Method for determining key roof-cutting drilling parameters of dense drilling roof-cutting gob-side entry retaining

Abstract

The invention relates to the technical field of coal mining, and discloses a method for determining key roof-cutting drilling parameters of dense drilling roof-cutting gob-side entry retaining, which comprises the following steps of: collecting engineering geological data of a target roadway, and measuring geomechanical parameters of a roof rock mass by adopting a mode of combining in-situ exploration and indoor test; on the basis of the geomechanical parameters obtained in the pre-mining exploration step, a mechanical model is constructed, and the top cutting height, the top cutting angle, the drilling hole diameter and the drilling hole spacing of the dense drilling holes are sequentially calculated and determined; the roof cutting height, the roof cutting angle, the drill hole diameter and the drill hole spacing of the integrated drill hole are combined and applied to a field industrial test, a mine pressure monitoring system is arranged to monitor the entry retaining effect, and key parameters are subjected to feedback optimization according to a monitoring result. According to the parameter determination method combining theoretical calculation and field optimization, quantitative solution is carried out on the top cutting height, angle and the like, and design scientificity and geological adaptability are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal mining, in particular to a method for determining key cutting top drilling parameters of a dense drilling cutting top gob-side entry retaining. BACKGROUND

[0002] Gob-side entry retaining is a key technology in coal resource mining, which maintains and retains the original transport or return air roadway along the edge of the goaf after the working face is mined for the continuous use of the adjacent working face. This technology can significantly improve the recovery rate of coal resources, simplify the mine production system, and reduce the amount of roadway excavation. Dense drilling pre-splitting cutting top is one of the technical means to realize gob-side entry retaining, which is to construct a row of dense drilling along one side of the roadway roof to form a pre-splitting weakening surface, guide the roof to collapse at the predetermined position and form a stable gangue bank in the goaf to maintain the roadway.

[0003] In the existing dense drilling cutting top technology practice, the determination of key parameters of cutting top drilling (mainly including cutting top height, cutting top angle, drilling diameter, and drilling spacing) is usually based on engineering analogy and field experience. Specifically, the technical personnel will refer to successful cases of other mines with similar geological structure and roof lithology, or conduct a small-scale local test in the target roadway, select or adjust the parameters according to the test results, and finally form a complete construction plan.

[0004] Although the existing technology has solved the problem of cutting top for gob-side entry retaining to some extent, it still has some deficiencies in the scientificity, adaptability, and reliability of parameter design. First of all, this method relying on experience and analogy lacks systematic theoretical basis. Geological conditions have inherent complexity and variability. Even if the macroscopic geological conditions of two working faces are similar, the specific mechanical properties of the roof rock mass, the in-situ stress state, and the joint fissure development degree also have quantitative differences, which are enough to cause significant differences in cutting top effect. Directly applying the successful parameters of one work point to another work point ignores this difference, making the scientificity and accuracy of parameter design insufficient. Secondly, this method has poor adaptability to different geological conditions. When encountering complex or special geological conditions without similar engineering cases for reference, it will become extremely difficult to rely solely on experience to judge, often requiring multiple field trial and error, which not only prolongs the preparation period, but also increases engineering cost and safety risk. Finally, due to the lack of a closed-loop feedback mechanism from theoretical model to field monitoring to parameter optimization, the existing method is difficult to achieve reliable control and continuous improvement of the cutting top effect, and its success or failure largely depends on the experience level of individual engineers, limiting the reliability and repeatability of the technical solution. SUMMARY

[0005] In view of the deficiencies of the prior art, the application provides a method for determining key top cutting borehole parameters of dense borehole top cutting and gob-side entry retaining, and solves the problem that in the prior art, key parameter design of dense borehole top cutting technology mainly depends on engineering experience, lacks systematic theoretical calculation and quantitative basis, and thus the scientificity of parameter selection is insufficient and the geological adaptability is poor.

[0006] To achieve the above object, the application is implemented by the following technical solutions:

[0007] The application provides a method for determining key top cutting borehole parameters of dense borehole top cutting and gob-side entry retaining, which comprises the following steps:

[0008] First step:

[0009] The geological exploration report of the target roadway and working face, the working procedure of the working face, the roadway section drawing, the mining and excavation engineering plan drawing and the stratum comprehensive column drawing are collected systematically to master the macroscopic engineering geological background.

[0010] The method of "drilling-sampling-measuring" is used to accurately calibrate the mechanical properties of the roof rock mass. Specifically, before the roadway mining, the roof is drilled and detected by using a borehole peeping instrument to find out the lithology, thickness, integrity and structure characteristics of the roof stratum;

[0011] At the same time, the rock samples of the key stratum of the roof (including the immediate roof and the main roof) are collected in the mining area, and the standard test pieces are prepared in the laboratory to perform the rock mechanics test, so as to accurately measure the uniaxial compressive strength [σ c ], tensile strength [σ t ], shear strength [τ s ], cohesion C0 and internal friction angle φ of the rock mass.

[0012] Second step:

[0013] The determination of the top cutting height needs to meet the double criteria of effective filling of the goaf and reliable fracture of the roof. To ensure that the fractured roof rock mass can fill the goaf and form effective support to the overlying stratum, the theoretical top cutting height H c needs to meet the following conditions:

[0014]

[0015] In the formula, H c is the theoretical top cutting height; M c is the mining height of the coal seam; and K p is the crushing and swelling coefficient of the roof rock mass.

[0016] Based on the checking calculation of the rock beam tension fracture theory when the top is partially cut: when the construction condition is limited and the borehole cannot completely cut through the roof, the top cutting height is calculated by analyzing the tensile stress on the top cutting non-penetrating surface, and the calculation formula is:

[0017]

[0018] where σ w is the tensile stress on the unpenetrated face of the basic roof rock; M (d) is the bending moment on the unpenetrated face of the basic roof rock; W t is the bending modulus of the unpenetrated rock beam; [σ t ] is the tensile strength of the roof rock.

[0019] According to the above formula, the greater the height of the roof cutting seam, the greater the tensile stress σ w on the unpenetrated face of the basic roof rock. When σ w is greater than the tensile strength of the rock mass, the roof is subjected to tensile failure. When the height of the roof cutting seam is 7.8 m, σ w = 1.86 MPa, which is greater than the measured tensile strength of the roof. At this time, the roof can be cut and the broken gangue can fill the goaf.

[0020] According to the S-R stability theory of masonry beam structure, in order to ensure that the key rock mass formed after cutting the roof can slide and lose stability rather than form a stable hinged structure, the cutting angle θ must satisfy the following critical condition:

[0021]

[0022] where θ is the inclination angle of the roof cutting drill hole; φ is the internal friction angle between the fractured rock blocks; H b is the thickness of the key rock mass; Δ s is the rotational subsidence of the key rock mass; L o is the lateral span of the key rock mass.

[0023] The determination of the borehole diameter (d b ) regards the roof after the construction of the dense drill hole as a cantilever beam structure with holes. In order to ensure that the rock mass is smoothly fractured at the roof cutting position affected by the drill hole, the maximum normal stress σ max and the maximum shear stress τ max on the dangerous cross section need to be greater than the ultimate tensile strength and shear strength of the rock mass:

[0024] The calculation and checking formula of the maximum normal stress σ max is:

[0025]

[0026] The calculation and checking formula of the maximum shear stress τ max is:

[0027]

[0028] where σmax σ is the maximum normal stress of the rock mass between the holes; σ t ] is the tensile strength of the roof rock mass; τ max is the maximum shear stress of the rock mass between the holes; τ s ] is the shear strength of the roof rock mass; q o is the uniform load acting on the roof above; L o is the cantilever length of the roof on the side of the goaf; H r is the total thickness of the roof rock layer that needs to be cut off; H c is the actual roof-cutting height of the dense drilling; b is the unit thickness selected along the axis of the roadway in the calculation model; r b is the radius of the drilling.

[0029] Single-hole plastic zone radius calculation: first, calculate the plastic zone radius R p of the surrounding rock of a single drilling under the original rock mass stress:

[0030]

[0031] In the formula, R p is the plastic zone radius of the drilling surrounding rock; r b is the drilling radius determined by the foregoing steps; P0 is the original rock mass stress at the location of the drilling; C0 is the cohesion of the roof rock mass; and φ is the internal friction angle of the roof rock mass.

[0032] Drilling spacing determination: to ensure the formation of a continuous pre-splitting weak surface, the drilling spacing D b should be no greater than twice the plastic zone radius:

[0033] D b ≤ 2R p ;

[0034] In the formula, D b is the center-to-center spacing of the drillings; and R p is the calculated plastic zone radius of the drilling surrounding rock.

[0035] Step 3:

[0036] This step aims to verify and finally optimize the theoretical calculation parameters through field practice.

[0037] Field test: in the test roadway, strictly according to the "roof-cutting height- roof-cutting angle- drilling diameter- drilling spacing" parameter combination scheme calculated in Step 2, carry out roof-cutting drilling construction.

[0038] Effect monitoring: during and after the recovery of the working face, through the laying of a mine pressure monitoring system, continuously monitor the surface displacement of the roadway, the deep displacement and separation of the surrounding rock, the actual collapse pattern of the roof, and the filling and compaction conditions of the gangue in the goaf.

[0039] Feedback optimization: compare the measured data obtained by monitoring with the theoretical expectation. If there is a deviation between the actual effect and the expectation, adjust at least one of the aforementioned key parameters according to the analysis results until the optimal parameter combination is obtained.

[0040] The application provides a method for determining key top cutting borehole parameters of dense borehole top cutting along empty roadway.

[0041] The application has the following beneficial effects:

[0042] 1. The application overcomes the limitations of traditional methods mainly relying on engineering experience, and provides a clear implementation path for parameter design through the construction of a complete technical process of "pre-mining exploration-theoretical calculation-site optimization". Especially by establishing corresponding mechanical models and performing formulaic calculations for the top cutting height, angle, aperture and spacing in the key parameter theoretical calculation step, the parameter determination process is changed from qualitative judgment to quantitative analysis, which fundamentally ensures the scientificity of the design basis.

[0043] 2. The design process of the application starts with the accurate determination of the mechanical parameters of the target roadway roof rock mass, including uniaxial compressive strength, tensile strength, cohesion and internal friction angle, etc. These field measured geomechanical parameters will be used as the core input throughout the theoretical calculation formulas of all subsequent key parameters. Therefore, this method can ensure that the final output parameter combination is tailored to the geological characteristics of a specific engineering site, rather than using general standards, thereby improving its applicability and effectiveness in complex and variable geological conditions.

[0044] 3. The application not only includes theoretical calculation, but also sets up a field test and feedback optimization step, forming a closed loop connecting theory and practice. By laying out a mine pressure monitoring system in the field industrial test, the key indicators such as roadway displacement and roof caving form are monitored in real time, and the real response data of the theoretical scheme in the actual engineering can be obtained. Feedback and adjustment of the theoretical parameters according to the measured data can effectively correct the simplification error of the theoretical model, and ensure that the finally determined parameter scheme is safe, reliable and optimal in actual application. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 The figure is a schematic diagram of the method of the application;

[0046] Figure 2 The figure is a mechanical model of the application for analyzing the stress of the top cutting not penetrating surface;

[0047] Figure 3 The figure is a masonry balanced mechanical model of the application for determining the top cutting angle;

[0048] Figure 4The suspension beam mechanical model for calculating the hole diameter of the application;

[0049] Figure 5 The schematic diagram for determining the plastic zone range of the drill hole based on the hole diameter of the application. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the application will be clearly and completely described in the specification of the application combined with the drawings in the specification of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all the other embodiments obtained by those skilled in the art without creative work belong to the protection scope of the application.

[0051] Please refer to the drawings in the specification of the application Figure 1 - the drawings in the specification of the application Figure 5 , Figure 1 It is the flow schematic diagram of the method for determining the key top cutting drill hole parameters of the dense drill hole top cutting along empty roadway according to one embodiment of the application. The method provided by the application is completed through a systematic process, which can include the following steps:

[0052] S100, pre-mining exploration step.

[0053] This step is executed by a pre-mining exploration module 10. The function of the module is to provide necessary and accurate initial data for subsequent theoretical calculation. The specific execution content includes two aspects: one is to systematically collect the macroscopic engineering geological data of the target roadway and working face, including the geological exploration report, operation procedure and related drawings; the other is to accurately determine the physical and mechanical properties of the key rock stratum of the roadway roof through the combination of in-situ exploration and laboratory test, so as to obtain the uniaxial compressive strength [σ c ], tensile strength [σ t ], shear strength [τ s ], cohesion C0 and internal friction angle φ of the roof rock mass.

[0054] S200, key parameter theoretical calculation step.

[0055] This step is executed by a key parameter theoretical calculation module 20. The module receives the geomechanical parameters output by the pre-mining exploration module 10, and sequentially solves the four key parameters of the dense drill hole through the preset mechanical model and algorithm. The solving sequence is: top cutting height, top cutting angle, drill hole diameter and drill hole spacing.

[0056] When determining the top cutting height (H c ), the module first calculates based on the goaf filling theory to ensure that the broken roof rock mass can effectively fill the goaf after cutting, and the calculation formula is:

[0057]

[0058] H c is the theoretical roof cutting height; M c is the mining height of the coal seam; K p is the dilatancy coefficient of the roof rock mass.

[0059] When partial roof cutting is used due to limited construction conditions, the module further analyzes the stress state of the rock beam that is not penetrated after the roof cutting, and calculates and ensures that the rock beam is fractured in tension. The calculation and checking formula is:

[0060]

[0061] σ w is the tensile stress borne by the unpenetrated surface of the basic roof rock; M (d) is the bending moment on the roof surface when the cantilever beam rotates and sinks; W t is the bending section modulus of the unpenetrated rock beam; [σ t ] is the tensile strength of the roof rock mass.

[0062] When determining the roof cutting angle (θ), the module analyzes the sliding instability critical condition of the key rock block by establishing a mechanical model according to the “S-R” stability theory of the masonry beam structure, and the formula for the calculation is:

[0063]

[0064] θ is the inclination angle of the roof cutting borehole; φ is the internal friction angle between the fractured rock blocks; H b is the thickness of the key rock block; Δ s is the rotation and sinking amount of the key rock block; L o is the lateral span of the key rock block.

[0065] When determining the borehole diameter (d b ), the module simplifies the roof structure after dense drilling into a multi-hole cantilever beam model, and checks based on the rock mass strength condition to ensure that the rock mass between the holes does not fail prematurely before the roof fractures, so that the roof smoothly fractures at the drilling pre-splitting position. The formula for the calculation includes:

[0066] The calculation and checking formula for the maximum normal stress σ max is:

[0067]

[0068] The calculation and checking formula for the maximum shear stress τ max is:

[0069]

[0070] σmax is the maximum normal stress of the rock mass between the holes; [σ t ] is the tensile strength of the roof rock; τ max is the maximum shear stress of the rock mass between the holes; [τ s ] is the shear strength of the roof rock; q o is the uniform load acting on the roof above; L o is the cantilever length of the roof on the side of the mined-out area; H r is the total thickness of the roof rock layer that needs to be cut off; H c is the actual height of roof cutting by the dense drilling; b is the unit thickness selected along the axis of the roadway in the calculation model; r b is the radius of the drilling hole.

[0071] In determining the drilling hole spacing (D b ), the module calculates based on the theory of elastoplastic mechanics, taking as the criterion that the plastic zones of adjacent drilling holes can mutually overlap to form a continuous pre-splitting weak surface. The module first calculates the plastic zone radius R p around a single drilling hole:

[0072]

[0073] In the formula, R p is the plastic zone radius of the drilling hole surrounding rock; r b is the drilling hole radius determined by the foregoing step; P0 is the original rock mass stress at the location of the drilling hole; C0 is the cohesion of the roof rock; and φ is the internal friction angle of the roof rock.

[0074] Subsequently, the drilling hole spacing D b is determined based on the plastic zone radius:

[0075] D b ≤ 2R p ;

[0076] In the formula, D b is the center spacing of the drilling holes; and R p is the calculated plastic zone radius of the drilling hole surrounding rock.

[0077] S300, field test and feedback optimization step.

[0078] This step is executed by a field test and feedback optimization module 30. The function of this module is to verify and optimize the theoretical calculation results. The specific execution content includes:

[0079] Combining the parameters output by the key parameter theoretical calculation module 20 and applying them to the field for industrial tests;

[0080] During the test, a mine pressure monitoring system is laid out to continuously monitor the deformation of the roadway surrounding rock and the roof caving effect;

[0081] The measured data obtained is compared with the theoretical expectation, and if there is a deviation, the theoretical calculation parameters are adjusted accordingly, and the optimal parameter combination suitable for the engineering geological conditions is finally determined.

[0082] The first stage of the method is S100, a pre-mining exploration step, which is specifically executed by the pre-mining exploration module 10. The goal of this step is to obtain all the basic data required for subsequent theoretical calculations, and its execution process is divided into two parts: collection and analysis of macroscopic data and accurate determination of microscopic mechanical parameters. c In specific implementation, first, the collection and analysis of engineering geological data are performed. The pre-mining exploration module 10 collects complete engineering geological data of the target working face and the area of the roadway to be left, which specifically includes:

[0084] Geological exploration reports of the mine and working face, stratum comprehensive columnar diagram, mining working face operation procedure, mining engineering plan layout, and roadway cross section design diagram.

[0085] Through the analysis of the above data, the rock layer combination, thickness, occurrence, structural characteristics of the roadway roof, and the geological structure and hydrogeological conditions in the region can be mastered, providing a macroscopic basis for subsequent mechanical model establishment and parameter selection.

[0086] Subsequently, the accurate determination of the mechanical parameters of the roof rock mass is performed. To obtain accurate rock mass mechanical parameters, the pre-mining exploration module 10 adopts a combination of in-situ exploration and indoor mechanical testing. The specific operation is to arrange exploration boreholes along the axis direction of the roadway in the roof area of the roadway to be left. The borehole viewer is used to observe the borehole wall to identify and record the specific lithology, thickness, joint and fracture development of each rock layer of the roof, and accurately divide the range of the immediate roof and the basic roof.

[0087] After determining the key rock layers (usually the lower rock layers of the basic roof) that need to be cut through the operation through borehole viewing, rock cores are drilled from these key horizons. The obtained rock core samples are processed into rock mechanics test standard specimens that meet national standards in the laboratory.

[0088] The pre-mining exploration module 10 performs a series of indoor mechanical tests on these standard specimens to quantitatively obtain a set of core parameters representing their physical and mechanical properties. These tests at least include: uniaxial compression test to determine the uniaxial compressive strength [σ c ] of the rock mass; Brazilian splitting test or direct tension test to determine the tensile strength [σ t ] of the rock mass; and triaxial compression test or direct shear test to determine the shear strength [τ s ], cohesion C0 and internal friction angle φ of the rock mass.

[0089] After the above test, the pre-mining exploration module 10 will arrange a set of measured geomechanical parameters ([σ c ],[σ t ],[τ s ], C0, φ) and use this set of data as the initial input conditions for the subsequent theoretical calculation of key parameters in step S200.

[0090] The second phase of the method is S200, the step of theoretical calculation of key parameters, which is specifically implemented by the key parameter theoretical calculation module 20. This module receives a set of geomechanical parameters determined by the pre-mining exploration step S100 as input, and sequentially solves the four key borehole parameters according to the preset calculation sequence and mechanical principles.

[0091] At the beginning of the calculation process, the key parameter theoretical calculation module 20 first determines the height of the cut roof (H c ). The determination of this parameter integrates two different physical criteria. First, according to the goaf filling theory, the minimum theoretical height required to ensure that the cut-off roof rock mass can completely fill the goaf formed after mining, thereby providing effective support to the overlying rock strata. Second, for the working conditions where the construction conditions do not allow the borehole to completely penetrate the roof, the module makes a supplementary calculation based on the non-penetrating rock beam pull-off theory.

[0092] This calculation simplifies the non-penetrating rock layer above the cut joint into a cantilever beam structure, and by analyzing the bending moment generated at the dangerous section under the action of self-weight and overlying load, it checks whether the maximum tensile stress at this section exceeds the tensile strength of the rock mass, to ensure that the rock beam can reliably break. The final cut-off height is determined after considering the calculation results of the two theories.

[0093] After determining the cut-off height, the key parameter theoretical calculation module 20 then determines the cut-off angle (θ). The calculation of this parameter is based on the S-R stability theory of masonry beam structure. The module considers the key rock mass formed after cutting the roof as a block in the masonry beam structure, and establishes a mechanical equilibrium model of the block. The goal of the calculation is to solve a critical borehole inclination angle, at which the key rock mass can ensure that it slips and loses stability along the preset cut joint surface under the action of mine pressure, rather than forming a stable load-bearing structure through the hinged action between blocks. The calculation process is essentially to solve the angle condition required to overcome the inter-block friction and geometric stability of the rock mass when it slips.

[0094] Subsequently, the key parameter theoretical calculation module 20 calculates the borehole diameter (d bdetermination of the drilling hole spacing (D

[0095] To this end, the module analyzes the stress distribution of the dangerous section (usually located in the sidewall of the roadway) of the multi-hole cantilever beam under load based on the theory of material mechanics, and checks it according to the aforementioned rock mass strength conditions. Through solving, a hole diameter is obtained which can ensure that the maximum normal stress and the maximum shear stress are greater than or equal to the ultimate tensile strength and shear strength of the rock mass.

[0096] Finally, on the basis of the determination of the cutting height, angle and hole diameter, the key parameter theoretical calculation module 20 determines the drilling hole spacing (D b The theoretical basis of this calculation is the theory of plastic zone of surrounding rock of circular cavern in elastoplastic mechanics. The core criterion is to connect and penetrate the plastic zones formed around adjacent drilling holes under the action of in-situ stress, so as to form a continuous pre-splitting weakened surface with significantly reduced mechanical strength between the holes, and guide the regular fracture of the roof along this weakened surface. The module first calculates the plastic zone radius around a single drilling hole according to the input rock mass mechanical parameters and the determined drilling hole radius, and then determines the maximum allowable value of the drilling hole center spacing according to the principle of mutual overlap of the plastic zones.

[0097] The third stage of the method is S300, a field test and feedback optimization step, which is specifically performed by a field test and feedback optimization module 30. The module receives the "cutting height-cutting angle-drilling hole diameter-drilling hole spacing" parameter combination output by the key parameter theoretical calculation step S200, and its function is to verify the parameter combination through field industrial test, and to adjust according to the measured effect.

[0098] In specific implementation, the field test and feedback optimization module 30 first formulates a detailed field cutting drilling construction operation scheme according to the parameter combination obtained by theoretical calculation. The scheme clearly specifies the specific technology, equipment selection and quality acceptance standard of drilling construction. Subsequently, in the selected test roadway, the cutting drilling construction is organized and carried out strictly according to this scheme.

[0099] After the drilling construction is completed and the working face starts to be mined, the field test and feedback optimization module 30 starts the mine pressure monitoring program. The program is executed through a monitoring system pre-installed in the test roadway. The monitoring system is arranged along the roadway axis with several monitoring sections, and various monitoring instruments are installed on each section to obtain comprehensive dynamic data of surrounding rock.

[0100] The monitoring contents specifically include: determining the displacement of the roadway surface, i.e., the relative approaching amount of the roof and floor and the two sides, by using a roadway section convergence meter; laying measuring points in the deep part of the surrounding rock by using a multi-point displacement meter to monitor the displacement amount and separation at different depths in the surrounding rock; and obtaining the actual caving form of the roof and the filling and compaction conditions of the gangue in the goaf by means of fixed-point observation and image recording.

[0101] During the mining of the working face and after the mining is stable, the field test and feedback optimization module 30 processes and analyzes the measured data continuously collected by the monitoring system. The module compares the measured roadway surrounding rock deformation, roof caving range, gangue filling height and other data with the expected control target at the beginning of the design of the method.

[0102] If the comparative analysis result shows that the measured data deviates from the expected target, for example, the roadway deformation exceeds the early warning value, or the roof fails to cave along the pre-cut joint line in the predetermined form, the field test and feedback optimization module 30 performs a feedback optimization operation. The operation adjusts one or more parameters in the theoretical calculation steps S200 of the key parameters according to the specific circumstances of the deviation. For example, if the roof caving is insufficient, the drilling spacing (D b ) or the roof cutting height (H c ) may need to be appropriately reduced. This adjustment process can be repeated until the monitoring result shows that the roadway preservation effect meets the design requirements, thereby finally determining a set of optimal parameter combination suitable for the specific engineering conditions.

[0103] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for determining key drilling parameters for dense drilling for roof cutting and gob-side retention, characterized in that, The method includes the following steps: Pre-mining exploration steps: Collect engineering geological data for the target roadway, and determine the geomechanical parameters of the roof rock mass by combining in-situ exploration with laboratory tests; Key parameter theoretical calculation steps: Based on the geomechanical parameters obtained in the pre-mining exploration steps, a mechanical model is constructed, and the top cutting height, top cutting angle, borehole diameter and borehole spacing of the dense boreholes are calculated in sequence to determine them. Field test and feedback optimization steps: The cutting height, cutting angle, borehole diameter and borehole spacing of the aforementioned boreholes are combined and applied to the field industrial test. The effect of roadway retention is monitored by deploying a mine pressure monitoring system. The key parameters are then optimized based on the monitoring results.

2. The method for determining key top-cutting borehole parameters for dense borehole cutting and gob-side retention according to claim 1, characterized in that, The pre-mining exploration steps specifically include: Collect geological exploration reports, operating procedures, tunnel cross-section diagrams, and comprehensive stratigraphic columnar sections for the target tunnels and working faces; Furthermore, before mining, borehole inspection equipment was used to investigate the lithology, thickness, and integrity of the roof strata, and rock samples were collected from key roof strata. The uniaxial compressive strength [σ] was then determined through laboratory mechanical tests. c ], tensile strength [σ t ], cohesion C0 and internal friction angle φ.

3. The method for determining key top-cutting borehole parameters for dense borehole cutting and gob-side retention according to claim 1, characterized in that, In the theoretical calculation step of the key parameters, the cutting height (H) is determined. c The steps include: Based on the theory of goaf filling, the minimum theoretical roof cutting height required to ensure that the broken rock mass after the roof collapse can effectively fill the goaf is calculated. When construction conditions limit the drilling from completely cutting through the roof, the actual roof cutting height is further verified and determined based on the tensile strength theory of the incomplete rock beam. This is done by calculating and ensuring that the maximum tensile stress on the incomplete rock beam above the pre-crack under the action of mine pressure exceeds its tensile strength.

4. The method for determining key top-cutting borehole parameters for dense borehole cutting and gob-side retention according to claim 1, characterized in that, In the theoretical calculation steps of the key parameters, the step of determining the cutting angle (φ) is as follows: Based on the "SR" stability theory of masonry beam structures, the mechanical equilibrium relationship of the key rock block of the top plate formed after the top is cut is established. Based on the critical condition that the key rock block can slip and become unstable along the preset cut surface instead of forming a stable hinged structure, the top cutting angle is obtained.

5. The method for determining key top-cutting borehole parameters for dense borehole cutting and gob-side retention according to claim 4, characterized in that, The critical condition for ensuring the slippage and instability of the key rock block is defined by the following formula: In the formula, θ is the inclination angle of the top-cutting borehole; φ is the internal friction angle between the fractured rock blocks; H b The thickness of the key rock block; Δ s L represents the rotational subsidence of the key rock block. o The lateral span of the key rock block.

6. The method for determining key top-cutting borehole parameters for dense borehole cutting and gob-side retention according to claim 1, characterized in that, In the theoretical calculation step of the key parameters, the borehole diameter (d) is determined. b The steps are: The top structure after dense drilling is simplified into a multi-hole cantilever beam model with one end fixed. The functional relationships between the maximum normal stress and maximum shear stress at the critical section and the borehole radius are established. The maximum normal stress at this section is assumed to be greater than the rock mass compressive strength [σ]. c The maximum shear stress is greater than the shear strength of the rock mass [τ]. s [I] is a constraint condition, and the minimum borehole diameter that satisfies the condition is obtained by solving the problem.

7. The method for determining key top-cutting borehole parameters for dense borehole cutting and goaf retention according to claim 1, characterized in that, In the theoretical calculation step of the key parameters, the borehole spacing (D) is determined. b The steps are: After determining the borehole diameter, the radius R of the plastic zone of the surrounding rock under the original rock mass stress of a single borehole is first calculated. p Then, based on the criterion that the plastic zones of adjacent boreholes can overlap and connect to form a continuous pre-splitting weak surface, the borehole spacing D is determined. b It should not be greater than twice the radius R of the plastic zone. p .

8. The method for determining key top-cutting borehole parameters for dense borehole cutting and gob-side retention according to claim 7, characterized in that, The radius R of the plastic zone p The calculation formula is: In the formula, R p r is the radius of the plastic zone of the surrounding rock in the borehole. b P0 is the borehole radius determined by the borehole diameter; C0 is the original rock mass stress at the location of the borehole; φ is the rock mass cohesion; and φ is the internal friction angle of the rock mass.

9. The method for determining key top-cutting borehole parameters for dense borehole cutting and gob-side retention according to claim 1, characterized in that, The logical order of the theoretical calculation steps for the key parameters is as follows: After calculating the two macroscopic geometric parameters, the cutting height and cutting angle, the microscopic parameter, the borehole diameter, is then calculated. Finally, the borehole spacing is calculated based on the determined borehole diameter.

10. The method for determining key top-cutting borehole parameters for dense borehole cutting and gob-side retention according to claim 1, characterized in that, The specific steps of field testing and feedback optimization include: In the test tunnel, top-cutting drilling was carried out according to the parameter combination scheme obtained from theoretical calculations; During and after the mining of the working face, the monitoring system will obtain measured data on the surface displacement of the roadway, the deep displacement of the surrounding rock, the collapse mode of the roof, and the compaction status of the gangue in the goaf. The measured data are compared and analyzed with the theoretical expectations, and at least one of the top cutting height, top cutting angle, borehole diameter or borehole spacing is adjusted according to the analysis results to obtain the optimal parameter combination.

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