A coal seam roof directional pre-splitting slot parameter design method

Abstract

The application relates to the technical field of coal mining, in particular to a coal seam roof directional pre-splitting cutting seam parameter design method. The coal seam is mined by using the top cutting pressure releasing coal pillar free self-formed roadway technology; the directional pre-splitting cutting seam parameters comprise a top cutting height; a first calculation formula of the top cutting height is established by taking cutting off the basic roof as a target; a second calculation formula of the top cutting height is established by taking the gangue collapse to fill the goaf as a target; the top cutting height is the maximum value calculated between the first calculation formula and the second calculation formula. The application cuts off the lateral cantilever length of the roof by determining the reasonable top cutting height, so that the rock stratum within the top cutting height can fill the whole goaf after collapse, a better supporting effect is achieved on the upper rock stratum, the roadway roof structure is optimized, the disturbance effect of the top rock stratum rotation subsidence on the roadway is maximally reduced, the stress of the roadway surrounding rock is effectively improved, and the stability of the roadway surrounding rock is obviously improved.

Description

Technical Field

[0001] This application relates to the field of coal mining technology, and in particular to a method for designing parameters for directional pre-splitting cuts in the roof of a coal seam. Background Technology

[0002] The core idea of ​​the roof-cutting and pressure-relief pillarless self-forming roadway technology is to achieve roof pressure relief and forced caving by directional pre-splitting of the coal seam roof, thereby forming a pillarless mining roadway, eliminating the need for traditional coal pillars, improving coal resource recovery rate, and optimizing the stress environment of the surrounding rock in the roadway. In this technical system, the design of the directional pre-splitting parameters of the coal seam roof is a crucial core element. Its rationality directly determines the implementation effect of roof-cutting and pressure relief and gangue caving and filling, thus affecting the construction safety and mining efficiency of the pillarless self-forming roadway. However, existing technologies lack a systematic design scheme for the corresponding parameters.

[0003] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0004] The purpose of this application is to provide a method for designing parameters of directional pre-splitting cuts in coal seam roof, so as to solve or alleviate the problems existing in the prior art.

[0005] To achieve the above objectives, this application provides the following technical solution: A method for designing parameters of directional pre-splitting cuts in the roof of a coal seam, wherein the coal seam is mined using roof-cutting, pressure-relief, pillarless, self-forming roadway technology; The directional pre-splitting cut parameters include the cut top height; With the goal of cutting off the basic top, a first formula for calculating the cutting height is established; A second formula for calculating the cutting height is established with the goal of filling the goaf with collapsed gangue. The cutting height is taken as the larger value calculated between the first calculation formula and the second calculation formula.

[0006] Preferably, the cutting height The first calculation formula is: , In the formula, The thickness of the immediate top rock layer is in meters (m). The thickness of the basic top rock layer is in meters (m).

[0007] Preferably, the cutting height The second calculation formula is: , In the formula, The coal seam thickness is in meters (m). is the average coefficient of rock strata fragmentation.

[0008] Preferably, the cutting height The second calculation formula is: , In the formula, The coal seam thickness is in meters (m). The average coefficient of rock strata swelling; The value is the amount of roof settlement, expressed in meters (m). This is the volume of the bottom drum.

[0009] Preferably, the directional pre-splitting cutting parameters further include the cutting top angle. ; Taking the slippage and instability of the main top rock block as the objective, the stress analysis of the main top rock block at the pre-splitting cut surface yields the following results: , Right now, ; In the formula, The horizontal thrust exerted on the basic top rock block of the working face, kN; The shear force, in kN, is the shear force exerted on the top rock block of the working face. The load intensity of the basic top is kN / m; The length of the basic apex, in meters; Let m be the thickness of the basic top. The subsidence of the basic top rock block of the working face, in meters (m); The friction angle between the basic top rock blocks of the working face is °.

[0010] Preferably, the cutting angle Pick: .

[0011] Preferably, directional pre-splitting is performed using bidirectional shaped charge blasting technology.

[0012] Preferably, the directional pre-splitting parameters further include the borehole charge amount; The target is that the minimum directional crack length for quasi-static pressure initiation inside the borehole is greater than the maximum random crack length in the surrounding rock of the borehole wall. The charge quantity for the borehole is then calculated as follows: , In the formula, The charge amount in the borehole is in kg; The borehole diameter is in meters (m). The diameter of the propellant charge is in meters (m). The density of the explosive charge in the borehole is kg / m³. 3 ; The borehole charge coefficient; Let be the length of the borehole, in meters (m). For the fracture toughness of the rock, MN / m 3 / 2 ; Let V be the detonation velocity of the explosive, in m / s; The maximum random crack length in the surrounding rock of the borehole wall, in meters; Let be the borehole radius, in meters. This is the shape influence factor.

[0013] Preferably, the directional pre-splitting parameters further include the borehole spacing; Stress intensity factor at the crack tip Let be a variable, let Calculate the borehole spacing: , In the formula, The length of the directional crack is in meters (m). The borehole spacing is in meters (m). The stress intensity factor is MN / m. 3 / 2 ; The quasi-static pressure inside the borehole is expressed in MPa.

[0014] Compared with the closest prior art, the technical solution of this application has the following beneficial effects: This application determines a reasonable roof cutting height and cuts off the lateral cantilever length of the roof, so that the rock strata within the roof cutting height can fill the entire goaf after collapse, providing better support for the upper rock strata, optimizing the roof structure of the roadway, minimizing the disturbance effect of the roof rock strata rotation and subsidence on the roadway, effectively improving the stress of the surrounding rock of the roadway along the goaf, and significantly improving its stability. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. Wherein: Figure 1 This is a schematic diagram of a self-forming roadway structure with roof cutting and pressure relief and no coal pillars provided according to some embodiments of this application; Figure 2 This is a schematic diagram of the bidirectional shaped charge blasting principle provided according to some embodiments of this application.

[0016] Explanation of reference numerals in the attached figures: 1. Roadway; 2. Pre-splitting cut surface; 3. Immediate roof; 4. Main roof; 5. Main roof rock block; 6. Goaf. Detailed Implementation

[0017] The present application will now be described in detail with reference to the accompanying drawings and embodiments. Various examples are provided by way of explanation and not by way of limitation. In fact, those skilled in the art will recognize that modifications and variations can be made to the present application without departing from the scope or spirit thereof. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the present application encompass such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0018] In the following description, the terms "first / second / third" are used merely to distinguish similar objects and do not represent a specific order of objects. It is understood that "first / second / third" may be interchanged in a specific order or sequence where permitted, so that the embodiments of this application described herein can be implemented in an order other than that illustrated or described herein.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing embodiments of this disclosure only and is not intended to limit this disclosure.

[0020] In the description of this application, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and do not require that this application be constructed and operated in a specific orientation, and therefore should not be construed as limiting this application. The terms "connected," "linked," and "set up" used in this application should be interpreted broadly. For example, they can refer to fixed connections or detachable connections; direct connections or indirect connections through intermediate components; wired connections, radio connections, or wireless communication signal connections. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0021] The following will be combined with the appendix Figure 1-2 This application provides a more detailed description of a method for designing directional pre-splitting cut parameters for coal seam roof.

[0022] For clarity, the following technical principles in this field will now be explained.

[0023] The roof-cutting and pressure-relief pillarless self-forming roadway technology involves: before the working face is mined, the roof of the reserved roadways 1 on both sides of the working face is reinforced with constant resistance large deformation anchor cables; subsequently, bidirectional shaped charge tensile blasting technology is used to pre-split the roof of the two roadways 1 near the mining side. That is, before the working face is mined, a structurally weak surface that runs through the entire length of the working face is created, ensuring the rapid collapse of the roof after the working face is mined. Two-way shaped charge tensile blasting technology and constant resistance large deformation anchor cable support technology can maintain the integrity of the roof strata to the greatest extent, change the group of moving strata in the roof of the mining side of roadway 1, especially the lower basic roof 4 is transformed into the direct roof 3, increasing the thickness of the caving zone strata; after the working face is mined, the "caving zone strata" above the working face near the cut face collapses rapidly under the periodic pressure of the stope. The roadway side retaining rock support technology ensures that the collapsed rock automatically forms the roadway side. Due to its own fragmentation and expansion characteristics, the rock fills the goaf 6, quickly forming a support structure for the first moving rock beam of the basic roof 4; when the basic roof 4 fractures and sinks, its fracture location will generally be located on the side of the pre-splitting cut face 2, and then move together with the basic roof rock block 5 above the goaf 6. After the movement ends, a plastic hinge structure will be formed between the rock blocks that make up the moving rock beam, and the force transmission effect will continue to be maintained around the goaf 6. Compared with the fracture state of the basic roof rock block 5 under the traditional mining mode, the contact point of the basic roof rock block 5 above the roadway 1 after the roof is cut will move forward, and its given deformation and fracture angle will be reduced, thereby weakening the load acting on the roof of the roadway 1. Under the combined effect of the protective effect of the roof-cutting short arm beam structure formed above the roadway 1 after the roof is cut, the support effect of the constant resistance large deformation anchor cable, and the support effect of the goaf 6 gangue on the basic roof 4, the stability of the roadway 1 is improved. After the movement of the roof above the goaf 6 is stable, the temporary support materials in the roadway are removed, and shotcrete sealing measures are taken according to the requirements of preventing air leakage and fire extinguishing.

[0024] Two-way shaped charge blasting technology: This refers to placing an explosive charge into a shaped charge device with a shaped charge effect in two predetermined directions. After the explosive detonates, the surrounding rock in the borehole is uniformly compressed in the non-predetermined direction, while being concentrated under tension in the predetermined direction, thus achieving tensile fracture of the blasted body according to the predetermined direction. In application, a two-way shaped charge device is used to load the explosive in the control borehole, with the shaped charge direction aligned with the controlled fracture direction. After the explosive detonates, the shock wave and stress wave generated by the detonation are preferentially concentrated and released along the predetermined shaped charge hole direction, acting on the borehole wall in the corresponding direction, forming a radial initial crack on the borehole wall consistent with the shaped charge hole direction; subsequently, the explosive gas rushes into the radial initial crack, generating tensile stress concentration in the predetermined direction, fracturing the rock mass, and driving the crack to propagate along the predetermined direction, achieving directional pre-splitting.

[0025] Cutting height: refers to the maximum vertical distance from the roof plane of roadway 1 to the upward development of the cut crack when the coal seam roof is directionally cut using bidirectional shaped charge blasting technology.

[0026] Cutting angle: The angle between the pre-splitting cut surface 2 and the vertical direction.

[0027] Type I crack: Under tensile stress orthogonal to the crack surface, the crack surface undergoes an opening displacement (the displacement is orthogonal to the crack surface), with the upper and lower surfaces having opposite displacements.

[0028] After the coal seam is mined from the working face, the immediate roof (3) first delaminates and collapses, losing its mechanical relationship with the lateral boundary of the goaf-side roadway. Meanwhile, the main roof (4) on the goaf side of the roadway (6) creates a long, unsuitable overhanging roof that also supports several weak overlying rock layers, generating significant additional stress on the goaf-side roadway and correspondingly increasing the difficulty of supporting it. By using shaped charge pre-splitting blasting to reduce the length of the lateral cantilever of the main roof (4), the rock fracture line can be shifted towards the goaf side, effectively alleviating the stress in the surrounding rock of the roadway.

[0029] A method for designing parameters of directional pre-splitting cuts in coal seam roof, wherein the coal seam is mined using roof cutting and pressure relief technology without coal pillars to form a self-forming roadway. Directional pre-splitting cut parameters include cut top height; With the goal of cutting off the basic top 4, a first calculation formula for the top cutting height is established; When the primary roof 4 is cut off and indirectly transformed into the direct roof 3, and the collapsed gangue still cannot fill the entire goaf 6, the overlying strata still have room to move, thus putting pressure on the roof of the roadway. Therefore, the cutting height needs to be further considered. By utilizing the characteristics of rock collapse and expansion after cutting the roof, the strata within the cutting range are made to collapse and fill the entire goaf 6, providing better support for the upper strata and minimizing the impact of the upper roof's rotation and subsidence on the roadway along the goaf.

[0030] With the goal of filling the goaf with collapsed gangue, a second calculation formula for the cutting height is established; The cut-off height is taken as the larger value calculated between the first and second calculation formulas.

[0031] Cutting height The first calculation formula is: (1), In the formula, The thickness of the directly topped rock layer is 3 m; The thickness of the basic top 4 rock strata is in meters.

[0032] Assume there are m rock layers within the cut-off height, from bottom to top as follows: At this point, the following conditions are met: (2), Furthermore, the cutting height The second calculation formula is: (3), In the formula, The coal seam thickness is in meters (m). The average coefficient of rock strata swelling; These are the fragmentation coefficients of the first, second, ..., m-th rock layers, respectively.

[0033] In conclusion, when At that time, the cutting height is taken as ;when At that time, the cutting height is taken as .

[0034] By determining a reasonable roof cutting height and cutting off the lateral cantilever length of the roof, the rock strata within the roof cutting height can fill the entire goaf after collapsing, providing better support for the upper rock strata, optimizing the roof structure of the roadway, minimizing the disturbance effect of the roof rock strata rotation and subsidence on the roadway, effectively improving the stress of the surrounding rock of the roadway along the goaf, and significantly improving its stability.

[0035] To better reflect the actual construction conditions on site and improve the accuracy of the cut-off height calculation, the cut-off height... The second calculation formula is: (4), In the formula, The coal seam thickness is in meters (m). The average coefficient of rock strata swelling; The value is the amount of roof settlement, expressed in meters (m). This is the volume of the bottom drum.

[0036] In a specific embodiment of this application, the average rock strata swelling coefficient Take 1.34, coal seam thickness Taking 4.2m as an example, the cut-off height is calculated. The depth of the cut hole is designed to be 13.5m (vertical height 13m) based on the lithological distribution of the roof of tunnel 1, with a depth of 15m drilled every 50m to determine the lithology of the roof.

[0037] Directional pre-splitting cutting parameters also include the cutting top angle. ; As the working face continues to advance, the basic roof 4 breaks into basic roof blocks 5 after reaching its ultimate span. These broken basic roof blocks 5 interlock due to horizontal compressive forces, forming a stable masonry beam structure. Similarly, after the end of the basic roof 4 breaks into arc-shaped triangular blocks, it also forms a three-hinged arch-like balanced structure. At this point, although the basic roof 4 has broken, the mutual restraints form a stable masonry structure, which can still effectively transmit forces to the lateral coal and rock mass, thus affecting the stability of the surrounding rock in the goaf-side roadway. When the roof-cutting, pressure-relief, pillarless self-forming roadway process is adopted, the cut surface becomes the interlocking surface between the basic roof 4 and the basic roof blocks 5. Only when the basic roof blocks 5 slip and become unstable along the cut surface can the smooth collapse of the basic roof 4 strata and the effective cutting off of the stress transmission path be achieved.

[0038] Taking the slippage and instability of the basic top rock block 5 as the target, the stress analysis of the basic top rock block 5 at the two pre-splitting cut surfaces yields the following results: (5), Right now, (6); In the formula, The horizontal thrust exerted on the top rock block 5 of the working face is kN; The shear force (kN) experienced by the top rock block 5 of the working face. The load intensity of the basic top 4 is kN / m; The length of the basic top 4 is in meters. The thickness of the basic top 4 is in meters (m). The subsidence of the basic top rock block 5 of the working face is expressed in meters. The friction angle between the five basic top rock blocks of the working face is °.

[0039] When the cutting angle Equal to the friction angle between 5 basic top rock blocks At that time, the three-hinged arch rock block structure could not achieve equilibrium, and the basic roof rock block 5 could be smoothly cut off along the cut surface to form the roadway sidewall, thereby cutting off the path of force transmission from the lateral blocks to the roof of roadway 1, fully relieving pressure and achieving a good roadway formation effect. However, the roof cutting angle The increase in the angle of the roof cut is indirectly equivalent to increasing the lateral cantilever length of the roof, which is not conducive to the maintenance of the roadway along the goaf. Therefore, while ensuring that the basic roof rock block 5 can collapse smoothly, the roof cutting angle should be minimized as much as possible. .

[0040] Cutting angle Pick: (7).

[0041] In a specific embodiment of this application, the friction angle between the basic top rock blocks 5 of the working face is... =27°, length of the basic apex =11m, the subsidence of the top rock block 5 of the working face =1.37m, thickness of the basic roof =3.76m, substituting into equation (7) yields: =14.7°. Considering the convenience of construction and a certain safety factor, 15° is chosen.

[0042] Directional pre-splitting is performed using bidirectional shaped charge blasting technology.

[0043] Two-way shaped charge blasting first creates directional cracks. Then, taking advantage of the fact that the length of the directional cracks is significantly greater than the length of the inherent random fine cracks in the rock, an appropriate quasi-static pressure value is controlled in the borehole according to the rock properties. This allows the directional cracks to expand stably, while the random fine cracks in the rock do not crack. This achieves both effective protection of the surrounding rock and a minimum number of boreholes, thus obtaining a good directional pre-splitting effect.

[0044] Determining the appropriate parameters for two-way shaped charge blasting is crucial for successful roof pre-splitting. When determining these parameters, it's essential to consider both achieving good engineering results and economic feasibility, avoiding excessive residual explosive energy. Generally, the borehole charge amount and borehole spacing have the greatest impact on the effectiveness of two-way shaped charge blasting.

[0045] The parameters for directional pre-splitting cuts also include the amount of explosive charge in the borehole; Quasi-static pressure generated by the explosion of explosives inside the borehole Under the influence of the surrounding rock of the borehole, the stress intensity factor at the crack tip is... for: (8), in, (9), When the rock fracture toughness The stress intensity factor smaller than the crack tip of the surrounding rock of the borehole wall At this time, both directional and random cracks in the surrounding rock of the borehole will initiate and propagate. To avoid the initiation of random cracks and achieve directional pre-fracture, the quasi-static pressure inside the borehole needs to be controlled. The minimum crack length that can initiate a crack is greater than the maximum random crack length in the surrounding rock of the borehole wall.

[0046] Based on the crack length of the surrounding rock of the borehole and the quasi-static pressure inside the borehole required for crack initiation The negative correlation is used to calculate the borehole charge amount, with the objective that the minimum directional crack length for quasi-static pressure initiation in the borehole is greater than the maximum random crack length in the surrounding rock of the borehole wall. (10) In the formula, The charge amount in the borehole is in kg; The borehole diameter is in meters (m). The diameter of the propellant charge is in meters (m). The density of the explosive charge in the borehole is kg / m³. 3 ; The borehole charge coefficient; Let be the length of the borehole, in meters (m). For the fracture toughness of the rock, MN / m 3 / 2 ; Let V be the detonation velocity of the explosive, in m / s; , where is the length of a random crack in the surrounding rock of the borehole wall, in meters. The maximum random crack length in the surrounding rock of the borehole wall, in meters; Let be the borehole radius, in meters. This is the shape influence factor.

[0047] After a directional crack initiates and propagates, on the one hand, the stress intensity factor at the crack tip increases due to the increase in crack length; on the other hand, the stress intensity factor at the crack tip decreases as the quasi-static pressure inside the borehole decreases. When these two factors act in combination, the stress intensity factor at the crack tip cannot meet the required standards. At that time, the crack stopped cracking.

[0048] The parameters for directional pre-splitting cuts also include the borehole spacing; Stress intensity factor at the crack tip Let be a variable, let Calculate the borehole spacing: (11), In the formula, The length of the directional crack is in meters (m). The borehole spacing is in meters (m). The stress intensity factor is MN / m. 3 / 2 ; The quasi-static pressure inside the borehole is expressed in MPa.

[0049] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for designing parameters for directional pre-splitting cuts in coal seam roof, characterized in that, The coal seam is mined using the roof-cutting, pressure-relief, pillarless, self-forming roadway technology. The directional pre-splitting cut parameters include the cut top height; With the goal of cutting off the basic top, a first formula for calculating the cutting height is established; A second formula for calculating the cutting height is established with the goal of filling the goaf with collapsed gangue. The cutting height is taken as the larger value calculated between the first calculation formula and the second calculation formula.

2. The method for designing parameters for directional pre-splitting cuts in coal seam roof as described in claim 1, characterized in that, The cutting height The first calculation formula is: , In the formula, The thickness of the immediate top rock layer is in meters (m). The thickness of the basic top rock layer is in meters (m).

3. The method for designing parameters for directional pre-splitting cuts in coal seam roof as described in claim 2, characterized in that, The cutting height The second calculation formula is: , In the formula, Where is the coal seam thickness, in meters (m). is the average coefficient of rock strata fragmentation.

4. The method for designing directional pre-splitting parameters for coal seam roof as described in claim 2, characterized in that, The cutting height The second calculation formula is: , In the formula, Where is the coal seam thickness, in meters (m). The average coefficient of rock strata swelling; The value is the amount of roof settlement, expressed in meters (m). This refers to the volume of the bottom drum.

5. The method for designing directional pre-splitting parameters for coal seam roof as described in claim 1, characterized in that, The directional pre-splitting cutting parameters also include the cutting angle. ; Taking the slippage and instability of the main top rock block as the objective, the stress analysis of the main top rock block at the pre-splitting cut surface yields the following results: ， Right now, ; In the formula, The horizontal thrust exerted on the basic top rock block of the working face, kN; The shear force, in kN, is the shear force exerted on the top rock block of the working face. The load intensity of the basic top is kN / m; The length of the basic apex, in meters; Let m be the thickness of the basic top. The subsidence of the basic top rock block of the working face, in meters; The friction angle between the basic top rock blocks of the working face is °.

6. The method for designing parameters for directional pre-splitting cuts in coal seam roof as described in claim 5, characterized in that, The cutting angle Pick: .

7. The method for designing parameters for directional pre-splitting cuts in coal seam roof as described in claim 1, characterized in that, Directional pre-splitting is performed using bidirectional shaped charge blasting technology.

8. The method for designing parameters for directional pre-splitting cuts in coal seam roof as described in claim 7, characterized in that, The directional pre-splitting parameters also include the amount of explosive charge in the borehole; The target is that the minimum directional crack length for quasi-static pressure initiation inside the borehole is greater than the maximum random crack length in the surrounding rock of the borehole wall. The charge quantity for the borehole is then calculated as follows: ， In the formula, The charge amount in the borehole is in kg; The borehole diameter is in meters (m). The diameter of the propellant charge is in meters (m). The density of the explosive charge in the borehole is kg / m³. 3 ; The borehole charge coefficient; Let be the length of the borehole, in meters (m). MN / m represents the fracture toughness of the rock. 3 / 2 ; Let V be the detonation velocity of the explosive, in m / s; The maximum random crack length in the surrounding rock of the borehole wall, in meters; Let be the borehole radius, in meters. This is the shape influence factor.

9. The method for designing parameters for directional pre-splitting cuts in coal seam roof as described in claim 8, characterized in that, The directional pre-splitting parameters also include the borehole spacing; Stress intensity factor at the crack tip Let be a variable, let Calculate the borehole spacing: ， In the formula, The length of the directional crack is in meters (m). The borehole spacing is in meters (m). The stress intensity factor is MN / m. 3 / 2 ; The quasi-static pressure inside the borehole is expressed in MPa.

Images