability of coal to support combustion and its association with toxic, flammable, and explosive gases. Underground coal mining entails higher safety risks than opencast coal mining, chiefly because of issues relating to mine ventilation and mine collapse. Furthermore, coal mine collapses mostly occur due to crumbling of mining supports, especially in room and pillar mining systems. To avoid such adverse occurrences, safety management systems need to be in place. This study reviews the various technological safety systems and principles that are used for safe-rescue and self-escape of miners in underground coal fires, particularly in South Africa, using data obtained from Mines Rescue Services in Carltonville, South Africa. The outcome of the review shows that practising safety culture has been given priority across many South African underground coal mines through setting up safety management systems and encouraging workers to stay committed to safety principles.

Simulation of hard rock pillar failure using 2D continuum-based Voronoi tessellated models: The case of Quirke Mine, Canada

The Quirke Mine, ON, Canada, is a typical example of a mine that experienced a chain reaction of pillar failure. In this mine, the rib pillars were initially laid out with their long axis parallel to the dip direction of the orebody. In the central part of the mine, the pillars were re-aligned at 45° to the orebody true dip. This realignment resulted in adverse shear loading conditions that led to their failure. In this study, a two-dimensional finite element program was used to simulate the failure of Quirke Mine pillars under compressive and shear loading conditions. The pillars were simulated as a heterogeneous material, consisting of randomly generated Voronoi blocks. The calibration of this model, referred to as a Voronoi Tessellated Model (VTM), was conducted against the rock mass strength estimated based on a tri-linear, brittle failure criterion. The calibrated VTM was then employed to investigate the pillar behavior during drift development and stope excavation. It was found that the pillar under shear loading experiences higher confinement loss and tensile stress at its core and, therefore, fails at a lower stress level than that under compression. The simulated pillar failure process was found to agree with documented field observations.

Research on Factors Affecting Mine Wall Stability in Isolated Pillar Mining in Deep Mines

This study takes the Dongguashan Copper Mine as its engineering background. Based on the mechanical model of the mine wall under the trapezoidal load of the backfill, a comprehensive evaluation index is proposed, and its calculation equation is derived. On this basis, an orthogonal test is designed to explore the influence of mining design parameters on mine wall stability. The results show that the width of the mine wall is the main factor affecting its stability, and increasing the width of the mine wall can significantly improve its stability. When the width of the mine wall is kept above 4 m, its stability is better. When the mechanical parameters of the backfill are poor, the mine wall is prone to overturning failure. The width of the mine room has an influence on the multi-directional loading of the mine wall, but the influence on the stability of the mine wall is low. According to the regression equation calculation, the mine wall safety factor is about 1.46 under the design of G5 mining of Dongguashan Line 52, the stability of the mine wall is good after actual mining and the engineering application effect is ideal, which can provide a theoretical basis for the design of isolation pillar mining in deep mines.

A non-coal pillar mining method by concrete carrier replacing coal pillar: a case study

A non-coal pillar mining method by concrete carrier replacing coal pillar: a case study

Field and simulation study of the rational retracement channel position and control strategy in close‐distance coal seams

AbstractDifferent from single coal seam mining, the stress evolution in the end mining stage of close‐distance coal seams is extremely complex. The unreasonable position and support of the lower retracement channel will cause serious deformation and damage to the surrounding rock. Taking the Yanzishan coal mine as the engineering background, the deformation and failure characteristics of the retracement channel under different overlay environments and the key influencing factors of position design were discussed by numerical simulation, theoretical analysis, and field investigation. The results show that the coupling superposition of upper coal pillar high stress and mining dynamic pressure will form a dangerous area with severe ground pressure behavior. The retracement channel should be preferentially designed in zone A (overlying mining roadways), followed by zone B (overlying end‐mining coal pillar), and finally, zone C (overlying section coal pillar). In addition, the rational horizontal distance between the lower retracement channel and the upper end‐mining coal pillar should make the channel in a good stress environment. The safety distance between the retracement channel and the nearest main roadway (end‐mining coal pillar width) should be greater than the severe range of advance abutment pressure. Finally, the design principle and control strategy for the lower retracement channel is proposed. The feasibility and rationality of the study are verified by industrial applications.

Study on Deformation and Fracture Evolution of Underground Reservoir Coal Pillar Dam under Different Mining Conditions

Coal mine underground reservoir water storage technology is an effective technical way to achieve high efficiency of coal mining and protection of water resources. The stability of coal pillar dam plays a decisive role in the safe and stable operation of underground reservoirs. Mining of adjacent working faces and long-term water erosion are the main influencing factors of stability of coal pillar dam. In this paper, a fluid-solid coupling calculation model for the deformation and evolution of coal pillar dam was established by FLAC3D numerical simulation software and the underground brine reservoir of Lingxin Coal Mine of Shenning group as an engineering background. The paper studied systematically the deformation, failure, and stress evolution of the dam with coal pillars soaked in water for a long time under different working face inclining length, coal pillar width, mining height, and water pressure. The simulation results showed that the degree of deformation and failure of the coal pillar dam continued to increase with the continuous advancement of the working face. The plastic zone of the coal pillar dam was increased by approximately 23.53%, the maximum vertical stress was increased by approximately 95.78%, and the maximum vertical deformation was increased by approximately 68.18%. The influence of each factor on the deformation and failure of overburden strata is quite different. The development range of plastic zone, the maximum vertical stress, and the maximum vertical deformation were increasing with the increased of working face inclined length and mining height. The increasing width of coal pillar would lead to the decrease of maximum vertical stress. The increase of water pressure would lead to the decrease of maximum vertical deformation. It can be seen that the inclined length of the working face is the main factor affecting the deformation and failure of the coal pillar dam. Coal pillar width and mining height are the main factors affecting the development of plastic zone. This study reveals the law of deformation and fracture evolution of coal pillar dam under different mining conditions, which can provide a reference for the design of coal pillar dam of coal mine underground reservoir.

Study on Reasonable Chain Pillar Size in a Thick Coal Seam

In order to solve the problem of low coal recovery rate caused by leaving large coal pillars in deep mines, the study determined the reasonable width of the section pillar, which based on the theory of coal pillar stress distribution, taking the 4102 headgate of Wenjiapo coal mine as the engineering background. Field monitoring and numerical simulation results show that the influence range of the lateral abutment pressure in the goaf is 50~56 m, and the abutment stress distribution in the coal pillar resembles a hump with two peaks of 38.9 MPa and 33.6 MPa, respectively. The positions of the double peaks are located at 12 m and 36 m in the coal pillar, respectively. In the range of “hump,” the section pillar vertical stress is in the original rock stress and is relatively stable. It can be regarded as an elastic zone in the coal pillar with strong bearing capacity, the coal in other areas have already undergone plastic yielding, and the bearing capacity has been reduced; the width of coal pillars in the determined section has been reduced from 46 m to 33 m, which is a reduction of 13 m. The research results have been applied in the 4106 headgate in the same mining area, and good test results have been obtained. The maximum subsidence of the roof-to-floor and rib-to-rib convergence is 286 mm and 150 mm, this indicates that its deformation was within the allowable limits, and the cross-section area was sufficient to satisfy the requirements.

Optimum Selection of Mining Plans for Pillars Containing Interlayers Based on Numerical Simulation

A reasonable selection of the pillar mining plan is the key to ensure smooth mining in the goaf group, which plays an important part in safe production. In formulating and optimizing the pillar mining plan, the influence of the ground pressure evolution law should be fully considered. This paper first introduces two mining plans for pillars, and then, numerical simulations were used to analyze the two mining plans from four perspectives such as stress evolution law, stress concentration degree, force state of pillars, and weak marble layers. The results show that the mining plan 1 that retreats from the middle of the ore body to the two wings is the optimal as it can realize sequential mining in high-stress concentration areas at the middle section. This effectively alleviates the stress on the surrounding rock during mining and will not aggravate the collapse of the marble-interbedded area.

Assessment of blasting impacts on the discontinuities in a salt stope and pillar mine using a developed image processing

Assessment of blasting impacts on the discontinuities in a salt stope and pillar mine using a developed image processing

Numerical Investigation on Stratum and Surface Deformation in Underground Phosphorite Mining Under Different Mining Methods

With the ending of deep-concave open-pit phosphorite extractions and gradual exhausting of shallow mineral resources, stoping of phosphorite seams has entered or will enter into underground mining. Particularly for excavating slightly inclined thin and medium-thick phosphorite orebodies, roof and surface control under different mining methods is crucial for safe and efficient exploitations. In this study, the study area is located in Kunyang Phosphorite Mine characterized by slightly inclined thin and medium-thick deposits. Based on the occurrence conditions, orebody thickness, dip angle, and more factors, the mining methods of underground phosphorite are selected, including room and pillar mining, cement backfill mining, and caving mining. Numerical analysis on roof deformation and surface subsidence under the three methods is performed. The results show that the amount of roof and surface subsidence decreases successively by the caving method, room and pillar method, and cement backfill method. The maximum roof and surface subsidence by the caving method is 45.7 and 13.3 cm, respectively. Regarding shallow orebodies, the open-pit slope is obviously disturbed by the caving method and room and pillar mining method. Hence, slope displacement monitoring should be emphasized. Compared with the other two methods, the backfill mining method can use mined wastes as backfill materials and has less influence on the roof and surface during stoping and is better at controlling slope stability.

Shape ratio effects on the mechanical characteristics of rectangular prism rocks and isolated pillars under uniaxial compression

Isolated pillars in underground mines are subjected to uniaxial stress, and the load bearing cross-section of pillars is commonly rectangularly shaped. In addition, the uniaxial compression test (UCT) is widely used for determining the basic mechanical properties of rocks and revealing the mechanism of isolated pillar disasters under unidimensional stress. The shape effects of rock mechanical properties under uniaxial compression are mainly quantitatively reflected in the specific shape ratios of rocks. Therefore, it is necessary to study the detailed shape ratio effects on the mechanical properties of rectangular prism rock specimens and isolated pillars under uniaxial compressive stress. In this study, granite, marble and sandstone rectangular prism specimens with various height to width ratios ( r ) and width to thickness ratios ( u ) were prepared and tested. The study results show that r and u have a great influence on the bearing ability of rocks, and thin or high rocks have lower uniaxial compressive strength. Reducing the level of r can enhance the u effect on the strength of rocks, and increasing the level of u can enhance the r effect on the strength of rocks. The lateral strain on the thickness side of the rock specimen is larger than that on the width side, which implies that crack growth occurs easily on the thickness side. Considering r and u , a novel strength prediction model of isolated pillars was proposed based on the testing results, and the prediction model was used for the safety assessment of 179 isolated pillars in the Xianglu Mountain Tungsten Mine.

Study on Energy Dissipation Characteristics and Damage Law of Backfill under Cyclic Impact

This research aims to study the damaging effect of underground blasting mining pillars on adjacent cemented filling bodies. The filling bodies were made by mixing ore rock with ash sand by the ratio of 1 : 4 and 1 : 6, respectively, which were subjected to cyclic impact tests with the split-Hopkinson pressure bar under the pressure of 0.2 MPa and 0.24 MPa to analyze the energy dissipation characteristics and damage law. The results showed that as the stress wave induced by the cyclic impact was transmitted to the composite specimen, the energy was absorbed for crack growth and development. Then, the energy reflection ratio increased while the energy dissipation ratio and transmission ratio decreased. For the combined specimen with the cement-sand ratio of 1 : 4, after five cycles of impact under the condition of Ip = 0.2 MPa, the damage variables were 0.07, 0.11, 0.51, and 0.56, respectively, since the second time; under the condition of Ip = 0.24 MPa, the damage variables were 0.17, 0.29, 0.55, and 0.66, respectively. After reaching the damage threshold of 0.63, the damage variable showed nonlinearity. Moreover, it was found that the mechanical properties of the filling body affect the whole combined specimen, and the dynamic strength of the combined specimen with the cement-sand ratio of 1 : 4 was higher than that of the cement-sand ratio of 1 : 6. Therefore, it can be concluded that during the two-step pillar recovery, the amount of blasting explosive can be appropriately reduced, and the number of blasting can be increased to reduce the damaging effect of blasting impact on the cemented pillar and reserved pillar to maintain stability.

Risks and challenges affecting opencast pillar mining in previously mined underground bord and pillar workings

South Africa is one of the leading producers and exporters of coal globally. A significant amount of the country's production is obtained from previously mined underground bord and pillar workings. This coal is in the form of pillars and remnants on the roof and floor of the old workings. The good quality coal pillars were left behind as primary support during underground bord and pillar mining operations. Due to the depletion of virgin coal reserves, the pillars and remnant coal are now removed using opencast mining rather than underground methods. However, the secondary extraction of pillars and remnant coal from the old workings using opencast methods entails some serious challenges that have a negative impact on the safety and productivity of the operations, affecting both personnel and machinery. If these risk factors and challenges are managed properly, then the opencast mining operations could remove the pillars safely at recoveries competitive with those of virgin coal operations. In this study we review the recurring challenges affecting opencast pillar mining by means of field investigations and consultations with experts at five opencast pillar mining operations, and evaluate the best practices used to combat these challenges. It was found that each mine has its own unique conditions and challenges.

Zoning Control Technology of Gob-Side Roadway Driving with Small Coal Pillar Facing Mining in a Special Isolated Island Working Face: A Case Study

The gob-side roadway in an isolated island working face is a typical representative of a strong mining roadway, which seriously restricts the efficient and safe production of underground coal mines. With the engineering background of the main transportation roadway 1513 (MTR 1513) of the Xinyi Coal Mine, this paper introduces the engineering case of gob-side roadway driving with small coal-pillar facing mining in an isolated island working face under the alternate mining of wide and narrow working faces. Through comprehensive research methods, we studied zoning disturbance deformation characteristics and stress evolution law of gob-side roadway driving under face mining. Based on the characteristics of zoning disturbance, MTR 1513 is divided into three zones, which are the heading face mining zone, the mining influenced zone, and the mining stability zone. A collaborative control technology using pressure relief and anchoring is proposed, and the differentiated control method is formed for the three zones. For the heading face mining zone, the control method of anchoring first and then pressure relief is adopted; for the mining influenced zone, the control idea of synchronous coordination of pressure relief and anchorage is adopted; for the mining stability zone, the control method of anchoring without pressure relief is adopted. Engineering practices show that the disturbance influence distance of working face 1511 on MTR 1513 changes from 110 m advanced to 175 m delay. At this time, the surrounding rock deformation is effectively controlled, which verified the rationality of the division and the feasibility of three zoning control technology. The research results can provide reference for gob-side roadway driving with small coal pillar facing mining in a special isolated island working face.

Study on the gas migration laws of non-pillar mining with gob-side entry retaining in high gas outburst coal seam

Mining fractures are the channel of gas migration, and it is important to figure out the gas migration laws for gas control. Combined with the actual geological conditions of Shaqu No. 2 coal mine, a numerical model of no-pillar mining with automatically retained entry was built to simulate the deformation and fracture of overburden rock and the evolution laws of cracks above the goaf during mining. Subsequently, CFD software is used to theoretically stimulate the gas concentration distribution laws of non-pillar mining with the automatically retained entry in the stope under non-drainage and high-level borehole drainage conditions. The laws of gas concentration in the stope were compared and analyzed under the condition of the Y-type ventilation of non-pillar mining and U-type ventilation of coal pillar mining. The results show that Y-type ventilation of non-pillar mining reduces the gas concentration in the upper corner of the working face and the goaf, and effectively solves the gas accumulation problem in the upper corner of the working face in the mode of U-type ventilation of coal pillar mining. On this basis, the high-level borehole drainage technology is adopted to effectively reduce the gas concentration in the goaf. The research has certain guiding significance for the gas management of non-pillar mining with gob-side entry automatically retained.

Development of Fuzzy Pattern Recognition Model for Underground Metal Mining Method Selection

Selection of underground metal mining method is a crucial task for the mining industry to excavate the ore deposit with proper safety and economy. The objective of the proposed study is to demonstrate the application of a fuzzy pattern recognition model for the decision-making of the most favourable underground metal mining method for a typical ore deposit. The model considers eight factors (shape, depth, dip, rock mass rating [RMR] of ore zone, RMR of footwall, RMR of hanging wall, thickness of the ore body, grade distribution), which influence the mining method, as input variables. The weights of these factors were determined using the analytic hierarchy process (AHP). The study used the pair-wise comparison method to determine the relative membership degrees of qualitative and quantitative criteria as well as weights of the criteria set. The model validation was done with the deposit characteristics of Uranium Corporation of India Limited (UCIL), Tummalapalle mine selected. The weighted distances for easiest to adopt are found to be 0.1436, 0.0230, 0.0497, 0.2085, 0.0952, 0.1228, and 0.1274, respectively, for block caving, sublevel stoping, sublevel caving, room and pillar, shrinkage stoping, cut and fill stoping, and squares set stoping. The results indicate that the room and pillar mining method is having the maximum weighted distance value for the given ore deposit characteristics and thus assigned the first rank. It was observed that the mining method selected using fuzzy pattern recognition model and the actual mining method adopted to extract the ore deposit are the same.

Experimental Investigation on Uniaxial Compression Mechanical Behavior and Damage Evolution of Pre-Damaged Granite after Cyclic Loading

Failure behavior of pillars in deep mines is affected by various cyclic loads that cause initial pre-damage. Pillars will be further damaged and developed in the long-term compressive stress until they are destroyed. To reveal the strength characteristics and crack damage fracture laws after rock pre-damage, uniaxial compression tests were carried out on granite specimens damaged by cyclic loading using the digital speckle correlation method. The experimental results indicate that the mechanical properties of pre-damaged specimens show large damage differences for different cycles. The damage variable of the pre-damaged specimens increases with the increase of cycle number and confining pressure. The damage of specimens is primarily due to the strength weakening effect caused by cycle numbers, and the confining pressure restriction effect is not obvious. The evolution laws of uniaxial compression damage propagation in the pre-damaged specimens show differences and obvious localization phenomenon. Pre-damaged specimens experienced three failure modes in the uniaxial compression test, namely tensile shear failure (Mode I), quasi-coplanar shear failure (Mode II), and stepped path failure (Mode III), and under different pre-damage stress environments with high confining pressures, the failure modes are dominated by Mode II and Mode III, respectively.