scholarly journals Mining-Induced Pressure-Relief Mechanism of Coal-Rock Mass for Different Protective Layer Mining Modes

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Xiang Cheng ◽  
Guangming Zhao ◽  
Yingming Li ◽  
Xiangrui Meng ◽  
Qingyi Tu ◽  
...  
Keyword(s):  
Rock Mass ◽  
Coal Seam ◽  
Volume Expansion ◽  
Axial Stress ◽  
Soft Rock ◽  
Protective Layer ◽  
Confining Pressure ◽  
Mining Area ◽  
Pressure Relief ◽  
Coal Rock

The protective layer mining method of the traditional deep coal seam in has been confronted with great challenges, and it is difficult for coal and gas to be extracted together. Taking the occurrence conditions of III1 mining area of Luling Coal Mine located at Huaibei, China, as engineering background, the influence law of the lithology on stress environment in front of the stope was analyzed by theoretical analysis and numerical simulations. The mining-induced mechanical effect of coal-rock mass was studied under different protective layer mining modes. The results showed that the peak value of the advanced abutment pressure decreased with the decrease of lithologic strength under the same mining conditions. For simulated geological conditions, the stress concentration coefficient of soft rock and coal seam protective layer mining modes was 1.9 and 1.7, respectively. Under the mining stress path of different protective layers, the ratio of axial stress increase and confining pressure unloading in secondary unloading phase were 2 : 1 and 1.5 : 1, respectively. The axial stress-strain curves of different protective layer mining modes had similar trends, and they had a volume expansion at the end of unloading (failure stage). In addition, it revealed the pressure-relief antireflection mechanism of the protective layer mining. Under the same confining pressure condition, the peak stress and peak strain increased with the increase of loading and unloading velocity ratio. The reduced value of the confining pressure increased, while the volume expansion decreased at failure. The results were applied to III1 mining area in soft rock protective layer mining, which created the mining way of traditional coal seam protective layer. Furthermore, the gas control technology of soft rock protective layer working face was put forward for deep coal seam with low permeability and high gas, enriching the pressure-relief mining theory of protective layer.

Study on Underlying Coal and Strata Pressure-Relief Principle and the Gas Extraction Technique under Upper Protective Layer Mining

2014 ◽  
Vol 875-877 ◽  
pp. 1863-1870 ◽  
Author(s):  
Jian Liu ◽  
Jie Zhao ◽  
Ming Song Gao
Keyword(s):  
Rock Mass ◽  
Coal Seam ◽  
Protective Layer ◽  
Extraction Technique ◽  
Efficient Production ◽  
Gas Extraction ◽  
Pressure Relief ◽  
Fracture Development ◽  
Floor Heave ◽  
Coal Rock

By study on underlying coal and strata pressure-relief principle and the gas extraction technique under upper protective layer mining, we obtain the stress change and distribution law of underlying coal-rock mass. We analyze the deformation law and fracture development characteristics of underlying coal-rock mass movement. With mining proceeding ahead, the total floor coal and rock experiences compression deformation first, then expansion deformation and re-compaction of the continuous periodic destruction. Based on different development characteristics and status of underlying coal-rock mass, the underlying coal-rock mass under an effect of upper protective layer mining was divided into the floor heave fracture zone and the floor heave deformation zone in this paper. The permeability coefficient of change law of underlying the coal seam as follows: the original value-small decreasing-increasing greatly-reducing-stability at last. The field test for upper protective layer mining of Zhang-ji coal mine of Huainan shows that the effect of pressure relief of protected seam is very good. So it eliminates the risk of gas outburst, ensuring safety mining of the protected seam. The research has an important significance for safety and efficient production under similar exploitation conditions of low-permeability with high gas and outburst risk coal seam.

scholarly journals Calculation Method of Overburden Damage Height Based on Fracture Mechanics Analysis of Soft and Hard Rock Layers

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Liang Chen ◽  
Shaowu Fan ◽  
Can Zhao ◽  
Lang Zhang ◽  
Zhiheng Cheng
Keyword(s):  
Fracture Mechanics ◽  
Coal Seam ◽  
Calculation Method ◽  
Hard Rock ◽  
Soft Rock ◽  
Mining Area ◽  
Overburden Rock ◽  
Rock Interaction ◽  
Mechanics Analysis ◽  
Seam Mining

Under the geological condition of soft and hard rock interaction stratum, the overburden damage height can provide a quantitative support for the design of the locations of gas drainage boreholes in the roof mining fracture zone and the determination of the hydraulic fracture zone in coal seam mining. The interbedded structure of overlying mud rock and sandstone in the Lu’an mining area in Shanxi is a typical soft and hard rock interaction stratum. In view of the lack of soft rock fracture mechanics analysis and the improper calculation of the damage height of overburden rock caused by constant rock residual bulking coefficient to be used regularly in the analysis, in this paper, we constructed a fracture model of soft and hard strata by giving a quantitative classification criterion of soft and hard rocks and introducing a fracture failure criterion of soft rock strata and the space constraint condition of broken-expansion rock formation. Aiming at improving the calculation precision of overburden damage height, we presented a calculation method based on fracture mechanics analysis of soft and hard strata, which could delineate the extent of intact rock in overlying strata from bottom to top to determine the damage height of overburden rock. This research took Yuwu coal mine in Lu’an mining area as an example. Results showed that (1) by the calculation method, the overburden damage height of the N1102 fully mechanized caving face in Yuwu coal mine was 51.44 m, which was less than the value obtained by an actual borehole TV method as well as the numerical simulation result of 53.46 m, with a calculation accuracy about 96.22%, which is quite high for both. The calculation accuracy of the proposed method was higher than that of the three conventional theoretical methods, and it effectively solved the limitation of the fracture analysis method without the inclusion of the soft rock layer in design and the distortion problem due to the residual bulking coefficient to be improperly used in simulation. (2) There was no noticeable fractures in the broken soft rock zone, and the whole fractures were mainly low-angle rupture; the fractures in hard rock layer had obvious ruptures and multiangle cracks, and the average fracture width of soft rock was 2.8 mm smaller than that of hard rock. The fracture modes of soft rock and hard rock were mainly tensile failure and tensile shear failure, which verified the correctness of the fracture mechanics model of soft and hard rock layers constructed in this paper. (3) It is noticed that the tensile strength of rock in this method needs to be obtained through rock mechanics experiment on overlying strata in the study area, and our proposed method was applicable to the mining conditions of near horizontal coal seam. The calculation accuracy of this method meets the engineering error requirements and can be applied to the prediction of overburden damage height in near horizontal coal seam mining.

scholarly journals Research and Application of Hydraulic Punching Pressure Relief Antireflection Mechanism in Deep “Three-Soft” Outburst Coal Seam

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Beifang Gu ◽  
Yanling Wu
Keyword(s):  
Coal Seam ◽  
Large Scale ◽  
Water Pressure ◽  
Pressure Relief ◽  
Gas Drainage ◽  
Technical Problems ◽  
Soft Coal ◽  
Coal Rock ◽  
Outburst Coal Seam ◽  
Soft Coal Seam

To solve the problems of gas predrainage in deep seams with “three softs” and low-air permeability, hydraulic punching pressure relief antireflection technology is proposed on the basis of the research background of gas predrainage technology in Lugou Mine to alleviate technical problems, such as low gas drainage efficiency, in this mine. Through the analysis of the mechanism of hydraulic punching and coal breaking, combined with FLAC3D software, a hydraulic punching pressure relief antireflection model is established. Then, the fracture radii of coal rock are simulated and calculated. The results show that, under hydraulic punching with a water pressure of 10 MPa and coal outputs of 3 m3, 6 m3, 9 m3, and 12 m3, the fracture radii of coal and rock are 3.4 m, 4.8 m, 5.5 m, and 5.9 m, respectively. Using the software to fit the relationship between coal output V and hydraulic punching fracture radius R under the same water pressure, R = 2.32479 V0.3839 is obtained. The field test is carried out in the bottom drainage roadway of 32141 in Lugou Mine. The application effect is as follows: the gas concentration of hydraulic punching with a coal output of 3 m3 is twice that of ordinary drilling, and the coal output of hydraulic punching with a coal output of 6 m3 is four times that of ordinary drilling. The extraction concentration is four times that of ordinary drilling, and the extraction concentration of hydraulic punching with a coal output of 9 m3 is 6.4 times that of ordinary drilling. Combining the results of the numerical simulation and taking into account the actual construction situation on site, the coal output of water jetting from the borehole is 9 m3, and the fracture radius is 5.5 m. This outcome means that the effective half radius is 5.5 m, and the borehole spacing is 7.7 m. These values are the construction parameters for large-scale applications. This proposal provides effective technology and equipment for gas drainage in the deep three-soft coal seam. Consequently, it has promotion and reference significance for gas drainage in coal seam of the same geological type.

scholarly journals Characteristics of Pressure Relief Gas Extraction in the Protected Layer by Surface Drilling in Huainan

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Xiaozhang Tong ◽  
Hu Wen ◽  
Xiaojiao Cheng ◽  
Shixing Fan ◽  
Chunhui Ye ◽  
...  
Keyword(s):  
Flow Rate ◽  
Protective Layer ◽  
Periodic Variation ◽  
Mining Area ◽  
Gas Content ◽  
Gas Extraction ◽  
Pressure Relief ◽  
Working Face ◽  
Extraction Volume ◽  
Extraction Processes

To study the behavior of gas extraction from the protected layer by surface drilling, the common characteristics of gas extraction concentration and gas extraction quantity are summarized through the collection of key parameters of surface drilling and a combination of data and figures, with the background of 11−2 coal protection 13−1 coal in the Huainan mining area. The research results show that the flow of pressure relief gas extraction of the protected layer by surface drilling has three stages: a rising period, stable period, and decay period. When the extraction processes of multiple surface wells on the same working face are coordinated, the extraction flow is superimposed, and the extraction volume of surface drilling shows an increasing trend and fluctuates with the location of the drilling. The extraction flow rate before ground drilling is relatively small, and the extraction flow rate increases after ground drilling. This behavior is further confirmed by field observation of mining changes in the protective layer and the expansion and deformation of the protected layer. The periodic variation in the surface drilling and extraction quantity is affected primarily by the mining movement of the working face of the protective layer. Specifically, it is affected by factors such as the mining progress of the working face of the protective layer, mining height, degree of compacted goaf, degree of pressure relief of the protected layer, original gas content, and other measures taken to extract the protected layer.

Study on Pressure Relief Scope of Underlying Coal Rock with Upper Protective Layer Mining

2013 ◽  
Vol 734-737 ◽  
pp. 661-665
Author(s):  
Ben Qing Yuan ◽  
Yong Jiang Zhang ◽  
Jian Jun Cao ◽  
Guo Jian Cheng
Keyword(s):  
Theoretical Analysis ◽  
Protective Layer ◽  
Calculation Model ◽  
Infinite Plane ◽  
Pressure Relief ◽  
Discrimination Criterion ◽  
Coal Rock ◽  
Elastic Mechanics ◽  
The Impact ◽  
Scope Of Protection

In this paper,in the case of upper protective layer mining of a mine for the engineering background, based on the model of semi-infinite plane body in elastic mechanics, the theoretical calculation model of verticalhorizontalshear stress of floor coal rock is established, and it is concluded that the stress expression of any point in the impact of distributed force. By introducing the rock strength index I and generalized Hooke's law, it is concluded that the discrimination criterion of guide gas fissure zone and pressure relief desorption belt of underlying coal rock with upper protective layer mining. The pressure relief scope of protection with the mining of upper protective layer is determined. Theoretical analysis shows that: the "pressure relief desorption zone" of the underlying protected coal seam that the vertical distance to the protective layer is 40m lags behind 22.2m.Through field test, the results show that the obtained pressure relief scope of protection is 26.98m,and the theoretical analysis results are basically similar.

scholarly journals An Influence Study of Face Length Effect on Floor Stability under Water-Rock Coupling Action

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Baojie Fu ◽  
Bo Wang
Keyword(s):  
Rock Mass ◽  
Coal Seam ◽  
Mine Pressure ◽  
Length Effect ◽  
Pressure Relief ◽  
Limestone Aquifer ◽  
Study Results ◽  
Face Length ◽  
The Face ◽  
Floor Stability

The Taiyuan Formation limestone aquifer and Ordovician limestone aquifer are widely distributed in the coal seam floor of coal measures in North China; the water hazard safety problem of the stope floor under the influence of mining is very prominent. The risk of the water inrush from the coal seam floor is closely related to the degree of full exploitation, so it is necessary to study the stability of the stope floor under aquifer conditions, especially the influence of the working face length effect on floor stability. Through numerical simulation of water-rock coupling action, the mine pressure behaviors of the water-resisting floor under different face lengths were analyzed based on the measured formation permeability coefficient. The Fish program was used to adjust rocks entering the plastic failure state into a strain softening model to investigate the influence of the face length effect, the damage degree of the water-resisting floor, and the morphology and deformation bearing capacity of the failure zone. The results show the following: (1) the face length effect is one of the main influence factors of the failure mode and failure degree of surrounding rocks in the stope; (2) as the face length increases, the obvious pressure relief zone of surrounding rocks presents a staged change, and the obvious pressure relief zone at the seam roof and floor is in an obvious “reverse saddle shape”; (3) the closer to the seam floor, the more remarkable the rock softening characteristic because of the compaction action of gangues caving from the roof; and (4) the rock mass close to the seam floor undergoes local tensile failure, and the water-resisting floor near the coal wall at two sides mainly bears compaction-shear action, leading to compression-shear failure of the rock mass at the floor and formation of water-conducting fractures. The study results can provide a reference for taking precautionary measures of safety mining above a confined aquifer.

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