Coal Panel Research Articles

Simulation of Rock Mass Horizontal Displacements with Usage of Cellular Automata Theory.

Abstract In the article there was presented two dimensional rock mass model as a deterministic finite cellular automata. Used to describe the distribution of subsidence of rock mass inside and on its surface the theory of automata makes it relatively simple way to get a subsidence trough profile consistent with the profile observed by geodetic measurements on the land surface. As a development of an existing concept of the rock mass model, as a finite cellular automaton, there was described distribution function that allows, simultaneously with the simulation of subsidence, to simulate horizontal displacements inside the rock mass model and on its surface in accordance with real observations. On the basis of the results of numerous computer simulations there was presented fundamental mathematical relationship that determines the ratio of maximum horizontal displacement and maximum subsidence, in case of full subsidence trough, in relation to the basic parameters of the rock mass model. The possibilities of presented model were shown on the example of simulation results of deformation distribution caused by extraction of abstract coal panel. Obtained results were consistent with results obtained by geometric-integral theory.

Collaborative mining using different equipment for a coal seam varying in thickness in a long wall working face

Efficient mining of coal seams varying in thickness has become increasingly important, especially for the coal resources located at the edges of coal seams, in corners or panels. Selecting the 4320 mechanised working face in the Daizhuang Coal Mine located in eastern China as example, collaborative mining technology with different mining equipment for a coal seam varying in thickness within the same long wall working face was studied. A number of key technologies were developed, including scraper conveyor lap technology, a separation device for coal and gangue and working face shortening technology. The roof movement formula for this working face was also monitored. The engineering application showed that this technology could greatly improve the degree of mechanisation, and reduce the labour intensity of workers. Besides, more than 8.3 Mt of coal were recovered. The results of monitoring the roof movement indicated that stress concentration was located at the junction of thin and thick coal seams, but it did not appear to affect normal operations within the coal mine, and the periodic pressure in this working face was steady. The above achievements could provide technical reference for coal mining under similar geological conditions in other locations. [Received: December 4, 2014; Accepted: September 20, 2015]

New Criteria to Assess Seismic and Rock Burst Hazard in Coal Mines / Nowe Kryteria Dla Oceny Zagrożenia Sejsmicznego I Tąpaniami W Kopalniach Węgla Kamiennego

Abstract The paper presents new criteria of seismic and rock burst hazard assessment in Polish hard coal mines where longwall mining system is common practice. The presented criteria are based on the results of continuous recording of seismic events and analysis of selected seismological parameters: spatial location of seismic event in relation to mining workings, seismic energy, seismic energy release per unit coal face advance, b-value of Gutenberg-Richter law, seismic energy index EI, seismic moment M0, weighted value of peak particle velocity PPVW. These parameters are determined in a moving daily time windows or time windows with fixed number of seismic tremors. Time changes of these parameters are then compared with mean value estimated in the analyzed area. This is the basis to indicate the zones of high seismic and rock burst hazard in specific moment in time during mining process. Additionally, the zones of high seismic and rock burst hazard are determined by utilization of passive seismic tomography method. All the calculated seismic parameters in moving time windows are used to quantify seismic and rock burst hazard by four level scales. In practice, assessment of seismic and rock burst hazard is used to make daily decision about using rock burst prevention activities and correction of further exploitation of monitored coal panel.

Research on Stability of Overburden Structure around Longwall Mining Face in Steeply Dipping Seam Group

The steeply dipping seam group is defined by the two or more coal seams ,a pitch between 35°~55°. Using masonry beam theory, longitudinal bending theory and “R-S-F” dynamics control theory built a lower area overburden structure mode. Analysed the stability of low position coal seam. The balance requirement and the strength of the structure which is affected by the caving rock and lower coal roof were given. It easily generates two lower position steps rock structure in inclination along working face. Regular breaking of the second structure is the main reason leads to the imbalance of the structure between upper coal pillar and upper coal mining face.The interaction among multiple coal seam panels and overburden structures is the main reason that causes the rock disaster, the unbalance of the lower area may lead to pushing accident, the imbalance of the upper area can generate shock pressure.

A fuzzy logic model to predict the out-of-seam dilution in longwall mining

The longwall mining method is often affected by the out-of-seam dilution (OSD). Therefore, predicting and controlling of dilution are important factors for reducing mining costs. In this study, the fuzzy set theory and multiple regression models with parameters, including variation in seam thickness, dip of seam, seam thickness, depth of seam, and hydraulic radius as inputs to the models were applied to predict the OSD in the longwall coal panels. Field data obtained from Kerman and Tabas coal mines, Iran were used to develop and validate the models. Three indices including coefficient of determination (R2), root mean square error (RMSE) and variance account for (VAF) were used to evaluate the performance of the models. With 10 randomly selected datasets, for the linear, polynomial, power, exponential, and fuzzy logic models, R2, RSME and VAF are equal to (0.85, 4.4, 84.4), (0.61, 7.5, 59.6), (0.84, 4.5, 72.7), (0.80, 4.1, 79.6), and (0.97, 2.1, 95.7), respectively. The obtained results indicate that the fuzzy logic model predictor with R2=0.97, RMSE=2.1, and VAF=95.7 performs better than the other models.

Supporting Technics of Easily Mudding and Ultrahigh Roadway in Soft Coal Rock

According to the situation of the great height wall, soft and weak surrounding rocks and sliming characteristics of the 15# coal west-third panel sump in the Gushuyuan mine, the deformation characteristics and mechanism of the sump were analyzed by field survey, laboratory tests and the numerical simulation method. The results show that the sump deformation and failure were determined by its low strength, weakness structural, sliming characteristics and excavation disturbance. The roadway deformation occurs mainly in the middle, upper and lower of the sides and the floor. A comprehensive solution is proposed, including sealing surrounding rocks, strengthening soft and weak surrounding rocks, strengthening the structure stability, improving the surrounding rocks stress environment. This method was applied in the coal mine. Field application results show that this method was suitable for control sump deformation, the maximum roadway roof subsidence is 15 mm, the two sides convergence is 30mm, and the maximum amount of floor heave is 21mm.

A dynamic method to determine the supports capacity in longwall coal mining

The determination of the correct design support capacity of shield supports is the key to the safe control of strata within the vicinity of longwall coal panels. There are a number of design methods that have been developed, dependant on the prevalent geological and mining conditions. However, these methods have been found to be inappropriate to the design of the supports for longwall panels practising either high seam height extractions or the top-coal caving methods practised within many Chinese underground thick seam mines. To address these conditions, a dynamic simulation method is proposed to determine the shield support capacity required for these conditions. Based upon the geological conditions experienced on the first caving event of the main roof, the shield support capacity for the four case study mine coal panels is determined and compared against the performance of the installed support capacities. It is concluded that the predicted support capacities compare well with the performance of the supports installed within the case study mines.

Longwall Shearer Cutting Force Estimation

Longwall mining is an underground coal mining method that is widely used. A shearer traverses the coal panel to cut coal that falls to a conveyor. Operation of the longwall can benefit from knowledge of the cutting forces at the coal/shearer interface, particularly in detecting pick failures and to determine when the shearer may be cutting outside of the coal seam. It is not possible to reliably measure the cutting forces directly. This paper develops a method to estimate the cutting forces from indirect measurements that are practical to make. The structure of the estimator is an extended Kalman filter with augmented states whose associated dynamics encode the character of the cutting forces. The methodology is demonstrated using a simulation of a longwall shearer and the results suggest this is a viable approach for estimating the cutting forces. The contributions of the paper are a formulation of the problem that includes: the development of a dynamic model of the longwall shearer that is suitable for forcing input estimation, the identification of practicable measurements that could be made for implementation and, by numerical simulation, verification of the efficacy of the approach. Inter alia, the paper illustrates the importance of considering the internal model principle of control theory when designing an augmented-state Kalman filter for input estimation.

Application of the spatial data mining module in analysis of mining ground deformation factors

Spatial data mining methods for example those based on artificial neural networks (ANN) allow extraction of information from databases and detection of otherwise hidden patterns occurring in these data and in consequence acquiring new knowledge on the analysed phenomena or processes. One of these techniques is the multivariate statistical analysis, which facilitates identification of patterns otherwise difficult to observe. In the paper an attempt of applying self-organising maps (SOM) to explore and analyse spatial data related to studies of ground subsidence associated with underground mining has been described. The study has been carried out on a selected part of a former underground coal mining area in SW Poland with the aim to analyse the influence of particular ground deformation factors on the observed subsidence and the relationships between these factors. The research concerned the uppermost coal panels and the following factors: mining system, time of mining activity and inclination, thickness and depth below the ground of the exploited coal panels. It has been found that the exploratory spatial data analysis can be used to identify relationships in multidimensional data related to mining induced ground subsidence. The proposed approach may be found useful in identification of areas threatened by mining related subsidence and in creating scenarios of developing deformation zones and therefore aid spatial development of mining grounds.

Detecting the footprint of a longwall mine panel claimed to infringe on a permit boundary at the Soma–Darkale coalfield (Manisa, Turkey) using surface fractures and microgravity measurements

A coal mine panel claimed to infringe on a permit boundary, or to create an hazard after subsidence has been the subject of lawsuits. We study at the Soma–Darkale coalfield (Manisa, Turkey), the footprint of a lignite coal mine panel at a depth of about 150–200 m by mapping all of the surface fractures we could observe, and by developing a post-subsidence density model that we verified through gravity measurements with positive Bouguer anomaly. With the analysis of the fracture map and the gravity data, we were able to identify the footprint of a mine panel from the effect of the anomalous mass due to denser overburden material filling up the space after the extraction of less-dense lignite. Whereas, using empirical methods like the so-called “limit line approach” to evaluate the extent of the area where mining can have subsidence-induced surface fracturing, one could not recognize for certain infringement of permit boundaries. The orientations of the fractures we mapped at the ground surface, the Bouguer gravity map, and a test borehole indicated the presence and dimensions of a coal panel in dispute. The presented approach based on gravity method and fracture observations may be an example to help settle conflicts related to the position of the longwall mine panel.

Modelling of fluid flow and heat transfer to assess the geothermal potential of a flooded coal mine in Lorraine, France

The flooding of the Lorraine coal mines (France), representing a huge reservoir of about 154 × 10 6 m 3, began in June 2006. After attaining thermal equilibrium with the surrounding rocks, the water temperature in the deepest parts is expected to reach 55 °C, giving the opportunity for the extraction of low-enthalpy geothermal waters that may be suitable for district heating purposes. We present some numerical modelling results of the thermally driven convective flow in an open vertical shaft and in the entire mine reservoir. A dual permeability/porosity approach was used in the reservoir model, which includes open galleries and vertical shafts, coal panels backfilled with sand, and intact rock masses. Two scenarios of heat extraction with different flow regimes were investigated. A sensitivity analysis shows that the temperature decline in the production zone is highly dependent on the permeability of the surrounding porous rocks. Larger permeabilities result in higher water temperatures at the production shaft due to greater inflows of warm water from those rock masses.

Tomographic Imaging of Rock Conditions Ahead of Mining Using the Shearer as a Seismic Source—A Feasibility Study

Roof falls due to poor rock conditions in a coal longwall panel may threaten miner's life and cause significant interruption to mine production. There has been a requirement for technologies that are capable of imaging the rock conditions in longwall coal mining, ahead of the working face and without any interruption to production. A feasibility study was carried out to investigate the characteristics of seismic signals generated by the continuous coal cutter (shearer) and recorded by geophone arrays deployed ahead of the working face, for the purpose of seismic tomographic imaging of roof strata condition before mining. Two experiments were conducted at a coal mine using two arrays of geophones. The experiments have demonstrated that the longwall shearer generates strong and low-frequency ( ~ 40 Hz) seismic energy that can be adequately detected by geophones deployed in shallow boreholes along the roadways as far as 300 m from the face. Using noise filtering and signal cross correlation techniques, the seismic arrival times associated with the shearer cutting can be reliably determined. It has proved the concept that velocity variations ahead of the face can be mapped out using tomographic techniques while mining is in progress.

Methodology for tomographic imaging ahead of mining using the shearer as a seismic source

Poor rock conditions in a coal longwall panel can result in roof collapse when a problematic zone is mined, significantly interrupting mine production. The ability to image rock conditions — stress and degree of fracturing — ahead of the face gives the miners the ability to respond proactively to such problems. This method uses the energy from mining machinery, in this case a coal shearer, to produce an image of the rock velocity ahead of the mining face without interrupting mining. Data from an experiment illustrates the concept. Geophones installed in gate-road roofs record the noise generated by the shearer after it has traversed the panel ahead of the mining face. A generalized crosscorrelation of the signals from pairs of sensors determines relative arrival times from the continuous seismic noise produced by the shearer. These relative times can then be inverted for a velocity structure. The crosscorrelations, performed in the frequency domain, are weighted by a confidence value derived from the spectral coherence between the traces. This produces stable crosscorrelation lags in the presence of noise. The errors in the time-domain data are propagated through to the relative traveltimes and then to the final tomographic velocity image, yielding an estimate of the uncertainty in velocity at each point. This velocity image can then be used to infer information about the stress and fracture state of the rock, providing advance warning of potentially hazardous zones.

Thermophysical Models of Underground Coal Gasification and FEM Analysis

In this study, mathematical models of the coupled thermohydromechanical process of coal rock mass in an underground coal gasification panel are established. Combined with the calculation example, the influence of heating effects on the observed values and simulated values for pore water pressure, stress, and displacement in the gasification panel are fully discussed and analyzed. Calculation results indicate that 38, 62, and 96 days after the experiment, the average relative errors for the calculated values and measured values for the temperature and water pressure were between 8.51–11.14% and 3–10%, respectively; with the passage of gasification time, the calculated errors for the vertical stress and horizontal stress gradually declined, but the simulated errors for the horizontal and vertical displacements both showed a rising trend. On the basis of the research results, the calculated values and the measured values agree with each other very well.

The stability of methane capture boreholes around a long wall coal panel

This paper describes the application of computational modelling to the prediction of the stability of methane drainage boreholes during the extraction life of an active long wall coal panel within a United Kingdom coal mine. The modelling was undertaken to investigate the affects that changes in the roof geology and roadway support system may have on the deformation and closure of the gas drainage boreholes drilled from the tailgate across the goaf of an active long wall panel. The paper also outlines the development of an analytical model to estimate the bending deformation, axial strain, and the rupture of borehole casing due to rock shear. This model was used in conjunction with the geomechanical strata models to predict the distance behind the face line at which excessive borehole deformation and closure would occur. This method was used to evaluate the optimum roadway support system and spacing between boreholes to maintain effective borehole drainage subject to the range of geological conditions encountered during the panel retreat. A good correlation was obtained between the model predictions and the geomechanical and gas drainage data measured at a UK Colliery.

Does coal mining induce methane emissions through the lithosphere/atmosphere boundary in the Ruhr Basin, Germany?

Underground coal mining is associated with the release of substantial quantities of coal bed methane. While the quantities of methane released from mine shafts are well known, little information is available about the extent of direct firedamp emissions across the earth's surface. On some farm lands, inflammable firedamp escapes have been reported to persist for more than 30 years. These incidents are restricted to hard coal mining areas in the Ruhr Basin and may indicate a causal link between underground coal panels and firedamp surface emissions. To investigate this, a study was initiated in which the emission and consumption rates for methane at the lithosphere/atmosphere boundary were measured using flux chambers. Only emission sites are presented here. As a result, methane emissions were traced not only inside coal mining regions, but for the first time outside the area of mining activities alongside natural normal faults also. The methane release at these faults was found to be correlated negatively to the atmospheric pressure. Furthermore, gas permeabilities for different rock units were calculated from hydraulic conductivities of these rocks and fluid characteristics. They allow the determination of the range of methane emissions possible through different rock units. Having compared these theoretical emission rates with the observed ones, the reason for some of the emission points might be natural, but others can be explained only by underground coal mining, disrupting the rock fabric, increasing the permeabilities and hence giving way to firedamp emissions.

Analytical solutions for mining induced horizontal stress in floors of coal mining panels

From the computational mechanics point of view, analytical solutions for any practical engineering problem are very valuable and important because (1) any numerical method, although powerful for dealing with practical problems, has to be validated before it is put into applications; (2) analytical solutions, in many circumstances, are often the sole resource to be used for validating a numerical method. Besides, analytical solutions can also provide a better understanding of basic physics behind practical engineering problems. For the above reasons, analytical solutions for the mining induced horizontal stress in the floors of coal mining panels have been rigorously derived in this paper. In particular, the following main factors are considered in the process of deriving the analytical solutions: (1) effect of the mining depth of a coal panel which reflects the virgin stress in a panel floor; (2) effect of the primary driving force on the top surface of the panel floor; (3) effect of the direct interaction of the panel floor with its underlying strata; (4) effect of the interaction of the panel floor with its left and right side media; (5) effect of the size and the material properties of the panel floor. Since the present analytical solution is derived from the mechanical model, which can be easily and exactly modelled by any numerical method such as the finite element method, it provides a very useful tool for validating such a numerical method for solving this kind of problem in engineering practice. Finally, the present solutions have been used to carry out a parametric study so as to draw many interesting conclusions for the problem considered.

Mathematical model for estimating the economic effectiveness of production process in coal panels and an example of its practical application

The paper includes the application foundations of the integrational method of mine production process modelling to planning the extraction process in coal panels. The main idea of mathematical model creation based on the principle of the integration of elementary structural units according to spatial, engineering, and time structures of the production process in longwall and exploitation panels is briefly described. The model can be used as an investigation tool for making optimal planning decisions according to the economic criterion assumed. An example of practical application of the method is briefly described. It takes into consideration the impact of exploitation panel dimensions on the optimal longwall face length. Selected conclusions derived from the calculation results are presented.

Electromagnetic wave propagation in disrupted coal seams

It is of economic importance to locate zones of geological disturbance in longwall coal panels prior to the start of mining operations. This can be done with electromagnetic (EM) longwall attenuation tomography in which the amplitude of a single frequency wave in the 300 kHz range is measured over a number of raypaths. The main component of the signal is a fundamental waveguide mode. Zones with high attenuation rates have been observed to be zones of geological disturbance. A two‐dimensional TM (magnetic field transverse to the plane of propagation) mode, time domain finite difference solution was developed and used to determine the excess attenuation (EA) that occurs in disturbed zones. EA is defined as the actual attenuation going through a disturbed zone less the attenuation for an equal length of the normal, undisturbed waveguide. A typical model has a coal seam bordered above and below by rock with a disturbed zone; various types of disturbances such as sand channels and faults were modeled. Synthetic magnetograms are computed at points along the seam and are Fourier transformed to get spectral amplitudes. Model results show that high attenuation can occur in disturbed zones. However the EA that occurs going through a zone is highly dependent on the properties of the zone and waveguide. Models with high conductivity (.05 S/m) roof and floor rock gave larger EA than low conductivity models (.001 S/m). However, low conductivity roof and floor models can still give 5 to 10 db of attenuation, which is consistent with observed values. With high conductivity, simple roof and floor faults can cause significant attenuation.

Numerical simulation of microseismicity induced by deep longwall coal mining

To find an effective numerical simulation method for microseismicity induced by deep mining activity, results obtained by using four simulation methods, namely: (1) the energy release rate method, based on Cook's study; (2) the strain energy release rate method, developed by the authors; (3) the volume excess shear stress index method, based on Spottiswoode's study; and (4) the maximum shear seismic moment release rate method, developed here by the authors; were compared with the microseismicity in a Japanese deep longwall coal mine. The maximum shear seismic moment release rate method was discovered to be the best method, since the intensity of microseismicity in a longwall coal panel, its variation with the face advance and the distribution of microseismic events were well simulated.