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

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.

Download Full-text

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

Geofluids ◽

10.1155/2020/8847003 ◽

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.

Download Full-text

Study on Temporal and Spatial Characteristics of Overlying Strata in Deep Coal Mining Process

10.21203/rs.3.rs-408320/v1 ◽

2021 ◽

Author(s):

Bang-an Zhang ◽

Yang yushun ◽

Dong-ming Zhang

Keyword(s):

Stress Concentration ◽

Coal Seam ◽

Coal Mining ◽

Three Dimensional ◽

In Situ Stress ◽

Three Dimensional Model ◽

Concentration Coefficient ◽

Working Face ◽

Stress Concentration Coefficient

Abstract This paper adopts the stress relief method to test the in-situ stress in the field to obtain the in-situ stress distribution characteristics of No. 2+3# coal seam. A three-dimensional model was established with the No. S3012 working face as the engineering background, and the measured in-situ stress values were applied to the three-dimensional model, and the spatial-temporal evolution characteristics of coal and rock mass around the stope during coal seam mining were studied. The specific conclusions are as follows: the three-dimensional stress distribution map in front of, behind and on both sides of the working face in the process of coal mining are obtained. As the working face goes on, the maximum value of the supporting stress formed in front of, behind and on both sides of the working face shifts to the corner, presenting a “hump-like” distribution. The stress concentration coefficient of front, back and both sides of stope increases linearly with the increase of mining size. Under the same mining size, the stress concentration coefficient in front of stope is the smallest, and the stress concentration coefficient on both sides is the largest. The three-dimensional displacement field distribution nephogram of overlying strata in the process of coal mining is obtained. With the continuous advance of the working face, the roof strata of coal seam undergo continuous dynamic subsidence process, and the roof subsidence increases continuously, showing the shape of "bowl" with sharp bottom. In the process of working face mining, the roof displacement of coal seam showed an "O" shape evolution characteristic. The three-dimensional distribution cloud map of the plastic zone of coal and rock mass in the process of working face mining was obtained, and the failure volume of the plastic zone gradually increases with the continuous progress of the working face.

Download Full-text

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

Shock and Vibration ◽

10.1155/2019/9412697 ◽

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.

Download Full-text

Study on Temporal and Spatial Characteristics of Overlying Strata in the Deep Coal Mining Process

Advances in Civil Engineering ◽

10.1155/2021/4914531 ◽

2021 ◽

Vol 2021 ◽

pp. 1-14

Author(s):

Bang’an Zhang ◽

Yushun Yang ◽

Dongming Zhang

Keyword(s):

Stress Concentration ◽

Coal Seam ◽

Coal Mining ◽

Three Dimensional ◽

In Situ Stress ◽

Three Dimensional Model ◽

Concentration Coefficient ◽

Working Face ◽

Stress Concentration Coefficient

This study adopts the stress relief method to test the in situ stress in the field to obtain the in situ stress distribution characteristics of no. 2 + 3# coal seam. A three-dimensional model was established with the no. S3012 working face as the engineering background, and the measured in situ stress values were applied to the three-dimensional model, and the spatial-temporal evolution characteristics of coal and rock mass around the stope during coal seam mining were studied. The specific conclusions are as follows: the three-dimensional stress distribution map in front of, behind, and on both sides of the working face in the process of coal mining are obtained. As the working face goes on, the maximum value of the supporting stress formed in front of, behind, and on both sides of the working face shifts to the corner, presenting a “hump-like” distribution. The stress concentration coefficient of front, back, and both sides of stope increases linearly with the increase of the mining size. Under the same mining size, the stress concentration coefficient in front of stope is the smallest, and the stress concentration coefficient on both sides is the largest. The three-dimensional displacement field distribution nephogram of overlying strata in the process of coal mining is obtained. With the continuous advance of the working face, the roof strata of coal seam undergo the continuous dynamic subsidence process, and the roof subsidence increases continuously, showing the shape of “bowl” with sharp bottom. In the process of working face mining, the roof displacement of coal seam showed an “O” shape evolution characteristic. The three-dimensional distribution cloud map of the plastic zone of coal and rock mass in the process of the working face mining was obtained, and the failure volume of the plastic zone gradually increases with the continuous progress of the working face.

Download Full-text

Study on the Relationship between the Diameter and the Stress Concentration

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.915-916.165 ◽

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.

Download Full-text

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

International Journal of Coal Science & Technology ◽

10.1007/s40789-021-00460-2 ◽

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.

Download Full-text

Influence of Stress Concentration on Fatigue Property of Welded Joints of 5083 Aluminum Alloy

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.456.451 ◽

2013 ◽

Vol 456 ◽

pp. 451-455

Author(s):

Jun Yang ◽

Bo Li ◽

Qiang Jia ◽

Yuan Xing Li ◽

Ming Yue Zhang ◽

...

Keyword(s):

Tensile Strength ◽

Aluminum Alloy ◽

Fatigue Strength ◽

Stress Concentration ◽

Welded Joints ◽

Weld Zone ◽

Fatigue Property ◽

Concentration Coefficient ◽

5083 Aluminum Alloy ◽

Stress Concentration Coefficient

Fatigue test of the welded joint of 5083 aluminum alloy with smooth and height of specimen and the weld zone than the high test measurement and theoretical stress concentration coefficient calculation, the weld reinforcement effect of stress concentration on the fatigue performance of welded joints. The results show that: Smooth tensile strength of specimens for 264MPa, fatigue strength is 95MPa, the tensile strength of the 36%. Higher tensile strength of specimens for 320MPa, fatigue strength is 70MPa, the tensile strength of the 22%. Higher specimen stress concentration coefficient is 1.64, the stress concentration to the weld toe becomes fatigue initiation source, and reduces the fatigue strength and the fatigue life of welded joints.

Download Full-text

Stress strain state of elastic plate with elliptical cut-out

Izvestiya vysshikh uchebnykh zavedenii. Fizika ◽

10.17223/00213411/63/11/3 ◽

2020 ◽

pp. 3-8

Author(s):

E.E. Deryugin ◽

Keyword(s):

Plastic Deformation ◽

Stress Concentration ◽

Driving Force ◽

Strain State ◽

Mechanical State ◽

Concentration Coefficient ◽

Stress Strain ◽

Crack Driving Force ◽

Stress Strain State ◽

Stress Concentration Coefficient

The article considers a crack in the form of a narrow cut with a certain cfn at the cut out in an unbounded plate. The characteristics of the mechanical state of this system under uniaxial loading are determined: the stress concentration coefficient, the crack-driving force, and the energy of a solid with a crack. The elastic energy expenditure during crack propagation is determined. The general regularities of the mechanical state of a solid with a crack, not necessary having the form of an ellipse, are revealed. An important parameter of a crack is the curvature at the tip. It is shown that the Griffiths crack does not actually have a singularity at the tip. The stress strain state of the plate with an elliptical crack is identical to the same of the plate with a focus of homogeneous plastic deformation.

Download Full-text