A cross-borehole pressure relief method for high-stress concentration areas in irregular coal mining faces

Abstract

The present invention relates to a method for pressure relief by intersecting boreholes in a high stress concentration area of an irregular coal mining face, including: judging the shape of the irregular coal mining face and obtaining the high stress concentration area; implementing the layout of intersecting boreholes in the high stress concentration area to achieve pressure relief in the high stress concentration area; wherein, the high stress concentration area includes: a face reduction section; the face reduction section includes: a transition face reduction section and a cut roadway section of a knife handle type working face. By implementing targeted intersecting borehole pressure relief measures in the high stress concentration area of the irregular coal mining face formed due to geological and mining factors, the present invention can reduce the coal seam stress concentration coefficient and reduce the impact risk during the working face production process.

Description

Technical Field

[0001] The present invention relates to the technical field of prevention and control of coal and rock dynamic disasters, and particularly relates to a cross-borehole pressure relief method for high-stress concentration areas in irregular coal mining faces. Background Art

[0002] As a typical dynamic disaster in coal mines, rock bursts often occur in stress concentration areas of coal and rock masses. A large amount of elastic energy is stored in the coal and rock masses. When the stress in the coal and rock masses exceeds its strength limit, the elastic energy accumulated in the coal and rock masses around the roadway or stope suddenly releases, causing equipment damage and casualties. Due to the unreasonable layout of mine development, non-standard mining design and geological structure in most coal mines in China, the working faces in each mining area mostly show irregular shapes at the end of coal mining. During the coal mining process of such working faces, the length of the working face will change, showing a "transition surface shrinkage" or "knife handle" shape, resulting in a higher stress concentration coefficient of the surrounding coal and rock masses. Under mining disturbance, rock bursts are more likely to be induced.

[0003] At present, the existing borehole pressure relief technology for stress concentration areas in conventional working faces can no longer meet the pressure relief requirements of stress concentration areas in this type of working face. There is an urgent need to design a targeted borehole pressure relief method for this type of working face to meet the mine rock burst prevention requirements. Summary of the Invention

[0004] The purpose of the present invention is to provide a cross-borehole pressure relief method for high-stress concentration areas in irregular coal mining faces. By implementing targeted cross-borehole pressure relief measures in the high-stress concentration areas of irregular coal mining faces formed by geological and mining factors, the stress concentration coefficient of the coal seam can be reduced, and the impact risk during the working face production process can be reduced.

[0005] To achieve the above purpose, the present invention provides the following solution:

[0006] A cross-borehole pressure relief method for high-stress concentration areas in irregular coal mining faces, comprising:

[0007] Judging the shape of the irregular coal mining face and obtaining the high-stress concentration area;

[0008] Implementing cross-borehole layout in the high-stress concentration area to achieve pressure relief in the high-stress concentration area;

[0009] Among them, the high-stress concentration area includes: a surface shrinkage section; the surface shrinkage section includes: a transition surface shrinkage section and a cut roadway section of the knife handle-shaped working face.

[0010] Preferably, implementing cross-borehole layout in the surface shrinkage section includes:

[0011] Construct two groups of spatially intersecting boreholes in the high-stress concentration areas on both sides of the roadway in the reduced-section section, construct them perpendicular to the coal wall in the reduced-section section to obtain the first group of boreholes, and calculate the depth \(x_0\) of the first group of boreholes and the borehole row spacing; vertically offset the corresponding height positions of the first group of boreholes downward, and based on the position where the midpoint between any two boreholes in the first group of boreholes forms an angle \(\alpha\) with the coal wall of the reduced-section roadway, obtain the second group of boreholes, and calculate the depth \(x_1\) of the second group of boreholes based on the angle \(\alpha\).

[0012] Preferably, constructing perpendicular to the coal wall in the reduced-section section includes:

[0013] Construct based on the distance perpendicular to the coal wall of the stress peak value of the superposition of stress concentration areas in the high-stress concentration area; the method for calculating the distance perpendicular to the coal wall of the stress peak value of the superposition of stress concentration areas in the high-stress concentration area is:

[0014]

[0015] where \(K\) is the stress concentration coefficient, \(p_1\) is the resistance of the support to the coal rib, \(m\) is the coal seam mining thickness, \(C\) is the cohesion of the coal body, is the internal friction angle of the coal body, and \(f\) is the friction coefficient of the contact surface between the coal seam roof and floor.

[0016] Preferably, the method for calculating the depth \(x_0\) of the first group of boreholes is:

[0017]

[0018] where \(r\) is the roadway radius; \(\gamma\) is the unit weight; \(H\) is the thickness of the overlying strata of the coal seam; is the internal friction angle of the coal body, and \(C\) is the cohesion of the coal body.

[0019] Preferably, the method for calculating the depth \(x_1\) of the second group of boreholes is:

[0020]

[0021] where \(x_0\) is the depth of the first group of boreholes, and \(\alpha\) is the angle between the second group of boreholes and the coal wall.

[0022] Preferably, implementing cross-borehole layout on the acute-angle side of the transition reduced-section section includes:

[0023] Obtain the included angle β between the extension line of the roadway centerline before the reduced-section segment and the roadway centerline of the reduced-section segment, and determine whether the distance between the last drill hole before the reduced-section segment and the inflection point of the reduced-section roadway is less than the first preset threshold. If it is less than the first preset threshold, arrange a first drill hole at a distance of 1 / 2d from the inflection point of the reduced-section roadway on the coal pillar side of the reduced-section roadway, and arrange a second drill hole at a distance of d from the inflection point of the reduced-section roadway on the coal pillar side of the reduced-section; if it is greater than the first preset threshold, arrange a third drill hole at a distance of 1 / 2d from the coal pillar side before the reduced-section segment, and arrange a fourth drill hole at a distance of 1 / 2d from the inflection point on the coal wall side of the reduced-section segment;

[0024] Among them, the drilling depths of the first drill hole, the third drill hole, and the fourth drill hole are all the first group of drill hole depths x0; the drilling depth of the second drill hole is the second group of drill hole depths x1.

[0025] Preferably, the direction of the first drill hole is perpendicular to the coal wall of the reduced-section segment and the inflection point of the reduced-section roadway, and the directions of the second drill hole and the third drill hole are both: 90° - β; the direction of the fourth drill hole is perpendicular to the coal pillar of the reduced-section segment.

[0026] Preferably, the method of arranging cross drill holes on the acute angle side of the cut roadway section of the knife-shaped working face is as follows:

[0027] Judge whether the distance between the last drill hole before the reduced-section segment and the inflection point of the reduced-section roadway is less than the second preset threshold. If it is less than the second preset threshold, arrange a fifth drill hole at a distance of 1 / 2d from the inflection point of the reduced-section roadway on the coal pillar side of the reduced-section roadway; arrange a sixth drill hole at a distance of 1 / 2d from the drill hole on the coal pillar side before the reduced-section; if it is greater than the second preset threshold, arrange a seventh drill hole at a distance of 1 / 2d from the drill hole on the coal pillar before the reduced-section, and arrange an eighth drill hole at a distance of 1 / 2d from the inflection point between the coal wall of the reduced-section segment and the reduced-section;

[0028] Among them, the drilling depths of the fifth drill hole, the sixth drill hole, the seventh drill hole, and the eighth drill hole are all the second group of drill hole depths x1.

[0029] Preferably, the fifth drill hole, the seventh drill hole, and the eighth drill hole all form an angle of 30° with the coal wall of the reduced-section segment, and the sixth drill hole forms an angle of 30° with the reduced-section roadway.

[0030] Preferably, according to the on-site geological conditions and numerical simulation analysis, determine the range and stress concentration coefficient of the high stress concentration area.

[0031] The beneficial effects of the present invention are:

[0032] The present invention implements targeted cross - borehole pressure relief measures in the high - stress concentration area of the irregular coal mining face formed by geological and mining factors, achieving the weakening of coal and rock masses, destroying the integrity of coal and rock masses, shifting the stress peak area deep into the coal body, and reducing the impact risk of the coal and rock masses around the roadway; compared with the large - diameter borehole pressure relief, the cross - borehole layout can reduce the strength of the coal and rock masses in the stress concentration area to a greater extent in terms of scope and effect, increase the scope of the plastic zone of the roadway coal and rock, protect the roadway and reduce the influence of mine tremors; overall, it achieves a pressure relief effect that cannot be achieved by conventional pressure relief measures in the high - stress concentration area of the irregular working face, fully releases the stress of the coal body, significantly reduces the occurrence probability and intensity of dynamic disasters, reduces the impact risk during the production process of the working face, and ensures the safe and efficient production of the coal mine. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0034] Figure 1(a) is a schematic diagram of the stress superposition area of the transition shrinkage section in the embodiment of the present invention;

[0035] Figure 1(b) is a schematic diagram of the stress superposition area of the cut - through roadway section of the knife - handle - shaped working face in the embodiment of the present invention;

[0036] Figure 2 is a schematic diagram of the spatial position of the cross - boreholes in the embodiment of the present invention;

[0037] Figure 3(a) is a schematic diagram of the borehole plane layout when x < 1 / 2d in the transition shrinkage section in the embodiment of the present invention;

[0038] Figure 3(b) is a schematic diagram of the borehole plane layout when x > 1 / 2d in the transition shrinkage section in the embodiment of the present invention;

[0039] Figure 4(a) is a schematic diagram of the borehole plane layout when x < 1 / 2d in the knife - handle - shaped working face in the embodiment of the present invention;

[0040] Figure 4(b) is a schematic diagram of the borehole plane layout when x > 1 / 2d in the knife - handle - shaped working face in the embodiment of the present invention;

[0041] Among them, 1 - influence area of the lateral abutment pressure of the roadway; 2 - superposition area of the advanced abutment pressure of the working face and the lateral abutment pressure of the roadway; 3 - sectional coal pillar; 4 - extraction roadway. DETAILED IMPLEMENTATION MANNER

[0042] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0043] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0044] As Figure 1(a) - Figure 1(b) shown, during the conventional working face mining, the sectional coal pillar 3 is affected by the load generated by the low-position broken overlying strata, and the roadway side support pressure influence area 1 is formed in the coal pillar. Under the mining disturbance of the working face, the gateway 4 is prone to plastic deformation. At this time, the stress concentration coefficient of the coal pillars on both sides is relatively low, and the stress concentration coefficient of the coal pillar can be reduced to a safe level by the conventional single row of large-diameter borehole pressure relief. However, when the coal mining face advances to the shrinking section (the length of the working face decreases), the sectional coal pillar 3 and the coal body in front of the working face are affected by the superposition of the advanced support pressure and the side support pressure of the working face, and a high-stress concentration area will be formed at area 2. The conventional single row of large-diameter borehole pressure relief method can no longer reduce the stress concentration coefficient of the coal pillar and coal seam in area 2 to a safe level, and another row of cross boreholes needs to be added to meet the pressure relief requirements.

[0045] As Figure 2 shown, during the shrinking process of the irregular coal mining face, the sectional coal pillar side is affected by the superposition of the advanced support pressure and the side support pressure of the working face, and strong stress concentration phenomena occur in the coal pillar and coal seam. According to the change trend of the working face length during the shrinking process, targeted borehole pressure relief measures are carried out, which are characterized by including the following steps:

[0046] 1. Layout of cross boreholes for the transition and shrinking of the irregular working face

[0047] Adopt a cross borehole pressure relief layout scheme on both sides of the roadway in the shrinking section to make the stress concentration degree of the coal bodies on both sides of the roadway during the shrinking process of the working face at a safe level, and protect the roadway from rock burst disasters due to the shrinking of the working face. The specific technical solution is as follows:

[0048] Construct two groups of spatial cross boreholes in the high-stress concentration areas on both sides of the roadway in the shrinking section. The first group of boreholes is constructed perpendicular to the coal wall, the borehole depth is x0, and the row and column spacing of the boreholes is d. After the second group of boreholes vertically deviate downward by 20 - 40 cm at the corresponding height position of the first group of boreholes, boreholes with a borehole depth of x1 are applied at the midpoint position between the two boreholes of the first group and at an angle α with the roadway coal wall;

[0049] The calculation formula for the depth x0 of the first set of drilling holes is shown in formula (1):

[0050]

[0051] Where r is the roadway radius, m; γ is the bulk density, kN / m 3 ; H is the thickness of the overlying rock layer of the coal seam, m; is the internal friction angle of the coal body, C is the cohesion of the coal body, MPa;

[0052] The calculation formula of the stress peak value superimposed on the stress concentration area and the distance xf from the coal wall is shown in formula (2):

[0053]

[0054] Among them, K is the stress concentration coefficient, p1 is the resistance of the support to the coal seam, m is the mining thickness of the coal seam, C is the cohesion of the coal body, is the internal friction angle of the coal body, f is the friction coefficient of the contact surface between the roof and floor of the coal seam;

[0055] The calculation formula of angle α is shown in formula (3):

[0056]

[0057] Among them, x f is the distance between the peak stress of the coal pillar and the coal wall, x j It is half of the spacing between drill holes, that is, 1 / 2d;

[0058] The calculation formula for the depth x1 of the second group of drill holes on the coal pillar side is shown in formula (4):

[0059]

[0060] In formula (4), x0 is the depth of the first group of drill holes, and α is the angle between the second group of drill holes and the coal wall.

[0061] Among them, in step a, the tunnel radius r, the thickness of the overlying rock layer H, the resistance of the support to the coal wall p1, the coal seam mining thickness m are determined by on-site measurements, the rock layer bulk density γ, the internal friction angle of the coal body The cohesion C of the coal mass and the friction coefficient f of the contact surface between the roof and floor of the coal seam are obtained from laboratory physical and mechanical experiments. The borehole spacing d is selected between 2 and 5 m according to the stress concentration degree. The higher the stress concentration coefficient, the smaller the value of d. The borehole diameter is selected between 150 mm and 200 mm according to the impact hazard degree. The higher the impact hazard, the larger the borehole diameter value. The construction height of the first group of boreholes from the floor is selected between 1.5 m and 2.0 m. The range and stress concentration coefficient of the high stress concentration area of coal mining faces with different shapes can be determined according to the on-site geological conditions and numerical simulation analysis.

[0062] Among them, the numerical simulation analysis is as follows: According to the on-site geological conditions and mining situation, a FLAC3D numerical model is established to simulate the actual coal mining plan, and the stress evolution of the coal mining face during the entire coal mining process is monitored, so as to determine the range of the high stress area. The stress concentration coefficient is the ratio of the real-time stress of the monitoring area during the coal mining process of the coal mining face to the stress value of the monitoring area before coal mining. When the stress concentration coefficient exceeds 1.5, it can be determined as a high stress concentration area.

[0063] 2. Borehole construction on the superior angle side of the roadway in the transition surface reduction section

[0064] When the working face starts to reduce the surface, the surface reduction angle of the working face (the included angle between the extension line of the roadway center line before surface reduction and the center line of the surface reduction section roadway) is β. Different borehole arrangements are implemented on the superior angle side of the roadway according to the distance x between the last borehole before the surface reduction section and the roadway inflection point:

[0065] As shown in Figure 3(a), when x is less than 1 / 2d, the first borehole on the coal pillar side of the surface reduction section roadway is constructed perpendicular to the coal wall side at a distance of 1 / 2d from the roadway inflection point, and the depth is x0. To ensure the pressure relief effect of the coal pillar at the roadway corner, a borehole at an angle of 90° - β with the roadway is arranged at a distance d from the roadway inflection point on the coal pillar side of the surface reduction section, so that it intersects with the first borehole in the surface reduction section, and the borehole depth is x1.

[0066] As shown in Figure 3(b), when x is greater than 1 / 2d, a borehole is constructed at a distance of 1 / 2d from the last borehole on the coal pillar side before surface reduction, and its direction is perpendicular to the coal pillar in the surface reduction section. A borehole is constructed at a distance of 1 / 2d from the inflection point on the coal wall side of the surface reduction section, and the included angle with the coal wall is 90° - β. The two boreholes intersect with each other, and the borehole depths are both x0.

[0067] Among them, 1 / 2d is the first preset threshold, and d is the borehole spacing.

[0068] 3. Borehole arrangement on the superior angle side of the cut roadway in the knife handle-shaped working face

[0069] When the working face starts to reduce the surface, different borehole arrangements are implemented on the superior angle side of the coal pillar in the cut roadway section according to the distance x between the last borehole before the surface reduction section and the roadway inflection point:

[0070] As shown in Fig. 4(a), when x is less than 1 / 2d, construction is carried out at a distance of 1 / 2d from the inflection point of the roadway on the coal pillar side of the roadway in the shrinkage section, with an angle of 30° with the coal wall; to ensure the pressure relief effect of the coal pillar at the roadway corner, a borehole at an angle of 30° with the roadway is arranged at a distance of 1 / 2d from the last borehole on the coal pillar side before shrinkage, so that it intersects with the first inclined borehole in the shrinkage section, and the depths of the two boreholes are x1;

[0071] As shown in Fig. 4(b), when x is greater than 1 / 2d, a borehole is constructed at a distance of 1 / 2d from the last borehole on the coal pillar side before shrinkage, with an angle of 30° with the coal wall, and a borehole is constructed at a distance of 1 / 2d from the inflection point on the coal wall in the shrinkage section, with an angle of 30° with the coal wall. The two boreholes intersect with each other, and the depths of the boreholes are both x1;

[0072] Among them, 1 / 2d is the second preset threshold, and d is the borehole spacing.

[0073] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A cross-borehole pressure relief method for high stress concentration areas in irregular coal mining faces, characterized in that Including: Judging the shape of the irregular coal mining face and obtaining the high stress concentration area; Implementing cross-borehole layout in the high stress concentration area to achieve pressure relief in the high stress concentration area; Among them, the high stress concentration area includes: the face reduction section; the face reduction section includes: the transition face reduction section and the cut roadway section of the knife handle type working face; Implementing cross-borehole layout in the face reduction section includes: Constructing two groups of spatially cross-boreholes in the high stress concentration area of the roadway in the face reduction section, constructing perpendicular to the coal wall in the face reduction section to obtain the first group of boreholes, and calculating the depth x0 of the first group of boreholes and the borehole row spacing; vertically offsetting the corresponding height position of the first group of boreholes downward, based on the position where the midpoint of any two boreholes in the first group of boreholes forms an angle α with the coal wall in the face reduction section, obtaining the second group of boreholes, and calculating the depth x1 of the second group of boreholes based on the angle α; Implementing cross-borehole layout on the acute angle side of the transition face reduction section includes: Obtaining the included angle β between the extension line of the roadway center line before the face reduction section and the roadway center line of the face reduction section, judging whether the distance between the last borehole before the face reduction section and the inflection point of the roadway in the face reduction section is less than the first preset threshold. If it is less than the first preset threshold, arranging the first borehole at a distance of 1 / 2d from the inflection point of the roadway in the coal pillar side of the face reduction section and arranging the second borehole at a distance of d from the inflection point of the roadway in the coal pillar side of the face reduction section; if it is greater than the first preset threshold, arranging the third borehole at a distance of 1 / 2d from the coal pillar side before the face reduction section and arranging the fourth borehole at a distance of 1 / 2d from the coal wall of the face reduction section to the inflection point of the roadway in the face reduction section; Among them, the drilling depths of the first borehole, the third borehole and the fourth borehole are all the depth x0 of the first group of boreholes; the drilling depth of the second borehole is the depth x1 of the second group of boreholes.

2. The method for pressure relief by intersecting boreholes in the high stress concentration area of the irregular coal mining face according to claim 1, characterized in that, Constructing perpendicular to the coal wall in the face reduction section includes: Constructing based on the distance perpendicular to the coal wall of the stress peak value of the superposition of stress concentration areas in the high stress concentration area; The method for calculating the distance perpendicular to the coal wall of the stress peak value of the superposition of stress concentration areas in the high stress concentration area is: Among them, K is the stress concentration coefficient, p1 is the resistance of the support to the coal rib, m is the coal seam mining thickness, C is the cohesion of the coal body, is the internal friction angle of the coal body, and f is the friction coefficient of the contact surface between the roof and the floor of the coal seam.

3. The cross-borehole pressure relief method for high stress concentration areas in irregular coal mining faces according to claim 1, characterized in that, The method for calculating the depth x0 of the first group of boreholes is: Among them, r is the roadway radius; γ is the unit weight; H is the thickness of the overlying strata of the coal seam; is the internal friction angle of the coal mass, and C is the cohesion of the coal mass.

4. The cross-borehole pressure relief method for high stress concentration area in irregular coal mining face according to claim 1, characterized in that, The method for calculating the depth x1 of the second group of boreholes is: Among them, x0 is the depth of the first group of boreholes, and α is the included angle between the second group of boreholes and the coal wall.

5. The method for pressure relief by intersecting boreholes in the high stress concentration area of the irregular coal mining face according to claim 1, characterized in that, The direction of the first borehole is perpendicular to the coal wall in the face reduction section and the inflection point of the roadway in the face reduction section, and the directions of the second borehole and the third borehole are both: 90° - β; the direction of the fourth borehole is perpendicular to the coal pillar in the face reduction section.

6. The cross-borehole pressure relief method for high stress concentration areas in irregular coal mining faces according to claim 1, wherein The method for implementing cross-borehole layout on the acute angle side of the cut roadway section of the knife handle type working face is: Judge whether the distance between the last drill hole before the reduced section and the inflection point of the reduced section roadway is less than the second preset threshold. If it is less than the second preset threshold, arrange the fifth drill hole at a distance of 1 / 2d from the inflection point of the reduced section roadway on the coal pillar side of the reduced section roadway; arrange the sixth drill hole at a distance of 1 / 2d from the drill hole on the coal pillar side before the reduced section. If it is greater than the second preset threshold, arrange the seventh drill hole at a distance of 1 / 2d from the drill hole on the coal pillar side before the reduced section, and arrange the eighth drill hole at a distance of 1 / 2d from the inflection point of the reduced section roadway on the coal wall side of the reduced section; Among them, the drilling depths of the fifth drill hole, the sixth drill hole, the seventh drill hole and the eighth drill hole are all the second group of drilling depths x1.

7. The cross-borehole pressure relief method for the high stress concentration area of the irregular coal mining face according to claim 6, characterized in that, The fifth drill hole, the seventh drill hole and the eighth drill hole are all at an angle of 30° with the coal wall of the reduced section roadway, and the sixth drill hole is at an angle of 30° with the reduced section roadway.

8. The method for cross-borehole pressure relief in the high stress concentration area of the irregular coal mining face according to claim 1, characterized in that, According to the on-site geological conditions and numerical simulation analysis, determine the range and stress concentration coefficient of the high stress concentration area.

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