Blasting roof-cutting pressure relief method for lateral stress peak position of wide coal pillar

Abstract

The invention discloses a wide coal pillar lateral stress peak position blasting roof-cutting pressure relief method which comprises the following steps: step 1, according to a working face drilling histogram, calculating and determining a low-position key rock layer position by adopting a formula; 2, calculating the width of a working face coal pillar goaf side plastic zone by adopting a formula; 3, blasting drilling parameters are determined according to the position of the low-position key rock layer and the width of a plastic zone on the coal pillar goaf side; and 4, after blasting drilling parameters are determined, blasting drilling is conducted, in the working face advanced mining influence range, blasting top cutting is conducted on a working face air side roadway low-position key rock stratum cantilever structure, and continuous forward implementation is conducted along with working face stoping till working face stoping is completed. According to the method, the length of the lateral cantilever of the low-position key rock stratum of the goaf is reduced, the influence of the cantilever structure on stress concentration of the coal pillar is weakened, the internal stress of the coal pillar is reduced, and the stability of the goaf side roadway of the working face in the working face stoping period is ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of coal seam mining and relates to a method for blasting and top cutting to relieve pressure at a lateral stress peak position of a wide coal pillar. Background Art

[0002] At present, in order to improve the recovery rate of coal resources, underground mines leave 3~10m small coal pillars or no coal pillars at the coal mining face, which has been tested and applied in many mines. However, in mines with multiple disasters such as water, fire, and gas, leaving 20~40m wide coal pillars is still of great significance in the prevention and control of multiple disasters. Unlike the small coal pillars that have been fully plasticized, there is an elastic area in the middle of the wide coal pillar, which can play a certain supporting role for the overlying roof rock layer.

[0003] During the mining of the open working face in underground mines, the rock strata on the roof of the goaf are supported by the coal pillars and the coal wall of the working face. The low-level key rock strata are prone to form a cantilever structure in the goaf. Due to the certain support effect of the wide coal pillar, the load carried by the cantilever roof directly acts on the coal pillar, and a high stress concentration occurs in the middle of the coal pillar. When the advanced support pressure during the mining of the working face is superimposed on the higher stress in the coal pillar, a coal pillar-type rock burst disaster is prone to occur. Therefore, how to deal with the cantilever structure of the low-level key rock strata in the goaf, reduce the stress in the middle of the coal pillar, and protect the safety and stability of the tunnel during mining is an urgent problem to be solved. Summary of the invention

[0004] The purpose of the present invention is to provide a method for blasting and cutting the top to relieve pressure at the peak position of lateral stress of a wide coal pillar, thereby reducing the lateral cantilever length of the low-position key rock stratum in the goaf during the mining of the empty working face, weakening the influence of its cantilever structure on the stress concentration of the coal pillar, reducing the internal stress of the coal pillar, and ensuring the stability of the empty side tunnel of the working face during the mining of the working face.

[0005] The technical solution adopted by the present invention is a method for blasting and cutting the top to relieve pressure at the lateral stress peak position of a wide coal pillar, comprising the following steps: Step 1: According to the drilling column chart of the working face, the position of the low-level key rock layer is determined by formula calculation; Step 2: Calculate the plastic zone width on the side of the coal pillar goaf of the working face using a formula; Step 3, determining the blasting drilling parameters according to the low-level key rock layer position and the width of the plastic zone on the side of the coal pillar goaf; Step 4: After determining the blasting drilling parameters, drill the blasting holes. Within the influence range of the advanced mining of the working face, blast the top of the cantilever structure of the low-lying key rock strata in the empty side tunnel of the working face, and continue to move forward with the mining of the working face until the mining of the working face is completed.

[0006] The present invention is also characterized in that: In step 1, the low-level key rock layer position is calculated and judged using the following formula:

[0007] Where: q n )1——No. n The load of the first rock layer on the first rock layer, MPa; q n+1 )1——No. n The load of +1 layer of rock on the 1st layer of rock, MPa; E 1, E 2, ..., E n , E n+1 ——Elastic modulus of overlying rock layers, MPa; ρ 1, ρ 2, ..., ρ n , ρ n+1 ——Density of overlying rock layers, kg / m 3 ; h 1, h 2, ..., h n , h n+1 ——thickness of overlying rock layers, m; g ——acceleration due to gravity, N / kg; when n The load of the +1 layer on the 1st layer is less than that of the n When the load of the first layer of rock is applied to the first layer of rock, determine the n The +1 layer is the low-lying key rock layer.

[0008] In step 2, the width of the plastic zone on the side of the coal pillar goaf is determined by the following formula:

[0009] Where: x 0——Width of plastic zone on the side of coal pillar goaf, m; M ——tunnel height, m; λ ——lateral pressure coefficient; φ 0——internal friction angle, °; C 0——cohesion, MPa; K ——stress concentration factor; γ ——Average bulk density of rock formation, N / m 3 ; H —— burial depth, m; F ——Lateral force in tunnel, MPa.

[0010] In step 3, the blasting drilling parameters include the blasting drilling inclination angle, the blasting drilling depth and the length of the charging section. The blasting drilling parameters are determined using the following formula:

[0011] Where: α ——Drill hole inclination angle, °; H ——Distance from the bottom of the low-lying key rock layer to the top of the roadway, m; h ——Thickness of low-lying key rock formation, m; B ——coal pillar width, m; x 0——Width of plastic zone on the side of coal pillar goaf, m; L ——Drilling depth for blasting, m; L z ——Charging section length, m.

[0012] In step 4, the plane projection of the blasting borehole is perpendicular to the direction of the empty side tunnel facing the working face, the hole spacing is 1.0m, and concentrated blasting is used. The sealing length of the blasting hole is not less than 1 / 3 of the drilling length.

[0013] The beneficial effects of the present invention are: The method for blasting and cutting the top to relieve pressure at the lateral stress peak position of a wide coal pillar of the present invention determines the position of the low-position key rock layer on the roof and the width of the plastic zone on the goaf side of the coal pillar, and performs blasting and pressure relief at the peak stress position of the coal pillar, thereby reducing the cantilever length of the low-position key rock layer on the goaf side, reducing the load on the roof rock layer above the coal pillar, and reducing the stress concentration degree inside the coal pillar. At the same time, the supporting effect of the coal body in the plastic zone on the goaf side of the coal pillar is utilized to make the cut low-position key rock layer blocks fall smoothly into the goaf, thereby avoiding the cut rock blocks directly falling into the goaf to cause secondary disasters, and ensuring the safe implementation of blasting measures during the recovery of the working face and the stability of the goaf side tunnel of the working face during the recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a flow chart for realizing the method for blasting and cutting the top to relieve pressure at the lateral stress peak position of a wide coal pillar according to the present invention; Figure 2 It is a schematic diagram of determining parameters such as blast hole angle and hole depth of the present invention; Figure 3 It is a schematic diagram of blasting drilling implemented by the present invention; Figure 4 It is a schematic plan view of the arrangement of blasting drilling holes along the direction of the tunnel implemented by the present invention; Figure 5 It is a schematic diagram of rock formation collapse after blasting according to the present invention; In the figure, 1-coal seam at the coal mining working face, 2-goaf side tunnel at the working face, 3-coal pillar, 4-blasting drill hole, 5-roof rock layer one, 6-roof rock layer two, 7-roof rock layer three, 8-low-level key rock layer, 9-goaf, 10-cut-off low-level key rock layer blocks, 11-rock layer fracture position. DETAILED DESCRIPTION

[0015] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] The present invention provides a method for blasting and cutting the top to relieve pressure at the peak position of lateral stress of a wide coal pillar, the flow chart of which is as follows: Figure 1 The specific steps are as follows: Step 1: According to the drilling column chart of the working face, the position of the low-level key rock layer is determined by formula calculation; In step 1: according to the current drilling column chart of the mining face, the position of the low-level key rock layer of the roof is determined by calculation using the formula. The low-level key rock layer 8 is a thick and hard rock layer. After the working face is mined, it is easy to form a cantilever structure laterally in the goaf, which can play a certain supporting role on the overlying rock layer, causing stress concentration in the coal pillar 3 under the cantilever structure, affecting the stability of the goaf side tunnel 2 facing the working face.

[0017] The position of the low-level key rock formation is calculated and judged using the following formula:

[0018] Where: q n )1——No. n The load of the first rock layer on the first rock layer, MPa; q n+1 )1——No. n The load of +1 layer of rock on the 1st layer of rock, MPa; E 1, E 2, ..., E n , E n+1 ——Elastic modulus of overlying rock layers, MPa; ρ 1, ρ 2, ..., ρ n , ρ n+1 ——Density of overlying rock layers, kg / m 3 ; h 1, h 2, ..., h n , h n+1 ——thickness of overlying rock layers, m; g ——acceleration due to gravity, N / kg.

[0019] when n The load of the +1 layer on the 1st layer is less than that of the n When the load of the first layer of rock is applied to the first layer of rock, determine the n The +1 layer is the low-lying key layer 8.

[0020] Step 2: Calculate the plastic zone width on the side of the coal pillar goaf of the working face using a formula; In step 2, there are plastic zones on both sides of the working face coal pillar 3 on the working face empty side tunnel 2 and the goaf 9, and there is an elastic zone in the middle of the coal pillar 3. A stress peak appears at the junction of the plastic zone and the elastic zone. The formula is used to calculate the width of the plastic zone on the goaf side of the coal pillar, and then the stress peak position on the goaf side of the coal pillar is determined.

[0021] The width of the plastic zone on the side of the coal pillar goaf is determined by the following formula:

[0022] Where: x 0——Width of plastic zone on the side of coal pillar goaf, m; M ——tunnel height, m; λ ——lateral pressure coefficient; φ 0——internal friction angle, °; C 0——cohesion, MPa; K ——stress concentration factor; γ ——Average bulk density of rock formation, N / m 3 ; H —— burial depth, m; F ——Lateral force in tunnel, MPa.

[0023] Step 3, determining the blasting drilling parameters according to the low-level key rock layer and the width of the plastic zone on the side of the coal pillar goaf, the blasting drilling parameters including the blasting drilling inclination angle, the blasting drilling depth and the length of the charging section; In step 3, refer to Figure 2 The diagram shows the parameters of the width of the plastic zone of the coal pillar, the inclination of the blasting borehole, the depth of the blasting borehole, and the length of the charging section. According to the position of the low-lying key rock strata and the width of the plastic zone of the coal pillar, the inclination of the blasting borehole, the depth of the blasting borehole, and the length of the charging section are determined by using the formula.

[0024] The blasting drilling parameters are determined by the following formula:

[0025] Where: α ——Drilling hole inclination angle, °; H ——Distance from the bottom of the low-lying key rock layer to the top of the roadway, m; h ——Thickness of low-lying key rock formation, m; B——coal pillar width, m; x 0——Width of plastic zone on the side of coal pillar goaf, m; L ——Drilling depth for blasting, m; L z ——Charging section length, m.

[0026] Step 4, after determining the blasting drilling parameters, drill several inclined blasting holes 4 from the empty side tunnel 2 facing the working face to the low-level key rock stratum 8 above the goaf 9, and within the influence range of the working face advanced mining, blast the top of the cantilever structure of the low-level key rock stratum in the empty side tunnel facing the working face, and continue to move forward with the mining of the working face until the mining of the working face is completed.

[0027] In step 4, the plane projection of the blasting hole 4 is perpendicular to the direction of the empty side tunnel 2 facing the working face, the hole spacing is 1.0m, and concentrated blasting is adopted. The sealing length of the blasting hole is not less than 1 / 3 of the drilling length.

[0028] In the method of the present invention, one side of the working face facing the empty side tunnel 2 is the coal seam 1 of the coal mining working face, and the other side is the coal pillar 3. An upwardly inclined borehole is drilled on the coal seam roof facing the empty side tunnel 2 of the working face toward the goaf 9, and the borehole penetrates the low-level key rock layer 8 of the roof. The blasting and top cutting position is selected to be the low-level key rock layer 8 above the plastic zone on the goaf side of the coal pillar. After the blasting and top cutting, the lateral fracture position of the low-level key rock layer is located above the plastic zone on the goaf side of the coal pillar, which reduces the hanging roof length and reduces the roof load above the coal pillar. At the same time, the cut rock blocks are subject to the weak support of the coal pillar in the plastic zone below, slowly sink and rotate, and fall toward the goaf, thereby preventing the cut rock blocks from falling directly into the goaf and causing other secondary disasters.

[0029] Example 1 Figure 3~Figure 5 The figure shows a technical example of a method for blasting and cutting the top to relieve pressure at the peak position of lateral stress of a wide coal pillar. In this technical example, an inclined blasting borehole 4 is drilled in the working face side tunnel 2 toward the low-level key rock layer 8 above the goaf 9; the low-level key rock layer 8 is Figure 1 Step 1 shows that the drilling angle and depth of the blasting borehole 4 are determined by Figure 1 As shown in step 2 and step 3, the rock blocks 10 of the low-level key rock stratum cut off after blasting break and collapse, reducing the cantilever length of the low-level key rock stratum 8, thereby achieving blasting and top cutting and pressure relief of the low-level key rock stratum 8 above the goaf 9.

[0030] In this example, along the inclination of the working face, blasting drill holes 4 are arranged in the direction of the goaf 9 above the coal pillar 3 roof (including roof rock layer 1 5, roof rock layer 2 6 and roof rock layer 3 7 arranged from bottom to top) in the empty side tunnel 2 facing the working face, and a blasting drill hole 4 is arranged at intervals of 1m along the empty side tunnel 2 facing the working face, and top cutting blasting is carried out within the influence range of the working face advance mining to ensure that the influence range of the working face advance mining is in the top cutting pressure relief area.

[0031] In this example, the blasting borehole 4 is drilled with a water drill rig. In order to better achieve the cutting effect of the low-lying key rock layer 8, the energy-focused blasting process is adopted. The charging section adopts an energy-focused tube. Explosives are placed in the energy-focused tube. The explosives are emulsion explosives for coal mines. The blasting hole mouth is sealed with gun mud. The sealing length is not less than 1 / 3 of the length of the blasting borehole 4. Detonating cords are connected in series to detonate 10 blasting boreholes at a time.

[0032] In this example, the low-level key rock block 10 cut off at the rock fracture position 11 slowly falls into the goaf under the support of the plastically yielded coal body on the goaf side of the coal pillar 3, avoiding the cut rock blocks from falling directly into the goaf and causing other disasters, thereby ensuring safety during the top cutting blasting construction.

[0033] The above examples and the accompanying drawings have described in detail the method for blasting and top cutting to relieve pressure at the lateral stress peak position of a wide coal pillar disclosed in the present invention. Those skilled in the art should have a clear understanding of the blasting method used in the present invention. The present invention first determines the low-level key rock layer above the coal pillar on the air side, then calculates the width of the plastic zone on the side of the coal pillar goaf, determines the relevant parameters of the blasting hole according to the position of the upper low-level key rock layer and the width of the plastic zone on the side of the coal pillar goaf, and performs top cutting blasting on the low-level key rock layer, thereby reducing the hanging top length of the low-level key rock layer above the coal pillar and reducing the stress concentration in the coal pillar; the cut rock layer is located above the plastic zone on the side of the coal pillar goaf, which not only ensures the top cutting length and removes the top plate load of the low-level key rock layer, but also ensures that the cut top plate rock layer slowly falls into the goaf under the weak support of the plastically yielded coal body below, thereby avoiding other disasters caused by the overall collapse of the cut rock body; the method of the present invention can accurately cut the top of the low-level key rock layer, effectively reduce the stress of the coal pillar, and protect the stability of the working face facing the air side tunnel during the working face mining period.

[0034] Example 2 The method for blasting and cutting the top to relieve pressure at the lateral stress peak position of a wide coal pillar comprises the following steps: Step 1: According to the drilling column chart of the working face, the position of the low-level key rock layer is determined by formula calculation; Step 2: Calculate the plastic zone width on the side of the coal pillar goaf of the working face using a formula; Step 3, determining the blasting drilling parameters according to the low-level key rock layer position and the width of the plastic zone on the side of the coal pillar goaf; Step 4: After determining the blasting drilling parameters, drill the blasting holes. Within the influence range of the advanced mining of the working face, blast the top of the cantilever structure of the low-lying key rock strata in the empty side tunnel of the working face, and continue to move forward with the mining of the working face until the mining of the working face is completed.

[0035] Example 3 The method for blasting and cutting the top to relieve pressure at the lateral stress peak position of a wide coal pillar comprises the following steps: Step 1: According to the drilling column chart of the working face, the position of the low-level key rock layer is determined by formula calculation; In step 1, the low-level key rock layer position is calculated and judged using the following formula:

[0036] Where: q n )1——No. n The load of the first rock layer on the first rock layer, MPa; q n+1 )1——No. n The load of +1 layer of rock on the 1st layer of rock, MPa; E 1, E 2, ..., E n , E n+1 ——Elastic modulus of overlying rock layers, MPa; ρ 1, ρ 2, ..., ρ n , ρ n+1 ——Density of overlying rock layers, kg / m 3 ; h 1, h 2, ..., h n , h n+1 ——thickness of overlying rock layers, m; g ——acceleration due to gravity, N / kg; when n The load of the +1 layer on the 1st layer is less than that of the n When the load of the first layer of rock is applied to the first layer of rock, determine the n The +1 layer is the low-lying key layer 8.

[0037] Step 2: Calculate the plastic zone width on the side of the coal pillar goaf of the working face using a formula; Step 3, determining the blasting drilling parameters according to the low-level key rock layer position and the width of the plastic zone on the side of the coal pillar goaf; Step 4: After determining the blasting drilling parameters, drill the blasting holes. Within the influence range of the advanced mining of the working face, blast the top of the cantilever structure of the low-lying key rock strata in the empty side tunnel of the working face, and continue to move forward with the mining of the working face until the mining of the working face is completed.

Claims

1. Blasting and cutting the top to relieve pressure at the peak position of lateral stress of wide coal pillars. It is characterized in that The following steps are involved: Step 1: According to the drilling column chart of the working face, the position of the low-level key rock layer is determined by formula calculation; Step 2: Calculate the plastic zone width on the side of the coal pillar goaf of the working face using a formula; Step 3, determining the blasting drilling parameters according to the low-level key rock layer position and the width of the plastic zone on the side of the coal pillar goaf; Step 4: After determining the blasting drilling parameters, drill the blasting holes. Within the influence range of the advanced mining of the working face, blast the top of the cantilever structure of the low-lying key rock strata in the empty side tunnel of the working face, and continue to move forward with the mining of the working face until the mining of the working face is completed.

2. The method for blasting and cutting the top to relieve pressure at the lateral stress peak position of a wide coal pillar according to claim 1, It is characterized in that In step 1, the low-level key rock layer position is calculated and judged using the following formula: Where: q n ) 1 ——No. n The load of the first rock layer on the first rock layer, MPa; ( q n+1 ) 1 ——No. n The load of +1 layer of rock on the 1st layer of rock, MPa; E 1 , E 2 , …, E n , E n+1 ——Elastic modulus of overlying rock layers, MPa; ρ 1 , ρ 2 , …, ρ n , ρ n+1 ——Density of overlying rock layers, kg / m 3 ; h 1 , h 2 , …, h n , h n+1 ——thickness of overlying rock layers, m; g ——acceleration due to gravity, N / kg; when n The load of the +1 layer on the 1st layer is less than that of the n When the load of the first layer of rock is applied to the first layer of rock, determine the n The +1 layer is the low-lying key layer (8).

3. The method for blasting and cutting the top to relieve pressure at the lateral stress peak position of a wide coal pillar according to claim 1, It is characterized in that In step 2, the width of the plastic zone on the side of the coal pillar goaf is determined by the following formula: Where: x 0 ——Width of plastic zone on the side of coal pillar goaf, m; M ——tunnel height, m; λ ——lateral pressure coefficient; φ 0 ——internal friction angle, °; C 0 ——cohesion, MPa; K ——stress concentration factor; γ ——Average bulk density of rock formation, N / m 3 ; H —— burial depth, m; F ——Lateral force in tunnel, MPa.

4. The method for blasting and cutting the top to relieve pressure at the lateral stress peak position of a wide coal pillar according to claim 1, It is characterized in that In step 3, the blasting drilling parameters include the blasting drilling inclination angle, the blasting drilling depth and the length of the charging section. The blasting drilling parameters are determined using the following formula: Where: α ——Drill hole inclination angle, °; H ——Distance from the bottom of the low-lying key rock layer to the top of the roadway, m; h ——Thickness of low-lying key rock formation, m; B ——coal pillar width, m; x 0 ——Width of plastic zone on the side of coal pillar goaf, m; L ——Drilling depth for blasting, m; L z ——Charging section length, m.

5. The method for blasting and cutting the top to relieve pressure at the lateral stress peak position of a wide coal pillar according to claim 1, It is characterized in that In step 4, the plane projection of the blasting borehole (4) is perpendicular to the direction of the empty side tunnel (2) facing the working face, the hole spacing is 1.0m, concentrated energy blasting is used, and the sealing length of the blasting hole is not less than 1 / 3 of the drilling length.

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