Study on Mining Pressure Control of Deep Coal Seam —— 1 Based on Artificial Fault Technology

: Based on the pressure transfer principle and stress distribution characteristics around a 10 fault, introducing artificial fault technology to control the propagation of abutment pressure, and a 11 mechanical model of abutment pressure under the influence of artificial fault was established. This 12 new mechanical model can well fit the distribution law of mining stress after roof cutting. The 13 pressure transfer mechanism of prefabrication support of rock blasting was analyzed, and the 14 transfer trend of pressure and the mining stress of rock top was determined. It is of great 15 significance to guide the implementation of the pressure relief work at the top of the stope. The 16 study shows that the total energy of the system is conserved, the integrity of rock layer is destroyed 17 by blasting, and the deformation and damage of pressure relief zone absorb a large amount of 18 energy. Thus, the accumulated strain energy of abutment pressure region is released, and the 19 influencing range of abutment pressure is reduced. As the horizontal distance from the cutting 20 surface is farther away from the working surface, the smaller the stress difference on both sides of 21 the cutting top, the less obvious the blocking effect of mining pressure. When the cutting point is 22 closer to the working surface, the higher the peak value of abutment pressure due to the 23 superposition of peripheral stress concentration caused by the cutting and peak of abutment pressure 24 caused by mining. Then, the numerical simulation analysis was carried out, the results show that the 25 technology of forming artificial fault by cutting the top can cut off the influence range of the mining 26 pressure. It can effectively control the deformation of dynamic pressure tunnl. Finally, a practice of 27 rock blasting pressure relief engineering was carried out, and the influencing range of abutment 28 pressure of working face before blasting pressure reduction was reduced by 1/3 compared with that 29 before the pressure relief. 30 pressure and the deformation of the tunnel before and after the pressure relief were analyzed by numerical simulation. The results show that after the pressure relief, the peak stress area in front of the coal wall disappears and transfers to the area near the pressure relief area, and the stress concentration appears on both sides of the blasting pressure relief area. After blasting and pressure relief, the influence range of the advance bearing stress


Introduction
out on site, and the remaining tunnel was cut due to the pressure transmission mechanism, so that   The large deformation of tunnel has always been a big problem in mine support work. At 89 present, the main treatment methods for tunnel include the enhanced surrounding rock support 90 strength method, tunnel deep hole relief pressure tank method, tunnel surrounding rock blasting 91 pressure relief. These methods do not cut off the propagation path of mining load from the root 92 source, nor change the stress distribution law at the far end. Therefore, this study focuses on the The key to the large deformation problem of tunnel in stope is to find the root cause of 114 disturbance of tunnel. Therefore, the formulation of a governing method is the key to analyze the 115 basis of stress distribution law of stope. To control the deformation of tunnel from the root source,  After rock blasting, the integrity of rock stratum is destroyed, and a blasting cavity and fracture 123 zone are formed in the rock stratum. The effect is similar to that of nonfalling fault. Because of the 124 fault rupture zone, the coal rock mass is relatively broken with the effect of stress relief and fracture.

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The stress unloading at the belt causes the stress distribution of leading working face to shift, 126 thereby acting as a pressure relief to reduce the influencing range of stress. The pressure transfer 127 mechanism can be analyzed using energy theory. Because the total energy of rock mass is 128 composed of rock mass fracture energy and strain energy is accumulated in the rock body, 129 according to the law of conservation of power: where f is the total energy of system; Wc is the strain energy reaccumulated by the rock mass after 132 the coal seam is opened; Wd is the strain energy absorbed by various forms such as deformation and 133 failure of rock mass.

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Eq. (1) shows that the abutment pressure at each point of rock layer can be reduced by 135 reducing the accumulated strain energy Wc at each point. Because the total energy of the system is 136 constant, to lower the Wc value, the Wd value should be increased. Increasing Wd means increasing 137 the deformation and damage of rock mass within a certain range. The principle of blasting pressure 138 relief is to form some broken and cracked areas in the overburden species, so that the deformation 139 absorbs a large amount of energy and increases the Wd. 140 At the same time, after rock blasting, the integrity of rock stratum is destroyed, and a blasting 141 cavity and fracture zone are formed in the rock stratum. The effect is similar to artificial fault.

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Therefore, the blasting can be analyzed using the prestressed stress distribution law under the effect 143 of faults. The distribution law of abutment pressure after the topping was determined, as shown in    The pressure functions can be expressed as follows:

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Section ab: Section bc: Section cd: After superimposing the vertical stresses of each load using the principle of stress 196 superposition, The vertical stress at any point produced by the whole load can be obtained as 197 follows: Because of the rupture of rock mass after the blasting pressure, the elastic half-plane theory   2) The medium in pressure relief belt is a completely elastic material. 3) The width of pressure relief belt is negligible compared to a large range of rock mass.

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The stress of four regions can be solved by equation (9) in combination with Fig. 6. 233 The distributed stress in the c-f zone (Zone 1) of blasting pressure relief zone can be calculated as follows: Blasting pressure relief affects the distribution stress calculation in Zone 2 as follows: Blasting pressure relief affects the distribution stress calculation in Zone 3 as follows: Blasting pressure relief affects the distribution stress calculation in Zone 4 as follows: In summary, an analytical formula for the distribution after the demolition of rock blasting can 243 be expressed as follows:   (14).

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The magnitude of abutment pressure formed by the overburden load in the coal seam can be 260 obtained, and the abutment pressure curve can be obtained after fitting, as shown in Fig. 8.    In the simulation process, setting of weakening parameters of the blasting zone with reference 309 to existing research, the weakening parameters of the blasting zone are: blasting cavity width is 310 0.2m; the blasting cavity is set as the center, and an area with a radius of 2 meters is the blasting 311 weakening area (Table 3).  It can be seen from Fig.11. that, compared with the scheme before pressure relief, the peak  It can be seen from Fig.12. that before the pressure relief, the deformation of the tunnel is large, 359 the roof sinks 32.7cm, the floor heave is 55.8cm, the roof and floor displacement reaches 88.4cm; 360 the deformation of the left side is 50.4cm, the deformation of the right side is 53.8cm, and the 361 displacement of the two sides reaches 104.2cm. After blasting, the deformation of surrounding rock 362 in the tunnel was well controlled. The roof subsidence was 10cm, the floor heave was 19.7cm, the 363 roof and floor displacement was 29.7cm, 66.4% less than before; the left side deformation was 364 13.5cm, the right side deformation was 17.9cm, the two sides displacement was 31.4cm, 69.8% less 365 than before. Therefore, the deformation of the tunnel in front of the work was effectively controlled 366 by pressure relief.   The method of ultrasonic detection is used to monitor the artificial fault formed by blasting, After normalizing the original amplitude data, the artificial fault formed by blasting is represented by dark bright spots, as shown in Fig. 18. The width of the artificial fault is about 2.5m, 426 the middle part is dark red, and the color on both sides gradually becomes lighter. This is because 427 the middle part of the blasting area, the rock damage is more serious, the color is dark red. The two 428 sides are fracture areas, where the rock damage is very small, so the color becomes lighter.    Fig.19 (b) shows the pressure change of Station 2. After the stress monitoring system was 462 arranged for 10 days, the reading of pressure gauge started to increase, indicating that the inner wall 463 of borehole is in full contact with the pressure gauge. At the same time, the pressure on pressure gauge slightly increased. At this time, the working surface is 80 m away from Station 2. After that, 465 the pressure curve continued to rise, and at 21 days after loading the table (the working surface is 30 466 m away from Station 2), the pressure increased significantly, indicating that the stress peak occurred 467 at this time. Because the working face is stopped at a distance of 25 m from Station 2, Station 2 468 failed to measure the overall stress of abutment pressure after blasting. However, according to the 469 above analysis, the effect of abutment pressure after blasting is 80 m. blasting, and carried out engineering practice. The following conclusions can be drawn:

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(1) Using the theory of energy conservation to analyze the principle of pressure transfer after 476 cutting the top of rock, it was found that the total energy of system is constant, composed of rock 477 energy and the accumulated strain energy. The blasting cut causes the fracture zone to deform and 478 destroy a large amount of energy. The accumulated strain energy in the abutment pressure region is 479 released, which in turn reduces the influencing range of abutment pressure.

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(2) Based on the pressure transfer principle and stress distribution characteristics around the 481 fault zone, and introducing the coefficient of stress change K, k and k', a new pressure transfer 482 mechanical model was constructed after blasting and cutting is. The stress mechanism of abutment 483 pressure was analyzed, and an analytical formula was deduced for the mining stress after the crest 484 of rock formation. The results show that the smaller the distance between the cut-off and top of 485 cut-off, the smaller the stress difference on both sides of cut-off within a certain range, but the effect 486 of stop pressure on the working face is less obvious. When the cutting point is closer to the working 487 surface, the higher peak value of abutment pressure is mainly due to the superposition of peripheral 488 stress concentration caused by the cutting and the peak of abutment pressure caused by the mining.

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(3) The distribution of the abutment pressure pressure and the deformation of the tunnel before 490 and after the pressure relief were analyzed by numerical simulation. The results show that after the 491 pressure relief, the peak stress area in front of the coal wall disappears and transfers to the area near 492 the pressure relief area, and the stress concentration appears on both sides of the blasting pressure 493 relief area. After blasting and pressure relief, the influence range of the advance bearing stress 494 decreased obviously, and the stress concentration around the tunnel was not obvious. The 495 displacement of roof and floor is 29.7cm, 66.4% less than that before pressure relief, and the 496 displacement of two sides is 31.4cm, 69.8% less than that before pressure relief. It can be seen that 497 blasting pressure relief can effectively control the deformation of the tunnel in front of the work.

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(4) The results of ultrasonic detection show that the artificial fault zone was well formed, the 499 width of the fault zone was about 2.5m, the damage in the middle was serious, and the damage on 500 both sides is reduced. The results of coal stress test show that the influencing range of abutment 501 pressure of working face before blasting pressure relief is 129.5 m. The influencing range of 502 abutment pressure after blasting pressure relief is 80 m. This is 49.5 m shorter than the pressure 503 before the pressure relief, which is reduced by nearly 1/3, shortened from the previous 150 m to 90 504 m. Therefore, rock blasting pressure relief can effectively shorten the influencing range of abutment 505 pressure of working face. The application of blasting pressure relief tunnel technology has great 506 significance to reduce the coal pillar size of tunnel and improve the mine recovery rate and dynamic 507 pressure tunnel deformation control.  516 The authors declare that they have no conflict of interest.

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The manuscript data used to support the findings of this study are available from the corresponding 519 author upon request.