A ground fracturing control method for an isolated working face in a very thick coal seam with a hard roof

Abstract

The present invention discloses a method for controlling ground fracturing in an isolated working face of a very thick coal seam with a hard roof, which relates to the technical field of safety in underground coal mining. The method includes: measuring mechanical parameters, identifying the fracturing target layer, and determining the thickness of the fracturing target layer; calculating the energy U released by the breaking of the hard roof target layer; calculating the impact resistance F of the support zj ; calculating the distance L0 from the key position of the suspended roof distance at the first breaking of the hard roof; calculating the periodic breaking step distance L of the hard roof p ; judging whether to perform fracturing; determining the ground fracturing position, and calculating the energy density distribution of the hard roof; drilling holes from the middle of the working face to perform ground fracturing on the position with the highest energy accumulation to release the accumulated energy. The present invention can judge whether ground fracturing is required for the isolated working face. If ground fracturing is required, the elastic energy density is calculated, and the hard roof is fractured according to the position with the maximum accumulation of elastic energy density as the fracturing position

Description

Technical Field

[0001] The present invention relates to the technical field of safety in underground coal mining, and particularly to a method for controlling ground fracturing of an isolated working face in a very thick coal seam with a hard roof. Background Technique

[0002] The breakage of the hard roof in coal mines and the resulting strong mine tremors are one of the common dynamic disasters in coal mining as it enters the deep strata, and it becomes more serious as the mine depth increases. An isolated working face is a working face with three mined-out areas caused by unreasonable mining design and working face succession. Due to the large amount of coal left in the isolated working face of the very thick coal seam, based on the needs of the national economy and relevant national laws, the coal mining in the isolated working face of the very thick coal seam has become a huge problem faced by coal mining enterprises. When the hard roof of the isolated working face with a hard roof breaks, it will be accompanied by violent impacts and vibrations, causing damage to the equipment in the coal mining stope and roadway, resulting in losses in equipment costs and increasing roadway maintenance costs. In severe cases of strong mine pressure and mine tremors, even casualties may occur. Controlling the roof breakage by ground fracturing and releasing the energy accumulated in the roof in advance is one of the effective means to control strong mine pressure and mine tremors.

[0003] At present, ground fracturing has become one of the prevention and control measures for mine tremors and strong mine pressure in the isolated working face of a very thick coal seam with a hard roof. However, there is a lack of corresponding methods for determining whether ground fracturing is needed and the fracturing position of ground fracturing. More often, empirical judgment is used or fracturing is carried out on the isolated working face of the very thick coal seam with a hard roof at a fixed distance. The fracturing effect is poor, and the fracturing position cannot be accurately judged. Although certain effects have been achieved after fracturing, a large amount of economic losses have also been caused.

[0004] Therefore, proposing a method for controlling ground fracturing of an isolated working face in a very thick coal seam with a hard roof to solve the difficulties existing in the prior art is an urgent problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a method for controlling ground fracturing of an isolated working face in a very thick coal seam with a hard roof, which solves the technical problems of the risk of strong mine pressure and mine tremors caused by the breakage of the hard roof in the isolated working face of the very thick coal seam with a hard roof in the related art, provides whether ground fracturing of the hard roof needs to be carried out, and how to determine the fracturing position of the hard roof when ground fracturing is required.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] A method for controlling ground fracturing of an isolated working face in a very thick coal seam with a hard roof, comprising the following steps:

[0008] S1. Measuring mechanical parameters, identifying the fracturing target layer, and determining the thickness h of the fracturing target layer;

[0009] In S1, collect the initial exploration and design data of the mine, and determine the target layer of energy accumulation according to the lithology and thickness parameters of the geological borehole columnar diagram;

[0010] Core samples are taken from the rock strata with a hardness grade of IV or higher in the overlying strata of the isolated island working face to measure their elastic modulus E i , Poisson's ratio μ i , tensile strength σ ni , and screen the target layer thickness that meets the conditions according to the measured parameters;

[0011] The calculation formula for the thickness h of the target layer is:

[0012]

[0013] The above formula is looped by MATLAB. In the formula, m is the strength factor, whose value starts from 0 and increases at intervals of 0.01. When m ≥ 5 or h > 10, the calculation stops;

[0014] S2. Calculate the energy U released by the fracture of the hard roof target layer;

[0015] The calculation formula for the energy U released by the fracture of the hard roof is:

[0016]

[0017] In the formula, l is the overhanging length of the initial fracture of the hard roof, q is the overlying load of the hard roof, E is the elastic modulus of the hard roof, D is the flexural rigidity of the hard roof, h is the thickness of the hard roof, and α, β are the elastic foundation factors of the underlying layer of the hard roof;

[0018] Among them: C = κGA,

[0019] k is the stiffness of the elastic foundation underlying the hard roof, C is the shear stiffness of the hard roof, b is the unit width of the hard roof, G is the shear modulus of the target layer; A is the cross-sectional area of the target layer, and κ is the cross-section factor of the target layer;

[0020] S3. Calculate the support impact resistance F zj ;

[0021] The impact force caused by the fracture of the hard roof will act on the hydraulic support, and the calculation formula for the support impact resistance F zj is:

[0022]

[0023] In the formula, l ZJ is the roof control distance of the working face hydraulic support; γ ZJD is the average bulk density of the coal and rock direct roof; dZJD is the thickness of the direct roof of coal and rock; g is the acceleration due to gravity; β is the fracture angle of overlying strata; b ZJ is the center distance of the support; s is the dynamic load transfer efficiency, with a value of 1 / 20, K ZJD is the stiffness of the direct roof of coal and rock, p D is the load borne by the thick and hard roof, L 1 is the cantilever length of the target layer;

[0024] S4. Calculate the distance of the cantilever roof when the hard roof fractures for the first time, and focus on the distance L 0 , L 0 The calculation formula for is:

[0025]

[0026] S5. Calculate the periodic fracture step distance L of the hard roof p , after the hard roof fractures for the first time, with the advancement of the working face, periodic fractures will form. The calculation formula for the periodic fracture step distance L p is:

[0027]

[0028] In the formula, L 1 is the periodic cantilever length of the hard roof;

[0029] S6. Judge whether to perform fracturing. The condition for judging fracturing is U≥1×10 7 J or F zj ≥25000 kN. If the fracturing condition is not met, the steps end here, and it is determined that the roof does not need to be fractured; if the condition is met, go to S7;

[0030] S7. Determine the ground fracturing position and calculate the energy density distribution of the hard roof;

[0031] S8. Drill holes from the middle of the working face and perform ground fracturing on the position with the highest energy accumulation to release the accumulated energy.

[0032] For the above method, optionally, in S6, when judging whether to perform fracturing, first take the length of l as 5m, 10m, 15m... and substitute it into steps S2 and S3. If l≤L 0 satisfies the condition U≥1×10 7 J or F zj ≥25000 kN, then take l as the fracturing step distance and perform step S7; otherwise, take L 0 , L p and substitute it into steps S2 and S3 to determine the energy U released by the fracture of the hard roof and the impact resistance F of the support zj, if the fracturing conditions are not met, the steps end here, and it is determined that the roof does not need to be fractured; if the conditions are met, proceed to step S7.

[0033] In the above method, optionally, in S7, determine the ground fracturing position and calculate the energy density distribution of the hard roof. The calculation formula is:

[0034]

[0035] Substitute the fracturing step distance determined in S6 into the above formula, compare the position with the maximum energy accumulation and the step distance size determined by the fracturing step distance, and take the smaller one as the fracturing position.

[0036] In the above method, optionally, in S8, arrange horizontal wells along the middle of the working face and perform fracturing in sequence according to the fracturing positions determined in S7.

[0037] It can be seen from the above technical solutions that, compared with the prior art, the present invention provides a ground fracturing control method for an isolated island working face in a thick coal seam with a hard roof, and has the following beneficial effects: The ground fracturing control method for an isolated island working face in a thick coal seam with a hard roof provided by the present invention determines the target layer thickness by measuring the hard roofs with different layers and different thicknesses occurring above the isolated island working face, calculates the energy released by the breaking of the hard roof, the impact load transmitted to the hydraulic support on the working face after the energy release, and calculates the primary breaking step distance and the periodic breaking step distance of the hard roof breaking; substitute the breaking step distance into the energy formula and the hydraulic support impact resistance formula to judge whether ground fracturing is required. If ground fracturing is required, calculate its elastic energy density, and fracture the hard roof with the position where the elastic energy density accumulates the most as the fracturing position. Description of the Drawings

[0038] 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 the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0039] Figure 1 It is a flowchart of a ground fracturing control method for an isolated island working face in a thick coal seam with a hard roof provided by the present invention;

[0040] Figure 2 It is an example illustration diagram of an embodiment of a ground fracturing control method for an isolated island working face in a thick coal seam with a hard roof provided by the present invention;

[0041] Figure 3 It is a graph of energy density data of an embodiment of a ground fracturing control method for an isolated island working face in a thick coal seam with a hard roof provided by the present invention;

[0042] Wherein:

[0043] 1 is an extra-thick coal seam; 2 is the first hard roof; 3 is the second hard roof; 4 is the third hard roof; 5 is the fourth hard roof; 6 is the fifth hard roof; 7 is a fracturing well; 8 is a fracturing device. Specific embodiments

[0044] 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. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0045] In this application, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. The terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "including one..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0046] Referring to Figure 1 As shown, the present invention discloses a ground fracturing control method for an isolated island working face in an extra-thick coal seam with a hard roof, including the following steps:

[0047] S1. Measure mechanical parameters, identify the fracturing target layer, and determine the thickness h of the fracturing target layer;

[0048] In S1, collect the initial exploration and design data of the mine, and identify the target layer of energy accumulation according to the lithology and thickness parameters of the geological borehole columnar diagram;

[0049] Core samples are taken from the rock layers in the overlying strata of the isolated island working face with a rock hardness grading standard of grade IV or higher to measure their elastic modulus E i , Poisson's ratio μ i , tensile strength σ ni , and the target layer thickness that meets the conditions is screened according to the measured parameters;

[0050] The calculation formula for the thickness h of the target layer is:

[0051]

[0052] The above formula is looped by MATLAB. In the formula, m is the strength factor, whose value starts from 0 and increases at an interval of 0.01. When m≥5 or h>10, the calculation stops;

[0053] S2. Calculate the energy U released by the fracture of the hard roof target layer;

[0054] The calculation formula for the energy U released by the fracture of the hard roof is:

[0055]

[0056] In the formula, l is the overhanging length of the initial fracture of the hard roof, q is the overlying load on the hard roof, E is the elastic modulus of the hard roof, D is the flexural rigidity of the hard roof, h is the thickness of the hard roof, and α, β are the elastic foundation factors of the underlying layer of the hard roof;

[0057] Among them: C = κGA,

[0058] k is the stiffness of the elastic foundation underlying the hard roof, C is the shear stiffness of the hard roof, b is the unit width of the hard roof, G is the shear modulus of the target layer; A is the cross-sectional area of the target layer, and κ is the cross-sectional factor of the target layer;

[0059] S3. Calculate the impact resistance F of the support zj ;

[0060] The impact force caused by the fracture of the hard roof will act on the hydraulic support, and the impact resistance F of the support zj The calculation formula is:

[0061]

[0062] In the formula, l ZJ is the roof control distance of the hydraulic support in the working face; γ ZJD is the average bulk density of the coal and rock immediate roof; d ZJD is the thickness of the coal and rock immediate roof; g is the acceleration due to gravity; β is the fracture angle of the overlying strata; b ZJ is the center distance of the support; s is the dynamic load transfer efficiency, with a value of 1 / 20, K ZJD is the stiffness of the coal and rock immediate roof, p D is the load borne by the thick and hard roof, L 1 is the cantilever length of the target layer;

[0063] S4. Calculate the distance L from the key point of the overhanging distance at the initial fracture of the hard roof 0 , L 0 The calculation formula is:

[0064]

[0065] S5. Calculate the periodic breaking step distance L of the hard roof p After the initial breaking of the hard roof, with the advancement of the working face, periodic breaking will occur, and the periodic breaking step distance L p is calculated by the formula:

[0066]

[0067] In the formula, L 1 periodic overhanging length of the hard roof;

[0068] S6. Judge whether to perform fracturing. The condition for performing fracturing is U≥1×10 7 J or F zj ≥25000 kN. If the fracturing condition is not satisfied, the procedure ends here, and it is determined that the roof does not require fracturing; if the condition is satisfied, go to S7;

[0069] S7. Determine the ground fracturing position and calculate the energy density distribution of the hard roof;

[0070] S8. Drill holes from the middle of the working face and perform ground fracturing on the position with the highest energy accumulation to release the accumulated energy.

[0071] Furthermore, in S6, when judging whether to perform fracturing, first take the length of l as 5m, 10m, 15m... and substitute it into Step S2 and Step S3. If U≥1×10 0 is satisfied when l≤L 7 J or F zj ≥25000 kN, then take l as the fracturing step distance and perform Step S7; otherwise, substitute L 0 , L p into Step S2 and Step S3 to determine the energy U released by the breaking of the hard roof and the impact resistance F of the support zj . If the fracturing condition is not satisfied, the procedure ends here, and it is determined that the roof does not require fracturing; if the condition is satisfied, perform Step S7.

[0072] Furthermore, in S7, when determining the ground fracturing position and calculating the energy density distribution of the hard roof, the calculation formula is:

[0073]

[0074] Substitute the fracturing step distance determined in S6 into the above formula, compare the position with the maximum energy accumulation and the step distance determined by the fracturing step distance, and take the smaller one as the fracturing position.

[0075] Furthermore, in S8, arrange horizontal wells along the middle of the working face and perform fracturing in sequence according to the fracturing position determined in S7.

[0076] In a specific embodiment, referring to Figure 2 as shown, taking the specific numerical values of a certain underground coal mine as an example, based on the initial exploration data of the coal mine, the hard roof existing in the coal mine roof was determined, and the thickness of the key stratum was obtained through calculation after experiments; through the calculation of all steps, the fracturing step distance was finally determined, and the key stratum was fractured on the ground, reducing the pressure on the support, reducing the energy accumulation of the hard roof, ensuring the safe production of the working face, and saving the cost of roof fracturing.

[0077] S1. Taking the specific data of a certain mine as an example, after collecting the relevant data of the mine, the suspended roof length at the first weighting of the working face reaches 60 m, the periodic weighting step distance is 35 m, the width L of the working face is 270 m, the coal seam thickness is 5 - 29 m, with an average of 16 m, belonging to extra-thick coal seam 1. Due to the previous requirements for production, the mine adopts the skip mining method, thus forming a certain isolated island working face. There are a total of 5 overlying strata with a rock hardness grading standard of grade IV or above in the overlying strata of the isolated island working face, namely hard roof 1 - 2, hard roof 2 - 3, hard roof 3 - 4, hard roof 4 - 5, and hard roof 5 - 6; their mechanical parameters are as follows: thickness h i = 5, 7, 8, 9, 10 m, elastic modulus E i = 2.6, 4, 2.4, 3.5, 2.7 GPa, Poisson's ratio μ i = 0.15, 0.2, 0.14, 0.17, 0.23, and the tensile strengths are respectively σ ti = 2.8, 5.5, 3.6, 4.5, 4.8 MPa, and the strata fracture angles are 25°, 35°, 30°, 42°, 53° respectively. The overlying load q transmitted to the thick and hard roof calculated by the key stratum theory is 1.25 MPa, the foundation stiffness k of the coal and rock mass in the mining bearing area is 1000 MN / m, the roof control distance l of the hydraulic support ZJ = 7.0 m, the center distance b of the support ZJ = 1.75 m, the thickness d of the direct roof of coal and rock ZJD = 16 m, the average unit weight γ of the direct roof coal and rock strata ZJD = 1600 kg / m 3 , and the acceleration due to gravity g = 9.8 m / s 2 .

[0078] Calculate the thickness h of the target layer. After calculation, when m = 0.35, h = 10.68 m is obtained. Therefore, the thickness of the fracturing target layer is determined to be 10 m, and the other parameters are respectively tensile strength = 5.5 MPa, elastic modulus E = 4 GPa, Poisson's ratio μ = 0.2, and strata fracture angle 35°.

[0079] Calculate the energy U released by the fracture of the hard roof target layer. κ is the cross-section factor of the target layer, which is related to the cross-section shape. Here, for a rectangular cross-section, it takes 5 / 6.

[0080] Calculate the impact resistance F of the support zj .

[0081] Calculate the suspended roof distance L, which is the key distance when the hard roof breaks for the first time 0 ; According to statistical data, the suspended roof length during the first weighting in the mine is 60m. Substitute each parameter into the above formula for calculation to obtain L 0 = 32.05m.

[0082] Calculate the periodic breaking step distance L of the hard roof p ; According to the data, the periodic weighting step distance of this mine is 35m. Substitute it into the above formula to obtain L p = 36.54m.

[0083] Judge whether to perform fracturing. The condition for performing fracturing is U≥1×10 7 J or F zj ≥25000kN; The specific implementation steps are as follows: First, take the lengths of l as 5m, 10m, 15m... and substitute them into S2 and S3. If l / 2≤L 0 satisfies the condition, then take l / 2 as the fracturing step distance and perform S7; otherwise, substitute L 0 , L p into S2 and S3 to determine the energy U released by the breaking of the hard roof and the impact resistance F of the support zj . If the fracturing condition is not satisfied, the steps end here, and it is determined that the roof does not need to be fractured; if the condition is satisfied, proceed to the next step.

[0084] After cyclic calculation through S2 and S3, the energy U released by the breaking of the target layer of the hard roof is as follows:

[0085] (5, 3.08E+03), (10, 3.71E+04), 15, 1.59E+05), (20, 4.45E+05), (25, 9.91E+05), (30, 1.91E+06), (35, 3.31E+06), (40, 5.35E+06), (45, 8.16E+06), (50, 1.19E+07), (55, 1.68E+07), (60, 2.29E+07), 65, 3.05E+07).

[0086] The output impact resistance F of the support zj is:

[0087] (5, 8139.933333), (10, 9918.766667), (15, 11697.6), (20, 13476.43333),

[0088] (25, 15255.26667), (30, 17034.1), (35, 18812.93333), (40, 20591.76667),

[0089] (45, 22370.6), (50, 24149.43333), (55, 25928.26667), (60, 27707.1),

[0090] (65, 29485.93333).

[0091] After the above calculations, the energy accumulated in the hard roof is U > 10 7 J when the overhanging length is 50 m. When the overhanging length is 55 m, the impact resistance F of the support caused by the fracture zj > 25000 kN. Therefore, the hard roof needs to be fractured.

[0092] Determine the surface fracturing position, calculate the energy density distribution of the hard roof. With the determined fracturing step of 25 m, substitute the overhanging length of 60 m and consider the range 50 m ahead and 50 m behind to calculate the energy density:

[0093] The output energy data is:

[0094] (-80.00000, 0.0055918), (-79.24858, 0.0110982), (-78.20448, 0.0211519), (-77.13872, 0.0394475), (-76.09296, 0.0705129), (-75.01635, 0.12474),

[0095] (-74.65828, 0.149972), (-74.32915, 0.177246), (-73.25769, 0.301199),

[0096] (-72.20762, 0.497232), (-71.13936, 0.81452), (-70.80675, 0.946891),

[0097] (-70.10882, 1.29), (-69.04047, 2.06), (-68.34566, 2.77), (-67.99966, 3.21),

[0098] (-67.27271,4.34)，(-66.22925,6.65)，(-65.16003,10.19)，(-64.10433,15.39)，(-63.06147,22.94)，(-62.01983,33.91)，(-61.30459,44.15)，(-60.24965,64.74)，(-59.21159,93.69)，(-58.13376,136.49)，(-57.09093,195.04)，(-56.03848,277.66)，(-55.34217,349.4)，(-54.2769,493.64)，(-53.21319,691.97)，(-52.84862,775.57)，(-52.15709,960.54)，(-51.11475,1317.9)，(-50.04288,1810.14)，

[0099] (-49.36141,2205.32)，(-48.29619,2981.89)，(-47.2475,3978.3)，

[0100] (-46.16399,5307.34)，(-45.12602,6926.74)，(-44.08548,8952.52)，

[0101] (-43.00785,11538.14)，(-42.31102,13499.86)，(-41.24598,16961.46)，

[0102] (-40.18508,20962.45)，(-39.13064,25426.8)，(-38.10249,30113.8)，

[0103] (-37.02219,35141.13)，(-36.34139,38193.8)，(-35.27911,42437.64)，

[0104] (-34.20751,45612.45)，(-33.16374,47223.46)，(-32.11913,47389.68)，

[0105] ((-31.31745,47150.8)，(-30.88257,47336.7)，(-30.52105,47958.13)，

[0106] (-30.34048,48514.52)，(-30,50191.77)，(-30,50191.77)，(-29.10139,41083.82)，(-28.79066,38244.7)，(-28.19471,33223.73)，(-27.28476,26579.36)，

[0107] (-26.0671,19470.5)，(-25.16461,15399.19)，(-24.28242,12311.47)，

[0108] (-23.97029,11415.25)，(-23.07815,9377.7)，(-22.17413,8043.52)，

[0109] (-21.26103,7364.21)，(-20.03679,7374.9)，(-19.15277,7949.56)，

[0110] (-18.23897,8968.23)，(-17.04775,10837.03)，(-16.13471,12605.19)，

[0111] (-15.23583,14567.88)，(-14.03243,17448.74)，(-13.11544,19772.54)，

[0112] (-12.21307,22115.81)，(-11.00456,25267.06)，(-10.09167,27605.13)，

[0113] (-9.18233,29856.85)，(-8.27853,31985.34)，(-7.07802,34593.1)，

[0114] (-6.17796,36350.43)，(-5.26231,37938.43)，(-4.0587,39685.93)，

[0115] (-3.16404,40714.42)，(-2.26866,41499.23)，(-1.36386,42034.65)，

[0116] (-1.05364,42157.41)，(0.76772,42242.77)，(2.25756,41507.38)，

[0117] (3.75958,40056.29)，(4.68721,38823.67)，(4.9615,38412.66)，

[0118] (5.88535,36880.82)，(6.7792,35196.79)，(7.6813,33317.3)，(8.88804,30563.42)，

[0119] (9.8103,28311.72)，(10.69863,26057.04)，(11.90165,22929.58)，

[0120] (12.82039,20534.74)，(13.7251,18218.23)，(14.93508,15264.47)，

[0121] (15.8268,13255.45)，(16.73266,11418.01)，(17.92673,9403.55)，

[0122] (18.2392,8967.93)，(18.85041,8242.05)，(19.74804,7514.33)，

[0123] (20.04765,7370.62)，(20.36059,7277.92)，(20.64882,7246.84)，

[0124] (21.56503,7520.54)，(22.17373,8043.09)，(23.05501,9334.71)，

[0125] (23.37424,9970.78)，(23.98098,11444.34)，(24.87661,14298.14)，

[0126] (25.77781,18059.78)，(26.6707,22751.12)，(26.989,24671.94)，

[0127] (27.88112,30798.16)，(28.1836,33135.35)，(29.70816,47083.89)，(30,50191.77)，

[0128] (30,50191.77)，(30.36803,48416.68)，(30.68826,47600.61)，(30.86832,47351.35)，

[0129] (31.04838,47212.15)(31.22964,47155.47)，(31.32026,47150.86)，

[0130] (31.77168,47262.49)，(32.10618,47385.54)，(32.27935,47433.04)，

[0131] (32.45253,47458.87)，(32.63163,47456.1)，(32.81073,47417.9)，

[0132] (32.98925,47340.34)，(33.16778,47220.26)，(33.35141,47050.13)，

[0133] (33.53505,46831.36)，(33.85854,46326.24)，(34.22271,45577.48)，

[0134] (34.58838,44643.35)，(34.94077,43584.64)，(35.26077,42502.79)，

[0135] (35.64129,41087.09)，(35.96364,39795.05)，(36.3386,38205.9)，

[0136] (36.67051,36739.24)，(37.03467,35083.79)，(38.0755,30239.45)，

[0137] (38.43388,28579.03)，(38.80614,26879.35)，(39.13019,25428.82)，

[0138] (39.48017,23899.81)，(39.84174,22367.67)，(40.19546,20920.74)，

[0139] (40.53771,19573.55)，(40.91772,18141.89)，(41.9541,14596.94)，

[0140] (42.31527,13487.17)，(42.6551,12501.75)，(43.01032,11531.6)，

[0141] (43.35762,10640.96)，(43.7212,9768.08)，(44.07138,8983.02)，(44.78462,7544)，

[0142] (45.8195,5804.15)，(46.89662,4372.34)，(47.22486,4002.74)，

[0143] (48.30837,2971.77)，(48.62883,2716.33)，(48.9938,2449.69)，(49.34634,2214.88)，

[0144] (50.04967,1806.55)，(51.09886,1324.19)，(51.46451,1186.18)，

[0145] (51.79552,1072.83)，(52.86128,772.51)，(53.22638,689.11)，(54.28728,491.99)，

[0146] (54.63156,440.35)，(54.98365,392.82)，(55.34172,349.46)，(55.67085,313.6)，

[0147] (56.0217,279.22)，(56.36987,248.63)，(56.74231,219.42)，(57.79238,153.52)，

[0148] (58.13097,136.62)，(59.19325,94.29)，(59.54647,83.22)，(59.89118,73.61)，

[0149] (60.26485,64.39)，(60.58818,57.3)，(60.95953,50.08)，(61.30863,44.08)，

[0150] (61.65434,38.82)，(62.00034,34.15)，(62.35323,29.94)，(62.72729,26.02)，

[0151] (63.07027,22.86)，(63.40883,20.1)，(63.77075,17.5)，(64.13188,15.23)，

[0152] (64.45601,13.43)，(64.83997,11.56)，(65.16126,10.18)，(65.53703,8.77)，

[0153] (65.89567,7.6)，(66.21589,6.68)，(66.57602,5.78)，(66.93853,4.98)，

[0154] (67.29932,4.29)，(67.63381,3.74)，(67.98017,3.23)，(68.33836,2.78)，

[0155] (68.69541,2.39)，(69.06268,2.04)，(69.38617,1.77)，(69.75035,1.51)，

[0156] (70.11602,1.29)，(70.46841,1.1)，(70.78841,0.954745)，(71.86624,0.583172)，

[0157] (72.19815,0.499447)，(72.56231,0.420576)，(72.90907,0.356415)，

[0158] (73.27088,0.299276)，(73.60313,0.254426)，(73.96152,0.213101)，

[0159] (74.33377,0.176833)，(74.65783,0.150007)，(75.00781,0.125293)，

[0160] (75.36938,0.103753)，(75.7231,0.086031)，(76.06535,0.0715758)，

[0161] (76.44536, 0.0581609), (76.78681, 0.0481159), (77.15138, 0.039164),

[0162] (78.18274, 0.0214299), (78.53796, 0.0172803), (78.88525, 0.0139465),

[0163] (79.24884, 0.0110964), (79.59901, 0.00886731), (79.95712, 0.00702212),

[0164] (80.00000, 0.0055513),

[0165] According to the energy density data, it is plotted into an energy density data graph. Referring to Figure 3 as shown, the positions with the maximum energy accumulation are respectively at 30 m in the negative direction from the midpoint, the midpoint, and 30 m in the positive direction from the midpoint. The fracturing step distance determined according to S6 is 25 m, and the fracturing position is 25 m from the midpoint.

[0166] Drill holes from the middle of the working face, and through the fracturing well 7 and the fracturing device 8, conduct hydraulic fracturing on the positions with the highest energy accumulation to release the accumulated energy. Specifically: before the initial fracture of the working face, the fracturing step distance is at the position when the cantilever length reaches 50 m. After exceeding this range, pre-fracture is carried out every 25 m as the fracturing step distance to prevent mine pressure disasters.

[0167] Each embodiment in this specification is described in a progressive manner. For the same or similar parts between each embodiment, reference can be made to each other. The key point of each embodiment is to illustrate the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple. For the relevant parts, reference can be made to the partial description of the method embodiment. The systems and system embodiments described above are only illustrative. The units described as separated components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art can understand and implement it without creative work.

[0168] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling ground fracturing in an isolated working face of a hard roof extra-thick coal seam, characterized in that: The following steps are involved: S1, measuring mechanical parameters, identifying the target layer for fracturing, and determining the thickness h of the target layer for fracturing; In S1, the initial exploration and design data of the mine are collected, and the target layer for energy accumulation is determined based on the lithology and thickness parameters of the geological drill hole column chart; The elastic modulus E of the rock layer with a grade greater than or equal to grade IV in the rock hardness classification standard in the overlying rock layer of the isolated working face is measured by core sampling. i , Poisson's ratio μ i , tensile strength σ ni , select the target layer thickness that meets the conditions according to the measurement parameters; The calculation formula of the thickness h of the target layer is: The above formula is looped by MATLAB, where m is the intensity factor, and its value increases from 0 with an interval of 0.

01. When m≥5 or h>10, the calculation stops; S2. Calculate the energy U released by the breaking of the hard top target layer; The calculation formula for the energy U released by the breaking of the hard roof is: Where l is the overhang length of the hard roof for the first break, q is the overburden load on the hard roof, E is the elastic modulus of the hard roof, D is the bending stiffness of the hard roof, h is the thickness of the hard roof, α and β are the elastic ground elements under the hard roof; in: D=EI, C=κGA, k is the stiffness of the elastic foundation under the hard roof, C is the shear stiffness of the hard roof, b is the unit width of the hard roof, G is the shear modulus of the target layer; A is the cross-sectional area of ​​the target layer, and κ is the cross-sectional factor of the target layer; S3. Calculate the impact resistance F of the bracket zj ; The impact force caused by the breaking of the hard top plate will act on the hydraulic support, and the support impact resistance F zj The calculation formula is: In the formula, l ZJ Control the top distance of the hydraulic support on the working surface; γ ZJD is the average bulk density of the immediate roof of coal rock; d ZJD is the thickness of the immediate roof of coal rock; g is the acceleration of gravity; δ is the fracture angle of the overburden rock; b ZJ is the center distance of the bracket; s is the dynamic load transfer efficiency, which is 1 / 20, K ZJD is the stiffness of the immediate roof of coal rock, p D For the thick hard top plate to bear the load, L1 is the cantilever length of the target layer; S4. Calculate the distance L0 from the midpoint of the suspended top distance when the hard top plate breaks for the first time. The calculation formula of L0 is: S5. Calculate the periodic breaking step L of the hard top plate p After the hard roof is broken for the first time, periodic breaking will occur as the working face advances. The periodic breaking step distance L p The calculation formula is: Where, L1 is the periodic overhang length of the hard roof; S6. Determine whether to perform fracturing. The condition for determining whether to perform fracturing is U ≥ 1 × 10 7 J or F zj ≥25000kN, if the fracturing condition is not met, the step ends here and it is determined that the top plate does not need fracturing; if the condition is met, enter S7; S7, determine the surface fracturing location and calculate the energy density distribution of the hard roof; S8. Drill holes in the middle of the working surface and perform ground fracturing at the location where energy accumulation is highest to release the accumulated energy.

2. The method for controlling ground fracturing in isolated island working face of hard roof extra-thick coal seam according to claim 1 is characterized in that: In S6, to determine whether to perform fracturing, first take the length of l as 5m, 10m, and 15m and bring it into S2 and S3. If l≤L0 satisfies the condition U≥1×10 7 J or F zj ≥25000kN, then use l as the fracturing step and proceed to S7; otherwise, use L0, L p Substitute into S2 and S3 to determine the energy U released by the breaking of the hard top plate and the impact resistance F of the bracket zj If the fracturing conditions are not met, the step ends here and it is determined that the top plate does not need fracturing; if the conditions are met, proceed to S7.

3. The method for controlling ground fracturing in isolated island working face of hard roof extra-thick coal seam according to claim 2, characterized in that: In S7, the ground fracturing position is determined and the energy density distribution of the hard roof is calculated. The calculation formula is: Substitute the fracturing step determined in S6 into the above formula, compare the distance represented by x at the position with the maximum energy accumulation with the step size determined in S6, and take the smaller one as the fracturing step for fracturing.

4. The method for controlling ground fracturing in isolated island working face of hard roof extra-thick coal seam according to claim 3 is characterized in that: In S8, horizontal wells are arranged along the middle of the working face, and fracturing is performed in sequence according to the fracturing positions determined in S7.

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