A method for grouting and filling in cross-layer area of residual mining area coal pillar group

Abstract

The application discloses a kind of for residual mining area coal pillar group strata-span area grouting filling method, it is related to coal mining technical field, including the following steps: (1) selection key layer;(2) construction borehole in key layer, in borehole by sandblasting water jet cutting forms directional initial crack, after both ends of borehole are set and seal, using the way of injecting high-pressure fluid to sealing hole section, make initial crack expand and form crack network;(3) using grouting material to the borehole in step (2) is segmented grouting construction: first use low viscosity slurry filling crack network formed by fracturing, then use middle viscosity slurry filling coal pillar plastic zone affected by mining, finally adopt high viscosity slurry filled with accelerator roof broken rock mass and empty area empty roadway;(4) slurry consolidation forms " coal pillar-pulse body-surficial rock" composite bearing structure.The application can significantly enhance the adhesion of rock mass in multiple mining area and overall strength, improve the stability of multiple mining roadway and working face surrounding rock.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal mining, in particular to a method for grouting and filling in a cross-layer area of a coal pillar group in a residual mining area. BACKGROUND

[0002] With the continuous expansion of the scale of coal mining, coal resources are decreasing, and residual coal mining has become an important direction of coal resource development in China. However, multiple goafs, empty roadways and caving areas exist in the residual mining area. These areas are hidden and difficult to explore, and are usually only discovered during excavation or mining. If discovered during mining, the surrounding rock is often severely broken, and the overlying loose rock mass lacks effective support, which is prone to collapse or rheology, and can easily cause safety hazards and seriously interfere with the normal production of the working face.

[0003] In view of this, a pre-mining disposal method is proposed to solve the above technical problems in the process of re-mining. SUMMARY

[0004] The purpose of the present application is to provide a method for grouting and filling in a cross-layer area of a coal pillar group in a residual mining area to solve the above-mentioned problems existing in the prior art, which can significantly enhance the bonding force and overall strength of the rock mass in the residual mining area, and improve the stability of the surrounding rock of the re-mining roadway and working face.

[0005] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0006] The present application provides a method for grouting and filling in a cross-layer area of a coal pillar group in a residual mining area, comprising the following steps:

[0007] (1) According to the lithology, thickness and mechanical parameters of the overlying rock of the coal seam, a hard rock layer with a thickness greater than the adjacent rock layer and a strength higher than the adjacent rock layer is selected as a key layer;

[0008] (2) Drilling is carried out in the key layer, and an initial directional crack extending in the direction of the surface and extending in the direction of the coal seam is formed by cutting in the vertical plane in which the drilling diameter is located using abrasive water jet, and then the two ends of the drilling are set and sealed, and the initial crack is expanded to form a crack network by injecting high-pressure fluid into the sealing section;

[0009] (3) The drilling is used as a grouting hole, and the grouting hole is subjected to segmented grouting construction using grouting materials: first, low-viscosity slurry is used to fill and crack the crack network, then medium-viscosity slurry is used to fill the plastic zone of the coal pillar affected by mining, and finally high-viscosity slurry with added accelerator is used to fill the broken rock mass of the roof and the empty area and roadway;

[0010] (4) After the slurry is solidified, a "coal pillar-grouting vein-overburden rock" composite bearing structure is formed;

[0011] The drilling interval is determined by the following formula:

[0012] (1),

[0013] (2),

[0014] In the formula: is the drilling interval, m; T is the grouting hole thickness, m; R is the effective diffusion radius of the slurry, m; r 1 is the grouting hole radius, m; α is the fracturing efficiency coefficient; η is the key layer fissure rate, %; K is the key layer permeability coefficient, m / d; C 1 and C are the viscosities of the slurry and water, respectively, cP; δ is the fissure connectivity coefficient; p is the grouting pressure, m; t is the slurry gel time, d.

[0015] In an embodiment, in step (3), the grouting material is a coal gangue-fly ash-desulfurized gypsum-cement-based grouting material, and the mass ratio is: desulfurized gypsum 4-6%, fly ash 28-32%, coal gangue 53-57%, and cement 9-11%.

[0016] In an embodiment, in step (3), the injection pressure of the low-viscosity slurry is 2-3 MPa, the flow rate is 15-20 L / min, the injection pressure of the medium-viscosity slurry is 4-5 MPa, the flow rate is 10-15 L / min, the injection pressure of the high-viscosity slurry is 1-2 MPa, and the flow rate is 5-8 L / min.

[0017] In an embodiment, in step (2), the height of the drilling hole is higher than the caving zone.

[0018] In an embodiment, in step (2), a drill, a matched drill bit and a drill rod are used to construct a borehole in a roadway roof; the hole sealer and the abrasive jet device are connected and sent to a preset position of the borehole, the water jet system is turned on and switched to the jet mode, high-pressure water with abrasive sand is sprayed from the nozzles on the upper and lower sides of the abrasive jet device, the drill is uniformly retreated at a constant speed, and an initial directional fracture extending in the direction of the surface and extending along the coal seam is cut in the vertical plane in which the borehole is located; the abrasive pump is turned off, the high-pressure pump is adjusted to the hole sealing mode, high-pressure water is injected into the hole sealer, and the hole sealers at both ends of the borehole are set; the high-pressure pump is switched to the fracturing mode, high-pressure water is continuously injected into the hole sealing section from the water outlet hole at the front end of the abrasive jet device, the initial fracture continuously expands along the fracture tip, and the high-pressure pump is turned off when the pump pressure suddenly drops or the fracturing time reaches the designed time, the initial fracture expands to form a fracture network.

[0019] In an embodiment, in step (3), drilling peeping or microseismic monitoring is used to determine the main direction of the fracture, and a ground mixed grouting station is built in the wind well field area, and the grouting hole is subjected to staged grouting construction.

[0020] In an embodiment, in step (3), an intermittent grouting method is used, the pump is stopped for 5 minutes every 30 minutes, and the thixotropy of the slurry is used to prevent blind diffusion of the slurry.

[0021] In an embodiment, in step (3), a filtering device is arranged at the borehole opening, and the un-solidified slurry is recycled.

[0022] The present application has the following technical effects compared with the prior art:

[0023] The present application implements regional fracturing-grouting-filling technology on the coal pillar group in the residual mining area, actively constructs a controllable fracture network, and makes the slurry penetrate the plastic zone of the coal pillar and the overlying loose rock mass, thereby achieving two goals: on the one hand, the overlying loose body in the residual mining area is subjected to fracture grouting reinforcement, and on the other hand, the body of the goaf and the air lane is subjected to grouting and filling. After the slurry is solidified, a "coal pillar-slurry vein-overburden" composite bearing structure is formed, which effectively coordinates the cooperative bearing action of the coal pillar and the loose overburden, significantly enhances the rock mass adhesion and overall strength, and thus improves the stability of the surrounding rock of the repeated mining roadway and working face. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings described in the following only constitute some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0025] Figure 1A planar projection drawing of directional drilling in a working face drilling field in an embodiment of the present application;

[0026] Figure 2 A profile drawing of directional drilling in a working face drilling field in an embodiment of the present application;

[0027] Figure 3 A schematic diagram of a directional fracture network in a drilling field in an embodiment of the present application;

[0028] Figure 4 A schematic diagram of a "coal pillar-slug vein body-overburden" composite bearing structure in an embodiment of the present application.

[0029] In the drawing: 1, 1# directional drilling; 2, 2# directional drilling; 3, 3# directional drilling; 4, 4# directional drilling; 5, 5# directional drilling; 6, caving area; 7, fracture network; 8, empty roadway; 9, goaf; 10, coal pillar; 11, slug vein body; 12, overburden; 13, empty area empty roadway filling area; 14, loose fissure reinforcement area; 15, drilling. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0031] The purpose of the present application is to provide a residual mining area coal pillar group cross-layer area grouting filling method to solve the problems existing in the prior art, which can significantly enhance the adhesion and overall strength of the rock mass in the residual mining area, and improve the stability of the surrounding rock of the residual mining roadway and working face.

[0032] In order to make the above-mentioned purposes, characteristics and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0033] The present application provides a residual mining area coal pillar group cross-layer area grouting filling method, comprising the following steps:

[0034] (1) According to the lithology, thickness and mechanical parameters of the overburden of the coal seam, a hard rock layer with a thickness greater than the adjacent rock layer and a strength higher than the adjacent rock layer is selected as a key layer;

[0035] (2) Drilling is carried out in the key layer, and an initial directional fracture extending in the direction of the surface and extending in the direction of the coal seam is formed in the vertical plane in which the drilling diameter is located by cutting with abrasive water jet, and then the two ends of the drilling are set and sealed, and the initial fracture is expanded to form a fracture network by injecting high-pressure fluid into the sealing section;

[0036] (3) Take the drill hole as a grouting hole, and adopt grouting material to conduct sectional grouting construction on the grouting hole: firstly, use low-viscosity slurry to fill the crack network formed by fracturing, then use medium-viscosity slurry to fill the plastic zone of the coal pillar affected by mining, and finally use high-viscosity slurry added with a rapid-setting agent to fill the broken rock mass of the roof and the empty space and roadway;

[0037] (4) The slurry is solidified to form a "coal pillar-grout vein body-overburden rock" composite bearing structure;

[0038] wherein the drill hole spacing is determined by the following formula:

[0039] (1),

[0040] (2),

[0041] In the formula: is the drill hole spacing, m; T is the grouting hole thickness, m; R is the effective diffusion radius of the slurry, m; r 1 is the grouting hole radius, m; α is a fracturing efficiency coefficient, representing the degree of crack propagation after fracturing, and is taken as 1.1-1.5; η is the key layer crack rate, %; K is the key layer permeability coefficient, m / d; C 1 and C are the viscosities of the slurry and water, respectively, cP; δ is a crack connectivity coefficient, representing the effective penetration rate of the slurry in the overburden rock cracks, and is taken as 0.8-1.0; p is the grouting pressure, m; t is the slurry gel time, d.

[0042] In step (3), the grouting material is a coal gangue-fly ash-desulfurized gypsum-cement-based grouting material, and the mass ratio is as follows: desulfurized gypsum 4-6%, preferably 5%, fly ash 28-32%, preferably 30%, coal gangue 53-57%, preferably 55%, cement 9-11%, preferably 10%. If there is a higher requirement for the strength of the grouting filling body in actual engineering, the amount of fly ash and cement can be appropriately increased. The viscosity of the slurry is mainly realized by controlling the water-material ratio (water-cement ratio).

[0043] In step (3), the injection pressure of the low-viscosity slurry is 2-3 MPa, and the flow rate is 15-20 L / min. The goal is to achieve the penetration of the far-field fractures, and the termination criterion is the slurry returning from the adjacent hole. The fracture main channel network (fracture network) formed by fracturing has the characteristics of large scale, good connectivity, and long extension distance. The low-viscosity slurry has significant advantages in such a network: it has strong fluidity and can quickly spread along the main channel under the action of a pressure of 2-3 MPa, and it can penetrate deep into the far-field area. Compared with the medium-viscosity slurry, the low-viscosity slurry is more likely to penetrate the slender fracture branches and does not stay in the middle due to high viscosity, and it can efficiently fill the main channel and the connected far-field fractures. The flow rate of 15-20 L / min can provide enough power for the slurry to flow to the far-field, and it can also avoid excessive impact on the fracture wall to prevent the fracture from collapsing and blocking the channel. The far-field fracture refers to the fracture area that is far away from the injection hole and connected to the injection hole through the main channel network. The penetration of these areas can enhance the overall stability and permeability control effect of the rock mass. Under the action of pressure, the low-viscosity slurry quickly advances along the main channel formed by fracturing, continuously spreads to the branch fractures, and gradually connects the dispersed far-field fractures, eventually forming a whole, thereby improving the stability and anti-permeability performance of the rock mass. During the grouting process, the low-viscosity slurry spreads to the far-field along the main channel network, and when it reaches the adjacent hole (adjacent hole), it flows out of the adjacent hole, i.e., the adjacent hole returns the slurry. This indicates that the slurry has successfully penetrated the main channel and the far-field fractures between the injection hole and the adjacent hole, and achieved the goal of penetrating the far-field fractures. At this time, the grouting is terminated, which can ensure the full filling and penetration of the fracture network, and avoid the waste of slurry and the damage to the rock mass caused by excessive grouting and high pressure.

[0044] The injection pressure of the medium viscosity slurry is 4-5 MPa, and the flow rate is 10-15 L / min. The goal is to achieve saturation in the near-field area, and the termination criterion is a 10% sharp rise in grouting pressure. The plastic zone of the coal pillar is affected by mining, and the rock mass structure is loose, with complex and mostly small-scale fissures. The injection of medium viscosity slurry in this area has unique advantages: its moderate viscosity can effectively penetrate the fissure network in the plastic zone under the action of 4-5 MPa pressure, and it will not quickly flow away due to too low viscosity, and can form sufficient filling in the near-field area. The flow rate of 10-15 L / min can ensure continuous supply of slurry to promote fissure filling, and can avoid excessive flow rate causing local pressure to rise sharply, damaging the coal pillar structure or causing slurry overflow. The near-field area refers to the plastic zone of the coal pillar within a certain range around the grouting hole, which is the key part of the coal pillar bearing capacity that is easily affected. Under the action of pressure, the medium viscosity slurry will gradually diffuse along the fissures in the plastic zone, first filling larger fissures, and then penetrating smaller fissures through pressure transmission, until the slurry is fully filled in the near-field area, forming a continuous reinforced body, thereby improving the integrity and bearing capacity of the coal pillar. During grouting, as the slurry continuously fills the fissures, the fissures in the near-field area are gradually saturated, and the resistance to slurry flow will gradually increase. When the near-field area reaches saturation, the slurry will have difficulty continuing to diffuse, and the pressure in the grouting system will suddenly rise. When the pressure rises by 10% compared to the stable injection stage, it indicates that the fissures in the near-field area have been fully filled with slurry, and continued grouting not only cannot effectively expand the saturated range, but also may cause secondary damage to the plastic zone of the coal pillar or cause the slurry to break through the near-field area under high pressure, resulting in ineffective loss.

[0045] The injection pressure of the high-viscosity slurry is 1-2 MPa, the flow rate is 5-8 L / min, and the termination criterion is that the suction volume is less than 5 L / min continuously. The high-viscosity slurry with the addition of the accelerator has unique performance advantages, and is very suitable for the filling requirements of the broken roof rock mass and the goaf and roadway. The high-viscosity characteristic makes it difficult to flow away during the flow process, can stay and fully fill in the cracks of the broken rock mass and the goaf and roadway, and avoids the leakage from the weak part of the broken rock mass due to the too strong flowability of the slurry. The addition of the accelerator greatly shortens the setting time of the slurry, can quickly form strength, and timely supports the broken rock mass to prevent the further collapse of the rock mass before the slurry sets and affects the filling effect. The injection pressure of 1-2 MPa is relatively moderate, which can not only push the slurry into the fine cracks of the broken rock mass and the corners of the goaf and roadway, but also will not cause secondary damage to the broken roof rock mass due to the too high pressure, thereby avoiding causing more serious collapse. The flow rate of 5-8 L / min can ensure that the slurry is slowly and uniformly injected, so that the slurry has enough time to diffuse and fill in place in the broken area and the goaf and roadway, and prevents the slurry from accumulating unevenly or overflowing due to too large flow rate. The broken roof rock mass often has a large number of irregular cracks and voids, and the goaf and roadway are relatively large hollow areas, which seriously affect the stability of the roof. After the high-viscosity slurry with the addition of the accelerator is injected, it can quickly set under the action of the accelerator, fill these cracks, voids and hollows, and cement the broken rock blocks together to form an integrated bearing structure, thereby improving the stability of the roof and reducing the risk of roof collapse. The suction volume reflects the suction capacity of the rock mass or the goaf and roadway to the slurry. In the early stage of grouting, due to the existence of a large number of spaces to be filled in the broken rock mass and the goaf and roadway, the suction volume will be relatively large. As the grouting proceeds, the slurry continuously fills these spaces, the cracks and hollows available for the slurry to enter gradually decrease, and the suction volume also decreases. When the suction volume is less than 5 L / min continuously, it indicates that the broken roof rock mass and the goaf and roadway have been fully filled with the slurry, and further grouting not only is difficult to further improve the filling effect, but also will cause waste of the slurry, and even may cause unnecessary pressure due to too much slurry.

[0046] In step (2), the height of the drill hole is higher than the caving zone. The fracturing drill hole higher than the caving zone can reduce the influence of the caving zone collapse on the fracturing hole. The rock mass in the caving zone has poor stability, and if the fracturing drill hole is located therein or has a height close thereto, the drill hole structure is easy to be damaged due to the rock mass collapse, which affects the fracturing and subsequent grouting operations. A higher position can provide a more stable construction environment for the fracturing drill hole, guarantee the integrity of the crack network formed by fracturing, and thus lay a good foundation for the diffusion of the slurry. During grouting, the slurry can fill the voids of the caving zone and the cracks of the broken roof rock mass under the action of gravity, and the slurry can set in time after reaching the target area due to its accelerator characteristics, thereby enhancing the compactness of the filling.

[0047] In step (2), a drilling machine, a matching drill bit and a drill rod are used to construct a borehole in a roadway roof; the hole sealer and the abrasive jet device are connected and sent to a preset position of the borehole, a water jet system is turned on and switched to a jet mode, high-pressure water with abrasive sand is sprayed from the nozzles on the upper and lower sides of the abrasive jet device, the drilling machine is uniformly retreated at a constant speed, and an initial directional fracture extending in the direction of the ground and the coal seam is cut in a vertical plane in which the borehole is located; the abrasive pump is turned off, the high-pressure pump is adjusted to the hole sealing mode, high-pressure water is injected into the hole sealer, and the hole sealers at both ends of the borehole are set; the high-pressure pump is switched to the fracturing mode, high-pressure water is continuously injected into the hole sealing section from the water outlet hole at the front end of the abrasive jet device, the initial fracture continuously expands along the fracture tip, and the high-pressure pump is turned off when the pump pressure suddenly drops or the fracturing time reaches the designed time, the initial fracture expands to form a fracture network.

[0048] In step (3), drilling peeping or microseismic monitoring is used to determine the main direction of the fracturing fissure, a ground mixed grouting station is built in the wind well field area, and segmented grouting construction is performed on the grouting holes (boreholes drilled during fracturing).

[0049] In step (3), an intermittent grouting method is used, the pump is stopped for 5 minutes every 30 minutes, and the thixotropy of the slurry is used to prevent blind diffusion of the slurry. The method can effectively solve the problems of "incomplete filling" and "insecure solidification" in traditional grouting, and is particularly suitable for broken surrounding rock conditions. During grouting construction, the grouting parameters should be adjusted according to the actual conditions underground.

[0050] In step (3), a filtering device is arranged at the borehole opening, and the un-solidified slurry is recycled.

[0051] The invention will be further explained and described below by taking a drilling field of a 3# coal seam in a certain mine as an example.

[0052] 1. Directional construction of key fracturing layer fissure network

[0053] (1) Selection of key fracturing layer

[0054] 1) Geological column analysis: Through borehole data and logging curves, the lithology, thickness and mechanical parameters (compressive strength, elastic modulus, etc.) of the overburden rock of the coal seam are extracted, the hard rock layer with larger thickness and significantly higher strength than the adjacent rock layer is selected as the candidate key fracturing layer, and the height of the fracturing borehole should be higher than the height of the caving zone.

[0055] 2) Numerical simulation verification: The stress distribution and failure law of the overburden rock after coal pillar mining are simulated by using software such as FLAC3D or UDEC, the deformation characteristics and fracture propagation path of different rock layers are analyzed, and the crack control effect of the key fracturing layer is further verified.

[0056] (2) Determination of borehole spacing

[0057] The drilling spacing needs to be determined comprehensively in combination with the fracturing and grouting effects (the drilling hole is used as a fracturing hole and a grouting hole), and the formula for calculating the slurry diffusion radius is as follows:

[0058] (1),

[0059] The drilling spacing calculation formula is:

[0060] (2),

[0061] In the formula: is the drilling spacing, m; T is the grouting hole thickness, m; R is the effective diffusion radius of the slurry, m; r 1 is the grouting hole radius, m; α is the fracturing efficiency coefficient, representing the degree of fracture propagation after fracturing, and is taken as 1.1-1.5; η is the key layer fracture rate, %; K is the key layer permeability coefficient, m / d; C 1 and C are the viscosities of the slurry and water, respectively, cP; δ is the fracture connectivity coefficient, representing the effective penetration rate of the slurry in the overburden fracture, and is taken as 0.8-1.0; p is the grouting pressure, m; t is the slurry gel time, d.

[0062] (3) Directional drilling arrangement scheme

[0063] The fracturing drilling arrangement scheme is specifically shown in Figure 1 and Figure 2 , and five drilling holes are arranged, which are 1# directional drilling hole 1, 2# directional drilling hole 2, 3# directional drilling hole 3, 4# directional drilling hole 4 and 5# directional drilling hole 5. The diameter of each drilling hole is 120 mm, and all are open hole sections. The drilling hole length penetrates the entire mining area roof. The drilling hole inclination, elevation and drilling site position can be adjusted according to the actual situation on the mine, but the drilling spacing, coal seam roof key fracturing layer position (i.e. the distance from the determined key layer to the coal seam) cannot be adjusted.

[0064] (4) Directional construction of fracture network

[0065] 1) A drilling machine, a matching drill bit and a drill rod are used to construct a drilling hole with a certain aperture in the roadway roof;

[0066] 2) After connecting the hole packer and the frosted jet device, they are sent to the pre-set position of the drilling hole, the water jet system is turned on and switched to the jet mode;

[0067] 3) High-pressure water containing abrasive sand is sprayed from the nozzles on both sides of the jet injector. The drill rod is retracted at a constant speed by the drill rig. Vertically, upward directional fractures extending towards the ground surface and downward directional fractures extending towards the coal seam are formed on the borehole wall.

[0068] 4) Turn off the abrasive pump and switch the high-pressure pump to the sealing mode. Inject high-pressure water into the sealing device to set the sealing device at both ends of the borehole.

[0069] 5) Switch the high-pressure pump to fracturing mode. At this time, high-pressure water is continuously injected into the sealing section from the water outlet at the front end of the ejector. The initial fracture continues to expand along the fracture tip. When the pump pressure suddenly drops or the fracturing time reaches the designed time, shut off the high-pressure pump and depressurize the sealing device, completing the fracturing work for this section. Figure 3 The diagram shows a directional fracture network in the drilling site. Borehole 15 is used as a fracturing hole. Through high-pressure water fracturing, a fracture network 7 is formed in the rock mass. The fracture network 7 is distributed vertically with the collapse zone 6, the goaf 8, and the goaf 9.

[0070] 6) Start the drilling rig, operate the drill rod to move the jet nozzle to the next cutting position, and carry out the construction of the next section in the same way as above.

[0071] 2. Crack network grouting and void filling technology

[0072] (1) Grouting materials

[0073] To meet the requirements of low viscosity and high flowability (ensuring sufficient penetration into fine cracks or silty sand layers) for grouting materials within crack networks, and considering both economic and technical factors, a coal gangue-fly ash-desulfurized gypsum-cement-based grouting material is selected. The recommended mix ratio is: 5% desulfurized gypsum, 30% fly ash, 55% coal gangue, and 10% cement. If higher strength requirements are placed on the grout filling material in actual projects, the amounts of fly ash and cement can be appropriately increased.

[0074] (2) Grouting and filling process design

[0075] The dominant orientation of the fracturing fractures was determined by borehole inspection or microseismic monitoring. A surface-mounted mixed grouting station was constructed in the ventilation shaft area to perform segmented grouting on the boreholes drilled during fracturing: borehole 15 was used as a grouting hole, with the grout primarily filling the fracturing fracture network before diffusing to the plastic zone of the coal pillar, and then to the roof bulk material and empty roadways, forming a loose fracture reinforcement zone 14 and an empty roadway filling zone 13. After solidification, a composite load-bearing structure of "coal pillar 10 - grout vein 11 - overburden 12" was formed. Figure 4 As shown in Table 1, the grouting process coordinates the bearing capacity of the coal pillar and the loose overburden. The grouting process is implemented in three stages, and the grouting parameters for each stage are shown in Table 1.

[0076] Table 1 Grouting Parameters

[0077]

[0078] The viscosity ranges and applicable scenarios for low, medium, and high viscosity slurries are shown in Table 2 (based on measurements using a Marsh funnel viscometer):

[0079] Table 2 Viscosity parameters and applicable scenarios for low, medium, and high viscosity slurries

[0080]

[0081] Note: The viscosity value is the time (in seconds) required for 1 liter of slurry to flow out of the Marshall funnel. The specific value needs to be adjusted according to the cement grade and the type of additives.

[0082] 1) Phase I (Main Fracture Channels): Low-viscosity slurry (pressure 2~3 MPa, flow rate 15~20 L / min) is preferentially injected into the fracture main channel network formed by fracturing. The goal is to achieve far-field fracture penetration, and the termination criterion is slurry return from adjacent holes.

[0083] 2) Phase II (Coal Pillar Plastic Zone): Medium-viscosity grout (pressure 4~5 MPa, flow rate 10~15 L / min) is injected into the coal pillar plastic zone affected by mining. The goal is to achieve near-field saturation, and the termination criterion is a sharp increase of 10% in grouting pressure.

[0084] 3) Phase III (Roof loose mass, empty areas and tunnels): Inject high-viscosity grout (pressure 1~2 MPa, flow rate 5~8 L / min) with added quick-setting agent to fill the broken rock mass of the roof and empty areas and tunnels. The termination criterion is that the grout intake rate is continuously less than 5 L / min.

[0085] (3) Process control technology

[0086] Intermittent grouting: The pump is stopped for 5 minutes after every 30 minutes of grouting to prevent blind diffusion by utilizing the thixotropic properties of the material; grout recovery: A filter device is installed at the wellhead to recover unsolidified grout for recycling. This process effectively solves the problems of "incomplete filling and weak consolidation" in traditional grouting, and is particularly suitable for fractured surrounding rock conditions. In actual construction, parameter fine-tuning is required based on the results of downhole ground-penetrating radar scanning.

[0087] This invention addresses the challenge of surrounding rock instability and safety risks caused by unclear exploration of hidden voids in residual coal mining areas. It proposes an integrated fracture network construction and synergistic grouting and filling technology based on fracturing-grouting-filling, which offers the following significant advantages:

[0088] (1) A three-dimensional fracture network is formed in the key layer by directional fracturing, and coal gangue-fly ash-desulfurized gypsum-cement-based slurry is injected. After consolidation, a "coal pillar-slurry vein-overburden" composite structure is formed, realizing the synchronous reinforcement of the plastic zone of the coal pillar and the overburden, so that the support structure and the surrounding rock form a unified force system, effectively suppressing the separation of coal wall spalling and roof.

[0089] (2) After constructing the fracture by directional fracturing, grouting is performed to reinforce it, and the two are combined to establish a more complete fracturing-grouting system.

[0090] (3) It solves the problems of blind diffusion of grout and insufficient filling of cracks in conventional one-time crack grouting. Through the phased grouting process, it effectively solves the problem of "not being able to fill the cracks completely and not being able to solidify the cracks" in traditional grouting.

[0091] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for grouting and filling cross-stratum areas of coal pillar groups in residual mining areas, characterized in that, Includes the following steps: (1) Based on the lithology, thickness and mechanical parameters of the overlying strata of the coal seam, select the hard rock strata that are thicker and stronger than the adjacent strata as the key strata; (2) Drilling is carried out in the key layer. The initial directional fractures extending in the direction of the surface and the coal seam are formed by cutting in the vertical plane of the borehole radial direction through the abrasive water jet. Then, the two ends of the borehole are sealed and high-pressure fluid is injected into the sealed section to expand the initial fractures and form a fracture network. (3) Use the borehole as a grouting hole and use grouting material to carry out segmented grouting construction: first, use low viscosity grout to fill the fracture network formed by fracturing, then use medium viscosity grout to fill the plastic zone of the coal pillar affected by mining, and finally use high viscosity grout with added quick-setting agent to fill the broken rock mass of the roof and the empty roadway. (4) After the slurry solidifies, it forms a composite load-bearing structure of "coal pillar-slurry vein-overburden"; The borehole spacing is determined using the following formula: （1）， （2）， In the formula: The borehole spacing is in meters (m). T The thickness of the grouting hole is in meters (m). R Let be the effective diffusion radius of the slurry, in meters (m). r 1 Let be the radius of the grouting hole, in meters. α This is the fracturing efficiency enhancement coefficient; η The critical layer fracture rate is % K The key layer permeability coefficient is given in m / d. C 1 and C cP represents the viscosity of the slurry and water, respectively. δ The fracture connectivity coefficient; p The grouting pressure is in meters (m). t The gelation time of the slurry is d.

2. The method for grouting and filling cross-stratum areas of coal pillar groups in residual mining areas according to claim 1, characterized in that: In step (3), the grouting material is a coal gangue-fly ash-desulfurized gypsum-cement-based grouting material with the following mass ratio: desulfurized gypsum 4-6%, fly ash 28-32%, coal gangue 53-57%, and cement 9-11%.

3. The method for grouting and filling cross-stratum areas of coal pillar groups in residual mining areas according to claim 1, characterized in that: In step (3), the injection pressure of low viscosity slurry is 2~3 MPa and the flow rate is 15~20 L / min, the injection pressure of medium viscosity slurry is 4~5 MPa and the flow rate is 10~15 L / min, and the injection pressure of high viscosity slurry is 1~2 MPa and the flow rate is 5~8 L / min.

4. The method for grouting and filling cross-stratum areas of coal pillar groups in residual mining areas according to claim 1, characterized in that: In step (2), the height of the borehole is higher than the collapse zone.

5. The method for grouting and filling cross-stratum areas of coal pillar groups in residual mining areas according to claim 1, characterized in that: In step (2), a drilling rig, matching drill bit and drill rod are used to drill holes in the roof of the roadway; after connecting the sealing device and the abrasive jetting device, send them to the preset position of the drilling hole, turn on the water jetting system and switch it to the jetting mode, spray high-pressure water with abrasive sand from the nozzles on the upper and lower sides of the abrasive jetting device, operate the drilling rig to retract the drill rod at a uniform speed, cut and form directional initial fractures extending along the surface direction and the coal seam direction in the vertical plane where the borehole is located; turn off the abrasive pump and adjust the high-pressure pump to the sealing mode, inject high-pressure water into the sealing device, so that the sealing devices at both ends of the borehole are set; switch the high-pressure pump to the fracturing mode, continuously inject high-pressure water into the sealing section from the water outlet at the front end of the abrasive jetting device, the initial fractures continue to expand along the fracture tip, and when the pump pressure suddenly drops or the fracturing time reaches the design time, turn off the high-pressure pump, depressurize the sealing device, and the initial fractures expand to form a fracture network.

6. The method for grouting and filling cross-stratum areas of coal pillar groups in residual mining areas according to claim 1, characterized in that: In step (3), the dominant direction of the fracturing fracture is determined by borehole inspection or microseismic monitoring, and a ground-based mixed grouting station is constructed in the ventilation shaft area to carry out segmented grouting construction of the grouting holes.

7. The method for grouting and filling cross-stratum areas of coal pillar groups in residual mining areas according to claim 1, characterized in that: In step (3), intermittent grouting is adopted, with the pump stopped for 5 minutes after every 30 minutes of grouting, and the thixotropic properties of the grout are used to prevent the grout from spreading blindly.

8. The method for grouting and filling cross-stratum areas of coal pillar groups in residual mining areas according to claim 1, characterized in that: In step (3), a filter device is installed at the borehole opening to recover unsolidified slurry for recycling.

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