scholarly journals Characteristics of Stratum Structure and Fracture Evolution in Stratified Mining of Shallow Buried High-Gas-Thick Coal Seam by Similarity Simulation

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-18
Author(s):  
Qin Guangpeng ◽  
Cao Jing ◽  
Wang Chao ◽  
Wu Shuo ◽  
Zhai Minghua
Keyword(s):  
Coal Seam ◽  
Coal Mine ◽  
Coal Pillar ◽  
Structure Evolution ◽  
Thick Coal Seam ◽  
Fracture Structure ◽  
Working Face ◽  
Rock Structure ◽  
Type Fracture ◽  
Overlying Strata

The stratified mining of super thick coal seam is a process of repeated disturbance of the top roof, especially in the lower stratification, the upper complex rock layer has a greater settlement space, resulting in great changes in the strata structure and fissure distribution. The main coal seam thickness of Rujigou Coal Mine exceeds 20 m, due to the high gas content of the coal seam, it is prone to spontaneous combustion, and the stratified mining method is adopted. When a small-size section coal pillar (less than 10 m) is used, the complex rock structure evolution and fissure development characteristics during the stratified mining of shallow buried thick coal seam will directly affect the movement of gas transportation between the working face and the goaf and will directly affect the safety of the working face. Taking Rujigou coal mine as engineering background, this paper analyzes the breaking structure, fracture development, and evolution law of overlying strata in different layers and different sections of coal seam when the buried depth is shallow, and the extra-thick coal seam is stratified mining. The results show that in the process of stratified mining, the overlying strata break, in addition to the whole trapezoidal failure structure, will also form a local F type fracture structure, and with the stratified downward mining, the F type fracture structure will continue to move up and disappear until it is compacted. The “V” type and “U” type subsidence characteristics of different strata overburden are presented after mining in stratified working face of extra-thick coal seam, and the subsidence amount is approximately symmetrical distribution along the middle line of goaf. In the mining process of the lower part of the layer, the end broken rock block is easy to slip along the hinge point by the hinged rock beam structure, and the sliding instability occurs. In the process of stratified mining of ultrathick coal seam, the main fissure of overburden is mainly longitudinal fissure, and it is very easy to form through with the upper layer and will finally connect with the surface under the condition of shallow buried depth. The inclined cracks connected with the adjacent goaf are formed above the coal pillar of the section, which becomes the passage of gas migration in the goaf. The research conclusion shows that for the stratified mining of high gas thick coal seam, special attention should be paid to the treatment of the gas on the stratified working face. In addition to the conventional gas treatment measures such as coal seam prepumping, the buried pipe pumping in the mining area can also be adopted, which can effectively reduce the gas concentration of the working surface.

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 Control of Gob-Side Roadway with Large Mining Height in Inclined Thick Coal Seam: A Case Study

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Xie Fuxing
Keyword(s):  
Numerical Simulation ◽  
Coal Pillar ◽  
Simulation Software ◽  
Surrounding Rock ◽  
Mine Pressure ◽  
Thick Coal Seam ◽  
Working Face ◽  
Rock Structure ◽  
Large Mining Height ◽  
Mining Height

The gob-side roadway of 130205, a large-mining-height working face in the Yangchangwan coal mine, was investigated in terms of the mine pressure law and support technology for large mining heights and narrow coal pillars for mining roadways. The research included field investigations, theoretical analysis, numerical simulation, field tests, and other methods. This paper analyzes the form of movement for overlying rock structure in a gob-side entry with a large mining height and summarizes the stress state and deformation failure characteristics of the surrounding rock. The failure mechanism of the surrounding rock of the gob-side roadway and controllable engineering factors causing deformation were analyzed. FLAC3D numerical simulation software was used to explore the influence law of coal pillar width, working face mining height, and mining intensity on the stability of the surrounding rock of the gob-side roadway. Ensuring the integrity of the coal pillar, improving the coordination of the system, and using asymmetric support structures as the core support concept are proposed. A reasonably designed support scheme for the gob-side roadway of the working face for 130205 was conducted, and a desirable engineering effect was obtained through field practice verification.

Similarity simulation study on displacement and stress changes response to coal mining in Longdong coal mine, China

2020 ◽  
pp. qjegh2020-111
Author(s):  
Kai Huang ◽  
Long Xu ◽  
Fusheng Zha ◽  
Zhitang Lu ◽  
Jiwen Wu ◽  
...  
Keyword(s):  
Coal Seam ◽  
Coal Mine ◽  
Water Inrush ◽  
Coal Pillar ◽  
Working Face ◽  
Field Investigations ◽  
Geological Conditions ◽  
Stress Changes ◽  
Continuous Mining ◽  
The Stability

The complicated geological conditions, including the Fault Sun, in East No. 2 mining sub-area of the Longdong coal mine will influence the stability of strata during mining, leading to serious geological hazards. To circumvent this issue, a similarity simulation experiment was designed and performed in this study, in which the failure characteristics and evolution of displacement and stress within the strata were investigated, and the optimum width of a waterproof coal pillar was determined. The results showed that, as the working face progressed, the coal seam roof gradually deformed, from initial caving of the immediate roof to complete movement and curved subsidence of the entire roof. Significant changes in displacement and stress within the coal seam roof were recorded, and these increased during continuous mining activity. Displacement and stress difference on either side of the fault gradually increased and reached remarkable values with increase in mining distance. On the basis of the experiment results, water inrush is believed to be caused by the interaction between mining and the fault, and, as calculated from parameters collected in field investigations, a waterproof coal pillar of 50 m width should be established to prevent Fault Sun activation, thereby reducing the risk of water inrush from neighbouring aquifers.

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 Law of Overlying Strata Breakage and Migration in Downward Mining of Extremely Close Coal Seams by Physical Similarity Simulation

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Xiaobin Li ◽  
Wenrui He ◽  
Zhuhe Xu
Keyword(s):  
Coal Seam ◽  
Coal Pillar ◽  
Coal Seams ◽  
Monitoring Point ◽  
Rock Stratum ◽  
Working Face ◽  
Roof Fall ◽  
And Migration ◽  
Close Coal Seams ◽  
Overlying Strata

Extremely close coal seam groups are widely distributed in China, and the main mining method is downward mining. In the downward mining process of extremely close coal seam groups, the violent movement of overlying strata will cause the redistribution of surrounding rock stress. It not only produces stress concentration on the pillar but also causes the roof of the lower coal seam to be broken and difficulty in maintaining the mining roadway. In this study, the physical similitude modeling method and field observations were used to study the breakage and migration law of overlying strata in the downward mining of extremely close coal seams. Results show that in the process of mining upper coal seam, the first weighting step of the main roof is 37.5 m and the periodic weighting step is 12.5 m. The occurrence of strata separation is beneficial to the prediction of roof weighting. When the working face advances to 25 m, the rock stratum approximating a parallelogram of height 5 m does not collapse, and the working face is relatively dangerous. When mining the lower coal seam, the overall pressure of the working face is large, but the periodic weighting of the working face is not obvious. The first collapse step of the immediate roof is 15 m. When mining the upper and lower coal seams, the subsidence of the monitoring point increases significantly at 17.5 and 15 m, respectively. The roof collapse of the lower coal seam occurs 2.5 m ahead of that of the upper coal seam. The hydraulic value of the support, roof fall height, and sloughing depth in the entire working face reach the maximum at the coal pillar, and the extreme points at the coal pillar are relatively concentrated. This research provides some guidance for the safe and efficient mining of extremely close coal seams in the future.

Research on Stability of Overburden Structure around Longwall Mining Face in Steeply Dipping Seam Group

2015 ◽  
Vol 724 ◽  
pp. 100-110
Author(s):  
Shi Guang Ren ◽  
Yong Ping Wu ◽  
Jian Hui Yin
Keyword(s):  
Coal Seam ◽  
Longwall Mining ◽  
Coal Pillar ◽  
Beam Theory ◽  
Coal Seams ◽  
Working Face ◽  
Rock Structure ◽  
Longitudinal Bending ◽  
Mining Face ◽  
The Stability

The steeply dipping seam group is defined by the two or more coal seams ,a pitch between 35°~55°. Using masonry beam theory, longitudinal bending theory and “R-S-F” dynamics control theory built a lower area overburden structure mode. Analysed the stability of low position coal seam. The balance requirement and the strength of the structure which is affected by the caving rock and lower coal roof were given. It easily generates two lower position steps rock structure in inclination along working face. Regular breaking of the second structure is the main reason leads to the imbalance of the structure between upper coal pillar and upper coal mining face.The interaction among multiple coal seam panels and overburden structures is the main reason that causes the rock disaster, the unbalance of the lower area may lead to pushing accident, the imbalance of the upper area can generate shock pressure.

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.

scholarly journals Study on Reasonable Stopping and Time-Sharing Partition Support of Fully Mechanized Top Coal Caving Face Under the Interference of Stopping Line in Close-Up Coal Seam

2021 ◽  
Author(s):  
Dongdong Chen ◽  
Yiyi Wu ◽  
Shengrong Xie ◽  
Fangfang Guo ◽  
Fulian He ◽  
...  
Keyword(s):  
Coal Seam ◽  
Coal Pillar ◽  
Time Sharing ◽  
Working Face ◽  
Rock Structure ◽  
Stopping Line ◽  
Stress Environment ◽  
Arch Structure ◽  
Stress Superposition ◽  
Mining Coal

Abstract Close-distance coal seams are widely distributed in China, and there is a problem of stopping mining in a large number of working faces. Taking Yanzishan mine as the engineering background, the mined-out area and the remaining end-mining coal pillar of No.4 coal seam (upper coal seam) mined in advance caused strong interference to the stopping mining of N316 working face of No.3 coal seam under it. Through field observation, laboratory experiment, and support data collection, the mechanical parameters of coal and rock mass and periodic weighting condition of the working face were mastered, and numerical simulation and similar model experiments were carried out. Three positional relationships between the stopping position of the underlying N316 working face and the upper stopping line were obtained: “externally staggered with the upper stopping line” (ESUL), “overlapped with upper stopping line” (OUL), and “internally staggered with the upper stop line” (ISUL, ISUL-SD for shorter internal staggered distances, ISUL-LD for longer ones). The formation and evolution of the stress arch structure of ESUL → OUL → ISUL-SD → ISUL-LD are obtained from the analysis: ① ESUL: there is a double stress arch structure of goaf side and end-mining coal pillar side in the overburden and stress superposition appears in the middle arch foot (stopping mining place). ② OUL: it evolved into a single arch structure of goaf-solid coal, and the stress at the stop of mining was relatively minimum. ③ ISUL-SD: it is still a single arch structure, and the stress at the stop of mining is still small. ④ ISUL-LD: the double stress arch is regenerated and stress superposition occurs at the front arch foot (stopping mining place). At the same time, the morphological evolution process of stress arch is as follows: “front and back stress arches, superimposed with middle arch foot” → “front arch gradually decreases” → “front arch dies, and two arches merge into single arch” → “single arch gradually increases” → “two arches are regenerated, superimposed with front arch foot”. On-the-spot analysis from the combination of stress and overburden structure: ① ESUL: the stress concentration degree is the highest above the stopping space, and the overburden block in the large-scale caving zone directly acts on the support, which makes the stopping operation difficult. ② OUL: although the stress environment is the best, the overlying key blocks will have hidden dangers of overall rotation or sliding instability. ③ ISUL-SD: the stress environment is good, and the overlying rock can realize the stable structure of the cantilever plate (the internal staggered distance is less than the periodic weighting step), and the mining is stopped at this position to realize the safe and smooth withdrawal of the support. ④ ISUL-LD: it is basically consistent with stopping mining when single-layer coal is used but is limited by the limited length of the end-mining coal pillar. In addition, the self-digging retracement channel is designed to serve the whole retracement process, and the idea of time-sharing partition support for a large cross-section of mining stoppage and its corresponding scheme is put forward according to the retracement process. Through the simulation of prestressed field and field practice, the roof overlying rock structure is stable during the whole retracement period, thus realizing the safe and smooth mining stoppage and retracement of the working face.

scholarly journals Physical Experiment and Numerical Modeling on the Failure Mechanism of Gob-Side Entry Driven in Thick Coal Seam

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5425 ◽  
Author(s):  
Xinshuai Shi ◽  
Hongwen Jing ◽  
Zhenlong Zhao ◽  
Yuan Gao ◽  
Yuanchao Zhang ◽  
...  
Keyword(s):  
Coal Seam ◽  
Failure Mechanism ◽  
Coal Pillar ◽  
Stability Control ◽  
Shear Cracks ◽  
Thick Coal Seam ◽  
Physical Model Tests ◽  
The Stability ◽  
Roof Strata ◽  
Overlying Strata

In this paper, a combination of physical model tests and numerical simulations were carried out to explore the overlying strata movement laws, failure mechanism, and cracks evolution of the gob-side entry driven in a thick coal seam. The physical experimental results indicated that the hanging cantilever beam was easily developed above the coal pillar after mining out the 2101 panel, resulting in a larger and stronger stress concentration. The overburden loads acting on the coal pillar can be greatly released after the hanging roof strata were cut down with an 18 m cutting line. Additionally, we adopted Universal Discrete Element Code (UDEC) software to investigate the deformation and crack evolution mechanism of the gob-side entry under different conditions. The primary-supported roadway underwent severe deformation, filling with a great quantity of tensile and shear cracks to the inner coal pillar. Both the physical and numerical results proved that the optimized-support parameters combined with roof-cutting measures could effectively guarantee the stability of the gob-side entry. This research can provide valuable guidance for the stability control of the gob-side entry in mines under similar conditions.

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