Mining separation layer fracture filling method based on ground comb type directional drilling group

Abstract

The invention discloses a mining separation layer crack filling method based on a ground comb type directional drilling group. The mining separation layer crack filling method comprises the following steps that (1) the position of each key layer is determined; (2) selecting a proper key layer as a grouting layer position; (3) establishing a numerical calculation model by adopting numerical simulation software, and simulating and analyzing the evolution law of the separation layer in the advancing process of the coal face; (4) a drill site is arranged outside the influence range of the mining area, and a main hole for ground comb type directional drilling is constructed; (5) designing a branch hole track of the ground comb type directional drilling by using Landmark software; (6) a ground comb type directional drilling group is arranged; and step (7), performing separation fracture filling on a grouting layer in the overlying strata on the coal mining working face by constructing multiple groups of ground comb type directional drilling holes. By means of the method, ground surface settlement control of mining-filling synchronous operation can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of mine rock layer control and geological disaster prevention and control, and more particularly to a method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group. Background Art

[0002] Coal mining, particularly longwall mechanized mining, while efficiently recovering coal resources, inevitably causes movement, deformation, and damage to the overlying rock strata. During this process, as the working face advances, significant delamination spaces (delamination fissures) form beneath the hard rock strata (critical strata) above the coal seam, while the relatively weaker rock strata above it break and collapse. These dynamically developing delamination fissures serve as important pathways for water and gas conduction, causing mine water hazards and increased surface subsidence, posing a serious threat to coal mine safety and the ecological environment in mining areas.

[0003] To address these issues, grouting is the primary method used in engineering practice to seal delamination fissures. However, conventional delayed filling typically requires grouting only after the delamination has stabilized, making it impossible to control developing delamination fissures and leading to irreversible settlement. Ground vertical drilling has poor targeting, and the coverage of drilling and grouting is limited, making it difficult to match the rapidly advancing working face and achieve "advanced pre-control" or "synchronous control," resulting in poor control effectiveness during critical stages. Furthermore, the presence of buildings (structures) and large bodies of water above the working face often prevents the placement of vertical drilling holes above the working face.

[0004] Chinese patent CN 117605524 A proposes a "three-down" coal-pressing targeted overburden stratum grouting and filling method. This method can be constructed from the outside of the "three-down" coal-pressing working face where there are surface structures or water bodies, quickly entering the target stratum and completing the overburden stratum grouting and filling, thus freeing the "three-down" coal-pressing working face. However, this method has the following drawbacks: 1. It is difficult to match the rapidly advancing working face and control the developing stratum cracks, resulting in irreversible subsidence; 2. This method only matches one underground filling borehole to each ground hole; 3. This method still requires the deployment of multiple surface drilling sites to control the stratum detachment caused by mining in the underground working face.

[0005] In summary, the core bottleneck faced by the existing grouting filling technology for delamination fissures is "how to efficiently, accurately and economically target and evenly distribute sufficient filling materials in the dynamically developing and spatially wide high-level delamination fissure zone". The traditional delayed filling surface subsidence is irreversible, and it is difficult to achieve "advanced pre-control" or "synchronous control" of vertical holes on the ground. Both are unable to meet the growing demand for refined control of delamination fissures in modern coal mining for safe, efficient and green mining. There is an urgent need to develop a new filling method that can be implemented from the ground, with a highly controllable drilling trajectory, can cover a large area of ​​the target delamination area, and has an efficient and accurate grouting process. Summary of the Invention

[0006] To this end, the technical problem to be solved by the present invention is to provide a method for filling mining-induced delamination cracks based on a ground comb-type directional drilling group. This method fills the delamination cracks in the key layers above the mining area in real time during the advancement of the coal mine working face, thereby realizing surface settlement control of simultaneous mining and filling operations.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] A method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group comprises the following steps:

[0009] Step (1) comprehensively determining the position, thickness and physical and mechanical parameters of each rock layer based on the geological drilling histogram, obtaining the position of each key layer, and determining the height of the "collapse zone", "fracture zone" and "bend sinking zone", and arranging to obtain the key layer occurrence state map;

[0010] Step (2), according to the height of the "fracture zone" and the grouting process, select the key layer above the "fracture zone" as the grouting target layer, and determine the specific position of the grouting layer; (when determining the grouting target layer, the separation layer in the overburden of the stope changes with time and space, and the position and layer selection of the grouting hole need to match various parameters such as the advancement of the stope, the grouting layer, the grouting speed and the advancement of the working face; because the grouting slurry has a certain fluidity and permeability, the hole position and layer selection of the grouting hole need to consider the penetration of the overburden fracture and the permeability of the grouting layer; in addition, the selection of the grouting pressure needs to fully consider the pressure of the overburden and the bearing capacity of the key layer).

[0011] Step (3): Based on the key layer occurrence state diagram, a numerical calculation model is established using numerical simulation software to simulate and analyze the evolution law of the separation layer during the advancement of the coal mining working face;

[0012] Step (4), arranging a drilling site outside the influence range of the mining area and constructing the main hole of the ground comb-type directional drilling; the main hole casing is far away from the influence range of the mining area;

[0013] Step (5), combining the analysis results of the numerical calculation model in step (3), using Landmark software to design the branch hole trajectory of the ground comb directional drilling, and determining the final hole formation time and final hole position of the branch hole of the ground comb directional drilling;

[0014] Step (6), arranging a ground comb-type directional drilling group, and determining the position of the first branch hole of the first group of ground comb-type directional drilling holes;

[0015] Step (7) is to fill the separation cracks in the grouting layer in the overlying rock stratum of the coal mining working face by constructing multiple groups of ground comb-type directional drilling holes.

[0016] In the above-mentioned method for filling stratum cracks caused by mining based on a ground comb-type directional drilling group, in step (1), a geological drilling histogram is obtained by constructing a core hole; the position of each key layer is determined by calculating the breaking distance; the calculation method of the breaking distance of the key layer is:

[0017]

[0018] In formula (1), L r is the breaking distance of the key layer; h k is the critical layer thickness; R r is the tensile strength of the key layer; q is the load borne by the key layer; after the key layer is identified, the occurrence state of the key layer is judged using the existing borehole columnar data to form a key layer occurrence state diagram to facilitate the selection of the appropriate key layer as the grouting layer;

[0019] Post-mining exploration holes are carried out in the goaf of the working face with similar mining conditions at an address near the planned grouting filling area. The maximum development heights of the collapse zone and fracture zone after the working face mining are determined by observing the consumption of drilling flushing fluid, observing the drill core and observing the cracks in the hole wall with color images in the hole. The heights of the "collapse zone", "fracture zone" and "bend subsidence zone" are obtained by comprehensive analysis combined with the nearby borehole histogram and geological data; the abscission space develops in the bend subsidence zone, and the grouting layer selection needs to be above the water-conducting fracture zone.

[0020] In the above-mentioned method for filling stratum cracks caused by mining based on a ground comb-type directional drilling group, in step (2), the principle for determining the specific position of the grouting layer is as follows:

[0021] (2-1) The grouting layer is located in the stratum below the critical layer;

[0022] (2-2) The grouting layer is located above the “fracture zone”, and there is a protective zone between the “fracture zone” and the grouting layer. The height of the protective zone is 5 to 10 times the mining height.

[0023] In the above-mentioned method for filling cracks caused by mining based on ground comb-type directional drilling groups, in step (3), the numerical simulation software is FLAC 3D Finite element software; the length, width and height of the numerical calculation model are 652m×10m×625m, the horizontal displacement is fixed on all sides of the numerical calculation model, the horizontal displacement and vertical displacement are fixed on the bottom, and gravity acceleration is applied to the whole; the number of layers established in the numerical calculation model is the total number of rock layers in the geological drilling column diagram, and the physical and mechanical parameters used in the simulation analysis are the data measured in step (1); the evolution law of the separation layer during the mining process of the coal mining working face is determined by simulation analysis, and the timing of ground comb directional drilling and grouting is determined.

[0024] In the above-mentioned method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group, in step (4), the main hole includes a first straight hole section extending vertically downward from the ground and a second inclined hole section with directionally inclined structure; the borehole diameter of the first straight hole section is 311.2 mm, and a Φ244.5×8.94 mm J55 steel-grade oil casing is inserted; the end of the first casing is inserted into a stable stratum 5 to 10 m; the borehole diameter of the second inclined hole section is 215.9 mm, and a Φ177.8×8.05 mm J55 steel-grade oil casing is inserted, and the landing point of the second opening is located in the stable bedrock adjacent to the target layer; both the first casing and the second casing are fixed with cement slurry with a specific gravity greater than or equal to 1.65.

[0025] In the above-mentioned method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group, in step (5), the branch holes of the ground comb-type directional drilling are three-opening horizontal section bare holes drilled into the target key layer by the ground comb-type directional drilling, and the borehole diameter is 152.4 mm; the three-opening horizontal section bare holes extend from the second opening landing point of the key layer from top to bottom and are inclined toward the middle of the grouting layer. Each three-opening horizontal section bare hole of the hole group includes 5 to 10 branch holes;

[0026] Based on the results of the numerical calculation model analysis of the development position of the overburden stratum delamination [simulation analysis was performed using the method disclosed in patent CN115392067A], and taking into account the grouting diffusion radius, the final hole completion time of the branch hole in the ground comb-type directional drilling was determined; assuming that the final hole completion time of the branch hole is when the coal mining working face advances a distance S, then before the overburden stratum delamination develops to the selected key layer, the distance S / 2 in front of the cutting eye is the final hole position of the branch hole, and the final hole completion time of the branch hole is ahead of the expansion period of the target key layer delamination space.

[0027] In the above-mentioned method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group, in step (6), for a group of ground comb-type directional drilling holes (a group of ground comb-type directional drilling holes is composed of one straight hole section, two inclined hole sections and three horizontal open hole sections with 5 to 10 branch holes): one branch hole is arranged at every interval S (equivalent to the final hole spacing between two adjacent branch holes) along the strike of the coal mining face, and the branch holes are arranged radially in a comb-like shape, S = 100 to 200m; 5 to 10 branch holes are arranged in each group of ground comb-type directional drilling holes; when the length of the coal mining face is less than 200 meters, one row of branch holes is arranged along the strike of the coal mining face; if the length of the coal mining face is greater than or equal to 20 0m, two rows of branch holes are arranged along the strike of the coal mining face; the number of ground comb-type directional drilling groups is determined in combination with the strike length of the coal mining face; L-shaped ground directional drilling is affected by the burial depth of the selected key layer, stratum lithology, etc., which will affect the longest borehole depth. Generally, the water-to-vertical ratio of the borehole is not greater than 2:1; assuming that the branch hole spacing is 100m, a comb-type directional drilling group with 5 branch holes can only control the strike range of 500m of the working face; if the actual strike length of the coal mining face is long, multiple directional drilling groups need to be arranged; the final hole trajectory of the branch hole covers the extension direction of the "separation fracture zone" and the angle between it and the advance line of the coal mining face is 30°~60°.

[0028] The above-mentioned method for filling mining-induced stratum fractures based on a ground comb-type directional drilling group comprises arranging two or more ground comb-type directional drilling groups simultaneously along the horizontal extension direction of the coal mining working face, and the horizontal branch holes of each ground comb-type directional drilling group are arranged in a staggered manner;

[0029] And / or: two groups of ground comb-type directional drill holes are arranged simultaneously along the vertical direction of the coal mining face; after the coal mining face advances a certain distance, the lower layer of ground comb-type directional drill holes are used to carry out high-position drilling filling from the ground to the goaf behind the coal mining face, and the upper layer of ground comb-type directional drill holes are used to carry out grouting filling of the mining-induced separation cracks below the selected key layer before the selected key layer is broken.

[0030] In the above-mentioned method for filling mining-induced stratum fissures based on a ground comb-type directional drilling group, in step (6), the position of the first branch hole of the first group of ground comb-type directional drilling holes is within the influence range of the mining area. If there are buildings (structures) on the ground, the protected object is protected when the influence is developed to the layer selected by the first branch hole; the distance between the first branch hole and the protected object is calculated as follows:

[0031]

[0032] In formula (2), L is the distance between the first branch hole and the protected object; H1 is the thickness of the topsoil layer; φ is the movement angle of the topsoil layer; H2 is the thickness of the bedrock; δ is the movement angle of the bedrock; C is the safety distance;

[0033] The distance between two adjacent branch holes is less than the strike length of the working face corresponding to the limit span of the selected key layer.

[0034] In the above-mentioned method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group, in step (7), the branch holes extend in the direction of the cut-hole of the coal mining working face, and the subsequent branch holes are drilled using a backward drilling process, that is, after the grouting and sealing of the previous branch holes are completed, the subsequent holes are drilled from the side of the previous drilling trajectory;

[0035] The grouting material is fly ash slurry and / or coal gangue slurry; the mass fraction of solid matter in the grouting material is controlled at 60-70wt%; and the injection-production ratio is 0.4-0.6.

[0036] The technical solution of the present invention achieves the following beneficial technical effects:

[0037] 1. The present invention is based on a method for filling delamination fissures caused by mining using a ground comb-type directional drilling group. Construction is carried out from the periphery of the mining area, accurately targeting the delamination fissures in the key layers, which can effectively avoid accidents such as casing compression and breakage caused by mine recovery. At the same time, the directional drilling design can avoid obstacle areas such as surface buildings and water bodies, thereby realizing grouting and filling of the overburden delamination of the "three-down" coal-pressing working face.

[0038] 2. The ground comb directional drilling of the present invention is based on FLAC 3D Numerical simulation dynamically optimizes the timing and location of drilling, allowing grouting operations to occur slightly earlier than the detachment expansion period, ensuring that the filling material seals the dynamic detachment cracks in real time, avoiding the irreversible settlement caused by traditional delayed grouting, thereby achieving simultaneous mining and filling operations and controlling surface settlement.

[0039] 3. The ground comb-type directional drilling group of the present invention arranges multiple branch directional drilling groups (5 to 10 branch holes in each group) in a single site, efficiently covers different target areas, reduces the frequency of equipment relocation and ground occupation, and can effectively reduce project costs; at the same time, the horizontal comb-shaped radial branch drilling group (the angle between the final hole trajectory and the advancement line is 30° to 60°) covers a large range of the extension direction of the delamination space, which can significantly improve the uniformity and efficiency of grouting.

[0040] 4. Compared with the method in background technology CN 117605524 A, the present invention completes the branch drilling construction before the stratum develops to the selected grouting layer by establishing a numerical calculation model, and monitors the development degree of the stratum space in real time, so as to realize the filling of the stratum cracks caused by mining; the present invention uses multi-branch side drilling technology to construct multiple horizontal branch boreholes, so that one ground hole can match multiple underground filling boreholes; and only one ground drilling site is required to control a large range of underground recovery working faces. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1A process flow chart of a method for filling stratum cracks caused by mining based on a ground comb-type directional drilling group in an embodiment of the present invention;

[0042] Figure 2 Schematic diagram of the distance between the first hole of a building (structure) on the ground in the mining area and the protected object in the embodiment of the present invention;

[0043] Figure 3 A schematic cross-sectional diagram of grouting during ground comb-type directional drilling in an embodiment of the present invention;

[0044] Figure 4 A schematic plan view of grouting of stratum separated by ground comb-type directional drilling groups in an embodiment of the present invention. DETAILED DESCRIPTION

[0045] The process of the mining-induced stratum crack filling method based on the ground comb-type directional drilling group in this embodiment is as follows: Figure 1 As shown, the specific steps include:

[0046] Step (1): Based on the geological borehole histogram and in combination with geological data, the position, thickness and physical and mechanical parameters of each rock layer are comprehensively determined to obtain the position of each key layer and determine the height of the "collapse zone", "fracture zone" and "bend sinking zone". The geological borehole histogram is obtained by construction core drilling. The position of each key layer is determined by calculating the breaking distance. The calculation method of the breaking distance of the key layer is:

[0047]

[0048] In formula (1), L r is the breaking distance of the key layer; h k is the critical layer thickness; R r is the tensile strength of the key layer; q is the load borne by the key layer; after the key layer is identified, the occurrence state of the key layer is judged using the existing borehole columnar data to form a key layer occurrence state diagram to facilitate the selection of the appropriate key layer as the grouting layer;

[0049] Post-mining exploration holes are carried out in the goaf of the working face with similar mining conditions at an address near the planned grouting filling area. The maximum development heights of the collapse zone and fracture zone after the working face mining are determined by observing the consumption of drilling flushing fluid, observing the drill core and observing the cracks in the hole wall with color images in the hole. The heights of the "collapse zone", "fracture zone" and "bend subsidence zone" are obtained by comprehensive analysis combined with the nearby borehole histogram and geological data; the separation layer develops in the bend subsidence zone, and the grouting layer selection needs to be above the water-conducting fracture zone.

[0050] Step (2): According to the height of the "fracture zone" and the grouting process, the key layer above the "fracture zone" is selected as the grouting target layer, and the specific location of the grouting layer is determined; the principle for determining the specific location of the grouting layer is:

[0051] (2-1) The grouting layer is located in the stratum below the critical layer;

[0052] (2-2) The grouting layer is located above the "fracture zone", and there is a protective zone between the "fracture zone" and the grouting layer. The height of the protective zone is 5 to 10 times the mining height. The protective zone at regular intervals can prevent slurry from entering the goaf and affecting coal mine production safety.

[0053] (2-3) The thickness of the key layer above the grouting layer should be as large as possible, and the lithology of the key layer should be as hard as possible;

[0054] (2-4) The grouting position should not be too shallow and should not be too far from the coal seam. The farther away from the coal seam, the smaller the range of stratum development, the smaller the grouting space, and the less sufficient the grouting downward compaction. At the same time, it is easy to penetrate the upper strata, causing slurry leakage and slurry seepage.

[0055] When determining the target grouting layer, the detachment layer in the overburden of the mining area changes with time and space. The location and layer selection of the grouting holes need to match various parameters such as the advancement of the mining area, grouting layer, grouting speed and working face advancement. Since the grouting slurry has certain fluidity and permeability, the location and layer selection of the grouting holes need to consider the penetration of the overburden cracks and the permeability of the grouting layer rock. In addition, the selection of grouting pressure needs to fully consider the pressure of the overburden layer and the bearing capacity of the key layer.

[0056] The results of the identification of the columnar shape and key overburden layers of the exploration holes in the coal mining face in this embodiment are shown in Table 1.

[0057] Table 1 Results of identification of columnar and overburden key layers in the exploration holes of the working face

[0058]

[0059]

[0060] Step (3): On the basis of reserving a protective layer of sufficient thickness, the numerical simulation software FLAC was used based on the key layer occurrence state diagram. 3D Finite element software was used to establish a numerical calculation model to simulate and analyze the evolution of the stratum separation during the advancement of the coal mining working face. The length, width and height of the numerical calculation model were 652m×10m×625m. The horizontal displacement was fixed on all sides of the numerical calculation model, and the horizontal and vertical displacements were fixed on the bottom. Gravity acceleration was applied to the whole model. The number of layers established in the numerical calculation model was the total number of rock layers in the geological drilling column diagram. The physical and mechanical parameters used in the simulation analysis were the data measured in step (1). By simulating and analyzing the evolution of the stratum separation during the advancement of the coal mining working face, the timing of ground comb directional drilling and grouting was determined.

[0061] Step (4), arranging a drilling site outside the influence range of the mining area and using directional drilling technology to construct the main hole of the ground comb-type directional drilling; the main hole casing is far away from the influence range of the mining area; avoiding accidents such as casing collapse and breakage caused by mine recovery;

[0062] like Figure 3 and Figure 4 As shown, the main hole includes a straight hole section extending vertically downward from the ground and a second inclined hole section with directionally inclined hole; the borehole diameter of the straight hole section is 311.2 mm, and a Φ244.5×8.94 mm oil casing is run into it; the end of the first casing is 5 to 10 m deep into the stable formation; the borehole diameter of the second inclined hole section is 215.9 mm, and a Φ177.8×8.05 mm oil casing is run into it, and the landing point of the second opening is located in the stable bedrock adjacent to the target layer; both the first and second casings are fixed with cement slurry with a specific gravity greater than or equal to 1.65; all the oil casings used are smooth, crack-free, and J55 steel-grade oil casings with intact threads.

[0063] Step (5), combining the analysis results of the numerical calculation model in step (3), using Landmark software to design the branch hole trajectory of the ground comb directional drilling, and determining the final hole formation time and final hole position of the branch hole of the ground comb directional drilling;

[0064] The branch holes of the ground comb directional drilling are three-opening horizontal section open holes drilled into the target key layer. The borehole diameter is 152.4mm, exposing the delamination below the key layer and grouting the mining-induced delamination fractures. The three-opening horizontal section open holes extend from the second opening point of the key layer from top to bottom and are inclined toward the middle of the grouting layer. The three-opening horizontal section open holes include multiple branch holes.

[0065] Based on the results of the numerical calculation model analysis of the development position of the overburden stratum delamination [simulation analysis was performed using the method disclosed in patent CN115392067A], and taking into account the grouting diffusion radius, the final hole formation time of the branch hole in the ground comb-type directional drilling was determined; assuming that the final hole formation time of the branch hole is when the coal mining working face advances a distance S, S = 100 to 200m, then before the overburden stratum delamination develops to the selected key layer, the distance S / 2 in front of the cutting eye is the final hole position of the branch hole, and the final hole formation time of the branch hole is ahead of the expansion period of the target key layer delamination space.

[0066] By establishing a numerical model, the optimal drilling time and drilling location for ground grouting drilling are determined, and the impact of working face advancement on drilling is analyzed. To ensure that the grouting operation is completed in a timely and sufficient manner during the expansion of the stratum, the final drilling time of the drilling should be slightly ahead of the expansion period of the main stratum space, so as to avoid grouting too late and not filling all the stratum spaces, or hole wall collapse due to early drilling, which affects grouting. Therefore, the appropriate drilling time can be determined according to the working face advancement speed and the final drilling time.

[0067] The drilling structure of the ground comb-type directional drilling in this embodiment is shown in Table 2.

[0068] Table 2 Drilling structure

[0069]

[0070] Step (6), arrange the ground comb-type directional drilling group, determine the position of the first branch hole of the first group of ground comb-type directional drilling; for a group of ground comb-type directional drilling (a group of ground comb-type directional drilling is composed of one straight hole section, two inclined hole sections and three horizontal open hole sections with 5 to 10 branch holes): arrange one branch hole at every interval S along the direction of the coal mining working face, and the branch holes are arranged radially in a comb-tooth shape; each group of ground comb-type directional drilling is arranged with 5 to 10 branch holes; when the length of the coal mining working face is less than 200 meters, arrange one row of branch holes along the direction of the coal mining working face; if the length of the coal mining working face is greater than or equal to 200 meters, arrange two rows of branch holes along the direction of the coal mining working face; determine the number of ground comb-type directional drilling hole groups based on the length of the coal mining working face; execute according to the above method to form a targeted comb-type directional drilling group within the coal mining working face; the terminal hole trajectory of the branch hole covers the extension direction of the "separation space" and the angle between the branch hole and the advancement line of the coal mining working face is 30° to 60°. Each horizontal branch hole extends in the direction of the cut hole on the working face. After the previous branch hole is grouting and sealing, the subsequent hole is drilled from the side of the previous hole trajectory. L-shaped ground directional drilling is affected by the depth of the selected key layer and the lithology of the formation, which will affect the longest drilling depth. Generally, the vertical-to-horizontal ratio of the drilling hole is not greater than 2:1.

[0071] In some other embodiments, two or more groups of ground comb-type directional drill holes can be arranged simultaneously along the horizontal extension direction of the coal mining face, and the horizontal branch holes of each group of ground comb-type directional drill holes are staggered; or: two groups of ground comb-type directional drill holes can be arranged simultaneously along the vertical direction of the coal mining face; after the coal mining face advances a certain distance, the lower layer of ground comb-type directional drill holes are used to perform high-position drilling and filling from the ground to the goaf behind the coal mining face, and the upper layer of ground comb-type directional drill holes are used to perform grouting and filling of the mining-induced delamination cracks below the selected key layer before the selected key layer is broken; or the above two methods can be performed simultaneously.

[0072] The location of the first branch hole of the first group of ground comb directional drilling is within the influence range of the mining area. If there are buildings (structures) on the ground, the protected objects shall be protected when the influence is developed to the layer selected by the first branch hole; Figure 2 As shown in the figure, the distance between the first branch hole and the protected object is calculated as follows:

[0073]

[0074] In formula (2), L is the distance between the first branch hole and the protected object; H1 is the thickness of the topsoil layer; φ is the movement angle of the topsoil layer; H2 is the thickness of the bedrock; δ is the movement angle of the bedrock; C is the safety distance;

[0075] The spacing between two adjacent branch holes: calculated based on the critical layer limit span, the spacing between branch holes should be less than the strike length of the working face corresponding to the critical layer limit span. In this embodiment, the spacing between branch holes is 100 to 200 meters.

[0076] Step (7) is to fill the separation cracks in the grouting layer in the overlying rock stratum of the coal mining working face by constructing multiple groups of ground comb-type directional drilling holes.

[0077] When the coal mining face advances a distance S, gangue or fly ash slurry is injected into the separation zone (grouting layer) in the overlying stratum of the coal mining face through ground comb directional drilling. The mass fraction of solids in the grouting material is controlled at 60-70wt%. Before the formal grouting project begins, the timing of grouting should be comprehensively judged based on the mining situation of the working face and the water pressure of the borehole. 3D Numerical simulation results predict that after the working face advances a distance S, the overburden delamination develops before the selected key layer. The delamination space generally develops from the middle position below the key layer to the two ends. Grouting can be carried out when the working face advances to a distance S / 2 from the grouting hole or when the water pressure increases significantly. Grouting materials can be selected from fly ash, coal gangue slurry, etc., following the principles of environmental protection and economy. The amount of ash injected (fly ash or coal gangue) is calculated based on the injection-production ratio, which is generally calculated at 0.4 to 0.6. If subsidence reduction indicators are involved, the minimum injection-production ratio is calculated based on 0.5. It is also recommended to refer to similar projects with similar mining geological conditions for comprehensive determination. Grouting can be terminated when the injection volume reaches the designed grouting volume and the grouting pressure reaches the designed end-hole pressure and is maintained for a period of time, or when the surface movement and deformation have reached a stable period.

[0078] After the grouting and sealing of the current branch hole are completed, the next branch hole is drilled from the side of the current drilling trajectory, and the cycle is repeated. By constructing multiple groups of ground comb-type directional drilling holes, the mining-induced delamination cracks in the mining area can be efficiently filled.

[0079] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the claims of this patent application.

Claims

1. A method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group, characterized in that: The steps include: Step (1) comprehensively determining the position, thickness and physical and mechanical parameters of each rock layer based on the geological drilling histogram, obtaining the position of each key layer, determining the height of the "collapse zone", "fracture zone" and "bend sinking zone", and compiling to obtain the key layer occurrence state map; Step (2): According to the height of the "fracture zone" and the grouting process, the key layer above the "fracture zone" is selected as the grouting target layer, and the specific position of the grouting layer is determined; Step (3): Based on the key layer occurrence state diagram, a numerical calculation model is established using numerical simulation software to simulate and analyze the evolution law of the separation layer during the advancement of the coal mining working face; Step (4), arranging a drilling site outside the influence range of the mining area and constructing the main hole of the ground comb-type directional drilling; the main hole casing is far away from the influence range of the mining area; Step (5), combining the analysis results of the numerical calculation model in step (3), using Landmark software to design the branch hole trajectory of the ground comb directional drilling, and determining the final hole formation time and final hole position of the branch hole of the ground comb directional drilling; Step (6), arranging a ground comb-type directional drilling group, and determining the position of the first branch hole of the first group of ground comb-type directional drilling holes; Step (7) is to fill the separation cracks in the grouting layer in the overlying rock stratum of the coal mining working face by constructing multiple groups of ground comb-type directional drilling holes.

2. The method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group according to claim 1 is characterized in that: In step (1), the geological drilling histogram is obtained by constructing the core hole; the position of each key layer is determined by calculating the breaking distance; the calculation method of the key layer breaking distance is: In formula (1), L r is the breaking distance of the key layer; h k is the critical layer thickness; R r is the tensile strength of the key layer; q is the load borne by the key layer; after the key layer is identified, the occurrence state of the key layer is judged using the existing borehole columnar data to form a key layer occurrence state diagram; Post-mining exploration holes were drilled in the goaf of the working face with similar mining conditions at an address near the planned grouting filling area. The maximum development heights of the collapse zone and fracture zone after the working face were determined by observing the consumption of drilling fluid, observing the drill core, and observing the cracks in the hole wall with color images inside the hole. The heights of the "collapse zone", "fracture zone" and "bend subsidence zone" were obtained by comprehensive analysis combined with the histogram of nearby drill holes and geological data.

3. The method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group according to claim 2, characterized in that: In step (2), the principle for determining the specific location of the grouting layer is: (2-1) The grouting layer is located in the stratum below the critical layer; (2-2) The grouting layer is located above the "fracture zone", and there is a protective zone between the "fracture zone" and the grouting layer. The height of the protective zone is 5 to 10 times the mining height.

4. The method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group according to claim 3 is characterized in that: In step (3), the numerical simulation software is FLAC 3D Finite element software; the length, width and height of the numerical calculation model are 652m×10m×625m, the horizontal displacement is fixed on all sides of the numerical calculation model, the horizontal displacement and vertical displacement are fixed on the bottom, and gravity acceleration is applied to the whole; the number of layers established in the numerical calculation model is the total number of rock layers in the geological drilling column diagram, and the physical and mechanical parameters used in the simulation analysis are the data measured in step (1); the evolution law of the separation layer during the mining process of the coal mining working face is determined by simulation analysis, and the timing of ground comb directional drilling and grouting is determined.

5. The method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group according to claim 4, characterized in that: In step (4), the main hole includes a straight hole section extending vertically downward from the ground and a second inclined hole section with directionally inclined structure; the borehole diameter of the straight hole section is 311.2 mm, and a J55 steel-grade oil casing of Φ244.5×8.94 mm is inserted; the end of the first casing is inserted into a stable formation 5 to 10 m; the borehole diameter of the second inclined hole section is 215.9 mm, and a J55 steel-grade oil casing of Φ177.8×8.05 mm is inserted, and the landing point of the second opening is located in the stable bedrock adjacent to the target layer; both the first and second casings are fixed with cement slurry with a specific gravity greater than or equal to 1.

65.

6. The method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group according to claim 5, characterized in that: In step (5), the branch holes of the ground comb directional drilling are three-opening horizontal section bare holes drilled into the target key layer by the ground comb directional drilling, and the borehole diameter is 152.4 mm; the three-opening horizontal section bare holes extend from the second opening landing point of the key layer from top to bottom and are inclined toward the middle of the grouting layer. Each hole group three-opening horizontal section bare holes includes 5 to 10 branch holes; Based on the results of the numerical calculation model analysis of the development position of the overburden stratum delamination and taking into account the grouting diffusion radius, the final hole completion time of the branch hole in the ground comb directional drilling is determined; assuming that the final hole completion time of the branch hole is when the coal mining working face advances a distance S, then before the overburden stratum delamination develops to the selected key layer, the distance S / 2 in front of the cutting eye is the final hole position of the branch hole. The final hole completion time of the branch hole is ahead of the expansion period of the delamination space of the target key layer.

7. The method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group according to claim 6, characterized in that: In step (6), for a group of ground comb-type directional drilling holes: a branch hole is arranged at every interval S along the strike of the coal mining face, and the branch holes are arranged radially in a comb-teeth shape, S = 100 to 200 m; 5 to 10 branch holes are arranged in each group of ground comb-type directional drilling holes; when the length of the coal mining face is less than 200 m, one row of branch holes is arranged along the strike of the coal mining face; if the length of the coal mining face is greater than or equal to 200 m, two rows of branch holes are arranged along the strike of the coal mining face; the number of ground comb-type directional drilling hole groups is determined based on the strike length of the coal mining face; the final hole trajectory of the branch hole covers the extension direction of the "separation fracture zone" and the angle between the branch hole and the advance line of the coal mining face is 30° to 60°.

8. The method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group according to claim 7, characterized in that: Along the horizontal extension direction of the coal mining face, two or more groups of ground comb-type directional drilling holes are arranged at the same time, and the horizontal branch holes of each group of ground comb-type directional drilling holes are arranged in a staggered manner; And / or: two groups of ground comb-type directional drill holes are arranged simultaneously along the vertical direction of the coal mining face; after the coal mining face advances a certain distance, the lower layer of ground comb-type directional drill holes are used to carry out high-position drilling filling from the ground to the goaf behind the coal mining face, and the upper layer of ground comb-type directional drill holes are used to carry out grouting filling of the mining-induced separation cracks below the selected key layer before the selected key layer is broken.

9. The method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group according to claim 7, characterized in that: In step (6), the position of the first branch hole of the first group of ground comb directional drilling is within the influence range of the mining area. If there are buildings (structures) on the ground, the protected object will be protected when the mining impact develops to the layer selected by the first branch hole; the distance between the first branch hole and the protected object is calculated as follows: In formula (2), L is the distance between the first branch hole and the protected object; H1 is the thickness of the topsoil layer; φ is the movement angle of the topsoil layer; H2 is the thickness of the bedrock; δ is the movement angle of the bedrock; C is the safety distance; The distance between two adjacent branch holes is less than the strike length of the working face corresponding to the limit span of the selected key layer.

10. The method for filling mining-induced stratum cracks based on a ground comb-type directional drilling group according to claim 9, characterized in that: In step (7), the branch holes extend in the direction of the cutting eye of the coal mining face, and the subsequent branch holes are drilled using a backward drilling process, that is, after the grouting and sealing of the previous branch holes are completed, the subsequent holes are drilled from the side of the previous drilling trajectory; The grouting material is fly ash slurry and / or coal gangue slurry; the mass fraction of solid matter in the grouting material is controlled at 60-70wt%; and the injection-production ratio is 0.4-0.6.

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