scholarly journals Study on the Mechanism and Control of Rock Burst of Coal Pillar under Complex Conditions

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-19
Author(s):  
Xingping Lai ◽  
Huicong Xu ◽  
Jingdao Fan ◽  
Zeyang Wang ◽  
Zhenguo Yan ◽  
...  
Keyword(s):  
Stress Concentration ◽  
Rock Burst ◽  
Coal Mine ◽  
High Stress ◽  
Coal Pillar ◽  
Vertical Stress ◽  
Body Area ◽  
High Stress Concentration ◽  
Solid Coal ◽  
Working Face

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.

scholarly journals Stress Analysis of Negative Coal Pillar Gob-Side Entry and Its Principle of Preventing Rock Burst

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Zhiqiang Wang ◽  
Peng Wang ◽  
Lei Shi ◽  
Wenyu Lv ◽  
Chao Wu ◽  
...  
Keyword(s):  
Stress Concentration ◽  
Rock Burst ◽  
Longwall Mining ◽  
Limit Equilibrium ◽  
High Stress ◽  
Coal Pillar ◽  
Stress Transfer ◽  
Peak Stress ◽  
Solid Coal ◽  
Seam Mining

Gob-side entry is an area where it is difficult to prevent and control the frequent occurrence of rock burst. Based on “Longwall Mining with Split-level Gateways” (LMSG), this paper puts forward the technology of preventing rock burst by a new gob-side entry (NCPG). The abutment pressure distribution of LMSG shows that the stress peak of solid coal is lower than the conventional panel, and the width of the limit equilibrium zone is also reduced by a small percentage. After the narrow coal pillar gob-side entry has been excavated, the peak stress in solid coal increases, and the width of the limit equilibrium zone decreases, so the practical stress concentration increases. However, the NCPG located in areas of lower stress. The peak stress in solid coal of the NCPG does not increase, but the width of the limit equilibrium zone increases, so the practical stress concentration decreases. NCPC makes the concentrated stress transfer into the deep coal body and plays the role of pressure avoidance. Compared with the narrow coal pillar gob-side entry, the NCPG reduces the energy stored in coal and rock masses and increases the energy consumption. It has significantly improved the regionality, initiative, safety, and timeliness of rock burst prevention in deep high-stress coal seam mining.

scholarly journals Research on Reasonable Width of Coal Pillars of Non-equal Width Isolated Working Face Heading Goaf in Deep Mine

2021 ◽  
Author(s):  
weili yang ◽  
Quande wei ◽  
Zhonghui Wang ◽  
Zhizeng Zhang ◽  
Xiaocheng Qu ◽  
...  
Keyword(s):  
Rock Burst ◽  
Critical State ◽  
Research Result ◽  
High Stress ◽  
Coal Pillar ◽  
Stress Monitoring ◽  
Equilibrium Relation ◽  
Deep Mine ◽  
Working Face ◽  
Coal Pillars

Abstract Setting reasonable coal pillar is a key to ensure safe mining of island coal face heading goaf in deep mine. With determination of reasonable width of coal pillars of non-equal width isolated working face 3201 in worked-out area in one mine in Shandong as the engineering background, a research was conducted on the mechanism of rock burst induced by and the reasonable width of coal pillars of isolated working face in worked-out area and the main conclusions are as follows: (1) the coal pillars of isolated working face 3201 in worked-out area changed from pillars with goaf on two sides→pillars with goaf on three sides→pillars with goaf on four sides, resulting in evolution of overlying strata from pre-mining static “┒-shaped” structure→“C-shaped” structure→“O-shaped” structure and corresponding spatial stress from “saddle-shaped” profile→“platform-shaped” profile→“arch-shaped” profile; (2) the rock burst was induced by coal pillars, because the high stress on coal pillars at critical state of a rock burst was greater than their comprehensive strength and induced a rock burst due to sudden instability; (3) by establishing a bearing and load model of coal pillars at critical state of a rock burst and based on the equilibrium relation, an method for estimating reasonable width of coal pillars of isolated working face in worked-out area in deep mine was derived and applied to the isolated working face 3201 in worked-out area, thus comprehensively determining that the width of coal pillars should be 130m. The field stress monitoring verified the reasonability. The research result is of great significance to prevention of rock burst induced by coal pillars of isolated working face in worked-out area in deep mine.

scholarly journals Mechanism and Evolution Control of Wide Coal Pillar Bursts in Multithick Key Strata

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Wenhao Guo ◽  
Anye Cao ◽  
Chengchun Xue ◽  
Yang Hu ◽  
Songwei Wang ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Stress Concentration ◽  
Theoretical Analysis ◽  
Coal Mine ◽  
Coal Pillar ◽  
Western China ◽  
Key Strata ◽  
Working Face ◽  
Microseismic Events ◽  
Evolution Control

Coal mine pillar burst frequently occurs in Western China, which seriously restricts safe production. This paper takes the 35 m coal pillar of the 3102 working face of MKQ coal mine as the engineering background. The mechanism and evolution control of pillar bursts in multithick key strata are studied using field investigation, theoretical analysis, and numerical simulation. The mechanism of dynamic and static stress-induced pillar bursts was revealed combining the “O-X” broken features for key strata and numerical simulation of pillar stress evolution. A prevention scheme is put forward for strata presplit blasting and adjusting coal pillar width to minimize the dynamic and static stresses. The results demonstrate the following. (1) In the multithick strata, the first and second near-field subkey strata have perpendicular “O-X” broken features, whereas the third far-field subkey has parallel “O-X” broken features. The working face has three kinds of periodic weighting phenomena: long, medium, and short. (2) The simulated vertical stress curve of 35 m coal pillar goes through three states: two-peak, asymmetric trapezoidal and symmetrical trapezoidal shape with the different advancing position of working face. The stress concentration is extensively promoting a high-risk area for rock burst. (3) The coal pillar burst was induced by the superposition of energy released by the key strata breaking and the elastic energy accumulated in the wide coal pillar. (4) The monitoring data showed that the long, medium, and short periodic weighting steps of multithick key strata are 141.6 m, 43.2–49.6 m, and 17.6–27.2 m, respectively. The microseismic events energy, frequency, and stress of hydraulic support increment are the highest during the long periodic weighting, and the spatial distribution of microseismic events coincides with the stress concentration area. The theoretical analysis is confirmed with the field practice.

scholarly journals Distribution and Variation of Mining-Induced Stress in the Reverse Fault-Affected Coal Body

2021 ◽  
Vol 2021 ◽  
pp. 1-23
Author(s):  
Rui Zhou ◽  
Yujin Qin ◽  
Zhizhen Zhang
Keyword(s):  
Stress Concentration ◽  
Stress Distribution ◽  
Bearing Capacity ◽  
Coal Mine ◽  
Hanging Wall ◽  
Vertical Stress ◽  
Reverse Fault ◽  
Concentration Coefficient ◽  
Working Face ◽  
Stress Concentration Coefficient

This study aimed to explore the stress distribution and variation of reverse fault-affected mined coal body. A mechanical analysis model of the coal body in the reverse fault area was first established, then the coal body stress characterization equation was derived, and the stress distribution pattern on the coal body was calculated. Subsequently, applying the Mohr–Coulomb strength criterion revealed the following relationship: the closer is the distance to the reverse fault, the worse is the stability of the coal body, and that the coal body strength influences the stress concentration of the coal body in front of the working face. Moreover, simulation with FLAC3D was carried out to verify the coal body stress calculated by the mechanical model as well as the fluctuation of the coal body stress concentration. It could be concluded that while mining the hanging wall of the reverse fault, the stress concentration of mined coal body decreases with the increase of reverse fault dip angle, but increases with the increase of reverse fault throw; the stress concentration magnitude generated during footwall mining is lesser than that during hanging-wall mining. In other words, the magnitude of coal body stress concentration can be affected by the hanging wall and footwall mining, as well as parameters of the reverse fault. Finally, intrinsically safe GZY25 borehole stress sensors were used to monitor the coal body stresses in the reverse fault area under the influence of mining in Xinchun Coal Mine and ZuoQiuka Coal Mine. It was found that the coal body stress concentration in front of the working face either increased gradually or increased first before decreasing. It can be concluded that with the decrease of the distance between the working face and reverse fault, the vertical stress of the coal body increases, and the vertical stress of the coal body begins to increase obviously at a certain position. At this point, the vertical stress of the coal body can be generalized to 1.02–1.39 times of the initial vertical stress. Furthermore, the stress concentration coefficient of coal body is related to the distance from the reverse fault, and two changes occur: ① if the coal-bearing capacity does not exceed its strength, the coal stress in front of the working face increases gradually, and the stress concentration factor increases gradually; ② the stress concentration coefficient of mining coal body increases first, such that when the coal body bearing capacity exceeds its strength, the coal body fails and loses all its effective bearing capacity, followed by the decrease in coal body stress concentration coefficient.

scholarly journals Stability of Split-Level Gob-Side Entry in Ultra-Thick Coal Seams: A Case Study at Xiegou Mine

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 628 ◽  
Author(s):  
Junwen Zhang
Keyword(s):  
Coal Mine ◽  
Coal Pillar ◽  
Peak Stress ◽  
Coal Seams ◽  
Solid Coal ◽  
Stress Fluctuation ◽  
Pillar Mining ◽  
The Stability ◽  
Rock Specimens

Split-level longwall gob-side entry (SLGE) has been applied as a special form of small gate pillar mining (or non-coal pillar mining) in thick coal seams. The stability of the coal pillar directly affects the rationality of the layout of the SLGE. Starting from the mining-induced influence around the SLGE, this paper compares the mechanical properties of coal under different mining effects, and studies the rationality of “zero pillar” location against the Xiegou coal mine. The study shows that the key to success of the application of the SLGE is the existence of an intact zone within the triangular coal pillar in spite of double disturbances due to tunneling and coal mining extraction. Laboratory testing shows that the density and uniaxial compressive strength of rock specimens obtained from the triangular coal pillar are smaller than that from the other part of the panel which is concluded to be due to the varied degree of mining-induced influence. The numerical modeling results show that most of the triangular coal pillar is intact after extraction of the panel, and that the peak stress is located in the solid coal beyond the triangular coal pillar. The plastic zone of the triangular coal pillar is only about 1 m after the excavation of the tail gate of the next split-level panel. The physical modeling shows that the tail gate of the next panel is in the destressed zone with only a very small stress fluctuation during the extraction of the next panel. The study shows that the location of the SLGE at Xiegou coal mine is reasonable. SLGE is preferable for ultra-thick coal seams.

scholarly journals Experimental and Numerical Study of Rock Stratum Movement Characteristics in Longwall Mining

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Wan-rong Liu
Keyword(s):  
Stress Concentration ◽  
Coal Seam ◽  
Longwall Mining ◽  
Roof Rock ◽  
Numerical Study ◽  
High Stress ◽  
Engineering Practice ◽  
Rock Stratum ◽  
Working Face ◽  
Coal Wall

The roof fracture is the main cause of coal mine roof accidents. To analyze the law of movement and caving of the roof rock stratum, the roof subsidence displacement, rock stratum stress, and the rock stratum movement law were analyzed by using the methods of the particle discrete element and similar material simulation test. The results show that (1) as the working face advances, regular movement and subsidence appears in the roof rock strata, and the roof subsidence curve forms a typical “U” shape. As the coal seam continues to advance, the maximum subsidence displacement remains basically constant, and the subsidence displacement curves present an asymmetric flat-bottomed distribution. (2) After the coal seam is mined, the overburden forms an arched shape force chain, and the arched strong chain is the path of the overburden transmission force. The farther away from the coal seam, the smaller the stress concentration coefficient is, but it is still in a high stress area, and the stress concentration position moves toward the middle area of the goaf. The stress concentration in front of the coal wall is the source of force that forms the abutment pressure. (3) Above the coal wall towards the goaf, a stepped fracture was formed in the roof rock stratum. The periodic fracture of the rock stratum is the main cause of the periodic weighting of the working face. Understanding the laws of rock movement and stress distribution is of great significance for guiding engineering practice and preventing the roof accidents.

Fracture Assessments of High Pressure Vessel Components Having Longitudinal Holes

2017 ◽  
Author(s):  
Yu Xu ◽  
Kuao-John Young
Keyword(s):  
High Pressure ◽  
Stress Concentration ◽  
Fracture Mechanics ◽  
Pressure Vessel ◽  
High Stress ◽  
Pressure Vessels ◽  
Crack Face ◽  
High Pressure Vessel ◽  
High Stress Concentration ◽  
Critical Locations

Small size longitudinal holes are common in components of high pressure vessels. In fracture mechanics evaluation, longitudinal holes have not drawn as much attention as cross-bores. However, longitudinal holes become critical at certain locations for such assessments because of high stress concentration and short distance to vessel component wall. The high stress concentration can be attributed to three parts: global hoop stress that is magnified by the existence of the hole, local stresses due to pressure in the hole, and crack face pressure. In high pressure vessel design, axisymmetric models are used extensively in stress analyses, and their results are subsequently employed to identify critical locations for fracture mechanics evaluation. However, axisymmetric models ignore longitudinal holes and therefore cannot be used to identify the critical location inside the holes. This paper is intended to highlight the importance of including longitudinal holes in fracture mechanics evaluation, and to present a quick and effective way of evaluating high stress concentration at a longitudinal hole using the combined analytical solutions and axisymmetric stress analysis results, identifying critical locations and conducting fracture mechanics evaluation.

Reduction of Stress Concentration Due to Interference Fits in an Infinite Plate With Two Holes

1978 ◽  
Vol 100 (4) ◽  
pp. 369-373
Author(s):  
T. Iwaki ◽  
K. Miyao
Keyword(s):  
Exact Solution ◽  
Stress Concentration ◽  
Elastic Properties ◽  
High Stress ◽  
Infinite Plate ◽  
Concentration Effects ◽  
Numerical Examples ◽  
High Stress Concentration ◽  
External Forces

This paper contains an exact solution for stresses which are produced in an infinite plate with two holes of different sizes by interference fits. It is assumed that the plate and the interference-fitted ring have the same elastic properties and are perfectly bonded to each other. Numerical examples of the solution are worked out and the interference fits are found useful for reducing the high-stress concentration effects which are induced in an infinite plate with two holes by external forces.

scholarly journals Research on the Redistribution Law of Lateral Mining Stress and the Bearing Characteristics of Section Coal Pillar in Extra-Thick Fully Mechanized Top-Coal Caving Mining

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Qingwei Bu ◽  
Min Tu ◽  
Baojie Fu
Keyword(s):  
Stress Concentration ◽  
Bearing Capacity ◽  
Load Condition ◽  
Coal Pillar ◽  
Critical Dimension ◽  
The Self ◽  
Working Face ◽  
Mining Pressure ◽  
Seam Mining ◽  
Pillar Size

Due to the change of ground stress environment caused by underground coal mining, the intense lateral mining stress concentration is formed around the stope; so section coal pillar is generally set up to bear the mining pressure, but the different sizes of coal pillars have obvious influence on the bearing capacity of those pillars and the characteristics of mining pressure. Mastering the mechanism characteristics by which coal pillars bearing capacity and mining stress distribution is crucial to identify the reasonable coal pillar size and give full play to the bearing role of section coal pillar, given their importance for the safety and bearing stability of engineering rock mass in underground coal mining. Therefore, the bearing characteristics of section coal pillar and the redistribution of mining stress are achieved with a mechanical model analysis on the basis of the analysis of coal pillar bearing and mining influence characteristics. Moreover, applying the elastic-plastic mechanics theory revealed the mechanical equations of the effective bearing size of coal pillar and redistribution of mining stress in longwall face. Combined with the analysis of a specific engineering example, the research results are as follows. During a roadway excavation, the continuous mining stress transfer occurs “stress redistribution” and the mechanical failure of bearing coal pillar consists of lateral mining and roadway side failures. The bearing coal pillar has two critical dimensions (i.e., the critical dimension W e of the self-bearing stability coal pillar and the critical dimension W p of failure through the coal pillar). The mechanical state of the lateral mining stress redistribution and bearing coal pillar is divided into the three situations: ① when the width of coal pillar W  <  W p , only one stress concentration area exists, the bearing capacity of the coal pillar is invalid at this stage, and the lateral mining stress concentration transfers to the roadway solid coal side; ② when the width of the coal pillar W e  ≥  W  ≥  W p , two stress concentration areas appear at this stage, and the coal pillar is in the critical state of self-bearing stability; ③ when the width of the coal pillar W  >  W e , three stress concentration areas are present, and the coal pillar at this stage is in a self-bearing stable state. Among all these factors, only the size of coal pillar is completely controllable, so the aspects of safe bearing and reserved size design of coal pillar, after estimating the critical size of coal pillar, the coal pillar size design is carried out according to the mine pressure control needs of mining engineering, and the cohesion, internal friction angle, interlayer friction coefficient, and coal seam mining height are improved by artificial technology, so as to realize the resource safe and efficient mining of all kinds of coal seam mining conditions; in the calculation of wide coal pillar size, the advance mining stress concentration at the end of the self-working face should be taken as the mining load condition, and the reserved size meets the condition of W  >  W e , thereby ensuring the stable bearing of the wide coal pillar despite the advanced mining stress concentration during the self-working face mining; in the calculation of narrow coal pillar size, the lateral mining stress concentration before mining should be taken as the mining load condition and the reserved size meets the condition W  <  W p , thereby realizing the effective transfer of mining stress concentration to the roadway solid coal side.

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