scholarly journals State Judgement Model of the Coal and Rock Medium and Its Engineering Application

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Chuanqi Zhu ◽  
Lei Wang ◽  
Xiangang Han
Keyword(s):  
Rock Mass ◽  
Coal Mine ◽  
Mass Medium ◽  
Engineering Application ◽  
Coal Mass ◽  
The State ◽  
Propagation Model ◽  
Bulk Solid ◽  
Working Face ◽  
State Index

In the loading and failure process of the coal and rock medium, with the increasing of the damaging and failure extent, the medium state gradually changed from the continuous, the quasicontinuous, and the discontinuous to the loose successively. To evaluate the damaging failure extent of the coal and rock mass and distinguish the state of the coal and rock mass medium, first, the medium state index was defined based on the acoustic wave propagation model. Then, based on the coal mass in the working face 8512 in the Chenjiagou Coal Mine in China, the acoustic character and the mechanical character experiments were conducted. Through experiments, the variation law of the ultrasonic wave velocity and the medium state index of the coal mass with the strain under the compressive state were acquired; with the increasing of the strain, the medium state indexes successively experienced the variation process including stabilising around 0, slow increasing, dramatic increasing, and stabilising around 1. Then, based on the variation law of the medium state index, the coal and rock mass medium state judgement model was constructed. This model was applied to judge the coal mass medium state. After it, the mudstones in the roof of the same working face were regarded as the research object, the mudstone medium state was divided into 4 types according to the medium state judgement model, namely, continuous, quasicontinuous, discontinuous, and bulk solid, and the mudstone failure state was basically consistent with the continuous, quasicontinuous, discontinuous, and bulk solid state. The adaptability and rationality of the judgement model was verified. Finally, engineering application of the judgement model was conducted. The distribution law of the top coal with different medium state was acquired. In the top coal that was 186 m away from the working face, it belonged to the continuous medium state. As for the top coal that was 6 m to 186 m far away from the working face, it was under the quasicontinuous medium state. For the top coal that was 3 m to 6 m far away from the working face, it was under the discontinuous medium state. For the top coal that was less than 3 m far away from the working face and behind the working face, it belonged to the bulk solid medium state. The state judgement model can successfully distinguish the medium state of the coal seam and mudstones in the roof in the working face 8512. This provided a new approach to evaluate the damaging failure extent of the coal and rock medium in the Chenjiagou Coal Mine.

scholarly journals Research on Deformation Mechanisms of a High Geostress Soft Rock Roadway and Double-Shell Grouting Technology

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Fengnian Wang ◽  
Shizhuang Chen ◽  
Pan Gao ◽  
Zhibiao Guo ◽  
Zhigang Tao
Keyword(s):  
Mechanical Properties ◽  
Rock Mass ◽  
Large Deformation ◽  
Coal Mine ◽  
Soft Rock ◽  
In Situ Stress ◽  
Deformation Monitoring ◽  
Deformation And Failure ◽  
Working Face ◽  
High Geostress

In this study, the deformation characteristics and mechanical properties of coal and rock mass in the S2N5 working face of the Xiaokang coal mine are analyzed to address the problem of large deformation of soft rocks with high in situ stress surrounding roadways. Through a newly developed grouting pipe, a double-shell grouting technology, consisting of low-pressure grouting and high-pressure split grouting, is proposed for the Xiaokang coal mine. In addition, the effect of grouting is evaluated by borehole peeping and deformation monitoring. The results show that the double-shell grouting technology can effectively improve the overall mechanical properties of the surrounding coal and rock mass, preventing the large deformation and failure of the roadway. This technology can be useful when analyzing and preventing large deformation of soft rock roadways.

scholarly journals Study on Rules of Fault Stress Variation Based on Microseismic Monitoring and Numerical Simulation at the Working Face in the Dongjiahe Coal Mine

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Ke Ma ◽  
Fuzhen Yuan ◽  
Duanyang Zhuang ◽  
Quansheng Li ◽  
Zhenwei Wang
Keyword(s):  
Numerical Simulation ◽  
Rock Mass ◽  
Coal Mine ◽  
Maximum Principal Stress ◽  
Microseismic Monitoring ◽  
Stress Variation ◽  
Fault Activation ◽  
Working Face ◽  
Damage Theory ◽  
Overlying Strata

Microseismic monitoring technology was used to study the real-time evolution of rock mass damage generated by a working face as it approached a fault in Dongjiahe Coal Mine. The influence of vertical zoning of overlying strata on damage at the fault was analyzed. Numerical simulation using finite element method based on meso-statistical damage theory was used to investigate the nonlinear and nonuniform failure behaviour of the rock mass near the fault. The response of the fault stress to excavation activity and the rule of fault activation were examined. The results show that the fault damage has segmental characteristics. Microcracks are first generated at the fractured zone that is divided into lower, middle, and upper sections, located 30∼70 m, 120∼180 m, and 230∼280 m above the coal seam, respectively. There was also a segmentation phenomenon in the stress response of fault. The risk of fault activation was evaluated by using the ratio of shear stress to the maximum principal stress. When the working face was 260 m and 140 m away from the fault, the activation risk at the upper-middle and lower sections began to increase, respectively. When the fault was within 60 m, the risk of fault activation was highest.

scholarly journals Study on the Relationship between Stress and Charge of Coal Mass under Uniaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Gang Wang ◽  
Yishan Pan ◽  
Xiaochun Xiao ◽  
Di Wu ◽  
Hongrui Zhao ◽  
...  
Keyword(s):  
Stress Concentration ◽  
Stress Distribution ◽  
Laboratory Test ◽  
Coal Mine ◽  
Coal Mass ◽  
Average Charge ◽  
Working Face ◽  
Close Relationship ◽  
Concentration Degree ◽  
The Relationship

This paper presents a new method to identify the stress concentration degree and stress distribution characteristics in front of working face in coal mine, based on the close relationship between charge and stress during fracture of coal mass. This method overcomes many disadvantages of conventional stress-monitored methods. First, the stress and charge relationship of coal mass was established through damage theory and statistical strength theory. Then, the relationship between stress and charge was studied by a laboratory test, and finally, the field charge monitoring test was performed. The results show that there is a nonlinear relationship between loading stress (σ) and cumulative charge (Q), which can be represented by polynomials. The fitting results of the laboratory test between σ and Q conform to a cubic polynomial function, Q=aσ3+bσ2+cσ+d. It verifies the rationality of the theoretical relationship formula. The field monitoring results show that average charge is great and cumulative charge changes from rapid upward to sharp upward before roof falling. The magnitude and position of average charge and the upward trend of cumulative charge can be used to identify the stress concentration and stress distribution in front of working face, and the abnormal stress area can be predicted. The results can provide certain guidance for the forecast of rock burst in coal mine.

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

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).

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.

Prediction of rockbursts in a typical island working face of a coal mine through microseismic monitoring technology

2021 ◽  
Vol 113 ◽  
pp. 103972
Author(s):  
Chao Zhang ◽  
Gaohan Jin ◽  
Chao Liu ◽  
Shugang Li ◽  
Junhua Xue ◽  
...  
Keyword(s):  
Coal Mine ◽  
Microseismic Monitoring ◽  
Monitoring Technology ◽  
Working Face

scholarly journals Numerical Simulation and Engineering Application of Coalbed Water Injection

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Yijie Shi ◽  
Pengfei Wang ◽  
Ronghua Liu ◽  
Xuanhao Tan ◽  
Wen Zhang
Keyword(s):  
Numerical Simulation ◽  
Process Parameters ◽  
Water Injection ◽  
Engineering Application ◽  
Working Environment ◽  
Engineering Practice ◽  
Characteristic Parameters ◽  
Injection Process ◽  
Working Face ◽  
Dust Reduction

Coalbed water injection is the most basic and effective dust-proof technology in the coal mining face. To understand the influence of coalbed water injection process parameters and coalbed characteristic parameters on coal wetting radius, this paper uses Fluent computational fluid dynamics software to systematically study the seepage process of coalbed water injection under different process parameters and coalbed characteristic parameters, calculation results of which are applied to engineering practice. The results show that the numerical simulation can help to predict the wetness range of coalbed water injection, and the results can provide guidance for the onsite design of coalbed water injection process parameters. The effect of dust reduction applied to onsite coalbed water injection is significant, with the average dust reduction rates during coal cutting and support moving being 67.85% and 46.07%, respectively, which effectively reduces the dust concentration on the working face and improves the working environment.

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