Room Mining Research Articles

THE OSKAR LIGNITE MINE IN SMOGÓRY (LUBUSZ LAND, WESTERN POLAND)

The paper presents history of one of the largest mines in the Lubusz Land, namely the Oskar Mine in Smogóry near Ośno Lubuskie. The mine operated between 1860 and 1945 under the name of Oskar and later as Smogóry until 1961. The paper focuses on the detailed pre-war history of the Oskar Mine, shows its mining area, location of shafts and descending galleries. Available data about the amount of extraction and employment level are presented. The paper is based on remaining German archived materials (Main Mining Office) and on Polish documents. The paper describes briefly the discovery of lignite deposits in the 19th century near Ośno Lubuskie. Underground room and pillar retreat mining used in this mine is also characterized. Complicated lignite bed structure, ­resulting from geological conditions (glaciotectonic deformation), is discussed. The geological structures is illustrated by a few geological cross-sections.

Research and application of roadway backfill coal mining technology in western coal mining area

In China’s western coal mining area, the traditional room mining technology is facing coal pillar instability, mine earthquake, large-area roof subsidence in the goaf, surface subsidence, water and soil loss, vegetation deterioration, and other environmental problems. To solve the aforementioned problems and to improve coal recovery, the roadway backfill coal mining (RBCM) method was proposed as a solution and its technical principle and key equipment were presented in this paper. In addition, the microstructure and mechanical behavior (strain-stress relation in confined compressive test) of aeolian sand and loess backfill materials were studied for a rational backfill design for underground mines. Further, coal pillar stress, plastic zone change, and surface deformation of the RBCM schemes were studied using the FLAC3D numerical simulation software, and a reasonable mining scheme of “mining 7 m and leaving 3 m” was determined. The engineering application in Changxing Coal Mine shows that the RBCM method with loess and aeolian sand as backfill materials allows a stable recovery of coal pillars with a recovery ratio of more than 70 %. The maximum accumulated surface subsidence and the maximum horizontal deformation were measured to be 15 mm and 0.8 mm/m respectively, indicating that the targeted backfilling effect can help protect the environment and also control surface subsidence.

Overlying strata movement of recovering standing pillars with solid backfilling by physical simulation

To analyze the overlying strata movement law of recovering room mining standing pillars with solid backfilling. Physical simulation experiments with sponge and wood as the backfilling simulation material were tested. The results show that: (i) The covering-rock mechanics of the overly strata comes from “two-arch structures+hinged girder+bend beam” to “backfilling material+hinged girder+bent beam” by increasing the fill ratio from 0% to 85%, the beginning of overlying strata movement appears later and the total duration of subsidence velocity increased from zero to the highest value increases. The trend of “single polarization” of the subsidence velocity curves becomes noticeable and the velocity variation trend becomes stable. (ii) The equiponderate aeolian sand was added to improve the anti-pressure ability of the loess, and the corresponding ground processing & transportation system was designed.

Geodetic Monitoring of the Surface within the Trial Operation of the Room and Pillar Mining Method in the Ostrava-Karvina Coal District

Mine Plant 2 is a part of the Ostrava-Karvina Coal District (OKD) that is located in the Czech part of the Upper Silesian Basin. The first coal was exhausted from Mine Plant 2 in 1968. The most used method of mining so far in this area has been strike longwall mining with controlled caving. Due to extensive changes in the surface, which occur as a consequence of deep mining by the method of longwall mining with controlled caving, it is not possible to use this method in densely populated areas. At the present time, therefore, the trial operation of a new mining method called room and pillar is carried out. The method was chosen with the aim to minimize subsidence and deformations of the surface. The room and pillar mining method has never been used before in the conditions of the OKR, therefore it is necessary to prove the real effect of mining by this method on the surface. For this purpose, a surface observation station was designed, consisting of 36 surface points. The position and height of all points of the observation station is determined in stages three times a year.

Review of support systems used in poor ground conditions in platinum room and pillar mining: A Zimbabwean case study

Paper written on project work carried out in partial fulfillment of BSc. (Mining Engineering).

Укрепление вмещающих пород при отработке урановых месторождений Стрельцовского рудного поля камерными системами разработки

Укрепление вмещающих пород при отработке урановых месторождений Стрельцовского рудного поля камерными системами разработки

Overlying strata movement rules and safety mining technology for the shallow depth seam proximity beneath a room mining goaf

Aiming at the shallow depth seam proximity beneath a room mining goaf, due to that the shallow depth seam is exploited using the longwall mining and overlain by thin bedrock and thick loose sands, many accidents are likely to occur, including roof structure instability, roof step subsidence, damages of shield supports, and the face bumps triggered by the large area roof weighting, resulting in serious threats to the safety of underground miners and equipment. This paper analyses the overlying strata movement rules for the shallow seams using the physical simulation, the 3DEC numerical simulation and the field measurements. The results show that, in shallow seam mining, the overburden movement forms caved zone and fractured zone, the cracks develop continuously and reach the surface with the face advancing, and the development of surface cracks generally goes through four stages. With the application of loose blasting of residual pillars, reasonable mining height, and roof support and management, the safe, efficient and high recovery rate mining has been achieved in the shallow depth seam proximity beneath a room mining goaf.

Event tree analysis for room and pillar mining affecting permeability beneath surface bodies of water

Underground mining and oil and gas drilling have increasingly encroached on public water reservoirs and dams because of the overwhelming demand for energy combined with the growing population. Cases of surface water reservoirs and mine waste impoundments being drained, as well as dam infrastructure being damaged, due to accidents have been documented. The methods used by regulators and industry for determining mining or drilling offset distances are based primarily on three approaches and studies performed in the early 1970s. The former US Bureau of Mines Information Curricular 8741 was the culmination of these studies and continues in use for determining offset distances for underground mining with respect to dams and reservoirs. This study used analytical and empirical methods based on subsidence effects to recommend offset distance extents specifically for miners' safety. A major limitation of the previous studies is that they did not detail the affect mining operations have on changes in groundwater flow due to soil and overburden permeability changes triggered by vertical ground surface subsidence that could lead to increased risk hazards for a reservoir or dam infrastructure. This paper presents a review of international literature related to mining under surface bodies of water (reservoirs) and presents a risk-based event tree analysis quantifying the probability of changes in subsurface permeability due to overburden strain changes. A sensitivity analysis quantifying probabilities of increased subsurface permeability in terms of offset distances from a reservoir is presented and discussed. Empirical results indicate the probability of permeability changes at a 350 ft (107 m) deep mine located at offsets of: 200, 400, and 600 ft (61, 122, and 183 m) were at 41, 0.66, and 0.0067%, respectively.

Parametric study of airflow separation phenomenon at face area during deep cut continuous mining

It is well known that a major ventilation problem during deep cut mining is delivering the required amount of air into the immediate face zone. Line brattice face ventilation systems are commonly applied for medium and low coal seams in room and pillar mining method utilising continuous miner. It is assumed that the blowing curtain, as opposed to the exhaust curtain, generally achieves greater efficiency in delivering air to ventilate the immediate face zone. However, in real mining conditions both, the blowing and the exhaust curtain face ventilation systems suffer from one significant disadvantage – the intake air separates early from the rib and does not fully penetrates to the immediate face zone. This phenomenon is called flow separation. The portion of the intake air reaching the face can be <20% with the exact amount being a function of various parameters associated with the mine and ventilation design. The results presented in this publication clearly shows that curtain tight-rib distance, width of the entry, and curtain setback distance govern the flow behaviour at the face area. The performed analysis confirmed that changes in the intake air quantity have no significant impact on the flow patterns and the amount of air delivered to the immediate face zone.

Deep-hole pre-split blasting mechanism and its application for controlled roof caving in shallow depth seams

The shallow depth coal seams mined in the Shendong Mining Area has led to large area roof weighting frequently due to large thickness, high tensile strength and small overlying load of the main roof. As a result, many accidents have happened including hydraulic support being iron-bound, water inrush through the penetrating cracks along coal wall, and potentially induce large area residual pillars instability and even wind blast damage particularly in the conditions beneath a room mining goaf. To prevent the large area roof weighting accidents, deep-hole pre-split blasting technology for controlled roof caving is a suitable method and has been widely applied in the mines, and many in situ trials have already achieved a sound performance. According to the field conditions of the shallow depth coal seams, this paper employs cylindrical cavity expansion theory to calculate the three blasting-induced divisions including break zone, fracture zone and elastic vibration zone. The software of LS-DYNA3D was applied to establish a deep-hole pre-split blasting model, which presented the rock stress field and the break scope affected by the high energy explosion stress wave. The simulation results revealed the blasting for controlled roof caving mechanism and also optimized the blasting parameters. The field observations showed that, with the application of deep-hole pre-split blasting technology in Shigetai Mine, Shendong Mining Area, the first main roof weighting length was about 17.4m, and neither a hydraulic support being iron-bound nor a serious roof subsidence in the form of step convergence in the mining face happened during the first weighting period. The field application of deep-hole pre-split blasting for controlled roof caving has achieved the expected effects.

Geological Hazard Tendency Analysis of Room and Pillar Mining Method Based on Energy Index

Geological hazards especially for the dynamic disasters are proven to be the most difficult problems encountered in the deep underground projects. This paper attempts to deal with the geological problem faced by Shizhuyuan multi-ploy metallic mine base on the results of mechanics tests and numerical simulation. In order to understand the mechanism dynamic disasters, a new energy index, the Local Energy Release Rate (LERR), is put forward in the simulating process. By tracking the peak and valley values of elastic strain energy intensity before and after brittle failure, the LERR is set as an index to ascertain the scope of the high dangerous region. The results showed that LERR can satisfactorily predict the dangerous region, and it will be more accurate with some necessary monitoring method. The study indicates the potential of LERR for evaluating geological hazards in deep underground excavations.

Evaluation of the Stability of Underground Rock Pillars through a Probabilistic Approach

Problem statement: When the room and pillar mining method is adopted, the dimensioning of the rock pillars is one of the most important aspects that need to be faced from the engineering point of view. The available calculation methods are usually simplified and involve the areas of influence method for the evaluation of the mean axial stress induced in the pillar and the empirical formula to estimate the global strength of the pillar. Approach: A new probabilistic approach is proposed in this study concerning the evaluation of the degree of safety of a pillar, as far as rupture of the rock is concerned. This approach is based on the exact evaluation of the stress state inside the pillar and it takes into due consideration the typical uncertainty of the geomechanical parameters of the rock mass that makes up the pillar. Results and Conclusion: The pillar can therefore be dimensioned through an analysis of the cumulative probability distribution of the point safety factor in one or more points inside it.

Optimisation of underground ventilation systems by means of neural networks

The optimisation of the auxiliary ventilation network of underground mines entails the right choice of fans and duct characteristics. Once the decision-making team has selected the appropriate set of ventilation hardware, the duct line is installed across a main drivage and ends up to the most productive working areas. However, when there are many possible duct line routes from the auxiliary fan to the duct line open end, as is the case in the room and pillar mining method, the choice of a cost effective duct line route, in terms of the total length and bending of the ducts involved, is important for the minimisation of the operating cost of ventilation. In this paper, the problem of finding a cost effective duct line route, among a definite number of possibilities, is tackled with a modified discrete Hopfield network. It is shown that the network provides the optimum result for a trivial case. The implementation of the network on a realistic case is shown to be superior to results from the A* algorithm. However, the feasibility of the proposed solution is highly dependent on mining issues and on the right choice of number and distribution of control points that realise all possible routes from the fan to the headings.

Study on the Monitoring Method of Overburden Failure of Shallow Wongawilli Mining Working Face

Through the practice and improvement of Wongawilli Mining method in Shendong Mining Area, it created Shendong Characteristic short wall mechanize room mining method. Due to the shallow coal seam, the fracture zones throughout the bedrock directly after the mining, therefore the bending sinking belt didn’t exist; the conventional "three zones" theory couldn’t explain the overburden rock deformation damage rule of this situation perfectly. In order to monitor the damage of overburden strata, based on the analysis of coal pillars stability in Wongawilli working face, the paper puts forward 3D monitoring methods of overburden strata damage as follows: underground borehole stress monitoring, roof separated strata and layer's internal monitoring, surface subsidence monitoring. The set of monitoring method can monitor the instability of coal pillars, roof caving, production of separated strata in the roof, overburden rock damage and subsidence, the study is of reference and significance.

Parameter Design and Application of Hydraulic Support with Hanging Chain and Splicing Beam in Shallow Seams

In view of actual situation of serious resources waste and less than 30% of face recovery ratio to shallow seams with existing features of harder roof at the process of room and pillar mining in northern Shaanxi province in China, reasonable support strength has been studied in both cases of normal mining and force caving for improved longwall mechanized mining face, and obtained reasonable working support resistance at the condition of force caving which was better than normal mining. Based on this condition, Shandong Xin Mei machinery Co, Ltd. has developed hydraulic support with hanging chain and splicing beam which was suitable to existing features of shallow seams. The support had advantages with flexible connection between supports to ensure that all pillars reached rated setting load, sub-size top beam to resolve "protection" and "cutting" dilemma for the roof, adjusting and locking support, etc. The company also has given concrete support parameters. By the field industrial test verification, the developed new support fully adapted strata behavior at the process of force caving with existing features of shallow depth and harder roof. The research has provided a useful reference for other coal mines with similar geological features.

Analysis and research of long-term stability about the gob site in Northern Shaanxi Province

Based on the analysis of the basic characteristics for the gob site in Northern Shaanxi Province and the room and pillar mining way about coal mine, the variety rule of the coal beds below the site was studied by the using of FEM during the process of coal mining. The statuses of the stresses and strains and the varieties of the plastic area were simulated in the whole rock and coal pillars. The characters of stresses and deformation of the gob area of the coalmine were analyzed and evaluated after the site built in weathering. Moreover, the long-term stability of the gob area was predicted. As a result, the deformation of the gob area under the site is not been finished, and there is the danger that the gob site will collapsing as a whole; therefore, relative measures must be taken.

Research on the Grouting Thickness of Roof Purdah in the Mining of Karstic Water-filling Deposit

The orebody roof grouting water protecting curtain technology is to drill hole in the orebody roof to enter into the limestone strong aquifer, forming grouting water protecting curtain. The reasonable thickness of ore deposit roof water protecting curtain is critical for the effective precautions against permeability of Karst flood deposits and the safety in production during the mine service period. Currently, there is no uniformly distributed water protecting thickness design specifications for the orebody roof curtain grouting. In allusion to the design conditions of the curtain grouting mining for Gujiatai iron ore, this paper utilized coal, tunnel specifications to determine the thickness of water protecting curtain. On this basis, this paper applied numerical analysis method to conduct simulation analysis and calculation for the stability of the water protecting curtain thickness. The results showed that the curtain thickness based on the empirical formula could not meet the watertight requirements, and it should properly increase the thickness of water protecting curtain in accordance with the sphere of stope room mining influence to ensure safety of exploitation, providing a basis and guidance for the design and construction of water protecting curtain, which had certain important theoretical and practical significance for the mining of Karst water ores.

Impact of the mechanical characteristics of weak rocks and trona ore beds on the main drift deformation at the beypazari mine, Turkey

Abstract In northern Turkey, the Main Drift, T-2000, and a roadway, T-3000, were excavated for Beypazari trona (natural soda) underground mine project between the years 1999 and 2001. This work was one of the most important mining projects in Turkey in the last decade. T-2000 was designed as a main drift with a length of 965 m, 14° inclined and excavated with a cross-sectional area of 18 m 2 . The T-3000 roadway was driven in the trona beds for the first production panel. In this study, in situ and laboratory studies have been made to define the formations through which the drift has been driven. In situ engineering geology measurements were carried out consisting of field observation, mapping, boreholes and laboratory tests on samples collected from the trona field and the boreholes. After drift excavation and support installation, the deformations and the loads on the supports were measured. As a result of this study, the deformational characteristics of the trona ore beds and weak rocks and their effect on the main drift (T-2000) deformation have been determined. The importance of this study lies in the fact that most natural soda mines in the world apply room and pillar mining methods. This study is probably the first investigation on underground openings with steel-set support systems and rock deformations in natural soda beds.

Seismological models for mining-induced seismic events

One possibility to estimate and to interpret the source parameters of low-stress drop seismic events to use the barrier or the asperity model. These models serve as the description of seismic events in a in which a horizontal room and pillar mining method is used in great depth.

Viscoelastic finite element analysis in design of potash mines

Computer simulation is playing an increasingly important role in evaluating the short and long term structural stability of underground mine openings, and in ground control studies related to mine design and layout. Such simulations are increasingly being used in the design of underground salt and potash mines. Because of the viscoelastic nature of salt rock, simulation models used in these deposits must take into consideration their time dependent properties if they are to correctly predict opening closures, ground stresses, and ground stability based on prescribed failure criteria. A number of computer codes have been developed in Canada in recent years meeting these requirements. This paper describes the use of one of these codes to predict the ground behaviour of a typical room and pillar mining section of a Western Canadian potash mine. Predicted ground behaviour, based on use of the code, was compared with actual behaviour through field measurements. The study provided good correlation between predicted and measured ground behaviour, and is an encouragement to greater use of numerical modelling in mine stability studies related to mine design.