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1
Jessu, Kashi, Anthony Spearing i Mostafa Sharifzadeh. "A Parametric Study of Blast Damage on Hard Rock Pillar Strength". Energies 11, nr 7 (20.07.2018): 1901. http://dx.doi.org/10.3390/en11071901.
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Pillar stability is an important factor for safe working and from an economic standpoint in underground mines. This paper discusses the effect of blast damage on the strength of hard rock pillars using numerical models through a parametric study. The results indicate that blast damage has a significant impact on the strength of pillars with larger width-to-height (W/H) ratios. The blast damage causes softening of the rock at the pillar boundaries leading to the yielding of the pillars in brittle fashion beyond the blast damage zones. The models show that the decrease in pillar strength as a consequence of blasting is inversely correlated with increasing pillar height at a constant W/H ratio. Inclined pillars are less susceptible to blast damage, and the damage on the inclined sides has a greater impact on pillar strength than on the normal sides. A methodology to analyze the blast damage on hard rock pillars using FLAC3D is presented herein.
2
Kamran, Muhammad, Waseem Chaudhry, Blessing Olamide Taiwo, Shahab Hosseini i Hafeezur Rehman. "Decision Intelligence-Based Predictive Modelling of Hard Rock Pillar Stability Using K-Nearest Neighbour Coupled with Grey Wolf Optimization Algorithm". Processes 12, nr 4 (13.04.2024): 783. http://dx.doi.org/10.3390/pr12040783.
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Pillar stability is of paramount importance in ensuring the safety of underground rock engineering structures. The stability of pillars directly influences the structural integrity of the mine and mitigates the risk of collapses or accidents. Therefore, assessing pillar stability is crucial for safe, productive, reliable, and profitable underground mining engineering processes. This study developed the application of decision intelligence-based predictive modelling of hard rock pillar stability in underground engineering structures using K-Nearest Neighbour coupled with the grey wolf optimization algorithm (KNN-GWO). Initially, a substantial dataset consisting of 236 different pillar cases was collected from seven underground hard rock mining engineering projects. This dataset was gathered by considering five significant input variables, namely pillar width, pillar height, pillar width/height ratio, uniaxial compressive strength, and average pillar stress. Secondly, the original hard rock pillar stability level has been classified into three types: failed, unstable, and stable, based on the pillar’s instability mechanism and failure process. Thirdly, several visual relationships were established in order to ascertain the correlation between input variables and the corresponding pillar stability level. Fourthly, the entire pillar database was randomly divided into a training dataset and testing dataset with a 70:30 sampling method. Moreover, the (KNN-GWO) model was developed to predict the stability of pillars in hard rock mining. Lastly, the performance of the suggested predictive model was evaluated using accuracy, precision, recall, F1-score, and a confusion matrix. The findings of the proposed model offer a superior benchmark for accurately predicting the stability of hard rock pillars. Therefore, it is recommended to employ decision intelligence models in mining engineering in order to effectively prioritise safety measures and improve the efficiency of operational processes, risk management, and decision-making related to underground engineering structures.
3
Xie, Xuebin, i Huaxi Zhang. "Research on Hard Rock Pillar Stability Prediction Based on SABO-LSSVM Model". Applied Sciences 14, nr 17 (2.09.2024): 7733. http://dx.doi.org/10.3390/app14177733.
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The increase in mining depth necessitates higher strength requirements for hard rock pillars, making mine pillar stability analysis crucial for pillar design and underground safety operations. To enhance the accuracy of predicting the stability state of mine pillars, a prediction model based on the subtraction-average-based optimizer (SABO) for hyperparameter optimization of the least-squares support vector machine (LSSVM) is proposed. First, by analyzing the redundancy of features in the mine pillar dataset and conducting feature selection, five parameter combinations were constructed to examine their effects on the performance of different models. Second, the SABO-LSSVM prediction model was compared vertically with classic models and horizontally with other optimized models to ensure comprehensive and objective evaluation. Finally, two data sampling methods and a combined sampling method were used to correct the bias of the optimized model for different categories of mine pillars. The results demonstrated that the SABO-LSSVM model exhibited good accuracy and comprehensive performance, thereby providing valuable insights for mine pillar stability prediction.
4
Korzeniowski, W. "Rheological model of hard rock pillar". Rock Mechanics and Rock Engineering 24, nr 3 (1991): 155–66. http://dx.doi.org/10.1007/bf01042859.
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Xu, Huawei, Derek B. Apel, Jun Wang, Chong Wei i Krzysztof Skrzypkowski. "Investigation and Stability Assessment of Three Sill Pillar Recovery Schemes in a Hard Rock Mine". Energies 15, nr 10 (21.05.2022): 3797. http://dx.doi.org/10.3390/en15103797.
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In Canada, many mines have adopted the sublevel stoping method, such a blasthole stoping (BHS), to extract steeply deposited minerals. Sill pillars are usually kept in place in this mining method to support the weight of the overburden in underground mining. To prolong the mine’s life, sill pillars will be recovered, and sill pillar recovery could cause failures, fatality, and equipment loss in the stopes. In this paper, three sill pillar recovery schemes—SBS, SS1, and SS2—were proposed and conducted to assess the feasibility of recovering two sill pillars in a hard rock mine by developing a full-sized three-dimensional (3D) analysis model employing the finite element method (FEM). The numerical model was calibrated by comparing the model computed ground settlement with the in situ monitored ground settlement data. The rockburst tendency of the stope accesses caused by the sill pillar recovery was assessed by employing the tangential stress (Ts) criterion and burst potential index (BPI) criterion. All three proposed sill pillar recovery schemes were feasible and safe to recover the sill pillars in this hard rock mine, and the scheme SBS was the optimum one among the three schemes.
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Ma, Hai Tao, i Jin An Wang. "Dynamic Simulation Method for Hard-Rock Pillar Failure in Open-Stope Goaf". Applied Mechanics and Materials 556-562 (maj 2014): 4055–60. http://dx.doi.org/10.4028/www.scientific.net/amm.556-562.4055.
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An attempt to simulate the cascading pillar collapse is made in this paper for a quick evaluation of a large number of mined-out area data that have been collected throughout China. Pillar collapse, load transfer and load redistribution are modeled by the area-apportioned method, and this methodology is general in sense and has been implemented in the expert system developed by the authors as an independent module. The proposed method can provide a quantitative criterion for determination of the failure pattern and identification of the key pillars in the stability analysis of the mined-out area formed by a pillar-room method.
7
Ile, D., i D. F. Malan. "A study of backfill confinement to reinforce pillars in bord-and-pillar layouts". Journal of the Southern African Institute of Mining and Metallurgy 123, nr 5 (13.07.2023): 223–33. http://dx.doi.org/10.17159/2411-9717/2452/2023.
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This study explores the use of backfill in hard rock bord-and-pillar mines to increase the pillar strength and extraction ratio at depth. The use of backfill will also minimize the requirement for tailings storage on surface and the risk of environmental damage. A literature survey indicated that backfill is extensively used in coal mines, but rarely in hard rock bord-and-pillar mines. To simulate the effect of backfill confinement on pillar strength, an extension of the limit equilibrium model is proposed. Numerical modelling of an actual platinum mine layout is used to illustrate the beneficial effect of backfill on pillar stability at greater depths. The magnitude of confinement exerted by the backfill on the pillar sidewalls is unknown, however, and this needs to be quantified using experimental backfill mining sections equipped with suitable instrumentation.
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Napier, J. A. L., i D. F. Malan. "Numerical simulation of large-scale pillar-layouts". Journal of the Southern African Institute of Mining and Metallurgy 123, nr 5 (13.07.2023): 203–10. http://dx.doi.org/10.17159/2411-9717/2451/2023.
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A number of shallow coal or hard rock mines employ pillar mining systems as a strategy for roof failure control. In certain platinum mine layouts, pillars are designed to 'crush' in a stable manner as they become loaded in the panel back area. The correct sizing of pillars demands some knowledge of the pillar strength and the overall layout stress distribution. It is particularly important to understand the impact of the layout geometry on the effective regional 'stiffness' of the rock mass around each pillar. An important design strategy is to model relatively detailed layout configurations which include a precise representation of the local pillar layout geometry and to analyse multiple mining scenarios and extraction sequences to select optimal pillar sizes and barrier pillar spacing. Although computational solution techniques are now impressive in terms of run time efficiency, a major difficulty is often encountered in assigning suitable material properties to the pillars and in devising an effective material description of the layered rock strata overlying the mine excavations. This paper outlines an efficient numerical strategy that can be used to assess large-scale pillar layout performance while retaining the ability to modify individual pillar constitutive behaviour. The proposed method is applied to selected layouts to compare estimated average pillar stress values against values determined by detailed modelling and against observed behaviour.
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Liu, Jiangwei, Changyou Liu i Xuehua Li. "Determination of fracture location of double-sided directional fracturing pressure relief for hard roof of large upper goaf-side coal pillars". Energy Exploration & Exploitation 38, nr 1 (4.11.2019): 111–36. http://dx.doi.org/10.1177/0144598719884701.
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After mining the upper-goaf side, large coal pillars and part of hard roof exposed above the pillars remain. The hard roof can significantly deform the roadway by transferring high stress through coal pillars to the roadway. This paper reports the use of hydraulic fracturing technology to cut the hard roof on both sides (i.e. the broken roof slides to the goaf) to relieve the pressure. The position of the roof fracture is the key to controlling the pressure relief. The bearing characteristics of the large coal pillars and hard roof are analyzed to establish a mechanical model of the broken-roof sliding instability after directional fracturing and determine the width of the coal pillars that can collapse under maximum overburden load on coal pillars as a reasonable hydraulic fracturing position. The results show that the distance from the mine gateway to the fracture location increases with increasing hard-roof length, coal pillar depth, coal pillar thickness (mining height), and goaf width. In addition, the distance to the mine gateway decreases with increasing coal strength, support of the coal pillar by the anchor rod, cohesive force, and internal friction angle of the coal–rock interface. Engineering tests were applied in coal roadway 5107 of coal seam 5# of the Baidong Coal Mine of the Datong Coal Mine Group. Given the site conditions, a reasonable fracturing length of 8.8 m was obtained. Next, directional hydraulic fracturing was implemented. The comparison of the roof deformation before and after fracturing suggests that this method reduces the local stress concentration in coal pillars, which allows the surrounding rock deformation in roadway 5107 to be controlled.
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Liang, Weizhang, Suizhi Luo, Guoyan Zhao i Hao Wu. "Predicting Hard Rock Pillar Stability Using GBDT, XGBoost, and LightGBM Algorithms". Mathematics 8, nr 5 (11.05.2020): 765. http://dx.doi.org/10.3390/math8050765.
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Predicting pillar stability is a vital task in hard rock mines as pillar instability can cause large-scale collapse hazards. However, it is challenging because the pillar stability is affected by many factors. With the accumulation of pillar stability cases, machine learning (ML) has shown great potential to predict pillar stability. This study aims to predict hard rock pillar stability using gradient boosting decision tree (GBDT), extreme gradient boosting (XGBoost), and light gradient boosting machine (LightGBM) algorithms. First, 236 cases with five indicators were collected from seven hard rock mines. Afterwards, the hyperparameters of each model were tuned using a five-fold cross validation (CV) approach. Based on the optimal hyperparameters configuration, prediction models were constructed using training set (70% of the data). Finally, the test set (30% of the data) was adopted to evaluate the performance of each model. The precision, recall, and F1 indexes were utilized to analyze prediction results of each level, and the accuracy and their macro average values were used to assess the overall prediction performance. Based on the sensitivity analysis of indicators, the relative importance of each indicator was obtained. In addition, the safety factor approach and other ML algorithms were adopted as comparisons. The results showed that GBDT, XGBoost, and LightGBM algorithms achieved a better comprehensive performance, and their prediction accuracies were 0.8310, 0.8310, and 0.8169, respectively. The average pillar stress and ratio of pillar width to pillar height had the most important influences on prediction results. The proposed methodology can provide a reliable reference for pillar design and stability risk management.
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Maritz, J. A., i D. F. Malan. "A study of the effect of pillar shape on pillar strength". Journal of the Southern African Institute of Mining and Metallurgy 123, nr 5 (13.07.2023): 235–44. http://dx.doi.org/10.17159/2411-9717/2473/2023.
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Pillar strength is affected by pillar shape, but this has largely been ignored in past research studies. Bord-and-pillar layouts are typically designed using empirical strength equations developed for square pillars. Owing to the poor quality of pillar cutting, many hard-rock pillars have an irregular shape and it is not clear how this affects pillar strength. Furthermore, the strength of rectangular pillars in comparison with square pillars is also difficult to quantify. The 'perimeter rule' is widely adopted for rectangular pillars, but its applicability for pillars with irregular shapes has never been tested. We used numerical modelling in this study to investigate the effect of pillar shape on strength. An analytical limit equilibrium model of a square and a strip pillar also provided useful insights. For slender pillars, the strength of a long rib pillar is essentially similar to that of a square pillar. In contrast, for rib pillars with a large width to height ratio, there is a substantial increase in strength. The study found that the perimeter rule should not be used for irregularly shaped pillars. Displacement discontinuity modelling, using a limit equilibrium approach, is proposed as an alternative to determine the strength of these pillars.
12
Liu, Wenjie, Ke Yang, Xiang He, Zhainan Zhang i Rijie Xu. "Mechanism and Control Technology of Rockburst Induced by Thick Hard Roof and Residual Coal Pillar: A Case Study". Geofluids 2023 (9.02.2023): 1–16. http://dx.doi.org/10.1155/2023/3523592.
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Rockburst caused by the fracture of thick hard roof and the instantaneous instability of residual coal pillar seriously jeopardize the deep coal mining safety. This study takes Boertai Coal Mine, Shendong, China, as the engineering background, in which dynamic instability mechanisms of the gob-side roadway surrounding rock are analyzed by integrating field research, theoretical analysis, and numerical simulation. The results show that the overlying residual coal pillar, side abutment pressures, and front abutment pressures together induce high static stresses in the surrounding rock of the gob side roadway, with peak values exceeding the in situ stress by one order of magnitude. High stresses accumulated in the goaf-side roadway surrounding rock can easily induce dynamic disaster. With the working face advanced, overburdens are caved in succession, resulting in a continuously decreasing of the overlying residual coal pillar width, once the working face entered the influence area of the residual coal pillar. As the morphology of abutment pressure in the residual coal pillar changes from “unimodal distribution” to “bimodal distribution,” the residual coal pillar gradually changes from elastic state to plastic state. When the width of the overlying residual coal pillar is less than the critical width, the thick hard roof and residual coal pillar structure (THRRCPS) lose stability suddenly, resulting in strong dynamic load on the surrounding rock of gob-side roadway. In order to prevent the rockburst of the gob-side roadway under the influence of THRRCPS, regional and local prevention measures are adopted to mitigate the accumulation of stress in the thick hard roof and gob-side roadway surrounding rock by hydraulic fracturing technology and large diameter pressure relief drilling hole.
13
Shen, Wen-long, Wen-bing Guo, Hua Nan, Chun Wang, Yi Tan i Fa-qiang Su. "Experiment on Mine Ground Pressure of Stiff Coal-Pillar Entry Retaining under the Activation Condition of Hard Roof". Advances in Civil Engineering 2018 (18.10.2018): 1–11. http://dx.doi.org/10.1155/2018/2629871.
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In mining excavation, the retained entry with stiff coal pillar is situated in the strong mine ground pressure. Influenced by mining abutment stress and dynamic stress (the vibration signal) induced from the hard roof activation, the retained entry may be subjected to roof separation, supporting body failure, severe floor heave, and even roof collapse. Based on a 2D physical model, an experimental method with plane-stress conditions was used to simulate the mechanical behavior of the rock strata during mining. In this experiment, three monitoring systems were adopted to reveal the characteristics of the strong mine ground pressure in the stiff coal-pillar entry retaining. The results show that the hard roof undergoes bending down, fracture, and caving activation successively until it is able to support overlying loads. The abutment stress which is induced from the loading transfer in stiff coal pillar is larger than that in other rocks around the retained entry in amplification, and overlying loads above the worked-out area have a loading effect on the unworked-out area. When the hard roof is situated in the activation state, the dynamic stress is generated from the hard roof activation, which is verified by the great saltation of acoustic emission signals. The results of mining ground pressure in the physical model can clearly illustrate the mechanical behavior of the rock around the retained entry with stiff coal pillar.
14
Oates, T. E., i D. F. Malan. "A study of UG2 pillar strength using a new pillar database". Journal of the Southern African Institute of Mining and Metallurgy 123, nr 5 (13.07.2023): 265–73. http://dx.doi.org/10.17159/2411-9717/2656/2023.
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A recent experimental pillar extraction project at a UG2 bord-and-pillar mine presented a unique opportunity to compile a new pillar database. Currently, the South African hard rock bord-and-pillar mines are designed using the Hedley and Grant formula with a modified K-value. This empirically derived formula was developed for uranium mines in the Elliot Lake district of Canada. The use of this formula for the design of pillars in South Africa is questionable. Very few pillar failures have nevertheless been observed and its current calibrations for the various reef types are possibly too conservative. A new UG2 pillar database of 66 pillars, of which seven are classified as failed, was compiled by the authors. This enabled a revised 'first-order' calibration of the K-value for the Hedley and Grant formula. The new estimated value for the UG2 is K = 75 MPa. This gives a pillar strength that is more conservative than the PlatMine formula. This work should nevertheless be considered as only a preliminary calibration as the database was small. Further work is also required to determine whether the exponents in the formula for the width and height parameters are appropriate for UG2 pillars.
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Gu, Shitan, Huaixu Chen, Wenshuai Li, Bangyou Jiang i Xiang Chen. "Study on Occurrence Mechanism and Prevention Technology of Rock Burst in Narrow Coal Pillar Working Face under Large Mining Depth". Sustainability 14, nr 22 (20.11.2022): 15435. http://dx.doi.org/10.3390/su142215435.
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This paper presents a collaborative control scheme involving “unloading-solidifying” to prevent rock bursts during narrow pillar recovery at large mining depths. In this study, the stress distribution rule of coal rock mass during the excavation and mining process is studied, and the energy accumulation characteristics of the overlying hard and thick roof structure are investigated. In this way, the rock burst inducing mechanism of the narrow coal pillar working face under complex conditions is investigated. The results show that the peak lateral bearing pressure of the goaf and the maximum horizontal principal stress provide the static load condition for the occurrence of rock burst during roadway excavation. Affected by the superposition of “near-field high static load + far-field dynamic load”, it is extremely easy to reach the critical destabilization value during the mining period at the narrow coal pillar working face. According to the monitoring results, the developed coordinated control scheme, which focuses on the strong pressure relief and strong support in near-field high-bearing pressure coal mass and the pressure relief in far-field high-level hard roof with an advanced pre-cracking roof, can effectively avoid the occurrence of rock burst accidents on narrow coal pillar working face.
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Liu, Xiaoyu, Manchao He, Jiong Wang i Zimin Ma. "Research on Non-Pillar Coal Mining for Thick and Hard Conglomerate Roof". Energies 14, nr 2 (7.01.2021): 299. http://dx.doi.org/10.3390/en14020299.
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This article introduces a new non-pillar coal mining technology (i.e., Gob-side Entry Retaining by Roof Cutting (GERRC)) under the condition of thick and hard roofs. First, we theoretically analyzed the solution to the large suspension span of the thick and hard roof in coal mining. Three-Zone pre-split blasting design in non-pillar coal mining for thick and hard roofs was proposed, based on the principles of rock mechanics. After field experiments, the technology was successfully applied to the non-pillar coal mining of a huge thick conglomerate roof. This research supplements the non-pillar mining technology system. The proposed technologies and methods have strong applicability and have certain guiding significance for the safe and efficient mining of related coal mines.
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Liu, Xiaoyu, Manchao He, Jiong Wang i Zimin Ma. "Research on Non-Pillar Coal Mining for Thick and Hard Conglomerate Roof". Energies 14, nr 2 (7.01.2021): 299. http://dx.doi.org/10.3390/en14020299.
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This article introduces a new non-pillar coal mining technology (i.e., Gob-side Entry Retaining by Roof Cutting (GERRC)) under the condition of thick and hard roofs. First, we theoretically analyzed the solution to the large suspension span of the thick and hard roof in coal mining. Three-Zone pre-split blasting design in non-pillar coal mining for thick and hard roofs was proposed, based on the principles of rock mechanics. After field experiments, the technology was successfully applied to the non-pillar coal mining of a huge thick conglomerate roof. This research supplements the non-pillar mining technology system. The proposed technologies and methods have strong applicability and have certain guiding significance for the safe and efficient mining of related coal mines.
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Jessu, K. V., T. R. Kostecki, A. J. S. Spearing i G. S. Esterhuizen. "Effect of discontinuity dip direction on hard rock pillar strength". Transactions 344, nr 1 (1.01.2018): 25–30. http://dx.doi.org/10.19150/trans.8745.
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Mitri, Hani S. "Assessment of horizontal pillar burst in deep hard rock mines". International Journal of Risk Assessment and Management 7, nr 5 (2007): 695. http://dx.doi.org/10.1504/ijram.2007.014094.
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Deng, J., i D. S. Gu. "Buckling mechanism of pillar rockbursts in underground hard rock mining". Geomechanics and Geoengineering 13, nr 3 (7.02.2018): 168–83. http://dx.doi.org/10.1080/17486025.2018.1434241.
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Wang, Fengnian, Gan Li i Chi Liu. "Investigation on Rock Strata Fracture Regulation and Rock Burst Prevention in Junde Coal Mine". Mathematical Problems in Engineering 2021 (25.09.2021): 1–11. http://dx.doi.org/10.1155/2021/2583707.
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Through the establishment of structural mechanics model, this paper analyzes the fracture of super thick rock stratum. Through the model, it can be seen that the fracture of low-level super thick rock stratum produces large elastic energy release and dynamic load, which is easy to produce disasters such as rock burst. The numerical calculation shows that under the influence of low hard and thick rock stratum, the leading area of coal mine roadway will produce energy concentration, and the coal pillar will also produce energy accumulation. Thick rock stratum is in bending state and has large bending elasticity. Coal pillar has large compression elasticity, which is the main reason for rock burst. The accumulation of elastic properties of overburden and rock burst caused by coal pillar energy storage can be effectively controlled by using advanced presplitting blasting, coal seam drilling pressure relief, and strengthening support.
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Gu, Wei, Dalong Xu, Zhenfei Han i Hao Zhang. "Research on the Reasonable Width of Coal Pillar Driving along Goaf under Thick Hard Roof". Applied Sciences 14, nr 14 (22.07.2024): 6381. http://dx.doi.org/10.3390/app14146381.
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There are fewer studies on the width of coal pillar retaining under a thick, hard roof. This paper takes the thick limestone roof in the 10110 working face of Jinniu Coal Mine as the background, taking the reasonable coal pillar width and its stability control technology as research objectives. Taking the theoretical analysis and calculation, numerical simulation to study the stress distribution along goaf under different parameters of the roof cutting, the stress distribution of the roadway, and displacement of the surrounding rock under different coal pillar widths, finally examined through on-site industrial experiments. The results show that (1) the vertical stress along goaf shows a gradual decrease with the increase of the roof cutting height and angle; after considering the cost and the difficulty, the optimal height and angle are chosen to be 21 m and 15°; (2) the vertical peak stress of coal pillar decreases with the increase of the width, coal pillar is gradually transformed from the crushed state to the elastic state, the displacement of the roadway also decreases with the increase of the width of the pillar, and the width of the coal pillar is chosen to be 8.0 m after comprehensive analysis; (3) during the roadway excavation and working face mining, the deformation of the surrounding rock is in a reasonable range, and the anchors and bolts are in a good state of stress, which indicates that retaining 8 m coal pillar is a success. This paper also provides theoretical references and implications for coal pillar retaining in similar geological mining conditions.
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Lai, Xingping, Huicong Xu, Jingdao Fan, Zeyang Wang, Zhenguo Yan, Pengfei Shan, Jie Ren, Shuai Zhang i Yanbin Yang. "Study on the Mechanism and Control of Rock Burst of Coal Pillar under Complex Conditions". Geofluids 2020 (27.10.2020): 1–19. http://dx.doi.org/10.1155/2020/8847003.
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In order to explore the mechanism of coal pillar rock burst in the overlying coal body area, taking W1123 working face of Kuangou Coal Mine as the engineering background, the full mining stage of W1123 is simulated by FLAC3D. It is found that the high stress concentration area has appeared on both sides of the coal pillar when W1123 does not start mining. With the advance of the working face, the high stress concentration area forms X-shaped overlap. There is an obvious difference in the stress state between the coal pillar under the solid coal and the coal pillar under the gob in W1123. The concrete manifestation is that the vertical stress of the coal pillar below the solid coal is greater than the vertical stress of the coal pillar below the gob. The position of the obvious increase of the stress of the coal pillar in the lower part of the solid coal is ahead of the advancing position of the working face, and the position of the obvious increase of the stress of the lower coal pillar in the gob lags behind the advancing position of the working face. At the same time, in order to accurately reflect the true stress environment of coal pillars, the author conducted a physical similarity simulation experiment in the laboratory to study the local mining process of the W1123 working face, and it is found that under the condition of extremely thick and hard roof, the roof will be formed in the gob, the mechanical model of roof hinged structurer is constructed and analyzed, and the results show that the horizontal thrust of roof structure increases with the increase of rotation angle. With the development of mining activities, the self-stable state of the high stress balance in the coal pillar is easily broken by the impact energy formed by the sudden collapse of the key strata. Therefore, the rock burst of coal pillar in the overlying coal body area is the result of both static load and dynamic load. In view of the actual situation of the Kuangou Coal Mine, the treatment measures of rock burst are put forward from the point of view of the coal body and rock mass.
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He, Fulian, Qingtao Kang, Shuaifeng Yin, Yuli Liu, Zhishuai Wang i Linsheng Gao. "Stratification Failure Mechanism of Coal Pillar Floor Strata with Different Strength in Short Distance Coal Seams". Geofluids 2022 (15.07.2022): 1–14. http://dx.doi.org/10.1155/2022/2598738.
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The failure of strata with different strength under coal pillar in close distance coal seams has its particularity. Theoretical analysis, numerical simulation, and similar test were used to obtain the failure mechanism of the soft and hard stratification of floor strata under the boundary of wide coal pillar and make out the influence of the strata failure on roadway layout. It shows that the failure of the soft and hard stratification is not synchronous and with different failure forms. The deformation and plastic failure of the soft strata occurs at first; then the fracture of the main bearing hard stratum occurs. Based on the main bearing stratum unbalanced forces acted by upper and lower strata, the initial fracture position and broken blocks span were calculated by bending fracture mechanics model of ultimate span beam. The coal pillar side of the roadway under coal pillar forms “column-beam-column” superimposed structure. The roadway layout under coal pillar and under coal pillar boundary with close distance has large influence on the plastic extension of the “column-beam-column” superimposed structure and the broken of main bearing stratum. The influence of roadway arrangement in floor strata outside coal pillar is smaller than those under coal pillar. It is difficult to control the deformation of roadway surrounding rock if the roadway locates beneath the broken blocks of the main bearing stratum.
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Zhang, Jie, Bin Wang, Wenyong Bai i Sen Yang. "A Study on the Mechanism of Dynamic Pressure during the Combinatorial Key Strata Rock Column Instability in Shallow Multi-coal Seams". Advances in Civil Engineering 2021 (2.03.2021): 1–11. http://dx.doi.org/10.1155/2021/6664487.
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In order to study the pressure changes and support failure in mining face under concentrated coal pillar in shallow coal seam, the concentrated coal pillar in 30105 working face of Nan Liang Coal Mine was selected as the research object. In this study, the mechanism of dynamic mine pressure in mining face under concentrated coal pillar was investigated through multiple simulation experiments, numerical simulations, and theoretical analysis. The results of similar simulation experiment indicate that the dynamic mine pressure occurred at 25 m under the concentrated coal pillar and 7 m beyond the coal pillar. The strata roof was observed with sliding down, resulting in collapse and severe fractures commonly seen in rock column. The overlying strata caused the overall subsidence and collapse synchronously, resulting in the sudden increase of the resistance of the support in the working face, and the dynamic load coefficients reach 3.4 and 3.5. The theoretical analysis indicates that the two hard strata in the overlying strata of 3−1 coal meet the theoretical criterion of the combined key strata with the concentrated coal pillar of 2−2 coal in the weak interlayer of the combined key strata. The combined key strata bear the load of the whole overlying strata. The sliding instability featured with the rock column-type fracture located in the combined key strata is considered as the primary trigger of the abnormal resistance of the support and the dynamic mine pressure in the mining face under the concentrated coal pillar. The dynamic pressure model of “combination key strata—immediate roof-support” was established, along with the dynamic load coefficient calculation related to the rock column-type fracture and instability. The characteristics of dynamic load coefficient of the rock column-type fracture and instability under different overlying rock structure conditions were analyzed, providing references and insights into mining under similar geographic conditions.
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Jiang, Lichun, i Wei Liu. "Stand-Up Time Dependence on Protective Roof–Pillar Bearing Structure of Bauxite". Applied Sciences 14, nr 1 (29.12.2023): 325. http://dx.doi.org/10.3390/app14010325.
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The immediate roof of Shanxi sedimentary bauxite is hard clay rock, which maintain stable difficultly in goaf. It is necessary to ensure the stability of the goaf during the mine production period. The relevant research objects did not involve soft rock mass such as bauxite and hard clay and did not pay attention to the weakening characteristics of load-bearing structures under the action of weathering and rheology. This paper provides theoretical support for the safety production of bauxite and similar mines. In order to study the relationship between the stability of the protective roof-pillar bearing structure and time, this paper uses elastic thin plates and rheological theory to build the physical model of the bauxite protective roof-pillar bearing structure, and gives the calculation formula of the stand-up time of the bearing structure. The influence of factors such as the thickness of the protective roof, the uniform surface force coefficient of pillar, the span of the goaf and the thickness of the overlying rock layer on the stand-up time of the bearing structure is analyzed. The relationship between the ultimate bearing capacity and stand-up time of the bearing structure is quantified. The results show that the bearing capacity of the bearing structure is affected by the mechanical properties of the rock mass and the structural parameters of the goaf. Under the condition that the influencing factors of the mechanical parameters of the rock mass remain unchanged, the stand-up time T, which represents the bearing capacity of the bearing structure, is positively correlated with the thickness of the protective roof, positively correlated with the uniform surface force coefficient of the pillar, negatively correlated with the span of the goaf and negatively correlated with the thickness of the overlying rock layer. The engineering example verifies the rationality of theoretical calculation and provides a new idea for mining safety.
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Xia, Hong Chun, Ru Nan Zhang i Wei Li. "Research on Surrounding Rock Control Technology in Two Hard Fully Mechanized Coal Mining". Advanced Materials Research 868 (grudzień 2013): 343–46. http://dx.doi.org/10.4028/www.scientific.net/amr.868.343.
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The coal 8210 big mining height of the Datong mine Jin hua gong face in the process of mining airport coal pillar fried state a, floor deformation intense, serious kick drum, eventually leading to rock failure .In the severe cases, easily induced by shock pressure and other disasters ,these have serious impact on the efficient production of face security in the large mining height. by the airport side of roadway roof pressure relief, combined with roadway bolting reinforcement technology effectively control the deformation of surrounding rock of roadway, Test results show that the security measures taken can meet the well production safety requirements.
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Mendrofa, Gabriella Aileen, Bevina Desjwiandra Handari i Gatot Fatwanto Hertono. "Ensemble learning model on Artificial Neural Network - Backpropagation (ANN-BP) architecture for coal pillar stability classification". ITM Web of Conferences 61 (2024): 01008. http://dx.doi.org/10.1051/itmconf/20246101008.
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Pillars are important structural units used to ensure mining safety in underground hard rock mines. Unstable pillars can significantly increase worker safety hazards and sudden roof collapse. Therefore, precise predictions regarding the stability of underground pillars are required. One common index that is often used to assess pillar stability is the Safety Factor (SF). Unfortunately, such crisp boundaries in pillar stability assessment using SF are unreliable. This paper presents a novel application of Artificial Neural Network-Backpropagation (ANN-BP) and Deep Ensemble Learning for pillar stability classification. There are three types of ANN-BP used for the classification of pillar stability distinguished by their activation functions: ANN-BP ReLU, ANN-BP ELU, and ANN-BP GELU. These three activation functions were chosen because they can solve the vanishing gradient problem in ANN-BP. In addition, a Deep Ensemble Learning process was carried out on these three types of ANN-BP to reduce the prediction variance and improve the classification results. This study also presents two labeling alternatives for pillar stability by considering its suitability with the SF. Thus, pillar stability is expanded into four categories: failed with a suitable safety factor, intact with a suitable safety factor, failed without a suitable safety factor, and intact without a suitable safety factor. There are five features used for each model: pillar width, mining height, bord width, depth to floor, and ratio. In constructing the model, the initial dataset is divided into training data, validation data, and testing data. In this case, four type of proportions are used. For training-testing division the proportions are: 80 % : 20 %, 70 % : 30 %, for training-validation-testing division the proportions are: 80 % : 10 % : 10 %, 70 % : 15 % : 15 %. Average accuracy, F1-score, and F2-score from 10 trials were used as performance indicators for each model. The results showed that the ANN-BP model with Ensemble Learning could improve ANN-BP performance with an average accuracy 86.48 % and an F2-score 96.35 % for the category of failed with a suitable safety factor.
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Cui, Feng, Shuai Dong, Xingping Lai, Jianqiang Chen, Chong Jia i Tinghui Zhang. "Study on the Fracture Law of Inclined Hard Roof and Surrounding Rock Control of Mining Roadway in Longwall Mining Face". Energies 13, nr 20 (14.10.2020): 5344. http://dx.doi.org/10.3390/en13205344.
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In the inclination direction, the fracture law of a longwall face roof is very important for roadway control. Based on the W1123 working face mining of Kuangou coal mine, the roof structure, stress and energy characteristics of W1123 were studied by using mechanical analysis, model testing and engineering practice. The results show that when the width of W1123 is less than 162 m, the roof forms a rock beam structure in the inclined direction, the floor pressure is lower, the energy and frequency of microseismic (MS) events are at a low level, and the stability of the section coal pillar is better. When the width of W1123 increases to 172 m, the roof breaks along the inclined direction, forming a double-hinged structure, the floor pressure is increased, and the frequency and energy of MS events also increases. The roof gathers elastic energy release, and combined with the MS energy release speed it can be considered that the stability of the section coal pillar is better. As the width of W1123 increases to 184 m, the roof in the inclined direction breaks again, forming a multi-hinged stress arch structure, and the floor pressure increases again. MS high-energy events occur frequently, and are not conducive to the stability of the section coal pillar. Finally, through engineering practice we verified the stability of the section coal pillar when the width of W1123 was 172 m, which provides a basis for determining the width of the working face and section coal pillar under similar conditions.
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Lu, Hai Feng, i Lin Wang. "Analysis on Water Abundance of Loose Aquifer and Quality Evaluation of Overburden Strata during Mining under Loose Aquifer". Advanced Materials Research 1006-1007 (sierpień 2014): 73–77. http://dx.doi.org/10.4028/www.scientific.net/amr.1006-1007.73.
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The establishment of pillars is one of the most effective methods to keep mining safety under loose aquifer. Water abundance of bottom aquifer of loose strata,strength and structure of overburden strata are the main factors controlling type and height of coal pillar.Taking Xiyi area in Pansan coal mine as an example, hydrogeology characteristics of the bottom aquifer of quaternaty system and engineering geological properties of overburden strata of No.8 seam were analyzed.The characteristics of weathered rock was particularly analyzed.The results indicated that the type of the water abundance and permeability in this aquifer were medium.When the No.8 seam in Xiyi area was at shallow depths mining, water-proof pillar had to be designed.The structure of overburden strata of No.8 seam belonged to the type of upper soft and lower hard,which can restrain the failure of overburden strata.The thickness of weathering zone was thick and distribution was also stable.Weathered rock had good water-resisting property and crack resistance.
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Cao, Xu, Saisai Wu i Qingyuan He. "Investigation into Influences of Hydraulic Fracturing for Hard Rock Weakening in Underground Mines". Applied Sciences 14, nr 5 (27.02.2024): 1948. http://dx.doi.org/10.3390/app14051948.
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The long overhanging distance of hard roofs and long-collapse steps induces a large area of suspension on the working face in underground coal mines, resulting in excessive pressure and deformation on the surrounding rocks of the adjacent roadway in the work face, which seriously threatens the safety of coal mining operations. In this study, in order to study the hydraulic fracturing effects on hard roofs, numerical simulation and in situ tests were conducted. The analysis and comparison of fracturing effects under different hydraulic fracturing parameters were carried out, and the reasonable hydraulic fracturing parameters of the hydraulic weakening of hard roofs were designed accordingly. Based on designed hydraulic fracturing, industrial tests were conducted in the field while stress and deformation were recorded. The results show that hydraulic fracturing could effectively reduce the pressure of the hard roof. Hydraulic fracturing effectively destroyed the cantilever beam structure above the coal pillar, reduced the stress concentration, and moderated mineral pressure at the working face. The proposed methods and obtained results provide theoretical and technical support for the treatment of underground mines with hard roofs.
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Li, Zhihua, Ke Yang, Xinzhu Hua, Cheng Liu, Peng Zhou i Shengwen Ge. "Mechanism and Control of Water–Rock Coupling-Induced Disaster when Mining below the Unconsolidated Confined Aquifer". Geofluids 2023 (24.01.2023): 1–14. http://dx.doi.org/10.1155/2023/6485987.
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Theoretical analysis and numerical simulation were conducted to study the disaster-causing mechanism of structural instability of the overlying strata induced by water–rock coupling and effectively prevent and control the powered support jammed accident during mining below the unconsolidated confined aquifer. The influencing factors on the stability of the overlying strata structure were analyzed, and the numerical simulation method of unconsolidated confined aquifer was designed. The disaster-causing mechanism and the evolution process of the stress–displacement–crack field of the overlying strata induced by water–rock coupling were discovered. Meanwhile, the prevention measures for the structural instability of the overlying strata were proposed and verified in some engineering practice. Results show that the stability of the overlying strata structure reduces with the increase in hydraulic pressure, the breaking interval of the main roof, and the decrease in the overlying strata strength and waterproof coal pillar height. The overlying strata structure keeps a stable equilibrium state before the fracture planes through a whole waterproof coal–rock pillar. When the hydraulic pressure is small or the bedrock surface is a thick topsoil layer, the sliding block is in a state of limit equilibrium for the decrease of pressure on the sliding block while the fracture planes through a whole waterproof coal–rock pillar because of the action of unloading during an overlying strata movement. When the hydraulic pressure is high, the pressure on the sliding block remains constant at about hydraulic pressure, and the intact shear fall of the sliding block occurs as a result of the hydraulic pressure of the confined aquifer and the weight of the sliding block, which may result in a powered support jammed accident. However, this type of accident can be prevented by drainage for decreasing hydraulic pressure, presplitting blasting of the hard main roof, overlying strata grouting reinforcement, and increasing the height of the waterproof coal–rock pillar.
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Rao, K. K., B. S. Choudhary i G. D. Raju. "Stability of Pillar and Drive Advances in Hard Rock Mine Through Numerical Modelling and Instrumentation". Current Science 120, nr 11 (10.06.2021): 1758. http://dx.doi.org/10.18520/cs/v120/i11/1758-1767.
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Watson, B. P., R. A. Lamos i D. P. Roberts. "PlatMine pillar strength formula for the UG2 Reef". Journal of the Southern African Institute of Mining and Metallurgy 121, nr 8 (13.10.2021): 1–12. http://dx.doi.org/10.17159/2411-9717/1387/2021.
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The Upper Group 2 (UG2) chromitite reef is a shallow-dipping stratiform tabular orebody in the South African Bushveld Complex, which strikes for hundreds of kilometres. Mining is extensive, with depths ranging from close-to-surface to 2 500 m. Pillars are widely used to support the open stopes and bords. Little work has been done in the past to determine the strength of pillars on the UG2 Reef and design was done using formulae developed for other hard-rock mines. This has led to oversized pillars with consequent sterilization of ore. In this paper we describe a back-analysis of stable and failed UG2 pillars on the Bushveld platinum mines, and provides a strength formula for UG2 pillars. The formula may be used cautiously on all Bushveld platinum mines with similar geotechnical, geometrical, and geomechanical conditions to the pillars in the database.
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Yue, Xizhan, Min Tu, Yingfu Li, Guanfeng Chang i Chen Li. "Stability and Cementation of the Surrounding Rock in Roof-Cutting and Pressure-Relief Entry under Mining Influence". Energies 15, nr 3 (27.01.2022): 951. http://dx.doi.org/10.3390/en15030951.
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The application of roof-cutting and pressure-relief gob-side entry retention plays a critical role in controlling the stability of the surrounding rock at the entry, easing continuity tension and improving resource recovery ratio. The excavation of the 360,803 airway in Xinji No. 1 Mine is affected by intense mining of the 360,805 working face. Hence, to address the stability problem of surrounding rock in the 360,803 airway, rock mass blast weakening theory was used in this study to analyze the blasting stress of columnar charged rock mass and obtain the radiuses of crushed, fractured, and vibration zones under uncoupled charging conditions. The reasonable array pitch, length, and dip angle of boreholes were determined according to the pressure-relief range of the blasting fracture. The migration laws of roof strata were explored based on a mechanical model of overlying roof strata structure on the working face. Subsequently, the horizon, breaking span, and caving sequence of hard roof strata were obtained to determine the roof-cutting height of this entry. On the basis of the theory of key stratum, the number of sequences at the roof caving limit stratum and hanging roof length in the goaf were calculated, the analytical solution to critical coal pillar width was acquired, the evaluation indexes for the stability of entry-protecting coal pillars were determined, and the engineering requirements for the 25 m entry-protecting coal pillars in the 360,803 airway were met. Moreover, various indexes such as roof separation fracture, displacement of surrounding rock, and loose circle of surrounding rock in the gob-side entry were analyzed. The stability and cementation status of surrounding rock in the 360,803 airway were evaluated, and tunneling safety was ensured.
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Walton, G., i S. Sinha. "Improved empirical hard rock pillar strength predictions using unconfined compressive strength as a proxy for brittleness". International Journal of Rock Mechanics and Mining Sciences 148 (grudzień 2021): 104934. http://dx.doi.org/10.1016/j.ijrmms.2021.104934.
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Forbes, Bradley, Nicholas Vlachopoulos, Mark S. Diederichs, Andrew J. Hyett i Allan Punkkinen. "An in situ monitoring campaign of a hard rock pillar at great depth within a Canadian mine". Journal of Rock Mechanics and Geotechnical Engineering 12, nr 3 (czerwiec 2020): 427–48. http://dx.doi.org/10.1016/j.jrmge.2019.07.018.
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Burtan, Zbigniew, i Dariusz Chlebowski. "The Effect of Mining Remnants on Elastic Strain Energy Arising in the Tremor-Inducing Layer". Energies 15, nr 16 (19.08.2022): 6031. http://dx.doi.org/10.3390/en15166031.
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A vast majority of hard coal deposits in Poland have a multi-seam structure, hence the presence of mining remnants left from previous operations. The impact of those remnants (exploitation edges or residual pillars) can further intensify geomechanical phenomena occurring in the rock mass, leading to changes in the original state of stress. This applies to all layers within the rock strata, including thick and coherent ones (referred to as tremor-inducing layers) where the impacts of mining remnants are likely to trigger tremors, thus enhancing the rock bursts hazard. In the light of the geomechanical model of rock strata recalled in the study, it is assumed that homogeneous and isotropic elastic layers are found between the considered mining remnant (which is revealed as the stress distribution), and the rock medium modelled as a homogeneous and isotropic half-plane. Development of the state of stress in the bedded medium was brought down to the analysis of interacting elastic layers, where the biharmonic equation is satisfied for each layer and for each respective half-plane. This equation can be solved by the integral Fourrier transform method. The impacts of the exploitation edge and the residual pillar on the elastic strain energy in the tremor-inducing layer is illustrated by recalling the Burzyński’s stress criterion. Strain energy in the tremor-inducing layer was analysed for various deformation properties of the surrounding strata and for various methods of coal extraction from the seam underneath the tremor-inducing layer. The results of the study evidence that a change in deformation properties of strata in the vicinity of the tremor-inducing layer may affect the state of stress and strain energy, which impacts on the tremor hazard levels in the vicinity of mining remnants areas.
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Zhou, Jian, Xibing Li i Hani S. Mitri. "Comparative performance of six supervised learning methods for the development of models of hard rock pillar stability prediction". Natural Hazards 79, nr 1 (10.06.2015): 291–316. http://dx.doi.org/10.1007/s11069-015-1842-3.
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Luo, Jianqiao, Shaohong Yan, Tuo Yang, Haoqi Mu, Wensheng Wei, Yupeng Shen i Hongtao Mu. "Mechanism of Hydraulic Fracturing Cutting Hard Basic Roof to Prevent Rockburst". Shock and Vibration 2021 (10.11.2021): 1–14. http://dx.doi.org/10.1155/2021/4032653.
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Rockburst is globally regarded as one of the most severe and complicated mining dynamic disasters to predict or control. Generally, the occurrence mechanism of rockbursts can be considered as a process of the elastic strain energy accumulation, emancipation, transmission, and occurrence. Tracing to the source, the reasons for large accumulation of elastic strain energy in coal and rock mass are the high stress of the roof layer that loads on the coal and rock masses around the mining space coupling effect with the natural horizontal tectonic stress. In this study, using the minimum energy theory and elasticity theory, the analytical formula for calculating elastic strain energy of the roof cantilever beam structure acting on the coal body load in front of the working face is deduced. Accordingly, we achieved a method of using hydraulic fracturing to improve the roof structure. In detail, we use a high-pressure jet to cut the cantilever roof structure, which can make a prelocated fracture surface, and then utilize the packers to make sure that the injected high-pressure fracturing fluid is propagating along the prelocated fracture surface and can cut off the cantilever roof structure eventually to prevent rockbursts in advance. Due to the rockburst occurrence mechanism and the quantitatively elastic strain energy analytical formula, a preconditioning water jet cutting induced fracture surface to create orientation-controllable hydraulic fracture strategy is proposed to guard against the high hazard caused by the massive elastic strain energy, which accumulated in the coal body in front of the working face and coal pillar.
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Zhou, Jinlong, Junfeng Pan, Yongxue Xia, Wengang Liu, Taotao Du i Jianhong Wu. "Investigation of Load Characteristics and Stress-Energy Evolution Laws of Gob-Side Roadways Under Thick and Hard Roofs". Applied Sciences 14, nr 20 (18.10.2024): 9513. http://dx.doi.org/10.3390/app14209513.
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The stress environments of gob-side roadways (GSRs) are becoming increasingly complex during deep coal mining under thick and hard roofs. This leads to strong strata behaviors, including roadway floor heave, roof subsidence, and even coal bursts. Among them, coal bursts pose the greatest threat to production safety in coal mines. Coal bursts in a GSR strongly correlate with the load characteristics and stress-energy evolution laws of the roadway. This study analyzes the roof structures of double working faces (DWFs) during the initial weighting stage (IWS) and full mining stage (FMS) of gob-side working faces (GSWFs). This study also explores how varying roof structures affect the stability of GSRs. Three-dimensional roof structure models of DWFs and mechanical models of dynamic and static loads superposition on a GSR throughout the IWS and FMS of a GSWF were developed. An analysis identified the primary stress sources affecting the GSR throughout various mining stages of the GSWF. Subsequently, the principle of “three-load” superposition was developed. A novel method was proposed to quantify the stress state in the GSR surrounding rock across different mining stages of the GSWF. The method quantitatively characterizes the load of the GSR surrounding rock. Based on this, the criterion for judging the burst failure of the roadway was established. Numerical simulations are used to analyze the stress-energy evolution laws of the working face, coal pillar, and GSR surrounding rock during the mining process of the GSWF. These findings offer valuable references for studying and preventing coal bursts in GSRs under equivalent geological situations.
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Hamediazad, Farzaneh, i Navid Bahrani. "Simulation of hard rock pillar failure using 2D continuum-based Voronoi tessellated models: The case of Quirke Mine, Canada". Computers and Geotechnics 148 (sierpień 2022): 104808. http://dx.doi.org/10.1016/j.compgeo.2022.104808.
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Dai, Xianglin, Rui Gao, Weichen Gao, Dou Bai i Xiao Huang. "Exploring the Distribution Characteristics of High Static Load in the Island Working Face of Extra-Thick Coal Seams with Hard Roof: Addressing the Challenge of Rock Burst Risk". Applied Sciences 14, nr 5 (28.02.2024): 1961. http://dx.doi.org/10.3390/app14051961.
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A high static load state significantly increases the risk of rock burst occurrences on the island working face, posing a significant threat to the safety of coal mine production. This paper focused on the engineering background of the 8204-2 working face at Tashan Coal Mine. Field research indicated that there were noticeable differences in the frequency of coal bursts in different regions and working face ranges, with the mine pressure being complex and severe. Through theory analysis, the stress concentration degree of the island working face was mainly affected by the buried depth, working face length, gob length, coal seam thickness, and coal pillar width. The stress distribution and plastic zone changes of the island working face, influenced by different factors, were studied by numerical simulation. The entity coal stress equation of the island working face was fitted and the mechanism of rock burst in the island working face was revealed. The research findings presented in this paper provide important theoretical support and technical guidance for the safe and efficient mining of island working faces.
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Wang, Gongyuan, Jianbiao Bai, Ningkang Meng i Xiangqian Zhao. "Study on the Three-Dimensional Behavior of Blasting Considering Non-Uniform In-Situ Stresses Distributed along the Blasthole Axis". Applied Sciences 14, nr 14 (18.07.2024): 6256. http://dx.doi.org/10.3390/app14146256.
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For roof-cutting by blasting in the gob-side entry under an overhanging hard roof, studies on the impacts of in-situ stresses on the propagation of blast-induced cracks have typically focused on uniform stresses but ignored the effects of non-uniform in-situ stresses (NIS) distributed along the blasthole axis. Therefore, the distribution patterns of hoop stress and rock damage caused by NIS distributed along the blasthole axis were investigated using numerical modeling and theoretical analysis. The results illustrate that with the rising NIS for the cross section along the blasthole axis, the peak values of hoop compressive stress at the same distance from the blasthole’s center gradually increase, resulting in a nonlinear attenuation trend in the damage range of the rock. Consequently, the spacing between blastholes should be determined based on the average length of the primary cracks under the maximum confining pressure. Additionally, for the cross section perpendicular to the blasthole axis, as the lateral pressure coefficient increases from 0.25 to 2, the damage range in the vertical direction significantly decreases. This results in varying extents of blast-induced cracks within the coal pillar, providing a reference for the design of shallow-borehole crack filling.
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Sun, H., X. L. Liu, S. G. Zhang i K. Nawnit. "Experimental investigation of acoustic emission and infrared radiation thermography of dynamic fracturing process of hard-rock pillar in extremely steep and thick coal seams". Engineering Fracture Mechanics 226 (marzec 2020): 106845. http://dx.doi.org/10.1016/j.engfracmech.2019.106845.
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Nguyen, V. N., T. N. Pham, P. Osinski, T. C. Nguyen i L. H. Trinh. "Substantiation of pillar parameters in mining of inclined coal seams in Quang Ninh Province, Vietnam". Gornye nauki i tekhnologii = Mining Science and Technology (Russia) 7, nr 2 (20.07.2022): 93–99. http://dx.doi.org/10.17073/2500-0632-2022-2-93-99.
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Design and operation of auxiliary underground workings in coal mines involves substantiation of parameters of coal pillars and requires development of new approaches to substantiate their geometrics. On the one hand, sufficient stability of a “rock mass – working – coal pillar” system should be ensured. On the other hand, the parameters of “frozen” coal reserves in the pillars should be justified. The joint solution of these two problems requires accurate forecasting based on modern digital models of a rock mass. In this study, a model of rock mass and mine workings with different dimensions of a coal pillar is presented with the use of Flac3D software. The simulation findings showed that when developing sloping coal seams, the volume of coal extraction in a longwall has an effect on the stress-strain state of the enclosing rock mass. During the study different factors having effect on geometrics of a coal pillar were analyzed, and their influence on the field of stresses and shear of inclined layers in a rock mass was studied, and the size of the plastic deformation zone around an auxiliary mine working was also determined. The study findings are also of practical importance in terms of substantiating the parameters of a working support design. The size of coal pillar is also connected with the support type. It should be taken into account that bolts should be of sufficient length to ensure firm fixing and located in the zone of intact rocks. The research showed that a coal pillar should be 10 to 15 m wide in order to ensure optimal mining conditions and safety.
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Le, Phuc Quang, i Duy Van Than. "Research on the stability of reused roadways at Khe Cham I coal mine". Journal of Mining and Earth Sciences 62, nr 5a (1.12.2021): 94–102. http://dx.doi.org/10.46326/jmes.2021.62(5a).12.
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The deformation and supporting methods, maintaining roadways stability are always important issues in coal mining and safe production, especially for roadways in complex geological conditions. To identify the cause and direction to overcome the disadvantages of supporting and maintaining the stability of reused roads, a case study at seam 11, Khe Cham coal mine I, is presented in this paper. Here, coal seams are exploited with a longwall system, and the roadway is reused with the function of transport and ventilation when mining adjacent panels. In the reuse phase, between the roadway and the goaf is a 20m wide coal pillar, and the main roof of the seam is a hard roof stratum. Based on the results of the detailed field survey, the deformation characteristics of the road and the damaged types of the supporting structure were investigated. The study results show that there is serious deformation and because SVP steel resistance cannot control the movement of the surrounding rock mass and ensure roadway stability. The deformation and narrowing of the roadway section have negatively affected the transportation and ventilation and labor safety. In addition, roadway repair and reinforcement must be carried out regularly, leading to an increase in workload and production costs by 1.5-2 times. To limit the deformation of re-used roadways, the development directions of the supporting structure have been recommended. The research results of the paper can provide reference for the stress-strain study direction of the roadways under similar geological conditions.
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Martin, C. D., i W. G. Maybee. "The strength of hard-rock pillars". International Journal of Rock Mechanics and Mining Sciences 37, nr 8 (grudzień 2000): 1239–46. http://dx.doi.org/10.1016/s1365-1609(00)00032-0.
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Rafiei Renani, H., i C. D. Martin. "Modeling the progressive failure of hard rock pillars". Tunnelling and Underground Space Technology 74 (kwiecień 2018): 71–81. http://dx.doi.org/10.1016/j.tust.2018.01.006.
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Sadovenko, I., V. Bondarenko, I. Salieiev i A. Zagrytsenko. "Substantination of hydromechanical parameters of water regulation using mine pillars during mines closure". Collection of Research Papers of the National Mining University 64 (2021): 55–67. http://dx.doi.org/10.33271/crpnmu/64.055.
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Purpose. Substantiation of hydromechanical parameters that make it possible to control the safe ratio of hydrodynamic levels in a mine shaft and a rock mass when closing mines using submersible pumps. Research methodology. An experimental-analytical method was used, which consists in the formation and analysis of data from field tests of fractured porosity, permeability and the position of groundwater levels in hard sandstones around mine shafts with concrete support. Research results. It has been established that the hydromechanical state around a mine shaft in stable water-bearing rocks is characterized by the development of mutually competing processes of nonlinear decrease in the permeability of the loaded rock contour and hydrogeomechanical unloading of structural elements of water-bearing rocks and filter attachment. The values of the hydrogeomechanical unloading of the shaft attachment in the range of 0.054 - 6.125105 Pa are close to the tensile strength limit of the "concrete-water-bearing rock" contact, which indicates the danger of its collapse. Scientific novelty. The problem of combining the elastic viscometric load of the rock mass attachment and the hydrodynamic planar-radial flow to the wellbore is solved, where the hydrogeomechanical state in stable water-bearing rocks is characterized by the development of mutually competing processes of nonlinear decrease in the permeability of the loaded rock contour and hydrostatic unloading of structural elements of the water-bearing rocks and filters. Practical value. The obtained solutions and their analysis explain the discrepancy between the calculated (standard) loads on the fastening, which is known from practical experience, and actually measurable values, and also have significant practical significance. The established fact of the approximation of the value of hydrogeomechanical unloading of the stovol attachment to the tensile strength of the contact "concrete - water-bearing rock" is dubious and requires a decrease in the hydrodynamic deflection to the mine stovol when controlling the process of flooding with submersible pumps.