scholarly journals Numerical Investigation on the Ground Response of a Gob-Side Entry in an Extra-Thick Coal Seam

2021 ◽  
Vol 2021 ◽  
pp. 1-7
Author(s):  
C.W. Zang ◽  
G.C. Zhang ◽  
G.Z. Tao ◽  
H.M. Zhu ◽  
Y. Li ◽  
...  
Keyword(s):  
Rock Mass ◽  
Coal Seam ◽  
Numerical Investigation ◽  
Large Scale ◽  
Shear Failure ◽  
Coal Pillar ◽  
Coal Mass ◽  
Thick Coal Seam ◽  
Anchor Cable ◽  
Study Results

This study was aimed at the large deformation phenomenon of rock mass surrounding the gob-side entry driven in a 20 m extra-thick coal seam. Taking tailgate 8211 as the engineering background, a numerical investigation was employed to analyze the deformation law of the gob-side entry. The study results are as follows. (1) Because the immediate roof was composed of weak coal mass with a thickness of 17 m, the roof coal mass was vulnerable to fail with the effect of overlying strata pressure; thus, a visual subsidence of roof coal mass with a maximum convergence of 800 mm was observed in the field. (2) The bearing capacity of the coal pillar was significantly less than that of the panel rib, resulting in the pillar failing more easily under the ground pressure and then generating large-scale squeezing deformation. (3) The roof and panel rib were in a state of shear failure with a failure depth of about 5 m. The coal pillar was entirely in a state of plastic failure. (4) A support scheme including an asymmetric anchor beam truss, roof angle anchor cable, and anchor cable combination structure was proposed. The field work confirmed that this support scheme could efficiently control the deformation and failure of the rock mass surrounding the gob-side entry. This study provides the theoretical basis and technical support for the control of rocks surrounding the gob-side entry in similar conditions.

scholarly journals An Influence Study of Face Length Effect on Floor Stability under Water-Rock Coupling Action

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Baojie Fu ◽  
Bo Wang
Keyword(s):  
Rock Mass ◽  
Coal Seam ◽  
Mine Pressure ◽  
Length Effect ◽  
Pressure Relief ◽  
Limestone Aquifer ◽  
Study Results ◽  
Face Length ◽  
The Face ◽  
Floor Stability

The Taiyuan Formation limestone aquifer and Ordovician limestone aquifer are widely distributed in the coal seam floor of coal measures in North China; the water hazard safety problem of the stope floor under the influence of mining is very prominent. The risk of the water inrush from the coal seam floor is closely related to the degree of full exploitation, so it is necessary to study the stability of the stope floor under aquifer conditions, especially the influence of the working face length effect on floor stability. Through numerical simulation of water-rock coupling action, the mine pressure behaviors of the water-resisting floor under different face lengths were analyzed based on the measured formation permeability coefficient. The Fish program was used to adjust rocks entering the plastic failure state into a strain softening model to investigate the influence of the face length effect, the damage degree of the water-resisting floor, and the morphology and deformation bearing capacity of the failure zone. The results show the following: (1) the face length effect is one of the main influence factors of the failure mode and failure degree of surrounding rocks in the stope; (2) as the face length increases, the obvious pressure relief zone of surrounding rocks presents a staged change, and the obvious pressure relief zone at the seam roof and floor is in an obvious “reverse saddle shape”; (3) the closer to the seam floor, the more remarkable the rock softening characteristic because of the compaction action of gangues caving from the roof; and (4) the rock mass close to the seam floor undergoes local tensile failure, and the water-resisting floor near the coal wall at two sides mainly bears compaction-shear action, leading to compression-shear failure of the rock mass at the floor and formation of water-conducting fractures. The study results can provide a reference for taking precautionary measures of safety mining above a confined aquifer.

scholarly journals Research on Low-density Cross-border Support Technology For Large-section Coal Roadway in Shallow-buried Thick Coal Seam

2021 ◽  
Author(s):  
Shiping Yan ◽  
feng guo ◽  
Fei Chen ◽  
Yuxiang Cao ◽  
Zhe He
Keyword(s):  
Large Scale ◽  
Coal Pillar ◽  
Peak Stress ◽  
Field Application ◽  
Efficient Production ◽  
Low Density ◽  
Control Effect ◽  
Thick Coal Seam ◽  
Cross Border ◽  
Coal Roadway

Abstract The slow excavation speed of coal roadways has always been a key factor restricting the safe and efficient production of large-scale coal mines in China, and the problem of unbalanced mining replacement caused by this is widespread. This paper takes the S1231 heading face of the Ningtiaota coal mine of Shaanxi Coal and Chemical Industry Group as the research object, analyzes the characteristics of the stress evolution of coal roadway driving, reveals the principle of low-density cross-border support, and proposes a low-density cross-border support plan. . Using FLAC 3D to study the roadway stress-displacement evolution law of the new support scheme during the driving and mining phases, the results show that the peak stress during the driving is 5.3 Mpa, and the coal pillar side stress concentration is the most obvious during the mining period, with the peak value being 7.9 Mpa. The moving distances of the two banks are both 10 mm, which verifies the feasibility of low-density cross-border support. Field application shows that during roadway excavation, the amount of roof subsidence and the displacement of the two sides are 9 mm and 11 mm, respectively, and the development depth of roof cracks is controlled within 0.5m. The overall control effect is good, and the speed of coal roadway driving is increased by 77.19% compared with the original. The new support builds a thick roof anchor structure to ensure the safety and stability of the roadway. At the same time, by reducing the number of bolts, the bolt support time has been greatly reduced, effectively alleviating the tight situation of mining replacement, and providing solutions for mines under the same conditions.

Studies of the Stress State of the Coal Pillar between the Treatment andPreparatory Workings by the Methods of Deformable Body Mechanics

2020 ◽  
pp. 26-31
Author(s):  
N.V. Cherdantsev ◽  
Keyword(s):  
Rock Mass ◽  
Stress State ◽  
Coal Seam ◽  
Solid Mechanics ◽  
Boundary Integral Equations ◽  
Coal Pillar ◽  
Boundary Integral ◽  
External Boundary ◽  
Mining Operations ◽  
Coal Rock

To ensure safe conditions for mining operations and increase labor productivity, a reliable assessment of the stress state of the coal-rock mass is required. The model is presented concerning the geomechanical state of the massif hosting the coal seam, treatment, and preparatory workings. The model is developed based on the fundamental methods of solid mechanics and ensures a computational experiment and the reliability of the results. Stress distribution in the coal-rock mass in the vicinity of the in-seam workings was calculated in two stages. First, the stress field in the edge zones of the coal seam and in the collapsed rocks was determined by the methods of mechanics of the flowing medium. Distribution of stresses in the extremely stressed zones of the seam and the layer of collapsed rocks behind the working excavation was found by the method of characteristics by solving differential equations of the hyperbolic type. They are obtained based on the of the joint solution of the equilibrium equations, general and special Coulomb — Mohr criteria of the transition of the seam and the collapsed layer, as well as their contacts with the lateral rocks to the limiting state. Then, by replacing extremely stressed zones of the coal seam and the layer of the collapsed rocks with stresses acting at the contacts with the surrounding massif, the problem is reduced to the integral equation of the second external boundary value problem of the theory of elasticity. It is solved by the method of boundary integral equations. Insignificant influence of changes in the angle of internal friction of the collapsed rocks on the parameters of the seam bearing pressure in the vicinity of the treatment and development workings is shown. However, it significantly effects on the bearing pressure in the extremely stressed zone of the collapsed rocks layer.

scholarly journals Evolution Characteristics of Overburden Strata Structure for Ultra-Thick Coal Seam Multi-Layer Mining in Xinjiang East Junggar Basin

Energies ◽  
2019 ◽  
Vol 12 (2) ◽  
pp. 332 ◽  
Author(s):  
Xufeng Wang ◽  
Dongdong Qin ◽  
Dongsheng Zhang ◽  
Weiming Guan ◽  
Mengtang Xu ◽  
...  
Keyword(s):  
Rock Mass ◽  
Coal Seam ◽  
Junggar Basin ◽  
Structure Evolution ◽  
Thick Coal Seam ◽  
Roof Structure ◽  
Gravity Load ◽  
Evolution Characteristics ◽  
Fracturing Process ◽  
Overburden Strata

The efficient and safe extraction of ultra-thick coal seam in the Xinjiang East Junggar Basin has been a major focus in the future of mining in China. This paper systematically studied the overburden strata fracturing process and the structure evolution characteristics based on a typical ultra-thick coal seam condition in Xinjiang, using both physical and numerical modeling studies. The interactions between shields and the roof strata were also examined, from the perspective of ground support. The results indicated that roof structure was mainly in the form of voussoir beam at the early mining stage, where overburden stability was affected by the rock mass properties and mining parameters. The support load mainly included top coal and immediate roof gravity load and the load caused by main roof rotary consolidation. As a result of mining disturbance and strata movement, the overlying strata re-fractured in the later mining stage. The roof structure changed from beam to arch gradually and propagates upwards with the increase of multi-layer mining times. The support load was mainly the gravity load of the friable rock mass within compression arch. The results will provide a guideline for the improvement of roof stability under similar mining conditions in Xinjiang.

scholarly journals Study on Intelligent Identification Method of Coal Pillar Stability in Fully Mechanized Caving Face of Thick Coal Seam

Energies ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 305 ◽  
Author(s):  
Jingjing Dai ◽  
Pengfei Shan ◽  
Qi Zhou
Keyword(s):  
Coal Seam ◽  
Simulation Experiment ◽  
Coal Pillar ◽  
Shanxi Province ◽  
Parameter Determination ◽  
Pillar Stability ◽  
Thick Coal Seam ◽  
Identification Method ◽  
Optimal Value ◽  
The Relationship

The combination of coal precise mining and information technology in the new century is one of the important directions for the future development of coal mining. Taking the fully mechanized top coal caving condition of a thick coal seam in the 90,101 working face of Baoshan Yujing Coal Mine in Shanyin City, Shanxi Province as an example, the intelligent identification method of section coal pillar stability was studied. The load transfer law of overlying strata in the upper part of coal pillar was analyzed, and the coal pillar values of each index were obtained by using an empirical formula, mean impact value-genetic algorithm-BP neural network (MIV-GA-BP) simulation experiment, and finite difference algorithm. The Delphi index evaluation system was used to calculate the optimal value of the coal pillar. The results showed that the non-contact cantilevered triangle on the two wings of the coal pillar in the goaf reduced the stress on the coal pillar; according to the width of the coal pillar at 10 m, 14 m, 16 m, and 20 m, combined with the relationship between the plastic zone and the core zone of coal pillar, and the relationship between the stress field and the ultimate strength of coal pillar, the numerical simulation value of the coal pillar was determined. The MIV (mean impact value) characteristics screened out the influencing factors of coal pillar width in the section near the horizontal fully mechanized top coal caving face order of importance; the relative error between the predicted value and the expected value of the MIV-GA-BP simulation experiment was less than 5%, which has good stability for the multi-factor nonlinear coupling prediction problem; and the optimal value of the coal pillar was 16.03 m by the intelligent identification method of the coal pillar. When the 16 m pillar was used, the surrounding rock deformation of the roadway was small, and the control effect was good. The research results provide a theoretical basis and reference for the parameter determination of similar projects.

scholarly journals The Mechanism and Control Technology of Strong Strata Behavior in Extra-Thick Coal Seam Mining Influenced by Overlying Coal Pillar

2019 ◽  
Vol 11 (1) ◽  
pp. 452-461
Author(s):  
Rui Gao ◽  
Tiejun Kuang ◽  
Yiwen Lan
Keyword(s):  
Coal Seam ◽  
Coal Pillar ◽  
In Situ Monitoring ◽  
Thick Coal Seam ◽  
Maximum Deformation ◽  
Working Face ◽  
Strata Behavior ◽  
Seam Mining ◽  
Roadway Deformation ◽  
And Control

Abstract This work aimed at revealing the mechanism of strong strata behavior in extra-thick coal seam mining which was influenced by an overlying coal pillar (OCP). To this end, the evolution characteristics of the stress and displacement in advance coal body of the working face were studied via numerical simulation. On this basis, the mechanism of strong strata behavior in working face affected by OCP was revealed. In situ monitoring also demonstrated that, as the working face mining near to the position of OCP, severe rib spalling and roadway deformation frequently appeared. The scheme of strengthening the hydraulic supports resistance and adding anchor cables was put forward to control the surrounding rocks in the stope. As a result, the maximum deformation of the roadway height was 0.66m and could completely meet the demands for safe mining. The study on the mechanism of strong strata behavior in working face and the strengthen supporting scheme would provide a theoretical basis for similar mining conditions, thus ensure safe and efficiency coal seam mining.

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 Longwall Top-Coal Caving Mechanism and Cavability Optimization with Hydraulic Fracturing in Thick Coal Seam: A Case Study

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4832
Author(s):  
Zhaohui Wang ◽  
Yuesong Tang ◽  
Hao Gong
Keyword(s):  
Coal Seam ◽  
Hydraulic Fracturing ◽  
Shear Failure ◽  
Tensile Failure ◽  
Hydraulic Fractures ◽  
Thick Coal Seam ◽  
Face Length ◽  
The Face ◽  
Upper Level ◽  
Longwall Top Coal Caving

Longwall top-coal caving mechanisms and cavability optimization with hydraulic fracturing are analysed in this study. Based on the geological and geotechnical conditions of the Dongzhouyao coal mine, it is revealed that top-coal failure mechanisms are dominated by both compressive and tensile stresses. Ahead of the face line, shear failure initiates at the lower level of the top-coal and propagates to the upper level. Compressive stress-induced damage leads to obvious deterioration in tensile strength, causing the onset of tensile failure in the top-coal behind the face line. Accumulated plastic strain (APS) is selected as a top-coal cavability indicator. The cavability degrades gradually at the higher elevation of the top-coal while it is greatly strengthened as the top-coal approaches closer to the face line. In a thick coal seam without hydraulic fractures, the maximum APS occurs at the middle section of the face length in the Longwall top-coal caving (LTCC) panel. After hydraulic fracturing, top-coal cavability is significantly enhanced. But the spatial distribution of the APS transitions from uniform to non-uniform type due to the existence of hydraulic fractures, causing great variety in the cavability along the panel width. With increasing fracture intensity and fracture size, the failure zone expands significantly ahead of the longwall face, which means the cavability becomes increasingly favourable.

scholarly journals Forecast changes in the geodynamic regime of geological environment during large-scale subsoil development

2021 ◽  
pp. 5-10
Author(s):  
M.B Nurpeisova ◽  
M.Zh Bitimbayev ◽  
K.B Rysbekov ◽  
Sh. Sh Bekbasarov
Keyword(s):  
Rock Mass ◽  
Large Scale ◽  
Structural Features ◽  
Educational Process ◽  
Industrial Safety ◽  
Geological Environment ◽  
Mining Operations ◽  
Capital Costs ◽  
Study Results ◽  
Geological Conditions

Purpose. Developing the methods for forecasting changes in the geological environment based on integrated monitoring, which ensures industrial and environmental safety of Central Kazakhstan region. Methodology. Integrated approach was used in the work, including: study on mining and geological conditions, structural features of rocks and conducting mine surveying at mines on the basis of modern methods and means of geomonitoring developed by the authors. Findings. Methodology for integrated geodynamic monitoring system is developed. A new method of geodynamic polygon establishment is proposed. Study results were implemented at operating mining enterprises during implementation of projects Comprehensive monitoring of slow deformation processes of the earths surface during large-scale development of ore deposits in Central Kazakhstan and Development of innovative methods for forecasting and assessing the state of rock mass to prevent technogenic emergencies, and the results were used in the educational process of Satbayev University. Originality. As a result of the research work carried out, the following were created and introduced into production: - geodynamic polygon (GDP) of the area, established on the basis of the nodal method, combined with leveling, satellite and seismological points, allowing monitoring coverage of exploration and mining operations, as well as increasing efficiency of observations and reducing capital costs for mineral production; - developed constructions of permanent (ground and underground) forced centering points (FCP), which allow increasing productivity and observations accuracy; - method for photographing structural features of rock mass using a 3D laser scanner, which makes it possible to study elements of cracks occurrence and faults in rocks in sufficient detail; - composition of strengthening solution from mining waste to increase stability of disturbed sections of open cast benches was developed. The novelty of the developed methods and means is confirmed by RK patents for invention. Practical value. Obtained results can be used to improve the level of industrial safety at mines and minimize environmental risks caused by subsoil development.

Sign in / Sign up

Export Citation Format

Share Document