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.

Study on the Relationship between the Diameter and the Stress Concentration

2014 ◽  
Vol 915-916 ◽  
pp. 165-168
Author(s):  
Jian Qin Zhao ◽  
Zhi Wang
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Stress Distribution ◽  
Concentration Coefficient ◽  
Test Technique ◽  
Finite Element Technology ◽  
Concentration Degree ◽  
Relief Groove ◽  
The Relationship ◽  
Stress Concentration Coefficient

In order to find out how much a relief groove can change the stress distribution in a shaft, In this paper, finite element technology and test technique have been used to study the stress concentration dates caused by a escape by different shaft models. Their diameters are all less than M30mm. The research solutions show that the stress concentration coefficients caused by the escapes grow with the increase of the diameters. The pressure on the shaft should be reduced to about 0.68 times of the normal one so that the shafts have the same lifetime as before. Stress concentration coefficient is the only parameter to estimate the stress concentration degree. The calculate dates were compared with the test one in this paper in order to check the models accuracy. The conclusions show that the error rate is less than 5%.It can be taken as a new method to replace the destructive test in the design products.

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.

Analysis of Stress in Aircraft Components Using Lock-In Thermography

2010 ◽  
Vol 663-665 ◽  
pp. 1073-1076 ◽  
Author(s):  
Xun Liu ◽  
Jun Yan Liu ◽  
Xu Dong Li ◽  
Guang Yu Zhang
Keyword(s):  
Stress Concentration ◽  
Stress Distribution ◽  
Stress Analysis ◽  
Aluminium Alloys ◽  
Thermoelastic Effect ◽  
Load Frequency ◽  
Effect Theory ◽  
Lock In ◽  
The Relationship

This paper describes a theoretical and experimental analysis on full-filed stress distribution from thermoelastic measurements and its application to determination of stress concentration. The sum of the principle stress can be measured by Thermal Stress Analysis (TSA). Lock-in Thermography is very effective tool to measure the structure stress distribution by its high thermal resolving. In this study, the thermoelastic effect theory is described and the relationship between the temperature and the applied stress is developed in an elastic material. Experiments were carried out with 2A12 aluminium alloys plate and ones with hole structure under cyclic load. The thermoelastic effect coefficient is obtained for 2A12 aluminium alloys materials, and the effect law is analyzed that the stress value measured was affected by load frequencies. The optional load frequency is obtained, and that is, the load frequency is selected greater than 3.5Hz for 2Al12 materilas, and it was found that the structure stress can be evaluated with good accuracies by the lock in thermography. The experiment was carried out for aircraft components stress distribution measurement and structure stress analysis. The experimental results show the stress concentration position is easy found from stress distribution by lock-in thermography.

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 Determination of cyclic filling length in gob-side entry retained with roadside filling and its application

2020 ◽  
Author(s):  
Zizheng Zhang ◽  
Jianbiao Bai ◽  
Xianyang Yu ◽  
Weijian Yu ◽  
Min Deng ◽  
...  
Keyword(s):  
Coal Seam ◽  
Coal Mine ◽  
Difference Method ◽  
Suggested Method ◽  
Stress Difference ◽  
Thick Coal Seam ◽  
Mechanics Model ◽  
Working Face ◽  
Geological Conditions ◽  
The Relationship

Abstract Gob-side entry retained with roadside filling (GER-RF) plays a key role in achieving coal mining without pillar and improving the coal resource recovery rate. Since there are few reports on the cyclic filling length of GER-RF, a method based on the stress difference method is proposed to determine the cyclic filling length of GER-RF. Firstly, a stability analysis mechanics model of the immediate roof above roadside filling area in GER was established, then the relationship between the roof stress distribution and the unsupported roof length was obtained by the stress difference method. According to the roof stability above roadside filling area based on the relationship between the roof stress and its tensile strength, the maximum unsupported roof length and rational cyclic filling length of GER-RF. Combined with the geological conditions of the 1103 thin coal seam working face of Heilong Coal Mine and the geological conditions of the 1301 thick coal seam working face of Licun Coal Mine, this suggested method was applied to determine that the rational cyclic filling lengths of GER-RF were 2.4 m and 3.2 m, respectively. Field trial tests show that the suggested method can effectively control the surrounding rock deformation along with rational road-in support and roadside support, and improve the filling and construction speed.

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 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.

Study on Numerical Simulation of Fully Mechanized Top Coal’s Caving Property of Tang Gong Ta Coal Mine

2015 ◽  
Vol 1094 ◽  
pp. 410-414
Author(s):  
Quan Ming Liu
Keyword(s):  
Numerical Simulation ◽  
Stress Concentration ◽  
Coal Mine ◽  
Peak Stress ◽  
Simulation Method ◽  
Numerical Simulation Method ◽  
Working Face ◽  
Coal Wall

Using numerical simulation method,fully mechanized top coal’s caving property of Tang gong ta coal mine was studied.The results show at primary mining period of fully mechanized working face, there were stress concentration regions at the front and rear of coal wall,but it was not distinct in the front and top coal’s caving property was not ideal.When it advanced to 84m of the working face,there would be obvious peak stress at the front and rear of coal wall. It accelerated top coal’s caving.When it advanced to 140m of the working face,top coal was caved with coal mining.Finally it was proved on the scene. The results of the study in fully mechanized mining’s safety and efficiency has some guiding role.

scholarly journals Determination of Cyclic Filling Length in Gob-Side Entry Retained with Roadside Filling and Its Application

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Zizheng Zhang ◽  
Jinlin Xin ◽  
Jianbiao Bai ◽  
Xianyang Yu ◽  
Weijian Yu ◽  
...  
Keyword(s):  
Coal Seam ◽  
Coal Mine ◽  
Difference Method ◽  
Suggested Method ◽  
Stress Difference ◽  
Thick Coal Seam ◽  
Mechanics Model ◽  
Working Face ◽  
Geological Conditions ◽  
The Relationship

Gob-side entry retained with roadside filling (GER-RF) plays a key role in achieving coal mining without pillar and improving the coal resource recovery rate. Since there are few reports on the cyclic filling length of GER-RF, a method based on the stress difference method is proposed to determine the cyclic filling length of GER-RF. Firstly, a stability analysis mechanics model of the immediate roof above the roadside filling area was established, and then, the relationship between the roof stress distribution and the unsupported roof length was obtained by the stress difference method. According to the roof stability above the roadside filling area based on the relationship between the roof stress and its tensile strength, the maximum unsupported roof length and rational cyclic filling length were determined. Combined with the geological conditions of the 1103 thin coal seam working face of Heilong Coal Mine and the 1301 thick coal seam working face of Licun Coal Mine, the suggested method was applied to determine that the rational cyclic filling lengths were 2.4 m and 3.2 m, respectively. Field trial tests show that the suggested method can effectively control the surrounding rock deformation along with rational road-in support and roadside support and improve the filling and construction speed.

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