scholarly journals Stress Distribution in a Coal Seam before and after Bump Initiation

10.14311/260 ◽  
2001 ◽  
Vol 41 (4-5) ◽  
Author(s):  
J. Vacek
Keyword(s):  
Rock Mass ◽  
Stress Distribution ◽  
Coal Seam ◽  
Mathematical Modelling ◽  
Rock Burst ◽  
Open Space ◽  
Longwall Mining ◽  
Time Dependent ◽  
Deep Tunnel ◽  
Before And After

This paper deals with to the behaviour of open rock that occurs, for example, during longwall mining in coal mines, in deep tunnel, or shaft excavation.Longwall instability leads to extrusion of rock mass into an open space. This effect is mostly referred to as a bump, or a rock burst. For 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 bumps may arise at the interfacial zones of two parts of the rock, that have principally different material properties.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 crack in the rock mass – the solution must allow an extrusion of rock into an open space (bump effect)

scholarly journals Rock Burst Mechanics: Insight from Physical and Mathematical Modelling

10.14311/1071 ◽  
2008 ◽  
Vol 48 (6) ◽  
Author(s):  
J. Vacek ◽  
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). 

scholarly journals Stress and deformation analysis of gob-side pre-backfill driving procedure of longwall mining: a case study

2021 ◽  
Author(s):  
Rui Wu ◽  
Penghui Zhang ◽  
Pinnaduwa H. S. W. Kulatilake ◽  
Hao Luo ◽  
Qingyuan He
Keyword(s):  
Rock Mass ◽  
Stress Distribution ◽  
Coal Seam ◽  
Abutment Pressure ◽  
Longwall Mining ◽  
Vertical Stress ◽  
Floor Level ◽  
Working Face ◽  
Floor Heave ◽  
Stress And Deformation

AbstractAt present, non-pillar entry protection in longwall mining is mainly achieved through either the gob-side entry retaining (GER) procedure or the gob-side entry driving (GED) procedure. The GER procedure leads to difficulties in maintaining the roadway in mining both the previous and current panels. A narrow coal pillar about 5–7 m must be left in the GED procedure; therefore, it causes permanent loss of some coal. The gob-side pre-backfill driving (GPD) procedure effectively removes the wasting of coal resources that exists in the GED procedure and finds an alternative way to handle the roadway maintenance problem that exists in the GER procedure. The FLAC3D software was used to numerically investigate the stress and deformation distributions and failure of the rock mass surrounding the previous and current panel roadways during each stage of the GPD procedure which requires "twice excavation and mining". The results show that the stress distribution is slightly asymmetric around the previous panel roadway after the “primary excavation”. The stronger and stiffer backfill compared to the coal turned out to be the main bearing body of the previous panel roadway during the "primary mining". The highest vertical stresses of 32.6 and 23.1 MPa, compared to the in-situ stress of 10.5 MPa, appeared in the backfill wall and coal seam, respectively. After the "primary mining", the peak vertical stress under the coal seam at the floor level was slightly higher (18.1 MPa) than that under the backfill (17.8 MPa). After the "secondary excavation", the peak vertical stress under the coal seam at the floor level was slightly lower (18.7 MPa) than that under the backfill (19.8 MPa); the maximum floor heave and maximum roof sag of the current panel roadway were 252.9 and 322.1 mm, respectively. During the "secondary mining", the stress distribution in the rock mass surrounding the current panel roadway was mainly affected by the superposition of the front abutment pressure from the current panel and the side abutment pressure from the previous panel. The floor heave of the current panel roadway reached a maximum of 321.8 mm at 5 m ahead of the working face; the roof sag increased to 828.4 mm at the working face. The peak abutment pressure appeared alternately in the backfill and the coal seam during the whole procedure of "twice excavation and mining" of the GPD procedure. The backfill provided strong bearing capacity during all stages of the GPD procedure and exhibited reliable support for the roadway. The results provide scientific insight for engineering practice of the GPD procedure.

scholarly journals Directional Hydraulic Fracturing (DHF) of the Roof, as an Element of Rock Burst Prevention in the Light of Underground Observations and Numerical Modelling

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 562
Author(s):  
Marek Jendryś ◽  
Andrzej Hadam ◽  
Mateusz Ćwiękała
Keyword(s):  
Rock Mass ◽  
Hydraulic Fracturing ◽  
Coal Mining ◽  
Rock Burst ◽  
Coal Mine ◽  
Seismic Activity ◽  
Black Coal ◽  
Directional Hydraulic Fracturing ◽  
Before And After ◽  
The Face

The following article analyzes the effectiveness of directional hydraulic fracturing (DHF) as a method of rock burst prevention, used in black coal mining with a longwall system. In order to define changes in seismic activity due to DHF at the “Rydułtowy” Black Coal Mine (Upper Silesia, Poland), observations were made regarding the seismic activity of the rock mass during coal mining with a longwall system using roof layers collapse. The seismic activity was recorded in the area of the longwall itself, where, on a part of the runway, the rock mass was expanded before the face of the wall by interrupting the continuity of the rock layers using DHF. The following article presents measurements in the form of the number and the shock energy in the area of the observed longwall, which took place before and after the use of DHF. The second part of the article unveils the results of numerical modeling using the discrete element method, allowing to track the formation of goafs for the variant that does not take DHF into consideration, as well as with modeled fractures tracing DHF carried out in accordance with the technology used at “Rydułtowy” coal mine.

scholarly journals Mining Stress Distribution and Fault-Slip Behavior: A Case Study of Fault-Influenced Longwall Coal Mining

Energies ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2494 ◽  
Author(s):  
Peng Kong ◽  
Lishuai Jiang ◽  
Jiaming Shu ◽  
Lu Wang
Keyword(s):  
Shear Stress ◽  
Stress Distribution ◽  
Coal Seam ◽  
Normal Stress ◽  
Longwall Mining ◽  
Hanging Wall ◽  
Fault Slip ◽  
Lagrangian Analysis ◽  
Slip Mechanism ◽  
3 Dimensional

It is well accepted that faults have significant impacts on the safe production of underground coal mines; however, the fault-slip mechanism during longwall mining through a fault still needs to be investigated. In this study, the distribution of microseismicity events during panel mining through a fault is analyzed, and 3-dimensional fast Lagrangian analysis of continua was used to study the mining stress distribution and fault-slip behavior under the two different mining directions, i.e., mining the panel through the fault from the footwall, or mining the panel through the fault from the hanging wall. The research shows that when the panel is mined through the fault from the footwall, the shear displacement of the fault is significantly greater than those created by mining the panel through the fault from the hanging wall. Under the two mining directions, the variation behaviors of the normal stress and shear stress on the fault are quite different, and fault-slips mainly occur in fault areas where the normal stress decreases. When mining the panel through the fault from the footwall, the slip mainly occurs in the coal-seam roof fault, and when mining the panel through the fault from the hanging wall, the slip mainly occurs in the coal-seam floor fault. According to the variations in the normal stress and shear stress of the fault during the period of mining the panel through the fault, the mechanism of the fault slip can be divided into three categories. 1: Normal stress and shear stress decrease abruptly, but the reduction of the normal stress is greater than that of the shear stress. 2: The normal stress is continuously reduced, the shear strength of the fault is decreased, and the shear stress is suddenly increased. 3: Both the normal stress and the shear stress increase, but the increase in the shear stress is greater than that of the normal stress. These research results can provide a reference for the layout of panels and for fault-slip-induced disaster prevention under similar conditions.

scholarly journals Reconstruction of 3D Micro Pore Structure of Coal and Simulation of Its Mechanical Properties

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
Guang-zhe Deng ◽  
Rui Zheng
Keyword(s):  
Rock Mass ◽  
Stress Distribution ◽  
Coal Seam ◽  
Pore Structure ◽  
Three Dimensional ◽  
Low Permeability ◽  
Deformation And Failure ◽  
Coal Rock ◽  
Shear Failures ◽  
Negative Exponential

This article takes the low permeability coal seam in the coalfield of South Judger Basin in Xinjiang, as a research object. The pore structure characteristics of coal rock mass in low permeability coal seam were analyzed quantitatively using scanning electron microscopy (SEM) through the methods of statistics and digital image analysis. Based on the pore structure parameters and the distribution function of the coal rock mass, a three-dimensional porous cylinder model with different porosity was reconstructed by FLAC3D. The numerical simulation study of reconstructed pore model shows that (1) the porosity and the compressive strength have obvious nonlinear relation and satisfy the negative exponential relation; (2) the porosity significantly affects the stress distribution; with the increase of micro porosity, the stress distribution becomes nonuniform; (3) the compressive failures of different models are mainly shear failures, and the shape of fracture section is related to porosity; (4) the variation of seepage coefficient of the pore reconstruction model is consistent with the development of micro cracks. The micro mechanism of the deformation and failure of coal and the interaction of multiphase flow with porosity are revealed, which provides a theoretical reference for the clean development of the low permeability coal seam.

scholarly journals A Numerical Study of Stress Distribution and Fracture Development above a Protective Coal Seam in Longwall Mining

Processes ◽  
2018 ◽  
Vol 6 (9) ◽  
pp. 146 ◽  
Author(s):  
Chunlei Zhang ◽  
Lei Yu ◽  
Ruimin Feng ◽  
Yong Zhang ◽  
Guojun Zhang
Keyword(s):  
Stress Distribution ◽  
Coal Seam ◽  
Gas Flow ◽  
Longwall Mining ◽  
Numerical Study ◽  
Stress Relief ◽  
Coal Industry ◽  
Gas Drainage ◽  
New Findings ◽  
Fracture Development

Coal and gas outbursts are serious safety concerns in the Chinese coal industry. Mining of the upper or lower protective coal seams has been widely used to minimize this problem. This paper presents new findings from longwall mining-induced fractures, stress distribution changes in roof strata, strata movement and gas flow dynamics after the lower protective coal seam is extracted in a deep underground coal mine in Jincheng, China. Two Flac3D models with varying gob loading characteristics as a function of face advance were analyzed to assess the effect of gob behavior on stress relief in the protected coal seam. The gob behavior in the models is incorporated by applying variable force to the floor and roof behind the longwall face to simulate gob loading characteristics in the field. The influence of mining height on the stress-relief in protected coal seam is also incorporated. The stress relief coefficient and relief angle were introduced as two essential parameters to evaluate the stress relief effect in different regions of protected coal seam. The results showed that the rock mass above the protective coal seam can be divided into five zones in the horizontal direction, i.e. pre-mining zone, compression zone, expansion zone, recovery zone and re-compacted zone. The volume expansion or the dilation zone with high gas concentration is the best location to drill boreholes for gas drainage in both the protected coal seam and the protective coal seam. The research results are helpful to understand the gas flow mechanism around the coal seam and guide industry people to optimize borehole layouts in order to eliminate the coal and gas outburst hazard. The gas drainage programs are provided in the final section.

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

2021 ◽  
Vol 9 ◽  
Author(s):  
Zhenhua Wu ◽  
Peng-Zhi Pan ◽  
Jianqiang Chen ◽  
Xudong Liu ◽  
Shuting Miao ◽  
...  
Keyword(s):  
Rock Mass ◽  
Coal Seam ◽  
Rock Burst ◽  
Roof Rock ◽  
High Energy ◽  
Coal Seams ◽  
Rock Bursts ◽  
Rock Pillar ◽  
Mining Depth ◽  
Rock Burst Mechanism

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.

scholarly journals Particle Size Distribution of Cemented Rockfill Effects on Strata Stability in Filling Mining

Minerals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 407 ◽  
Author(s):  
Jiangyu Wu ◽  
Meimei Feng ◽  
Jingmin Xu ◽  
Peitao Qiu ◽  
Yiming Wang ◽  
...  
Keyword(s):  
Particle Size ◽  
Rock Mass ◽  
Particle Size Distribution ◽  
Coal Seam ◽  
Size Distribution ◽  
Longwall Mining ◽  
Poisson Ratio ◽  
Triaxial Compression ◽  
Friction Angle ◽  
Economic Benefits

It is of great significance for engineering safety, economic benefits, environmental protection, and sustainable development to investigate the strata stability in filling mining with cemented rockfill. Consequently, this paper is based on a specific coal mine where we applied the fully-mechanized longwall mining and filling and designed a cemented rockfill material for which the particles satisfied the Talbot gradation. Uniaxial and triaxial compression experiments were carried out on the cemented rockfill specimen, which obtained the relations between the mechanical parameters (Poisson ratio, elastic modulus, compressive strength, cohesive force, internal friction angle, and tensile strength) and the particle size distribution of the aggregate. The excavation and filling processes in the coal seam were simulated based on the numerical software FLAC3D. The characteristics of the displacement and stress fields of the strata when the goaf was filled by cemented rockfill with different granule gradations were discussed. The influences of the particle size distribution and mining distance on the maximum subsidence displacement of the coal seam roof, internal stress of the backfill, and the stress of the rock mass in the coalface were analyzed. The feasibility and effectiveness of the filling mining with cemented rockfill to protect the integrity of the overlying strata were discussed. The results showed that optimizing the particle size distribution of the aggregate in cemented rockfill could increase the loading capacity of the backfill to improve the filling effect, effectively control the strata movement, and decrease the stress of rock mass in the coalface to reduce the potential danger.

scholarly journals Study on the Key Technology of Controlling the Instability of Deep High-Stress Coal and Rock Mass and Relieving the Danger

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Zhijing Zhang ◽  
Jianghong Zuo ◽  
Dongji Lei
Keyword(s):  
Rock Mass ◽  
Coal Seam ◽  
Rock Fracture ◽  
Mine Safety ◽  
Detection Accuracy ◽  
Pressure Relief ◽  
Rock Body ◽  
Thick Coal Seam ◽  
Before And After ◽  
Relief Effect

In order to solve the problem of stress concentration and gas overrun in the process of uncovering high gas and thick coal seam, combined with the occurrence characteristics of coal seams in Wuyang Coal Mine, the measures of “hydraulic and mechanical cavity making + steel screen pipe + surrounding rock grouting” are adopted to establish a method for mutual verification of multiple effect test indexes of residual stress, residual gas content, coal seam moisture content, and microseismic signal characteristics, and the three-dimensional accurate analysis of the influence range of hydraulic cavitation is effectively realized. By comparing and analyzing the gas extraction amount, the surrounding borehole stress change and the microseismic monitoring signals before and after the application of hydraulic cavitation technology are studied. The results show the following. (1) The pressure relief effect of the hydraulic cavity on surrounding coal decreases with the increase of distance, and the pressure relief effect is most obvious at 1.0∼2.5 m, in the range of 2.5–3.5 m around the hydraulic drilling hole, the duration, rate, and amplitude of pressure relief are reduced compared with those in the range of less than 2.5 m, while in the range of more than 3.5 m, the effect of pressure relief is very weak. (2) During the period of hydraulic cavitation release hole, the radius of water supply to coal seam is within 1.5 m, which accounts for 79% of coal wall area. (3) It is also a process where the stress distribution in the coal and rock body needs to be rebalanced before and after hydraulic caverning, which is often accompanied by microfracture of coal and rock mass. The analysis shows that, before hydraulic caverning, the waveform of coal and rock fracture signal has a short duration, large amplitude, and obvious signal mutation, and the dominant frequency of the signal is about 250 Hz, with large total energy. After hydraulic caverning, the intensity of coal and rock fracture events is greatly reduced. The research results can effectively identify the influence range of hydraulic cavitation, improve the detection accuracy and efficiency of hydraulic cavitation range, effectively predict and warn the hidden danger of mine safety, and provide a reference for the work of similar mines.

scholarly journals Research on Stress Distribution Characteristics for Uniquely Shaped Roadway with Hard Roof in Steeply Inclined Coal Seam and Support Technology of Reducing Vibration Impact

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Junhui Zhang ◽  
Hui Chen ◽  
Xiuzhi Shi ◽  
Weiming Guan ◽  
Xiaolong Sun
Keyword(s):  
Stress Distribution ◽  
Coal Seam ◽  
Rock Burst ◽  
Coal Mine ◽  
Surrounding Rock ◽  
Additional Stress ◽  
The Road ◽  
Hard Roof ◽  
Original Rock ◽  
The Impact

This paper presents a comprehensive study of the stress distribution and stability analysis of a uniquely shaped roadway having a steeply dipping hard roof. The coal seam and its roof have a certain impact tendency, which is the internal condition of rock burst. The syncline tectonic stress causes the original rock stress to reach a higher level. The large amount of coal produced in the coal mine and the large movement range of the upper strata cause the huge mining additional stress around the stope. The impact load caused by “cantilever beam” fracture of hard roof can induce and strengthen rock burst. Its engineering geological setting encompasses the mining process and surrounding rock conditions of No. 6 Coal Seam in the 2130 coal mine of Xinjiang. Numerical simulations with theoretical analysis and field measurements investigated a proposed new truss combined support scheme for implementation. A comparison was made of the differences in the state parameters of the road under the new and old support conditions. The application of the new combined support technology changed the form of the stress distribution around the road. Apart from the displacements of the two coal sidewalls, the new support system notably reduced the displacement of roof and floor by 67.8% and 83.6%, respectively. After the implementation of the new support scheme, the frequency of the original rock burst in the working face is greatly reduced, the surrounding rock control and field application effects also remained good, and personnel and equipment safety and production plan have a good guarantee.

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