Mechanism of Rock Bursts Induced by the Synthetic Action of “Roof Bending and Rock Pillar Prying” in Subvertical Extra-Thick Coal Seams

When studying the rock burst mechanism in subvertical extra-thick coal seams in the Wudong coal mine in Xinjiang, China, most studies focus on rock pillars, while the effect of the roof on rock bursts is usually ignored. In this paper, a rock burst mechanism in subvertical extra-thick coal seams under the control of a “roof-rock pillar” is proposed. A theoretical analysis is first performed to explain the effect of roof-rock pillar combinations on rock bursts in coal seams. Numerical modeling and microseismic analysis are implemented to further study the mechanism of rock burst. The main conclusions are as follows: 1) During the mining of the B3+6 coal seam, an obvious microseismic concentration phenomenon is found in both the roof and rock pillar of B3+6. The rock bursts exhibited obvious directionality, and its main failure characteristics are floor heave and sidewall heave, but there will also be some failures such as shoulder socket subsidence in some parts. 2) The stress transfer caused by rock pillar prying is the main reason for the large difference in rock burst occurrence near the vertical and extra thick adjacent coal seams under the same mining depth. 3) Under the same cantilever length, the elastic deformation energy of the roof is much greater than that of the rock pillar, which makes it easier to produce high-energy microseismic events. With an increasing mining depth, the roof will become the dominant factor controlling the occurrence of rock bursts. 4) The high-energy event produced by the rock mass fracture near the coal rock interface easily induces rock bursts, while the high-energy event produced by the fracture at the far end of the rock mass is less likely to induce rock burst. 5) Roof deformation extrusion and rock pillar prying provide high static stress conditions for the occurrence of rock bursts in the B3+6 coal seam. The superposition of the dynamic disturbance caused by roof and rock pillar failure and the high static stress of the coal seam is the main cause of rock burst in the B3+6 coal seam.

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Experimental Study of Prevention and Control of Rock Burst in Steeply Inclined Coal Seams by Mining Sequence and Filling

Shock and Vibration ◽

10.1155/2022/2450513 ◽

2022 ◽

Vol 2022 ◽

pp. 1-10

Author(s):

Zhihui Zhang ◽

Yangyi Liu ◽

Wenwen Zhu ◽

Jian Liu ◽

Tian Ma ◽

...

Keyword(s):

Stress Concentration ◽

Coal Seam ◽

Rock Burst ◽

Vertical Direction ◽

Geological Structure ◽

Coal Seams ◽

Rock Pillar ◽

Fundamental Information ◽

Mining Sequence ◽

Control And Prevention

The control and prevention of rock burst in a steeply inclined coal seam are essential. In order to figure out the effects of filling and mining sequence on rock burst in the steeply inclined coal seam, B3+6 and B1+2 coal seams in Wudong coal mine are chosen as the research objects, and an in-house experiment system of similarity simulation is established in this study. Combined with numerical simulation, the characteristics of collapse, stress distribution, and displacement variations can be measured, which provide useful information to study the effects of the filling body and mining sequence on rock burst. Experimental results show that the key reason for rock burst in a steeply inclined coal seam is the stress concentration of the rock pillar between B3+6 and B1+2 coal seams instead of the stress-lever-effect of a deeper rock pillar. The filling body can support the middle rock pillar, share the geological structure stress in the horizontal and vertical direction, eliminate the stress concentration zone largely, and prevent the occurrence of rock burst. When multiple working faces are working, the opposite side of the coal seam should be mined first to release the energy in the rock in advance, thus preventing the rock burst effectively. The research results provide fundamental information for better understanding the reason for rock burst and preventing rock burst in the steeply inclined coal seam.

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The Impact of the Coexistence of Methane Hazard and Rock-Bursts on the Safety of Works in Underground Hard Coal Mines

Energies ◽

10.3390/en14010128 ◽

2020 ◽

Vol 14 (1) ◽

pp. 128

Author(s):

Justyna Swolkień ◽

Nikodem Szlązak

Keyword(s):

Rock Burst ◽

Methane Concentration ◽

High Energy ◽

Hard Coal ◽

Coal Seams ◽

Safety Level ◽

Methane Drainage ◽

Innovative Methods ◽

Hard Coal Mining ◽

The Impact

Several natural threats characterize hard coal mining in Poland. The coexistence of methane and rock-burst hazards lowers the safety level during exploration. The most dangerous are high-energy bumps, which might cause rock-burst. Additionally, created during exploitation, safety pillars, which protect openings, might be the reason for the formation of so-called gas traps. In this part, rock mass is usually not disturbed and methane in seams that form the safety pillars is not dangerous as long as they remain intact. Nevertheless, during a rock-burst, a sudden methane outflow can occur. Preventing the existing hazards increases mining costs, and employing inadequate measures threatens the employees’ lives and limbs. Using two longwalls as examples, the authors discuss the consequences of the two natural hazards’ coexistence. In the area of longwall H-4 in seam 409/4, a rock-burst caused a release of approximately 545,000 cubic meters of methane into the excavations, which tripled methane concentration compared to the values from the period preceding the burst. In the second longwall (IV in seam 703/1), a bump was followed by a rock-burst, which reduced the amount of air flowing through the excavation by 30 percent compared to the airflow before, and methane release rose by 60 percent. The analyses presented in this article justify that research is needed to create and implement innovative methods of methane drainage from coal seams to capture methane more effectively at the stage of mining.

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The results of monitoring of hydroimpulsive disintegration of outburst-prone coal seams using ZUA-98 system

E3S Web of Conferences ◽

10.1051/e3sconf/202016800068 ◽

2020 ◽

Vol 168 ◽

pp. 00068

Author(s):

Vasyl Zberovskyi ◽

Kostiantyn Sofiiskyi ◽

Rishard Stasevych ◽

Artem Pazynych ◽

Jan Pinka ◽

...

Keyword(s):

Acoustic Emission ◽

Rock Mass ◽

Coal Seam ◽

High Frequency ◽

Strain State ◽

Monitoring And Evaluation ◽

Dynamic State ◽

Coal Seams ◽

Gas Dynamic ◽

Mine Workings

The paper represents the results of monitoring and evaluation of the efficiency of hydroimpulsive disintegration of outburst-prone coal seams in the stopes of development mine workings using a system of sound detecting facilities. Methods of acoustic emission control have been considered as well as the monitoring tasks to evaluate rock mass conditions before the procedure and after it inclusive of the results of sound accompaniment of hydraulic disintegration of the coal seam. It has been determined that the higher concentration of stresses within the rock mass is, the more efficient action of high frequency self-oscillations of cavitation transmitter is on both the fissuring and changes in gas-dynamic state of the coal seam. It has been recommended to apply a mode of impulsive fluid pumping under the conditions where coal seam is in the stress-strain state.

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Identification for Abutment Stress by Drilling Cuttings

Applied Sciences ◽

10.3390/app11209467 ◽

2021 ◽

Vol 11 (20) ◽

pp. 9467

Author(s):

Jian Tan ◽

Yunliang Tan ◽

Zihui Wang ◽

Yubao Zhang

Keyword(s):

Stress Concentration ◽

Coal Seam ◽

Rock Burst ◽

Abutment Pressure ◽

High Stress ◽

Coal Seams ◽

Cutting Test ◽

Key Factor ◽

Distribution Of Stress ◽

The Relationship

The concentration of abutment pressure acting on coal seams induced by mining is a key factor to trigger rock burst. Understanding of abutment pressure or stress concentration is fundamental in preventing and controlling rock burst. The influence on abutment pressure fluctuation caused by the inhomogeneity of coal seams needs to be considered, but it is difficult to obtain by the present usual ways such as acoustic transmission, electromagnetic wave transmission, etc. In this article, the relationship between the amount of cuttings drilled in a coal seam and stress level was analyzed by considering the effect of drilling cutting expansion, and the drilling cutting test was carried out in Xinglongzhuang Coal Mine, Shandong Energy Ltd. It is found that the amount of cuttings drilled is positively related to the degree of stress concentration in both the plastic fracture zone and elastic zone. The amount of drilling cuttings is closely related to the roof weighting. In addition, the irregular fluctuation of drilling cuttings is an approximate map of distribution of stress concentration because of the non-uniformity of cracks and other defects in the coal seam. In order to meet the need of rock burst prevention by accurate pressure relief in high-stress zones, enough boreholes are needed.

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Numerical Experiments of Drilling Pressure Relief Preventing Roadway Rock Burst

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.353-356.1583 ◽

2013 ◽

Vol 353-356 ◽

pp. 1583-1587 ◽

Cited By ~ 2

Author(s):

Yan Liang Wen ◽

Guo Jian Zhang ◽

Zhi Qiang Zhang

Keyword(s):

Rock Mass ◽

Rock Burst ◽

High Stress ◽

Simulation Software ◽

Control Technique ◽

Pressure Relief ◽

Main Factors ◽

Rock Burst Mechanism ◽

Research Situation ◽

Relief Effect

Based on rock burst mechanism and the present research situation of control technique, pressure relief process of drilling to rock burst roadway is modeled by numerical simulation software, the contrast and analysis of stress field of surrounding rock are put up with and without pressure relief. The results of the calculation indicate that after drilling high stress area on the both sides of the roadway reduces obviously, but stress peak increases and its position is not converted into the deep areas evidently. It is the energy of the high stress area that makes the rock mass between the drillings failure, which achieves the purpose of pressure relief. Drilling diameter and space between drillings are main factors influencing pressure relief effect. The major the drilling diameter and the smaller the space between boreholes, the more complete the rock mass between the drillings failure and the better the pressure relief effect.

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Geophysical Evaluation of Effectiveness of Blasting for Roof Caving During Longwall Mining of Coal Seam

Pure and Applied Geophysics ◽

10.1007/s00024-019-02321-1 ◽

2019 ◽

Vol 177 (2) ◽

pp. 905-917 ◽

Cited By ~ 4

Author(s):

Łukasz Wojtecki ◽

Petr Konicek ◽

Maciej J. Mendecki ◽

Iwona Gołda ◽

Wacław M. Zuberek

Keyword(s):

Coal Seam ◽

Stress Drop ◽

Longwall Mining ◽

High Energy ◽

Longwall Face ◽

Seismic Moment Tensor ◽

Coal Seams ◽

Rockburst Hazard ◽

Roof Caving ◽

Roof Rocks

Abstract Deep longwall mining of coal seams is made in the Upper Silesian Coal Basin (USCB) under complicated and mostly unfavourable geological and mining conditions. Usually, it is correlated with rockburst hazard mostly at a high level. One of the geological factors affecting the state of rockburst hazard is the presence of competent rocks in the roof of extracted coal seams, so rock falling behind the longwall face does not occur, and hanging-up of roof rocks remains. The long-lasting absence of caving may lead to an occurrence of high-energy tremor in the vicinity of the longwall face. Roof caving behind the longwall face may be forced by blasting. The column of explosives is then located in blastholes drilled in layers of roof rocks, e.g. sandstones behind the longwall face. In this article, a characterization of tremors initiated by blasts for roof caving during underground extraction of coal seam no. 507 in one of the collieries in the USCB has been made using three independent methods. By the basic seismic effect method, the effectiveness of blasting is evaluated according to the seismic energy of incited tremors and mass of explosives used. According to this method, selected blasts gave extremely good or excellent effect. An inversion of the seismic moment tensor enables determining the processes happening in the source of tremors. In the foci of provoked tremors the slip mechanism dominated or was clearly distinguished. The expected explosion had lesser significance or was not present. By the seismic source parameters analysis, among other things, an estimation of the stress drop in the focus or its size may be determined. The stress drop in the foci of provoked tremors was in the order of 105 Pa and the source radius, according to the Brune’s model, varied from 44.3 to 64.5 m. The results of the three mentioned methods were compared with each other and observations in situ. In all cases the roof falling was forced.

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Experimental and Numerical Simulation of Coal Rock Impact Energy Index Based on Peridynamics

Shock and Vibration ◽

10.1155/2021/7362696 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Feng He ◽

Tianjiao Ren ◽

Song Yang ◽

Hongjie Bian

Keyword(s):

Coal Seam ◽

Rock Burst ◽

Uniaxial Compression ◽

Elastic Deformation ◽

Impact Energy ◽

Elastic Energy ◽

Deformation Energy ◽

Energy Index ◽

Actual Impact ◽

Rock Bursts

In response to the increasing severity of the rock burst phenomenon and its relatively difficult prediction, peridynamics and indoor uniaxial compression experiments were used to calculate the changes of the internal elastic energy (t) and impact energy (c) for different rock masses during a loading process from an energy perspective. Two traditional indices for judging rock burst tendency—the rock elastic deformation energy index (WET) and the rock impact energy index (WCF)—were combined to define a new actual impact energy index (W) to more accurately determine the occurrence tendency of rock bursts. The LAMMPS software was used to simulate the internal energy changes of rock materials under pressure, and the results were compared with experimental results for verification. The results were as follows: (1) in the uniaxial compression experiments of different specimens, fine sandstone had the strongest impact resistance, followed by coarse sandstone, mudstone, bottom coal seam, and top coal seam, and the obtained material properties provide a reference for predicting the rock bursts of various rock types in practical engineering. (2) The values calculated using the actual impact energy index (W) and the simulation value were 1.75 and 1.77, respectively, which corresponded to a lower error than when the rock impact energy index (WCF) and the rock elastic deformation energy index (WET) were used individually. Thus, this index can better predict the rock burst. (3) The simulated specimen was subjected to a gradual increase in the internal stored elastic energy during compression, which gradually decreased after the ultimate compressive strength was exceeded. The degree of impact damage formed after macroscopic crushing occurred depended on its residual energy.

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Rock Burst Mechanics: Insight from Physical and Mathematical Modelling

Acta Polytechnica ◽

10.14311/1071 ◽

2008 ◽

Vol 48 (6) ◽

Cited By ~ 1

Author(s):

J. Vacek ◽

J. Chocholoušová

Keyword(s):

Rock Mass ◽

Mathematical Modelling ◽

Mathematical Models ◽

Rock Burst ◽

Material Properties ◽

Open Space ◽

Time Dependent ◽

Rock Bursts ◽

Uranium Mines ◽

Physical And Mathematical Models

Rock burst processes in mines are studied by many groups active in the field of geomechanics. Physical and mathematical modelling can be used to better understand the phenomena and mechanisms involved in the bursts. In the present paper we describe both physical and mathematical models of a rock burst occurring in a gallery of a coal mine.For rock bursts (also called bumps) to occur, the rock has to possess certain particular rock burst properties leading to accumulation of energy and the potential to release this energy. Such materials may be brittle, or the rock burst may arise at the interfacial zones of two parts of the rock, which have principally different material properties (e.g. in the Poíbram uranium mines).The solution is based on experimental and mathematical modelling. These two methods have to allow the problem to be studied on the basis of three presumptions:· the solution must be time dependent,· the solution must allow the creation of cracks in the rock mass,· the solution must allow an extrusion of rock into an open space (bump effect).

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Experimental Studies about Characteristics of the Rocks Displacement and State of Bearing Pressure on the Haulage Roadway

E3S Web of Conferences ◽

10.1051/e3sconf/201910501008 ◽

2019 ◽

Vol 105 ◽

pp. 01008

Author(s):

Duc Thang Pham ◽

Hung Thang Hoang ◽

Victor Vitcalov

Keyword(s):

Rock Pressure ◽

Roof Rock ◽

Experimental Studies ◽

Coal Seams ◽

Coal Basin ◽

Mining Depth ◽

The Face ◽

Mine Workings ◽

Roof Rocks ◽

Quang Ninh

Comprehensive studies were conducted using measuring stations to measure the rock pressure and displacements of the roof rocks in the mine workings adjacent to the face when extracting medium thick inclined coal seams with the use of longwall (seam 6 at the Quang Hanh mine of Quang Ninh coal basin, Vietnam). The results of the study show that the displacement of the roof rock on the parallel roadway increases sharply at a distance of 1 to 12 m to the face, varies from 20 to 40 mm when the mining depth of the coal seam is 200 m and the maximum rock pressure on the haulage roadway supports is located at a distance of 3–8 m ahead of the face and is from 14 to 16 tons ranges.

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Study on Rock Burst Event Disaster and Prevention Mechanisms of Hard Roof

Advances in Civil Engineering ◽

10.1155/2019/6910139 ◽

2019 ◽

Vol 2019 ◽

pp. 1-14

Author(s):

Nan Zhou ◽

Hengfeng Liu ◽

Jixiong Zhang ◽

Hao Yan

Keyword(s):

Rock Mass ◽

Energy Release ◽

Rock Burst ◽

Strain Energy ◽

Roof Rock ◽

Coal Mass ◽

Energy Evolution ◽

Hard Roof ◽

Working Face ◽

Coal Rock

Coal mining under hard roofs is jeopardized by rock burst-induced hazards. In this paper, mechanisms of hard roof rock burst events and key techniques for their prevention are analyzed from the standpoint of energy evolution within geological conditions typical of the hard roofs found in Chinese coal mines. Equations used to calculate the total strain energy densities of the coal-rock mass and hard roof working face are derived. Moreover, several failure-causing energy evolution rules are analyzed under various conditions. Various rock roof and coal mass thicknesses and strengths are considered, and a method of preventing hard roof rock burst events is proposed. The results obtained show that rock burst events can be facilitated by high stress concentrations, significant accumulation of strain energy in the coal-rock mass, and rapid energy release during roof breakage. The above conditions are subdivided into two classes: energy accumulation and energy release. The total strain energies of the coal mass and working faces in the roof are positively correlated with the roof thickness, roof strength, and coal mass strength. The coal mass strength primarily influences the overall accumulation of energy in the working face, and it also has the largest effect on the total energy release (i.e., the earthquake magnitude).

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