Hard roof extra-thick coal seam island working face ground fracturing control method

Abstract

The invention discloses a ground fracturing control method for a hard roof extra-thick coal seam island working face, and relates to the technical field of coal mine underground mining safety. Comprising the steps that mechanical parameters are measured, a fracturing target layer is identified, and the thickness of the fracturing target layer is determined; calculating energy U released by fracture of the target layer of the hard roof; calculating the impact resistance Fzj of the bracket; calculating the distance L0 from the suspended roof to the key point when the hard roof is broken for the first time; calculating a periodic fracture step Lp of the hard roof; whether fracturing is conducted or not is judged; a ground fracturing position is determined, and energy density distribution of the hard roof is calculated; a hole is drilled in the middle of the working face, ground fracturing is conducted on the position with the highest energy accumulation, and the accumulated energy is released. According to the method, whether the island working face needs ground fracturing or not can be judged, if ground fracturing is needed, the elastic energy density of the island working face is calculated, and the hard roof is fractured according to the position with the maximum elastic energy density accumulation as the fracturing position.

Description

Technical Field

[0001] The invention relates to the technical field of coal mine mining safety, and in particular to a ground fracturing control method for an isolated island working face of a hard roof and extra-thick coal seam. Background Art

[0002] The breaking of the hard roof of a coal mine and the resulting strong mine earthquake are one of the common dynamic disasters in deep coal mining, and become more serious as the depth of the mine increases. The isolated working face is a three-gap working face caused by unreasonable mining design and working face succession. Due to the large amount of coal left in the isolated working face of the extra-thick coal seam, based on the needs of the national economy and the provisions of relevant national laws, the mining of coal in the isolated working face of the extra-thick coal seam has become a huge problem for coal mining companies. When the hard roof of the isolated working face of the coal seam with a hard roof breaks, it will be accompanied by severe impact and vibration, causing damage to the coal mine and tunnel equipment, resulting in equipment cost losses and increased tunnel maintenance costs. In severe cases, strong mine pressure and mine earthquakes may even cause casualties. Ground fracturing to control the breaking of the roof and release the energy accumulated in the roof in advance is one of the effective means to control strong mine pressure and mine earthquakes.

[0003] At present, ground fracturing has become one of the means to prevent and control mine earthquakes and strong mine pressure in isolated working faces of hard roof and extra-thick coal seams. However, there is a lack of corresponding methods to determine whether ground fracturing is necessary and the fracturing location of ground fracturing. Most people use empirical judgment or a fixed distance to perform fracturing on isolated working faces of hard roof and extra-thick coal seams. The fracturing effect is poor and the fracturing location cannot be accurately determined. Although certain effects have been achieved after fracturing, it has also caused a lot of economic losses.

[0004] Therefore, it is an urgent problem for technical personnel in this field to propose a ground fracturing control method for an isolated working face of a hard roof and extra-thick coal seam to solve the difficulties existing in the prior art. Summary of the invention

[0005] In view of this, the present invention provides a ground fracturing control method for an isolated working face of an extremely thick coal seam with a hard roof, which solves the risk of strong mine pressure and mine earthquake caused by the breaking of the hard roof of an isolated working face of an extremely thick coal seam with a hard roof in the related technology, and provides technical problems such as whether ground fracturing of the hard roof is needed and how to determine the fracturing position of the hard roof when ground fracturing is needed.

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

[0007] A method for controlling ground fracturing in an isolated working face of a hard roof extra-thick coal seam comprises the following steps:

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

[0009] 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;

[0010] 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;

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

[0012]

[0013] 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;

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

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

[0016]

[0017] 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;

[0018] in: C=κGA,

[0019] 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;

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

[0021] 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:

[0022]

[0023] 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; dZJD is the thickness of the immediate roof of coal rock; g is the acceleration of gravity; β 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 taken as 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;

[0024] S4. Calculate the distance L0 from the top of the suspended roof when the hard roof is first broken. The calculation formula of L0 is:

[0025]

[0026] 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:

[0027]

[0028] Where, L1 is the periodic overhang length of the hard roof;

[0029] 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;

[0030] S7, determine the surface fracturing location and calculate the energy density distribution of the hard roof;

[0031] 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.

[0032] In the above method, optionally, in S6, to determine whether to perform fracturing, firstly, the length of l is 5m, 10m, 15m... and substituted into step S2 and step S3. If l≤L0 satisfies the condition U≥1×10 7 J or F zj ≥25000kN, then take l as the fracturing step and proceed to step S7; otherwise, take L0, L p In step S2 and step S3, 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 step S7.

[0033] In the above method, optionally, in S7, the ground fracturing position is determined and the energy density distribution of the hard top plate is calculated, and the calculation formula is:

[0034]

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

[0036] In the above method, optionally, in S8, horizontal wells are arranged along the middle of the working face, and fracturing is performed sequentially according to the fracturing positions determined in S7.

[0037] It can be seen from the above technical scheme that compared with the prior art, the present invention provides a ground fracturing control method for an isolated working face of an island coal seam with a hard roof and extra-thick coal seam, which has the following beneficial effects: the ground fracturing control method for an isolated working face of an island coal seam with a hard roof and extra-thick coal seam provided by the present invention determines the target layer thickness by measuring the hard roofs of different thicknesses in different layers above the isolated working face, calculates the energy released by the breaking of the hard roof, and the impact load transmitted to the hydraulic support of the working face after the energy is released, and calculates the initial breaking step and periodic breaking step of the hard roof; substitutes the breaking step into the energy formula and the hydraulic support impact resistance formula to determine whether ground fracturing is needed. If ground fracturing is needed, calculates its elastic energy density, and fractures the hard roof according to the position with the largest accumulation of elastic energy density as the fracturing position. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0039] Figure 1 A flow chart of a ground fracturing control method for an isolated island working face of a hard roof extra-thick coal seam provided by the present invention;

[0040] Figure 2 An example diagram illustrating an embodiment of a method for controlling ground fracturing in an isolated island working face of a hard roof extra-thick coal seam provided by the present invention;

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

[0042] in:

[0043] 1 is a very thick coal seam; 2 is a hard roof one; 3 is a hard roof two; 4 is a hard roof three; 5 is a hard roof four; 6 is a hard roof five; 7 is a fracturing well; 8 is a fracturing device. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] In this application, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. The terms "include", "comprise" or any other variants 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 explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, the elements defined by the sentence "comprise one..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

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

[0047] S1, measuring mechanical parameters, identifying the target layer for fracturing, and determining the thickness h of the target layer for fracturing;

[0048] 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;

[0049] 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;

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

[0051]

[0052] 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;

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

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

[0055]

[0056] 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;

[0057] in: C=κGA,

[0058] 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;

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

[0060] 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:

[0061]

[0062] 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; β 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 taken as 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;

[0063] S4. Calculate the distance L0 from the top of the suspended roof when the hard roof is first broken. The calculation formula of L0 is:

[0064]

[0065] S5. Calculate the periodic breaking step L of the hard top plate pAfter 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:

[0066]

[0067] Where, L1 is the periodic overhang length of the hard roof;

[0068] 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;

[0069] S7, determine the surface fracturing location and calculate the energy density distribution of the hard roof;

[0070] 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.

[0071] Further, in S6, it is determined whether to perform fracturing. First, the length of l is 5m, 10m, 15m, etc., and then the length is brought into step S2 and step S3. If l≤L0 satisfies the condition U≥1×10 7 J or F zj ≥25000kN, then take l as the fracturing step and proceed to step S7; otherwise, take L0, L p In step S2 and step S3, 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 step S7.

[0072] Further, in S7, the ground fracturing position is determined and the energy density distribution of the hard top plate is calculated, and the calculation formula is:

[0073]

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

[0075] Furthermore, in S8, horizontal wells are arranged along the middle of the working face, and fracturing is performed sequentially according to the fracturing positions determined in S7.

[0076] In a specific embodiment, referring to Figure 2As shown in the figure, taking the specific values ​​of a certain underground coal mine as an example, based on the initial exploration data of the coal mine, the existence of a hard roof in the coal mine roof was determined, and the thickness of the key layer was obtained by calculation after the experiment; after all the steps of calculation, the fracturing step was finally determined, and the key layer was fractured on the ground, which reduced the pressure on the support, reduced the energy accumulation of the hard roof, ensured the safe production of the working face, and saved the cost of roof fracturing.

[0077] S1. Taking the specific data of a mine as an example, after collecting relevant information of the mine, the length of the suspended roof of the working face for the first time is 60m, the step distance of the periodic pressure is 35m, the width of the working face is L=270m, the thickness of the coal seam is 5-29m, the average is 16m, which belongs to the extra-thick coal seam 1. Due to the requirements for production in the early stage, the mine adopts the skip mining method, thus forming a certain isolated working face. There are 5 layers of overlying rock strata with a grade greater than or equal to grade IV in the rock hardness classification standard in the overlying rock strata of the isolated working face, namely hard roof 1 2, hard roof 2 3, hard roof 3 4, hard roof 4 5, hard roof 5 6; their mechanical parameters are: thickness h i =5, 7, 8, 9, 10m, 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 σ ti =2.8, 5.5, 3.6, 4.5, 4.8MPa, and the rock fracture angles are 25°, 35°, 30°, 42°, 53° respectively. The overburden load q transferred to the thick hard roof by the key layer theory is 1.25MPa, the coal rock foundation stiffness k in the mining bearing area is 1000MN / m, and the hydraulic support top control distance is l ZJ =7.0m, bracket center distance b ZJ =1.75m, thickness of coal rock immediate roof d ZJD =16m, average bulk density of direct top coal stratum γ ZJD =1600kg / m 3 , gravitational acceleration g = 9.8 m / s 2 .

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

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

[0080] Calculate the impact resistance F of the bracketzj .

[0081] Calculate the distance L0 from the suspended roof when the hard roof is first broken; according to statistical data, the length of the suspended roof when the mine is first pressed is 60m. Substituting various parameters into the above formula, we get L0=32.05m.

[0082] Calculation of the periodic fracture step length L of the hard top plate p According to the data, the mine's periodic pressure step distance is 35m. Substituting it into the above formula, we get: L p =36.54m.

[0083] Determine whether to perform fracturing. The condition for determining whether to perform fracturing is U ≥ 1 × 10 7 J or F zj ≥25000kN; the specific implementation steps are as follows: first, take the length of l as 5m, 10m, 15m... and substitute it into S2 and S3. If l / 2≤L0 satisfies the condition, then take l / 2 as the fracturing step and proceed to S7; otherwise, replace 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 the next step.

[0084] After S2 and S3 cycle calculations, the energy U released by the breaking of the hard top target layer 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), (35,3.3 1E+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] Output support impact resistance F zj for:

[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 calculation, the energy accumulated in the hard roof is U>10 when the length of the suspended roof is 50m. 7 J, when the length of the suspended top is 55m, the impact resistance F of the support caused by the breakage zj >25000kN, so the hard roof needs to be fractured.

[0092] Determine the ground fracturing position and calculate the energy density distribution of the hard roof. Based on the determined fracturing step distance of 25m, bring in the overhang length of 60m, and consider the range of 50m ahead and 50m 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 drawn into an energy density data graph, refer to Figure 3 As shown, the positions where the energy accumulation is maximum are respectively 30 m negatively away from the midpoint, the midpoint, and 30 m positively away from the midpoint. The fracturing step distance determined by S6 is 25 m, and the fracturing position is 25 m away from the midpoint.

[0166] A hole is drilled in the middle of the working face, and hydraulic fracturing is carried out at the position with the highest energy accumulation through the fracturing well 7 and the fracturing device 8 to release the accumulated energy. Specifically, the fracturing step before the initial break of the working face is when the cantilever length reaches 50m. After exceeding this range, pre-fracture is carried out every 25m to prevent and control mine pressure disasters.

[0167] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on 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, and the relevant parts can be referred to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0168] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may 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 isolated working faces of hard roof and extra-thick coal seams. It is 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; β 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 taken as 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, L 1 is the cantilever length of the target layer; S4. Calculate the distance L from the top of the suspended roof when the hard roof is first broken 0 , L 0 The calculation formula 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, L 1 Periodic overhang length of 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. A method for controlling ground fracturing in isolated island working face of hard roof extra-thick coal seam according to claim 1, It is characterized in that In S6, to determine whether to perform fracturing, first take the length of l as 5m, 10m, 15m and bring it into S2 and S3. If l≤L 0 When the condition U≥1×10 7 J or F zj ≥25000kN, then take l as the fracturing step and proceed to S7; otherwise, take L 0 , 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. A method for controlling ground fracturing in isolated island working face of hard roof extra-thick coal seam according to claim 1, It is 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 position with the maximum energy accumulation and the step size determined by the fracturing step, and take the smaller one as the fracturing position.

4. A method for controlling ground fracturing in isolated working face of hard roof extra-thick coal seam according to claim 3, It 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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