Time Series Effect on Surface Deformation above Goaf Area with Multiple-Seam Mining
Abstract
:1. Introduction
2. Engineering Background and Numerical Model Construction
2.1. Engineering Background
2.2. Numerical Model Building
3. Analysis of Mining Time Series Effect on Ground Deformation Law in Goaf Collapse Area of Multiple Coal Seams
3.1. Determination of Different Mining Sequence Models
3.2. Analysis of the Results of Mining Timing Effects on the Law of Ground Deformation
3.2.1. Deformation Contour Map Description
- (1)
- Analysis of monitoring results of vertical ground settlement
- (2)
- Analysis of monitoring results of horizontal surface deformation
3.2.2. Analysis of Deformation Law of Near-Surface Deep Cover Rock in Goaf
3.2.3. Analysis of “S” Curve of Surface Subsidence Deformation Index of Typical Section
3.2.4. Analysis of “S” Curve of Horizontal Deformation Index of Typical Section
3.2.5. D Effect Reduction and Optimization of Mining Order in Goaf Surface Subsidence Area
- (1)
- As the depth of the first coal seam increases, the surface collapse gradually slows down. If the first coal seam is deep enough or overlies a hard rock layer, the surface collapse deformation may not extend to the surface, and the surface may be less (or not) affected by the goaf. However, if the first coal seam is shallow and the mechanical properties of the overlying rock layer are poor, it may cause significant deformation of the surface, such that the degree of cell grid distortion is greater, and the peak of the surface collapse is higher.
- (2)
- When the first coal seam is the same, the degree of ground subsidence is determined using the secondary coal seam. After the first coal seam is mined, the overburden moves, and the mechanical properties are reduced. The secondary coal seam mining is disturbed again, and the deformation of the overburden is intensified. Therefore, if the secondary coal seam is closer to the surface, the degree of surface collapse is more evident.
- (3)
- The four types of mining sequences cause large differences in the surface subsidence deformation. Nevertheless, comprehensively considering the indicators that characterize the stability and suitability of the surface (horizontal deformation indicators (displacement and slope) and vertical deformation indicators (settlement, slope, and curvature)), order IV is determined to be the best order. Simultaneously, it is considered that the mining sequence IV takes “7 coal” as the first coal seam. This can avoid the long construction period for the roadway, lack of output, and low mechanical operation efficiency, and can ensure a high utilization rate of the coal seam in the mining area. However, actual coal mines often adopt mining sequence I, which is considered to be the most unfavorable for the control of surface stability. Therefore, it is recommended that mine engineers comprehensively consider the actual stratum and mining factors and formulate and compare a variety of mining schemes, so as to obtain the optimal mining order.
4. Conclusions
- (1)
- The center position of the surface deformation (vertical settlement and horizontal deformation) of the four groups of mining sequences is stable, but the deformation ranges and amounts are quite different; however, the settlement deformation is the main difference. Among them, the deformation of mining sequence I is the largest at 62.7 cm. Mining sequences 2 and 4 are basically the same, at only 22% of the value of mining sequence I.
- (2)
- An analysis of multiple indicators (inflection point, stagnation point, and slope) of the surface deformation curve shows that the greater the surface deformation, the more evident the curve unevenness and slope change; the greater the unevenness of the foundation stress, the more severe the damage to the surface structure, and the worse suitability for surface construction.
- (3)
- As the depth of the first coal seam increases, the surface settlement gradually slows down. If the first coal seam is deep enough or overlies a hard rock layer, the mined-out area will have little or no impact on the surface settlement and deformation. However, if the first coal seam is shallow and/or the mechanical properties of the overlying rock layer are poor, it may result in significant surface deformation.
- (4)
- When the first coal seam is the same, the ground subsidence is determined by the secondary coal seam. After the first coal seam is mined, the overburden moves, and the mechanical properties are reduced. The secondary coal seam mining disturbs the overburden again, which intensifies the deformation of the overburden, causing the degree of the ground subsidence to be more evident.
- (5)
- Based on comprehensively considering the indicators that characterize the stability and suitability of the ground, mining sequence IV is considered as the optimal solution. It is recommended to make a rational choice of sequence before multi-seam mining, or to replace a less-effective sequence with the optimal mining sequence in time. This can not only avoid or overcome the long construction period for the roadway, lack of output, and low mechanical operation efficiency, but can also ensure a high utilization rate of the coal seam in the mining area.
Author Contributions
Funding
Conflicts of Interest
References
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Dot | X Coordinate Corresponding Value | Y Coordinate Corresponding Value | ||
---|---|---|---|---|
Real Mine | Model Mine | Real Mine | Model Mine | |
A1 | 4,009,900 | 1700 | 20,559,700 | 1000 |
A2 | 4,010,500 | 1900 | 20,559,900 | 1600 |
A3 | 4,011,900 | 1900 | 20,559,900 | 3000 |
A4 | 4,011,500 | 1100 | 20,559,100 | 2600 |
A5 | 4,010,300 | 900 | 20,558,900 | 1400 |
A6 | 4,009,900 | 900 | 20,558,900 | 1000 |
Mining depth: +137–350 m |
Lithology | Natural Density/kg·m−3 | Elastic Modulus E/×10 GPa | Poisson’s Ratio μ | Internal Friction Angle φ/° | Cohesion C/MPa | Tensile Strength/MPa |
---|---|---|---|---|---|---|
Quaternary | 1850 | 1.85 × 10−3 | 0.327 | 15.1 | 12 × 10−3 | 0 |
Changlu Group | 2380 | 2.75 | 0.227 | 35.4 | 1.15 | 0.77 |
Fangzi Group | 2360 | 2.87 | 0.234 | 36.1 | 1.11 | 0.65 |
Stone Box Group | 2320 | 3.28 | 0.303 | 33.2 | 1.14 | 0.74 |
Shanxi Group 1 | 2370 | 3.89 | 0.313 | 38.7 | 1.03 | 1.12 |
Coal seam 2# | 1460 | 0.35 | 0.412 | 23.9 | 1.18 | 0.27 |
Shanxi Group 2 | 2371 | 4.01 | 0.314 | 38.7 | 1.04 | 1.12 |
Coal layer 4# | 1460 | 0.37 | 0.411 | 23.9 | 1.18 | 0.27 |
Coal Seam | Mining Sequence | |||
---|---|---|---|---|
Sequence I | Sequence II | Sequence III | Sequence IV | |
2# | ① | ⑤ | ② | ③ |
4# | ② | ④ | ④ | ⑤ |
7# | ③ | ③ | ① | ① |
15# | ④ | ② | ⑤ | ④ |
19# | ⑤ | ① | ③ | ② |
Mining Sequence | Horizontal Deformation in X Direction | Horizontal Deformation in Y Direction | ||||
---|---|---|---|---|---|---|
Maximum/cm | Occurrence Coordinates | Maximum/cm | Occurrence Coordinates | |||
X/401- | Y/2055- | X/401- | Y/2055- | |||
I | 31.6 | 0500 | 9400 | 17.7 | 0200 | 9200 |
II | 6.5 | 0500 | 9400 | 4.4 | 0200 | 9200 |
III | 12.8 | 0500 | 9400 | 7.6 | 0200 | 9200 |
IV | 6.9 | 0500 | 9400 | 4.6 | 0200 | 9200 |
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Shi, Z.; Wang, Q.; Wang, P.; He, D.; Bai, Y.; You, H. Time Series Effect on Surface Deformation above Goaf Area with Multiple-Seam Mining. Symmetry 2020, 12, 1428. https://doi.org/10.3390/sym12091428
Shi Z, Wang Q, Wang P, He D, Bai Y, You H. Time Series Effect on Surface Deformation above Goaf Area with Multiple-Seam Mining. Symmetry. 2020; 12(9):1428. https://doi.org/10.3390/sym12091428
Chicago/Turabian StyleShi, Zhenyue, Qingbiao Wang, Pu Wang, Donglin He, Yun Bai, and Hongyue You. 2020. "Time Series Effect on Surface Deformation above Goaf Area with Multiple-Seam Mining" Symmetry 12, no. 9: 1428. https://doi.org/10.3390/sym12091428