scholarly journals Research on Surface Failure Law of Working Faces in Large Mining Height and Shallow Buried Coal Seam

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Zhenhua Li ◽  
Yingkun Pang ◽  
Yongsheng Bao ◽  
Zhanyuan Ma
Keyword(s):  
Near Field ◽  
Mining Area ◽  
Surface Cracks ◽  
Large Space ◽  
Key Strata ◽  
Key Stratum ◽  
Surface Failure ◽  
Working Face ◽  
Large Mining Height ◽  
Mining Height

In the process of high-intensity and large-space mining in Shendong mining area, various surface cracks are generated on the surface, resulting in serious damage to the surface buildings and the local ecological environment. To study the influence of overlying rock movement on surface failure of near-field single key strata of near-shallow buried and large mining height working face, the relationship between overburden movement, strata pressure appearance, and surface failure at working face 52307 in Daliuta mining area was analyzed by field measurement and numerical simulation. The results show the following: (1) there is only one thick and hard key stratum in the overburden of large mining height and near-shallow buried working face. Under the condition of presplitting roof blasting, the first weighting step is still as high as 95 m, and the periodic breaking step of roof is 20–30 m. During the weighting, the working resistance of support is still close to the rated resistance. (2) The single key stratum plays an obvious role in controlling overburden movement. After the first weighting of the working face, a stepped subsidence crack appears on the surface within a short time, and the crack lags behind the working face for about 5 m. (3) During each periodic weighting process, the breaking and subsidence of key blocks are accompanied by surface cracks.

scholarly journals Research on Overburden Movement Characteristics of Large Mining Height Working Face in Shallow Buried Thin Bedrock

Energies ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 4208 ◽  
Author(s):  
Qingxiang Huang ◽  
Yanpeng He
Keyword(s):  
Physical Simulation ◽  
Mining Area ◽  
Engineering Problem ◽  
Dynamic Crack ◽  
Working Face ◽  
Time Space ◽  
Movement Distance ◽  
Large Mining Height ◽  
Thin Bedrock ◽  
Mining Height

The overburden movement of the large mining height working face of shallow buried thin bedrock (SBTB) is a complex engineering problem with “time-space-intension”, which is of great significance to realize efficient and safe mining in the northern Shaanxi mining area. Based on the research object of No. 22201 working face in Zhangjiamao Coal Mine, the roof structure characteristics of large mining height working face in SBTB are researched by field drilling measurement, laboratory test, physical and numerical simulation. The results show that: (1) Based on the measured data of the drillholes, it is concluded that under the mining conditions of SBTB with large mining height, the roof movement is ahead of the weighting of the working face, and the working resistance has a significant time effect. The advanced movement distance is about 20 m, which can be used as an early warning index of the weighting. The lag movement distance in the roof with horizon of 30 m is two periodic weighting intervals, which are about 26 m. (2) The first weighting interval of the working face is 32 m. The roof first break has obvious step sinking phenomenon, and the measured surface appears at a position 45 m away from the transport slot. It is statistically concluded that the periodic weighting interval is 9.5~16.5 m, the average weighting interval is 13 m, which is equivalent to the periodic dynamic crack spacing of the surface. (3) The results of field measurement and physical simulation show that the breaking angle of the roof of the No. 22201 large mining height is about 66°, and the periodic stepping distance of the T-junction suspension area is 6~8m. Along the strike of the working face, the roof breaking is mainly arc arched. The research results ensure the safe and green mining of shallow coal seam.

The Three-Dimensional Similar Simulation of Stress Regular Pattern of Roof of Large Mining Height

2014 ◽  
Vol 945-949 ◽  
pp. 1190-1195 ◽  
Author(s):  
Xiao Tao Zeng ◽  
Ning Wang ◽  
Cong Jiang ◽  
Yun Yi Zhang ◽  
Gang Chen
Keyword(s):  
Three Dimensional ◽  
Mining Area ◽  
In Situ Stress ◽  
Stimulation Test ◽  
Mine Pressure ◽  
Pressure Behavior ◽  
Working Face ◽  
Large Mining Height ◽  
Roadway Deformation ◽  
Mining Height

Based on the distribution of in-situ stress and the special conditions of the large mining height in one mining area, the author conducted the analogy stimulation test of the mine pressure behavior and the roadway deformation law. This research, mainly based on the geographical conditions of 1 to 2 coal seam of this mining area, stimulated the mine pressure behavior of the working face and the roadways, as the mining height is 5meters and 6meters. Through this analogy stimulation test, the mine pressure behavior of working face, in the mining process with large mining height, is analyzed and summarized.

scholarly journals Research on the Roof Advanced Breaking Position and Influences of Large Mining Height Working Face in Shallow Coal Seam

Energies ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1685
Author(s):  
Qingxiang Huang ◽  
Yanpeng He ◽  
Feng Li
Keyword(s):  
Coal Seam ◽  
Field Measurement ◽  
Physical Simulation ◽  
Main Roof ◽  
Key Strata ◽  
Working Face ◽  
Measurement Results ◽  
Large Mining Height ◽  
Shallow Coal Seam ◽  
Mining Height

The large mining height (LMH) in shallow coal seam has been widely applied in the Shenfu coalfield, China. The dynamic load is obvious, and the rib spalling is serious when the LMH working face concerns roof weighting. The advanced breaking position of the roof affects the strength of the ground pressure when the roof is broken. Firstly, based on a large number of actual measurements and physical simulation experiments, the rock formation in the fall zone, where the articulated structure cannot be articulated between the coal seam and the main roof, is called the equivalent immediate roof (EIR). When the mining height increases, the thickness of the EIR increases non-linearly. Next, based on the theory of “elastic foundation beam”, a mechanical model for the advanced breaking of the roof is established in shallow coal seam, and the calculation equation for the advanced breaking position of the roof is given; then, designed and carry out boreholes of the no. 22201 working face in the Zhangjiamao Coal Mine. The theoretical calculation of key strata results (5.6–6.9 m) are in the range of field measurement results (5–8 m). According to the field measurement results, the roof movement of the LMH working face is ahead of the roof weighting. Finally, we define the thickness of EIR and the mining height ratio as the immediate mining ratio ki, which affects the degree of filling of the goaf and determines the structural form of the main roof. When the ki is small, the goaf is fully filled; when the ki is large, the goaf is fully filled. Under the same conditions, different filling rate conditions will form different roof structures. Results of this research can be helpful to control roof weighting and provide early warning of possible safety problems related to the LMH working face in shallow coal seam.

scholarly journals Study on Fracture and Stress Evolution Characteristics of Ultra-Thick Hard Sandstone Roof in the Fully Mechanized Mining Face with Large Mining Height: A Case Study of Xiaojihan Coal Mine in Western China

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Feng Ju ◽  
Meng Xiao ◽  
Zequan He ◽  
Pai Ning ◽  
Peng Huang
Keyword(s):  
High Strength ◽  
Western China ◽  
Stress Evolution ◽  
Working Face ◽  
Mining Condition ◽  
Evolution Characteristics ◽  
Large Mining Height ◽  
Evolution Laws ◽  
Mining Face ◽  
Mining Height

Ultra-thick hard sandstone roofs present high thickness, poor delamination, and wide caving range. The strata pressure of the working face during actual mining increases, having a significant influence on the safe mining of the working face. Especially, in the mining areas of western China, the fully mechanized mining faces with high mining height and high-strength mining are more prominent. Understanding the fractures and stress evolution characteristics of the ultra-thick hard sandstone roof during actual mining is of high significance to control the dynamic pressure on the working face. In this paper, the typical ultra-thick hard sandstone roof of the Xiaojihan coal mine was taken as an example. The structural and chemical composition characteristics were analyzed. Besides, the fracture characteristics of ultra-thick hard roof during the working face mining were analyzed. Moreover, the fracture structure consistency was verified through physical simulation and a field measurement method. Finally, the stress evolution laws in the ultra-thick hard sandstone roof fracture were studied through numerical simulation. The findings demonstrated that (1) the ultra-thick hard sandstone roof was composed of inlaid coarse minerals, which had compact structure, while the Protodyakonov hardness reached up to 3.07; (2) under the high-strength mining condition of fully mechanized mining face with large mining height, the ultra-thick hard sandstone roof had the characteristics of brittle fracture, with a caving span of 12 m; (3) under the high-strength mining condition of fully mechanized mining face with large mining height, the ultra-thick hard sandstone roof followed the stress evolution laws that were more sensitive to the neighboring goaf. Therefore, it was necessary to reduce the fracture span or layering of ultra-thick hard sandstone roof through the manual intervention method adoption or increase either the strength of coal pillar or supporting body, to resist the impact generated during ultra-thick hard sandstone roof fracture.

scholarly journals Determination of Optimal Extrication Location of High Extraction Roadway of Large-Mining-Height Fully Mechanized Face

2018 ◽  
Vol 2018 ◽  
pp. 1-7
Author(s):  
Xue-bo Zhang ◽  
Ming Yang
Keyword(s):  
Gas Extraction ◽  
Horizontal Distance ◽  
High Position ◽  
Working Face ◽  
Extraction Site ◽  
Large Mining Height ◽  
Porosity And Permeability ◽  
Permeability Distribution ◽  
Mining Height

Determining the optimal extrication location of the high extraction roadway can improve the gas extrication effect of highly gassy mine and solve the problem of gas concentration overrun at the upper corner, which is of great significance to safety and efficient mine production. According to the actual situation of mine, the gas gushing amount in the goaf, pressure difference at both ends of the working face, the 3D porosity, and permeability distribution of the caving zone and fissure zone were obtained by field measurement and numerical calculation. Through theoretical calculation, the proper extraction site of a high-position alley was determined. On this basis, the optimal extraction site of a high-position alley was determined by numerical analysis of the gas extraction effect at different sites. The results show that as the perpendicular distance between high-position alley and goaf floor increases, the gas extraction amount increases first and then decreases. The concentration of extraction gas gradually increases, and the increasing trend is gradually diminished. With the increase of the horizontal distance between the air return way and the high-position alley, the gas extraction amount and gas extraction concentration increase first and then decrease. The optimal extraction site of a high-position alley should be 39 m vertically away from the goaf floor and 30 m horizontally away from the air return way.

scholarly journals Movement Law and Discriminant Method of Key Strata Breakage Based on Microseismic Monitoring

2019 ◽  
Vol 2019 ◽  
pp. 1-19 ◽  
Author(s):  
Yang Li ◽  
Tianhong Yang ◽  
Weidong Song ◽  
Ling Yu
Keyword(s):  
High Intensity ◽  
Microseismic Monitoring ◽  
Geological Structure ◽  
Western China ◽  
Dynamic Monitoring ◽  
Ecological Environment ◽  
Environmental Damage ◽  
Key Strata ◽  
Key Stratum ◽  
Working Face

Because of the unique natural geography, geological structure, and ecological environment, there are serious geological disasters and environmental damage caused by the high-intensity mining in Western China. It seriously restricts the development of coal resources and the protection of ecological environment. In order to fully capture the law of key stratum breakage with high-intensity mining, the IMS microseismic system was introduced into Xiaojihan coal mine which is a typical high-intensity mining mine in Western China, and the whole process dynamic monitoring was carried out. The process of key stratum breakage was analysed by MS data, which were in agreement with the pressure analysis results of the hydraulic support of the working face. The results showed that there were the obvious forewarning characteristics in microseismic event number, energy release, energy index, Schmidt number, coefficient of seismic response, and b value when the key stratum was breaking. Then, a method to discriminate the breakage of key stratum was proposed by using the forewarning characteristics, which could provide the guidance for prevention and control of geological hazards in the working face with high-intensity mining.

scholarly journals Mining-Induced Stress Control by Advanced Hydraulic Fracking under a Thick Hard Roof for Top Coal Caving Method: A Case Study in the Shendong Mining Area, China

Minerals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1405
Author(s):  
Kaige Zheng ◽  
Yu Liu ◽  
Tong Zhang ◽  
Jingzhong Zhu
Keyword(s):  
Stress Transfer ◽  
Mining Area ◽  
Fracture Networks ◽  
Horizontal Fracture ◽  
Hard Roof ◽  
Working Face ◽  
Huge Impact ◽  
Mining Pressure ◽  
Impact Kinetic Energy ◽  
Mining Height

Fully mechanized top-coal caving mining with high mining height, hard roofs and strong mining pressure are popular in the Shendong mining area, China. The occurrence of dynamic disasters, such as rock burst, coal and gas outburst, mine earthquakes and goaf hurricanes during the coal exploitation process under hard roof conditions, pose a threat to the safe production of mines. In this study, the characteristics of overburden fracture in fully mechanized top-coal caving with a hard roof and high mining height are studied, and the technology of advanced weakening by hard roof staged fracturing was proposed. The results show that the hard roof strata collapse in the form of large “cantilever beams”, and it is easy to release huge impact kinetic energy, forming impact disasters. After the implementation of advanced hydraulic fracturing, the periodic weighting length decreases by 32.16%, and the length of overhang is reasonably and effectively controlled. Ellipsoidal fracture networks in the mining direction of the vertical working face, horizontal fracture networks perpendicular to the direction of the working face, and near-linear fracture planes dominated by vertical fractures were observed, with the accumulated energy greatly reduced. The effectiveness of innovation technology is validated, and stress transfer, dissipation and dynamic roof disasters were effectively controlled.

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