Surrounding rock stress regulation and control method based on near-far field pressure relief

Abstract

The invention provides a surrounding rock stress regulation and control method based on near-far field pressure relief. Aiming at the problem of surrounding rock instability caused by high ground stress and mining disturbance of a deep roadway, a grading response technical system is provided. Near-field regulation and control are achieved through high-strength active and passive composite supports (anchor net shotcreting and a steel tube concrete support), plastic zone form monitoring and differential pressure relief: based on dynamic monitoring of the radius of a surrounding rock plastic zone, a mining influence index K is calculated, and when 1 < = Klt; 2, a borehole pressure relief and wall back yielding layer cooperative control technology is adopted, and when a plastic zone distortion part does not change to a butterfly-shaped plastic zone, the plastic zone distortion part is induced to uniformly expand to a circle; when K is larger than or equal to 2, a far-field air cannon presplitting roof cutting technology is combined, the roof cutting technology forms a full-section crack along a weak surface of a rock body through a high-pressure gas sealing cavity, a mining-induced stress transmission path is cut off in advance, traditional static design limitation is broken through, gas presplitting is adopted for replacing blasting / hydraulic roof cutting, and zero pollution and accurate and controllable energy in the construction process are achieved; and the top cutting depth is dynamically optimized along with the K value.

Description

Technical Field

[0001] The present invention belongs to the field of underground engineering support, and specifically relates to a method for regulating surrounding rock stress based on near and far-field pressure relief. Background Art

[0002] With the extension of coal resource mining to deep areas, deep roadway faces the superimposed effects of high ground stress, strong mining disturbance, and complex geological structures, resulting in increasingly prominent problems such as large deformation of surrounding rock and stress concentration. Although traditional support technologies (such as bolt-net-shotcrete, U-shaped steel supports, etc.) can provide passive support, it is difficult to effectively regulate the stress redistribution of deep surrounding rock. Especially under the influence of mining, the plastic zone of roadway surrounding rock is prone to asymmetric expansion, triggering deformation disasters such as floor heave and rib heave, seriously threatening the safe and efficient production of mines.

[0003] Existing stress regulation technologies are mainly divided into two categories: near-field pressure relief (such as borehole pressure relief, behind-wall pressure relief) and far-field pressure relief (such as roof cutting pressure relief). Near-field pressure relief releases the stress of surrounding rock through local boreholes or reserved deformation space, but single near-field pressure relief has limited effect on roadways affected by mining disturbance and is difficult to control the malignant expansion of the plastic zone. Although far-field pressure relief technologies (such as blasting roof cutting, hydraulic fracturing) can cut off the stress transfer of the roof, they have significant defects: the energy of blasting roof cutting is uncontrollable, easily causing secondary damage to the surrounding rock, and the construction safety is low; hydraulic fracturing relies on a large amount of water resources, with low fracturing efficiency and high equipment cost; the problem of lagging construction is prominent. Most existing roof cutting technologies are implemented after the working face is mined, and it is impossible to achieve advance pressure relief, resulting in the difficulty of eliminating the superposition effect of mining and excavation disturbances.

[0004] In addition, existing technologies lack a quantitative judgment basis for the dynamic response characteristics of roadways, especially the research on the hierarchical response mechanism of the distance between the roadway and the mining face and the degree of mining influence is insufficient. Most methods are designed with fixed parameters or empirical values, and fail to flexibly adjust the pressure relief strategy according to the shape of the plastic zone of the surrounding rock (such as butterfly shape, circular shape) and the intensity of mining disturbance, resulting in poor adaptability of the support scheme and difficulty in balancing safety and economy. For example, Patent CN110259444A (Deep roadway composite pressure relief support system and method) proposes a stress regulation method combining near and far fields of bolt support (near field) and blasting roof cutting (far field), which cuts off the stress transfer path of the roof through blasting. However, the blasting energy is uncontrollable, easily causing secondary damage to the surrounding rock; and fixed blasting parameters are used, without dynamically adjusting the roof cutting depth according to the distance between the roadway and the mining face or the mining influence index, making it difficult to adapt to complex mining conditions. Summary of the Invention

[0005] In order to solve the technical problems existing in the prior art, the present invention proposes a method for regulating surrounding rock stress based on near and far-field pressure relief. The combination of near and far-field stress regulation technologies can solve the support problems of long-term large-deformation roadways under high stress conditions and frequently affected by dynamic pressure disturbances.

[0006] To achieve the above object, the present invention proposes a surrounding rock stress regulation method based on near and far field pressure relief, as follows:

[0007] Obtain the mining influence index, and the mining influence index wherein, R is the radius of the maximum plastic zone, and r is the average radius of the plastic zone;

[0008] When 1 ≤ K < 2, the surrounding rock pressure is adjusted by means of borehole pressure relief and behind-the-wall pressure relief;

[0009] When K ≥ 2, while adjusting the surrounding rock pressure by means of borehole pressure relief and behind-the-wall pressure relief, a pre-buried high-pressure air cavity is used to seal high-pressure gas into the borehole to form a high-pressure gas sealed cavity. As the working face is mined, the high-pressure gas expands along the weak points of the surrounding rock to form a full-section crack, realizing roof cutting pressure relief; and as the value of K increases, the roof cutting depth is increased.

[0010] As a further technical solution, a roof cutting pressure relief device using air cannon pre-splitting is used to seal high-pressure gas into the borehole to form a high-pressure gas sealed cavity, and expand along the weak points of the surrounding rock to form a full-section crack, realizing roof cutting pressure relief.

[0011] As a further technical solution, the roof cutting pressure relief device using air cannon pre-splitting includes a movable chassis, on which a lifting device and a gas storage tank are arranged. The gas storage tank is rotatably connected to the chassis, and the lifting device drives the gas storage tank to tilt upward relative to the chassis; a gas guide pipe is installed inside the gas storage tank, one end of the gas guide pipe is connected to a piston, the piston is controlled by a control handle, the other end of the gas guide pipe extends outside the gas storage tank and can be connected to a connecting conduit, the connecting conduit is connected to a detachable sealed jet head, and a fixing module and an expansion sealing bag are arranged on the detachable sealed jet head; an air inlet and a pressure gauge are also arranged on the gas storage tank.

[0012] As a further technical solution, connect the detachable sealed jet head to the connecting conduit, extend the detachable sealed jet head into the borehole, and successively increase the number of connecting conduits until the depth to be fractured is reached; adjust the lifting device of the air cannon roof cutting and pressure relief machine so that the air duct and the connecting conduit are on the same central axis, and connect the air duct to the connecting conduit; rotate the control handle to make the piston seal the end of the air duct, completely isolating the air inside the gas storage tank from the external air; connect the air inlet to the inflator, compress the external air and enter it into the gas storage tank, continuously compressing to increase the pressure inside the gas storage tank. When the air pressure in the gas storage tank exceeds the tensile strength limit value of the rock, close the air inlet and stop inflating; the outer surface of the expansion seal bag expands and fits completely with the borehole to form a closed space. Rotate the control handle to disconnect the piston from the air duct, and the air in the gas storage tank and the air duct is connected. The air in the gas storage tank quickly sprays out from the detachable sealed jet head through the air duct to pressurize the air in the borehole; when the high-pressure gas quickly passes through the detachable sealed jet head, the fixed module located inside the detachable sealed jet head is quickly ejected by the high-pressure gas and fixed to the surrounding rock of the borehole; then repeat this process until the last time when pressurizing the borehole, stop pressurizing when the pressure value on the pressure gauge reaches the maximum tensile strength of the rock. Finally, disconnect the detachable sealed jet head from the connecting conduit to form a high-pressure gas closed cavity in the borehole.

[0013] As a further technical solution, perform high-pressure gas sealing on each borehole to form a coherent advanced high-pressure gas fracturing system. As the construction of the coal seam in the lower section working face progresses, the top rock layer is disturbed and its strength decreases. The high-pressure gas extends by tensile fracture along the weakest part of the rock layer. The fractured boreholes form rock fractures extending in all directions, and the continuous borehole fractures intersect to form a full-span section of the roof cutting and pressure relief area. The top rock layer in the goaf collapses, realizing roof cutting and pressure relief in front of the working face.

[0014] As a further technical solution, the fixed modules are arranged in a circle along the circumferential direction of the detachable sealed jet head. Each fixed module includes a resistance-increasing plate, a one-way sliding module, and a spring. The resistance-increasing plate is arranged along the radial direction of the detachable sealed jet head and can extend outside the detachable sealed jet head under the action of an external force; the resistance-increasing plate cooperates with the one-way sliding module, and the one-way sliding module is driven by the spring; the spring is fixed on the inner wall of the detachable sealed jet head.

[0015] As a further technical solution, the detachable sealed jet head and the connecting conduit are connected by an automatically releasable buckle.

[0016] As a further technical solution, the connecting conduit and the detachable sealed jet head are fitted through a card slot, and a sliding module is arranged at the connection position of the connecting conduit and the detachable sealed jet head. The sliding module is arranged along the radial direction of the detachable sealed jet head.

[0017] As a further technical solution, the method for adjusting the surrounding rock pressure by means of borehole pressure relief and behind-wall pressure relief is as follows:

[0018] Peepholes are arranged at the peripheral position of the roadway. Through the peepholes, the deformation law of the surrounding rock of the roadway is analyzed by peeping, and the development law of the fracture zone of the roadway surrounding rock is regularly analyzed by peeping to accurately determine the shape of the fracture zone and the main deformation zone of the surrounding rock, and accurate pressure relief is carried out for different-shaped fracture zones.

[0019] As a further technical solution, for circular and elliptical fracture zones, it is recommended to mainly carry out peripheral pressure relief for the roadway. The peripheral pressure relief is achieved by controlling the thickness of the pressure relief layer. For circular fracture zones, an equal-thickness pressure relief space is adopted, and for elliptical fracture zones, the pressure relief space at the two sides is small and the pressure relief space at the roof and floor is large; for butterfly-shaped fracture zones or other fracture zones, borehole pressure relief is carried out at the roof, floor and two sides. The starting end of the borehole pressure relief area must be set outside the outer boundary of the surrounding rock fracture zone, and the end of the pressure relief area is on the concentric circle with the same radius as the outer boundary of the butterfly.

[0020] As a further technical solution, during the construction of the roadway, bolt-net-shotcrete support is carried out for the roadway, a yielding layer with a certain space is reserved, and a compression material is used to fill the yielding layer; and the yielding layer is not filled at the position where the peephole of the roadway is located, which serves as the peephole, and the invert arch is filled at the bottom of the roadway.

[0021] As a further technical solution, the size of the pressure relief space is adjusted according to the shape of the fracture zone obtained from the peephole. For butterfly-shaped and circular fracture zones, an equal-thickness pressure relief space is adopted, and for elliptical fracture zones, the pressure relief space at the two sides is small and the pressure relief space at the roof is large.

[0022] The beneficial effects of the present invention are as follows:

[0023] The present invention selects different pressure relief methods according to the mining influence index, that is, establishes a scientific decision-making basis to achieve: grading the selection of pressure relief strategies according to the shape of the roadway plastic zone and the intensity of mining disturbance; blocking the transmission path of mining stress through advanced roof cutting pressure relief; dynamically optimizing the pressure relief parameters by combining real-time monitoring data. Moreover, the roof cutting pressure relief technology of the present invention selects the principle of pre-burying a high-pressure air cavity in an air cannon for roof cutting pressure relief. By pressurizing the air, the high-pressure gas is compressed in advance inside the drill hole. As the working face is mined, the high-pressure gas continuously expands along the rock cracks, slowly splitting the rock, reducing the construction cost. The construction process is simple, does not cause pollution to the roadway environment and waste of resources, can adapt to various construction environments, and has a wide application range. Compared with the existing technology, this technology realizes the roof cutting pressure relief in front of the working face. The construction method will not be adversely affected by mining disturbances, and fully utilizes the characteristics of mining disturbances on the rock properties, realizing the self-initiated roof cutting pressure relief after the construction is completed, greatly improving the construction efficiency; realizes the whole-process detection of roof cutting pressure relief, avoids the influence of excessive construction on roadway support, and ensures the safety of the construction process. Description of the Drawings

[0024] Figure 1 Overall support and construction effect diagram;

[0025] Figure 2 Diagram of malignant expansion of plastic zone without induced pressure relief distortion;

[0026] Figure 3 Diagram of benign expansion of artificially induced distorted plastic zone;

[0027] Figure 4 Plan view of air cannon pre-splitting roof cutting pressure relief equipment;

[0028] Figure 5 Sectional view of detachable sealed jet head;

[0029] Figure 6 Schematic diagram of expansion seal bag;

[0030] Figure 7 Sectional connection view of detachable sealed jet head;

[0031] Figure 8 Sectional view of detachable sealed jet head and connecting conduit;

[0032] Figure 9 Schematic diagram of construction plan for regional stress adjustment technology;

[0033] Figure 10 Effect diagram of regional stress adjustment technology;

[0034] In the figure: 1 - peephole, 2 - peephole drilling, 3 - concrete-filled steel tube support, 4 - yielding layer, 5 - bolt, 6 - gangue bag filler, 7 - inverted arch filling, 8 - artificial induction direction of surrounding rock plastic zone, 9 - cavity formation at the end of pressure relief area, 10 - detachable sealed jet head, 11 - connecting conduit, 12 - air duct, 13 - gas storage tank, 14 - air inlet, 15 - piston, 16 - control handle, 17 - pressure gauge, 18 - chassis, 19 - lifting device, 20 - rotating shaft, 21 - fixed module, 22 - expansion seal bag, 23 - drilling hole, 24 - immediate roof, 25 - main roof, 26 - working face coal seam, 27 - reserved narrow coal pillar, 28 - gob-side entry, 29 - air cannon pre-splitting pressure relief equipment, 30 - gob-side roof cutting pressure relief, 31 - one-way sliding module, 32 - spring, 33 - resistance increasing plate, 34 - sliding module, 35 - spring knob, 36 - convex clamping groove. Detailed implementation manners

[0035] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0036] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the present invention clearly states otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof;

[0037] A surrounding rock stress control method based on near and far field pressure relief proposed in this embodiment has an overall scheme of a stress control technology that combines near field and far field in a complementary manner. This method is a stress control technology that combines near field and far field, aiming to solve the problems of surrounding rock failure and roadway deformation caused by high in-situ stress and strong mining influence in deep roadways; near field stress control mainly adopts measures such as high-strength active and passive composite support, borehole pressure relief, and backfill pressure relief to reduce surrounding rock stress concentration and the degree of roadway deformation; far field stress control adopts a new air cannon pre-splitting roof cutting pressure relief method to form full-section cracks with high-pressure gas to achieve roof cutting pressure relief. This method can be flexibly adjusted according to the distance between the roadway and the mining face and the degree of mining influence, can significantly improve the safety and stability of the roadway, and reduce construction costs and environmental pollution.

[0038] The specific plan for near-field stress control is: based on high-strength active and passive composite support, peepholes are set at specific locations around the tunnel, and the deformation law of the surrounding rock around the tunnel is analyzed through drilling observation. The shape of the fracture zone and the main deformation area of ​​the surrounding rock are accurately determined, and drilling unloading and behind-the-wall pressure relief are carried out according to different forms of fracture zones and surrounding rock deformation.

[0039] The far-field stress control scheme is: the method of pre-splitting and top cutting to relieve pressure in the empty area, which compresses the gas, sprays the high-pressure gas into the borehole through the pressure difference, and seals it. The high-pressure gas expands along the internal rock cracks, and multiple boreholes form full-section cracks to achieve top cutting and pressure relief.

[0040] Specifically, if the tunnel is far from the mining face and the mining impact is small, the purpose is to reduce the stress concentration in the tunnel and reduce the vicious expansion of the tunnel plastic zone, such as reducing the transmission of high vertical stress in the deep surrounding rock and high horizontal structural stress in the fault, so as to reduce the deformation of the surrounding rock and stress concentration, etc. Therefore, the near-field stress control scheme is given priority in the tunnel;

[0041] When the tunnel is close to the mining face and is subject to frequent dynamic pressure disturbances, in order to cut off the tunnel roof to reduce dynamic pressure disturbances, on the basis of the near-field stress control scheme, a far-field stress control scheme based on top-cutting and pressure relief by air cannon pre-cracking of the roof of the coal mine goaf should be combined. At this time, the top-cutting depth in the far-field stress control scheme can be increased to the direct roof 24 above the tunnel to cut off mining disturbances.

[0042] Specifically, the surrounding rock stress control method based on near-field and far-field pressure relief proposed in the present invention is as follows:

[0043] Get the mining impact index, the mining impact index Among them, R is the maximum plastic zone radius, r is the average radius of the plastic zone;

[0044] When 1≤K<2, the surrounding rock pressure is adjusted by means of drilling pressure relief and back-wall pressure relief;

[0045] When 2≤K, the surrounding rock pressure is adjusted by drilling pressure relief and behind-the-wall pressure relief. At the same time, the high-pressure gas is sealed into the borehole by pre-buried high-pressure air cavity to form a high-pressure gas sealing cavity. As the working face is mined, the high-pressure gas expands along the weak points of the surrounding rock to form full-section cracks, thereby achieving top cutting pressure relief. And as the K value increases, the top cutting depth increases.

[0046] In actual engineering, Figure 1 The plastic zone radius is monitored in the 8 peepholes shown in the figure. The maximum plastic zone radius is R and the average plastic zone radius is r based on the peep results obtained in the peepholes.

[0047] Furthermore, the near-field stress control method based on borehole pressure relief and back-wall pressure relief proposed in this embodiment is:

[0048] After the tunnel is excavated, in order to solve the problems of high stress concentration in the surrounding rock and vicious expansion of the plastic zone of the surrounding rock, this embodiment proposes a near-field stress control method based on borehole pressure relief and wall pressure relief. First, according to the shape of the surrounding rock plastic zone obtained by the peeping result, targeted borehole pressure relief is carried out to induce uniform expansion of the surrounding rock plastic zone (circular plastic zone). Taking the plastic zone peeping result as an example of a butterfly-shaped plastic zone, the specific method of borehole pressure relief is as follows: the beginning of the borehole pressure relief zone (i.e., the hole-making zone) must be set at the outer boundary of the surrounding rock fracture zone, and the end of the pressure relief zone and the outer boundary of the butterfly are on concentric circles with equal radius, so that the shape of the fracture zone develops toward a circle; secondly, according to the deformation of the tunnel, targeted wall pressure relief is carried out. Wall pressure relief adapts to the natural deformation of the surrounding rock by designing a reserved deformation space, actively induces the deformation of the surrounding rock within a controllable range, and implements a purposeful pressure relief operation. Thereby minimizing the adverse effects of deformation on the tunnel structure and reducing, and reducing the deformation acting on the support structure. For tunnels that require long-term maintenance, the near-field stress control method that combines drilling pressure relief with back-wall pressure relief can enable long-term control of tunnel deformation.

[0049] Furthermore, the present embodiment proposes a far-field stress control method based on air cannon top plate pre-cracking: by sealing high-pressure gas into the borehole to form a high-pressure gas sealing chamber, the high-pressure gas expands along the weak points of the surrounding rock, causing the rock cracks to extend, and multiple pressure relief holes are connected to form full-section cracks, thereby achieving top cutting and pressure relief.

[0050] The present invention will be further described below in conjunction with the accompanying drawings:

[0051] 1. Construction method of near-field stress regulation scheme based on drilling pressure relief and back-wall pressure relief:

[0052] First, steel tube concrete support 3 and anchor rod 5 are used for anchor mesh spraying support, and a certain space of pressure relief layer 4 is reserved as the pressure relief space behind the wall (such as Figure 1 As shown), the pressure layer 4 is filled with a material with good compressibility. In this embodiment, a gangue bag filler 6 is used; a specific position of the tunnel (such as Figure 1 The positions corresponding to the 8 peep holes 2 shown in the figure) are not filled, the bottom is filled with an anti-bottom arch 7, and 8 peep holes 2 as shown in the figure are set at specific positions (such as Figure 1 As shown), a peephole 1 is formed, and the aperture of the peephole 1 is greater than or equal to 40 mm. The size of the pressure relief space behind the wall is adjusted according to the deformation of the surrounding rock. If the surrounding rock around the tunnel is greatly deformed, an equal thickness pressure relief space is used.

[0053] If the surrounding rock of the roadway roof, floor and two sides deforms greatly, the pressure relief space behind the two side walls is small, and the pressure relief space behind the roof is large. According to the shape of the plastic zone after borehole peephole, determine the borehole position and borehole length to induce the benign expansion of the surrounding rock plastic zone (circular plastic zone) to achieve the purpose of controlling the stress concentration and large deformation of the surrounding rock; specifically, for circular and elliptical fracture zones, it is recommended to mainly relieve the pressure around the roadway, and the surrounding pressure relief is achieved by controlling the thickness of the pressure relief layer. For circular fracture zones, an equal-thickness pressure relief space is adopted. For elliptical fracture zones, the pressure relief space on the two sides is small, and the roof and floor are large; for butterfly-shaped fracture zones or other fracture zones, boreholes are drilled for pressure relief on the roof, floor and two sides. The starting end of the borehole pressure relief zone must be set outside the outer boundary of the surrounding rock fracture zone, and the end of the pressure relief zone is on the concentric circle with the same radius as the outer boundary of the butterfly piece; for specific reference, see Figure 3 ;

[0054] 2. Far-field air cannon pre-splitting roof cutting and pressure relief scheme:

[0055] (1) Overall scheme based on air cannon pre-splitting roof cutting and pressure relief equipment:

[0056] According to the known borehole angle, borehole height, borehole depth, borehole diameter and borehole spacing, drill holes through a drilling machine (for specific reference, see Figure 9 Drill hole 23), where the depth of drill hole 23 can reach the immediate roof 24, and then use an air cannon pre-splitting pressure relief device (such as Figure 4 ) for roof cutting and pressure relief.

[0057] Specifically, the air cannon pre-splitting pressure relief device 29 includes a movable chassis 18, on which a lifting device 19 and a gas storage tank 13 are arranged. The gas storage tank 13 is rotatably connected to the chassis 18, and the lifting device drives the gas storage tank 13 to tilt upward relative to the chassis; a gas guide pipe 12 is installed inside the gas storage tank 13, one end of the gas guide pipe 12 is connected to a piston 15, the piston 15 is controlled by a control handle 16, and the other end of the gas guide pipe 12 extends outside the gas storage tank 13 and is connected to a connecting conduit 11; the connecting conduit 11 is connected to a detachable sealed jet head 10, and a fixing module 21 and an expansion seal bag 22 are arranged on the detachable sealed jet head 10; among them, the fixing module 21 includes a resistance increasing plate 33, a one-way sliding module 31 and a spring 32, the resistance increasing plate 33 cooperates with the one-way sliding module 31, and the one-way sliding module 31 is driven by the spring 32; an air inlet 14 and a pressure gauge 17 are also arranged on the gas storage tank 13;

[0058] Connect the detachable sealed jet head 10 to the connecting conduit 11, extend the instrument into the borehole, and successively increase the number of connecting conduits 11 until the depth to be fractured is reached; adjust the lifting device of the air cannon roof cutting and pressure relief machine so that the air duct 12 and the connecting conduit 11 are on the same central axis, and connect the air duct 12 and the connecting conduit 11; rotate the control handle 16 to make the piston 15 seal the end of the air duct 12, so that the air inside the gas storage tank 13 is completely isolated from the outside air; connect the air inlet 14 to the inflator to compress the outside air and enter it into the gas storage tank 13, continuously compressing to increase the pressure inside the gas storage tank 13. A pressure gauge is provided on the outside of the gas storage tank 13 to measure the air pressure in the gas storage tank 13 in real time. When the air pressure in the gas storage tank 13 exceeds the tensile strength limit value of the rock, close the air inlet and stop inflating; the outer surface of the expansion seal bag 22 is made of reinforced expandable rubber material, and after expansion, it fits completely with the borehole to form a closed space. Rotate the control handle 16 to disconnect the piston 15 from the air duct 12, and the air in the gas storage tank 13 and the air duct 12 are in communication. Due to the different atmospheric pressures, the air in the gas storage tank 13 quickly sprays out from the detachable sealed jet head (such as Figure 5 shown) to pressurize the air in the borehole; when the high-pressure gas quickly passes through the detachable sealed jet head 10, the fixed module located inside the detachable sealed jet head is quickly ejected by the push of the high-pressure gas and fixed to the surrounding rock of the borehole; then repeat this process until the last time when pressurizing the borehole, stop pressurizing when the pressure value on the pressure gauge 17 reaches the maximum tensile strength of the rock. Finally, disconnect the detachable sealed jet head 10 from the connecting conduit 11 to form a high-pressure gas closed cavity in the borehole; subsequently, perform high-pressure gas sealing on each borehole to form a coherent advanced high-pressure gas fracturing system. As the construction of the coal seam in the lower section working face progresses, the top rock layer is disturbed and its strength decreases. The high-pressure gas extends by tensile fracture along the weakest part of the rock layer. The fractured boreholes form rock fractures extending in all directions, and the continuous borehole fractures intersect to form a full-span section of the roof cutting and pressure relief area. The top rock layer in the goaf collapses (such as Figure 10 shown), realizing roof cutting and pressure relief in front of the working face.

[0059] (2) Detachable sealed jet head

[0060] As Figure 5 shown, four fixed modules 21 are arranged along the radial direction inside the detachable sealed jet head. Before the high-pressure gas is ejected, the fixed module 21 is located inside the jet head and is embedded with the one-way sliding module 31. A spring is arranged at the top of the one-way sliding module 31, and the spring is in a compressed state, enabling the one-way sliding module 31 to slide up and down. When the high-pressure gas passes through, the high-pressure air flow impacts on the resistance-increasing plate 33 of the fixed module, pushing the fixed module to quickly pop out and fix it to the surrounding rock walls of the borehole; as Figure 6As shown in the figure, an expandable sealing jet head is installed at the top of the separable sealing jet head. The expandable sealing bag is made of fiber-reinforced rubber material and is filled with water for expansion inside. The hole sealing pressure can reach 60 Mpa, and the tensile strength of general rock mass generally does not exceed 40 Mpa. Therefore, it meets the hole sealing requirements.

[0061] (3) At the connection between the separable sealing jet head and the connecting conduit

[0062] The separable sealing jet head and the connecting conduit 11 are butt-jointed through special buckles. One side of the connecting conduit 11 is a convex clamping groove 36, and one side of the jet head is a sliding module connected by three springs. The two are mutually engaged and connected, as Figure 8 shown; in the natural state, one side of the jet head is in a closed state, as Figure 7 shown; when the jet head and the connecting conduit 11 are initially connected, it is necessary to manually adjust the spring knob to retract the sliding module 35 into the pipe wall to allow the convex clamping groove 36 to enter; when the air pressure in the drill hole reaches the specified value, due to the one-way design of the clamping groove, pulling the connecting conduit 11 unidirectionally can achieve the separation between the connecting conduit 11 and the separable sealing jet head. After separation, the sliding module automatically rebounds and closes to achieve sealing inside the pipeline.

[0063] 3. Stress control scheme combining near-field and far-field complementary: This scheme is a technology that flexibly adjusts the stress control strategy according to different distances between roadways and mining faces and the degree of mining influence. When the roadway is far from the mining face and the mining influence is small, the near-field stress control scheme is preferably adopted. Through measures such as high-strength active and passive combined support, borehole peep analysis, borehole pressure relief, and behind-the-wall pressure relief, the transfer of high vertical stress in the deep part of the surrounding rock and high horizontal tectonic stress of faults is reduced, thereby reducing the deformation and stress concentration of the surrounding rock. When the roadway is close to the mining face and is frequently disturbed by dynamic pressure, on the basis of near-field stress control, combined with the far-field stress control scheme, the air cannon pre-splitting roof cutting and pressure relief method is adopted. The high-pressure gas is sealed into the borehole to form a high-pressure gas sealing cavity, and a full-section crack is formed along the weak points of the surrounding rock to achieve roof cutting and pressure relief, and the roof cutting depth is adjusted as needed to cut off the influence of mining disturbance. This stress control technology combining near-field and far-field complementary has flexibility, complementarity, effectiveness, and wide applicability, and can ensure the long-term stability of deep roadways.

[0064] To sum up, the present invention proposes a technical scheme for overall regional stress adjustment combining near-field pressure relief and far-field pressure relief. The final effect diagram of the scheme is as Figure 10 shown.

[0065] Furthermore, the present invention is based on the concrete-filled steel tube support and bolt-net support. The concrete-filled steel tube support can also be replaced with other passive support structures, such as U-shaped steel supports.

[0066] Furthermore, the roadway filling materials mentioned in this solution can also be other filling materials with higher strength, such as hardwoods (oak, beech, birch, etc.), cast concrete, etc.

[0067] Furthermore, in addition to the relief hole bit for relief used in the present invention, hydraulic hole enlargement technology can also be used to replace mechanical hole enlargement. By injecting high-pressure water into the surrounding rock to fracture the rock, the purpose of pressure relief can be achieved.

[0068] Based on the combined support of bolt-net-shotcrete support and concrete-filled steel tubular support, the present invention designs a yielding layer and creates a post-wall pressure relief space according to the deformation of the roadway. Peepholes are set at the peripheral position of the roadway. According to the peep results, the morphology of the fissure zone in the surrounding rock is analyzed, and different borehole pressure reliefs are implemented for different rupture zones, so as to realize the development of the surrounding rock deformation in the pressure relief space within the surrounding rock, prevent or reduce the development of the surrounding rock deformation towards the roadway surface layer, reduce the load acting on the roadway support body, and achieve the purpose of stable roadway support.

[0069] The present invention is a technology for flexibly adjusting the stress control strategy according to the distances between different roadways and the coal mining face and the degrees of mining influence. When the roadway is far from the coal mining face and the mining influence is small, the near-field stress control scheme is preferably adopted. Through measures such as high-strength active and passive combined support, borehole peephole analysis, borehole pressure relief, and post-wall pressure relief, the transmission of high vertical stress in the deep part of the surrounding rock and the high horizontal tectonic stress of the fault are reduced, thereby reducing the surrounding rock deformation and stress concentration. When the roadway is close to the coal mining face and is frequently disturbed by dynamic pressure, on the basis of the near-field stress control, a far-field stress control scheme is combined, and the method of air cannon pre-splitting roof cutting and pressure relief is adopted. The high-pressure gas is sealed into the borehole to form a high-pressure gas sealed cavity, and full-section cracks are formed along the weak points of the surrounding rock to realize roof cutting and pressure relief. The cutting depth of the roof is adjusted according to needs to cut off the influence of mining disturbance. This stress control technology combining near-field and far-field complementarity has flexibility, complementarity, effectiveness, and wide applicability, and can ensure the long-term stability of deep roadways.

[0070] The roof cutting and pressure relief equipment and construction method using air cannon pre-splitting, compared with the existing technology, realizes the roof cutting and pressure relief ahead of the working face. The construction method will not be adversely affected by mining disturbance, and makes full use of the characteristics of mining disturbance on the rock properties, realizing the spontaneous roof cutting and pressure relief after the construction is completed, greatly improving the construction efficiency; realizing the whole-process detection of roof cutting and pressure relief, avoiding the influence of excessive construction on roadway support, and ensuring the safety of the construction process; the roof cutting and pressure relief technology selects the principle of air cannon pre-burying high-pressure air cavity for roof cutting and pressure relief. By pressurizing the air, the high-pressure gas is compressed inside the borehole. As the working face is mined, it expands continuously and slowly fractures the rock, reducing the construction cost. The construction process is simple, will not cause pollution to the roadway environment and waste of resources, and can adapt to various construction environments with a wide application range.

Claims

1. A surrounding rock stress control method based on near-field and far-field pressure relief, characterized in that: as follows: Get the mining impact index, the mining impact index Among them, R is the maximum plastic zone radius, r is the average radius of the plastic zone; When 1≤K<2, the surrounding rock pressure is adjusted by means of drilling pressure relief and back-wall pressure relief; When K≥2, the surrounding rock pressure is adjusted by drilling pressure relief and behind-the-wall pressure relief. At the same time, the high-pressure gas is sealed into the borehole by pre-buried high-pressure air cavity to form a high-pressure gas sealing cavity. As the working face is mined, the high-pressure gas expands along the weak points of the surrounding rock to form full-section cracks, thereby achieving top cutting pressure relief. As the K value increases, the top cutting depth increases.

2. The surrounding rock stress control method based on near-field and far-field pressure relief according to claim 1 is characterized in that: The top cutting and pressure relief equipment using air cannon pre-cracking seals the high-pressure gas into the borehole to form a high-pressure gas sealing chamber, which expands along the weak points of the surrounding rock to form full-section cracks, thereby achieving top cutting and pressure relief.

3. The surrounding rock stress control method based on near-field and far-field pressure relief according to claim 1 is characterized in that: The top cutting and pressure relief equipment using air cannon pre-cracking includes a movable chassis, a jacking device and an air tank are arranged on the chassis, the air tank is rotatably connected to the chassis, and the jacking device drives the air tank to tilt upward relative to the chassis; an air guide pipe is installed inside the air tank, one end of the air guide pipe is connected to a piston, the piston is controlled by a control handle, and the other end of the air guide pipe extends to the outside of the air tank and can be connected to a connecting conduit, the connecting conduit is connected to a detachable sealed jet head, and a fixed module and an expansion sealing bag are arranged on the detachable sealed jet head; an air inlet and a pressure gauge are also arranged on the air tank.

4. The surrounding rock stress control method based on near-field and far-field pressure relief according to claim 3 is characterized in that: Connect the detachable sealed jet head to the connecting conduit, extend the detachable sealed jet head into the borehole, and increase the number of connecting conduits in sequence until the depth required for fracturing is reached; adjust the lifting device of the air cannon top cutter and unload the pressure machine, connect the air guide pipe to the connecting conduit; close the end of the air guide pipe, connect the air inlet to the inflator, compress the external air into the gas tank, and when the air pressure in the gas tank exceeds the limit value of the tensile strength of the rock, close the air inlet and stop inflating; open the end of the gas guide pipe, and the air in the gas tank is quickly ejected from the detachable sealed jet head through the gas guide pipe to pressurize the air in the borehole; when the high-pressure gas quickly passes through the detachable sealed jet head, the fixed module located in the detachable sealed jet head is pushed by the high-pressure gas and quickly ejected and fixed to the rocks around the borehole; then repeat this process until the last time the borehole is pressurized, the pressure value on the pressure gauge reaches the maximum tensile strength of the rock, and the pressurization is stopped, and finally the detachable sealed jet head is detached from the connecting conduit to form a high-pressure gas closed chamber in the borehole.

5. The surrounding rock stress control method based on near-field and far-field pressure relief according to claim 4 is characterized in that: Each borehole is sealed with high-pressure gas to form a coherent advanced high-pressure gas fracturing system. With the construction of the coal seam in the lower section working face, the top rock stratum is disturbed and the rock stratum strength is reduced. The high-pressure gas stretches and extends along the weakest part of the rock stratum. The fracturing boreholes form rock cracks extending in all directions. Continuous borehole cracks intersect to form a full-span section of the top cutting and pressure relief area. The rock stratum on the top of the goaf collapses, realizing the top cutting and pressure relief of the advanced working face.

6. The surrounding rock stress control method based on near-field and far-field pressure relief according to claim 4 is characterized in that: The fixed modules are arranged in a circle along the circumferential direction of the detachable sealed jet head. Each fixed module includes a resistance increasing plate, a one-way sliding module and a spring. The resistance increasing plate is arranged along the radial direction of the detachable sealed jet head and can extend to the outside of the detachable sealed jet head under the action of external force; the resistance increasing plate cooperates with the one-way sliding module, and the one-way sliding module is driven by a spring; the spring is fixed on the inner wall of the detachable sealed jet head.

7. The surrounding rock stress control method based on near-field and far-field pressure relief according to claim 4 is characterized in that: The connecting conduit and the detachable sealing spray head are matched through a card slot, and a sliding module is arranged at the connecting position of the connecting conduit and the detachable sealing spray head, and the sliding module is arranged along the radial direction of the detachable sealing spray head.

8. The surrounding rock stress control method based on near-field and far-field pressure relief according to claim 1, characterized in that: The method of adjusting the surrounding rock pressure by means of drilling pressure relief and back wall pressure relief is as follows: Peepholes are set up at the periphery of the tunnel to analyze the deformation law of the surrounding rock around the tunnel through the peepholes. The development law of the fracture zone of the tunnel surrounding rock is analyzed regularly to accurately determine the shape of the fracture zone and the main deformation zone of the surrounding rock, and accurate pressure relief is carried out for fracture zones of different shapes.

9. The surrounding rock stress control method based on near-field and far-field pressure relief according to claim 8, characterized in that: For circular and elliptical fracture zones, it is recommended to mainly relieve pressure around the tunnel. The peripheral pressure relief is achieved by controlling the thickness of the pressure relief layer. The circular fracture zone adopts equal thickness pressure relief space, and the elliptical fracture zone has less pressure relief space on the two sides and larger top and bottom plates. For butterfly-shaped fracture zones or other fracture zones, pressure relief is carried out by drilling holes on the top, bottom and two sides. The starting end of the drilled pressure relief zone must be located at the outer boundary of the surrounding rock fracture zone, and the end of the pressure relief zone is on a concentric circle with the outer boundary of the butterfly. The circumference of the same radius.

10. The surrounding rock stress control method based on near-field and far-field pressure relief according to claim 1, characterized in that: The plastic zone radius is monitored by setting peepholes at the periphery of the tunnel. The maximum plastic zone radius R is obtained from the peep results obtained through the peepholes, and then the average plastic zone radius r is calculated based on the measured data.

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