A partitioned combination pressure relief method based on coal pillar stability safety factor

Abstract

The application discloses a partitioned and combined pressure relief method based on a coal column stability safety factor, collects coal column occurrence data and obtains stress distribution characteristics of the coal column at different positions, then determines a coal column stability safety factor calculation formula and sets coal column stability state classification conditions; influences of different factors on the coal column stability safety factor are analyzed according to the coal column stability safety factor calculation formula, finally, different position and size conditions of the coal column are divided into different stability state regions in combination with the coal column occurrence data; pressure relief parameters of the coal column are formulated for each type of region, and finally, corresponding pressure relief construction is carried out on different coal column stability state regions, so that energy stress sources and bearing structures of irregular coal columns are partitioned and combined for pressure relief, the pressure relief is more targeted, the bearing capacity of the coal column area is effectively improved, and the rock burst danger caused by insufficient or excessive pressure relief during the end mining period of the working face is reduced, which has important significance for guaranteeing the safe mining of the working face, improving the stability of the coal column roadway and improving the pressure relief efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pressure relief in coal pillar area of rock burst coal seam, and particularly relates to a partition combination pressure relief method based on a coal pillar stability safety factor. BACKGROUND

[0002] Part of the area of rock burst coal seam is left with a coal pillar due to unsuitable mining, which leads to high stress concentration near the coal pillar area and complex stress distribution, and rock burst disasters are easily induced under mining disturbance, which seriously threatens the safety production of the mine. Research shows that the occurrence of coal pillar rock burst is closely related to the spatial overburden structure and the stress degree of coal and rock mass, and such rock burst can be prevented by destroying the integrity of the overburden structure and releasing the elastic energy accumulation of the coal pillar. However, there is less systematic analysis of the stress state and stability state of the coal pillar area under the condition of large-scale goaf in the mining area and irregular size of the coal pillar (i.e. the width of the coal pillar is different at different positions in the mining area due to geological conditions), which leads to insufficient pertinence of rock burst prevention and control in irregular coal pillar area, that is, the stress state and stability state of different positions are different due to the irregular size of the irregular coal pillar at different positions. The existing method uses the same single pressure relief method for the coal pillar at different positions, which not only isolates the pressure relief means from each other and lacks connection of the pressure relief effect, but also may cause the coal pillar to lose bearing capacity due to excessive construction and increase the pressure relief cost.

[0003] Therefore, how to provide a new method for pertinently guiding the pressure relief in the coal pillar area by analyzing the stress distribution characteristics of the coal pillar and identifying the stability state of the coal pillar at different positions to reduce the rock burst hazard level in the coal pillar area and ensure the safety production of the rock burst coal seam is the research direction of the present application. SUMMARY

[0004] In view of the problems existing in the prior art, the present application provides a partition combination pressure relief method based on a coal pillar stability safety factor, which classifies the stability state of the coal pillar at different positions and different sizes according to the coal pillar safety factor, and formulates a coal pillar pressure relief scheme for each type of area, so as to perform partition and hierarchical collaborative pressure relief in the coal pillar area, change the structure of the impact force source and energy accumulation body in the coal pillar area, ensure the bearing capacity of the coal pillar, and have important significance for protecting the roadway structure and maximizing the pressure relief effect and controlling the pressure relief cost.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: a partition combination pressure relief method based on a coal pillar stability safety factor, and the specific steps are as follows:

[0006] Step one, collecting coal pillar occurrence data;

[0007] Step two, establishing a calculation formula for calculating the normal stress and shear force of the coal pillar for obtaining the stress distribution characteristics of the coal pillar at different positions;

[0008] Step three, according to the calculation formula established in step two, combined with Mohr-Coulomb criterion to establish the calculation formula of coal pillar stability safety factor;

[0009] Step four, set the coal pillar stability state including I, II, III, and set the corresponding coal pillar stability safety factor range of each type of coal pillar stability state;

[0010] Step five, according to the coal pillar stability safety factor calculation formula obtained in step three, analyze the influence of different factors on the stability state of coal pillar;

[0011] Step six, the coal pillar occurrence data collected in step one is substituted into the stability safety factor of coal pillar at different positions obtained in step three, and the obtained stability safety factor is identified by step four, and the stability state classification of coal pillar at different positions is obtained;

[0012] Step seven, according to the stability state classification of coal pillar at different positions obtained in step six, different unloading measures and unloading parameters are formulated according to different classification situations;

[0013] Step eight, according to the determination of step six and step seven, different unloading measures are combined to carry out partition unloading: when the stability state of coal pillar at a certain position is type I, large diameter drilling unloading is constructed; When the stability state of coal pillar at a certain position is type II, large diameter drilling unloading is constructed first, and then roof deep hole blasting unloading is constructed; When the stability state of coal pillar at a certain position is type III, large diameter drilling and roof deep hole blasting are combined to unload the coal pillar in the current area, and then additional coal pillar floor unloading drilling is added, so as to complete the partition combined unloading based on coal pillar stability safety factor.

[0014] Further, the coal pillar occurrence data in step one includes working face mining data and coal and rock stratum parameters.

[0015] Further, the step two is specifically:

[0016] According to formula (1), the normal stress σ n and shear stress τ in coal seam before mining are respectively:

[0017]

[0018] In the formula, γ is the unit weight of overburden rock of coal seam; H is the buried depth of coal seam; α is the inclination angle of coal seam; k is the pressure measurement coefficient;

[0019] After the working face is mined, the relationship between the coal pillar width and the two sides of the goaf should be considered, the coal pillar stress is analyzed according to the dependent area method, and the area recovery ratio r is introduced and expressed as:

[0020]

[0021] In the formula, b is the width of the goaf on both sides of the coal pillar; a is the width of the coal pillar;

[0022] The area extraction ratio r, the normal stress σ acting on the coal pillar p And the shear stress τ p Is expressed as:

[0023]

[0024] Thus, the calculation formula of the normal stress and shear stress of the coal pillar is established.

[0025] Further, the step three is specifically:

[0026] The ultimate strength σ of the coal pillar pc Is expressed as:

[0027]

[0028] In the formula, σ c Is the uniaxial compressive strength of the coal body; h is the height of the coal pillar;

[0029] According to the normal stress σ n And the shear stress τ n Acting on the coal pillar, the load σ ts Acting on the coal pillar is solved:

[0030]

[0031] Assuming that the load failure of the coal pillar conforms to the Mohr-Coulomb criterion, the stability safety factor formula of the coal pillar under the joint action of the normal stress and shear stress is established:

[0032]

[0033] Thus, the calculation formula of the stability safety factor of the coal pillar is established.

[0034] Further, the step four is specifically:

[0035] If the stability safety factor F of the coal pillar s >1, it indicates that the load strength acting on the coal pillar is small, and the coal pillar is in a relatively stable stress state. The stability state type of the coal pillar is recorded as type I;

[0036] If the stability safety factor of the coal pillar 0.5<F s ≤1, it indicates that the load strength acting on the coal pillar is large, which reduces the stability of the coal pillar. The stability state type of the coal pillar is recorded as type II;

[0037] If the stability safety factor of the coal pillar 0<F s ≤0.5, it indicates that the ultimate strength of the coal pillar is less than the load acting on the coal pillar, and the coal pillar will be broken. The stability state type of the coal pillar is recorded as type III.

[0038] Further, the step five is specifically:

[0039] According to the coal pillar stability safety factor calculation formula established in step three, it is obtained that the coal pillar stability safety factor is determined by the limit strength of the coal pillar itself and the load acting on the coal pillar, wherein the limit strength of the coal pillar itself is related to the uniaxial compressive strength σ c of the coal body, the coal pillar height h, the coal seam buried depth H and the coal pillar width a; the load acting on the coal pillar is related to the area mining ratio r, the coal seam buried depth H, the coal seam dip angle α and the lateral pressure coefficient k; the influence of different factors on the coal pillar stability safety factor is analyzed by the control single variable method (i.e. the change of the coal pillar stability safety factor when the value of a certain factor increases or decreases, which provides guidance for subsequent mining).

[0040] Further, the step seven is specifically:

[0041] If the stability state of the coal pillar at a position is type I, large-diameter drilling is used to relieve pressure on the coal pillar, the large-diameter drilling is arranged vertically along the sidewall of the roadway, parallel to the coal seam, the hole diameter φ1≥150mm; the hole spacing is 1±0.1m; the hole depth is 25m; in order to facilitate construction, the drilling distance from the coal seam floor is 1.5m;

[0042] If the stability state of the coal pillar at a position is type II, large-diameter drilling and roof deep-hole blasting are combined to relieve pressure on the coal pillar, wherein the construction parameters of the large-diameter drilling are the same as those when the stability state of the coal pillar is type I; the roof blasting holes are arranged by three holes from two roadways towards the inside of the coal pillar, the hole diameter φ2=65mm; the hole inclination angles of the holes 1#, 2# and 3# are 60°, 45° and 30° respectively; the final hole positions of the holes 1#, 2# and 3# are located at the top of the immediate roof, at 2 / 3 thickness of the immediate roof and at 1 / 2 thickness of the immediate roof respectively; the depths of the holes 1#, 2# and 3# are L1, L2 and L3 respectively, the charging lengths are L1 / 2, L2 / 2 and L3 / 2 respectively, and the charging amounts are all 3kg / m;

[0043] If the stability state of a coal pillar at a position is type III, combined pressure relief is performed by using large-diameter drilling, roof deep-hole blasting and floor drilling, the construction parameters of the large-diameter drilling are the same as those when the stability state of the coal pillar is type I; the roof deep-hole blasting is arranged in the direction of the inside of the coal pillar in front of the two roadways and the working face, wherein the construction parameters of the blast holes arranged in the direction of the inside of the coal pillar in front of the two roadways are the same as those when the stability state of the coal pillar is type II, the blast holes arranged in the direction of the inside of the coal pillar in front of the working face are arranged in three holes, denoted as holes 4#, 5# and 6#, the inclination angles are 60°, 45° and 30° respectively, the final hole positions are located at the top of the immediate roof, at 2 / 3 of the thickness of the immediate roof and at 1 / 2 of the thickness of the immediate roof respectively, the hole depths are L4, L5 and L6 respectively, the charging lengths are L4 / 2, L5 / 2 and L6 / 2 respectively, and the charging amounts are all 3 kg / m; pressure relief drilling holes are additionally drilled in the coal pillar floor, the hole diameter is greater than or equal to 150 mm, one group is three holes, denoted as holes 7#, 8# and 9#, hole 7# is arranged at the outer corner of the outer side and is in the direction of 60° with respect to the horizontal direction, hole 9# is arranged at the inner corner of the inner side and is in the direction of 60° with respect to the horizontal direction, and hole 8# is arranged at the center of the floor and is perpendicular to the horizontal direction, the group spacing is 2±0.2 m, and the final hole positions are all the coal seam floor, if the coal seam thickness is large, the length of each pressure relief drilling hole is arranged as 15 m.

[0044] Compared with the prior art, the coal pillar occurrence data is first collected, then the calculation formula of the normal stress and shear force of the coal pillar is established for obtaining the stress distribution characteristics of the coal pillar at different positions, then the calculation formula of the stability safety factor of the coal pillar is established in combination with the Mohr-Coulomb criterion; the classification of the stability state of the coal pillar and the corresponding stability safety factor range of each type are set; the influence of different factors on the stability safety factor of the coal pillar is analyzed according to the calculation formula of the stability safety factor of the coal pillar, finally, after the type of the stability state of the coal pillar is identified in combination with the coal pillar occurrence data, different positions of the coal pillar are divided into different stability state regions according to different size conditions; the pressure relief parameters of the coal pillar are developed according to different types of the stability state of the coal pillar, and finally, corresponding pressure relief construction is performed based on the divided stability state regions of the coal pillar, so that the partition combined pressure relief of the coal pillar region is realized. Through the method, the energy stress source and bearing structure of the irregular coal pillar region left after the mining of the rock burst coal seam can be partition combined pressure relieved, the pressure relief method is more targeted, the bearing capacity of the coal pillar region is effectively improved, the rock burst danger caused by insufficient or excessive pressure relief during the end mining of the working face is reduced, and the method has important significance for guaranteeing the safe mining of the working face, improving the stability of the roadway in the coal pillar region and improving the pressure relief efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 The figure is a flowchart of the present application;

[0046] Figure 2 The figure is a working face mining and coal pillar setting arrangement in the test verification;

[0047] Figure 3 For the test demonstration of the coal pillar and its stress analysis schematic diagram;

[0048] Figure 4 For the test demonstration of the coal pillar and its stress analysis schematic diagram;

[0049] Figure 5 For the test demonstration of the coal pillar and its stress analysis schematic diagram;

[0050] Figure 6 For the test demonstration of the coal pillar and its stress analysis schematic diagram;

[0051] Figure 7 For the test demonstration of the coal pillar and its stress analysis schematic diagram; DETAILED DESCRIPTION

[0052] The application will be further described below.

[0053] As Figure 1 shown, the specific steps of the application are:

[0054] Step one, collect coal pillar occurrence data, including working face mining data and coal and rock layer parameters;

[0055] Step two, establish a formula for calculating the normal stress and shear force of the coal pillar, which is used to obtain the stress distribution characteristics of the coal pillar at different positions, specifically:

[0056] According to formula (1), the normal stress σ n and shear stress τ in the coal seam before mining are respectively:

[0057]

[0058] In the formula, γ is the overburden density of the coal seam; H is the coal seam depth; α is the coal seam inclination; k is the pressure coefficient;

[0059] After the working face is mined, the relationship between the coal pillar width and the two side goaf should be considered, and the coal pillar stress is analyzed according to the dependent area method, and the area mining ratio r is introduced and expressed as:

[0060]

[0061] In the formula, b is the width of the two side goaf of the coal pillar; a is the width of the coal pillar;

[0062] Combined with the area mining ratio r, the normal stress σ p and shear stress τ p acting on the coal pillar are expressed as:

[0063]

[0064] Thus, the calculation formula of normal stress and shear stress of coal pillar is established.

[0065] Step three, according to the calculation formula established in step two, the calculation formula of stability safety factor of coal pillar is established combined with Mohr-Coulomb criterion, which is specifically:

[0066] The limit strength of coal pillar σ pc is expressed as:

[0067]

[0068] In the formula, σ c is the uniaxial compressive strength of coal; h is the height of coal pillar;

[0069] According to the normal stress σ n and shear stress τ n acting on the coal pillar, the load σ ts acting on the coal pillar is solved:

[0070]

[0071] Assuming that the destruction of coal pillar under load conforms to Mohr-Coulomb criterion, the stability safety factor analytical expression of coal pillar under the joint action of normal stress and shear stress is established based on the above:

[0072]

[0073] Thus, the calculation formula of stability safety factor of coal pillar is established.

[0074] Step four, set the stability state of coal pillar to include type I, type II and type III, and set the range of stability safety factor of coal pillar corresponding to each type of coal pillar stability state, which is specifically:

[0075] If the stability safety factor F s of coal pillar > 1, it indicates that the load strength acting on the coal pillar is small, and the coal pillar is in a relatively stable stress state, and the type of coal pillar stability state is recorded as type I;

[0076] If the stability safety factor of coal pillar 0.5<F s ≤ 1, it indicates that the load strength acting on the coal pillar is large, which reduces the stability of the coal pillar, and the type of coal pillar stability state is recorded as type II;

[0077] If the stability safety factor of coal pillar 0<F s ≤ 0.5, it indicates that the limit strength of coal pillar is less than the load acting on the coal pillar, and the coal pillar will be broken, and the type of coal pillar stability state is recorded as type III.

[0078] Step five, according to the calculation formula of stability safety factor of coal pillar obtained in step three, the influence of different factors on the stability state of coal pillar is analyzed, which is specifically:

[0079] According to the coal pillar stability safety factor calculation formula established in step three, it is concluded that the coal pillar stability safety factor is determined by the ultimate strength of the coal pillar itself and the load acting on the coal pillar, wherein the ultimate strength of the coal pillar itself is related to the uniaxial compressive strength σ c of the coal body, the coal pillar height h, the coal seam depth H and the coal pillar width a; the load acting on the coal pillar is related to the area mining ratio r, the coal seam depth H, the coal seam dip angle α and the lateral pressure coefficient k; the influence of different factors on the coal pillar stability safety factor is analyzed by the single variable control method (i.e. the change of the coal pillar stability safety factor when the value of a certain factor increases or decreases, which provides guidance for subsequent mining).

[0080] Step six, the coal pillar occurrence data collected in step one is substituted into step three to obtain the stability safety factor of the coal pillar at different positions, and the obtained stability safety factor is identified by step four to obtain the stability state classification of the coal pillar at different positions;

[0081] Step seven, according to the stability state classification of the coal pillar at different positions obtained in step six, different pressure relief measures and parameters are developed according to different classification situations, specifically:

[0082] If the stability state of the coal pillar at a certain position is type I, large-diameter drilling is used to relieve pressure on the coal pillar, the large-diameter drilling is arranged vertically along the roadway sides and parallel to the coal seam, the hole diameter φ1 is greater than or equal to 150 mm; the hole spacing is 1±0.1 m; the hole depth is 25 m; in order to facilitate construction, the drilling distance from the coal seam floor is 1.5 m;

[0083] If the stability state of the coal pillar at a certain position is type II, large-diameter drilling and roof deep-hole blasting are combined to relieve pressure on the coal pillar, wherein the construction parameters of the large-diameter drilling are the same as those when the stability state of the coal pillar is type I; the roof blasting holes are arranged by three holes from both sides of the roadway towards the inside of the coal pillar, the hole diameter φ2 is 65 mm; the hole inclination angles of holes 1#, 2# and 3# are 60°, 45° and 30° respectively; the final hole positions of holes 1#, 2# and 3# are located at the top of the immediate roof, at 2 / 3 of the thickness of the immediate roof and at 1 / 2 of the thickness of the immediate roof respectively; the depths of holes 1#, 2# and 3# are L1, L2 and L3 respectively, the charging lengths are L1 / 2, L2 / 2 and L3 / 2 respectively, and the charging amounts are all 3 kg / m;

[0084] If the stability state of the coal pillar at a position is type III, large-diameter drilling, roof deep-hole blasting and floor drilling are combined to release pressure, the construction parameters of the large-diameter drilling are the same as those when the stability state of the coal pillar is type I; the roof deep-hole blasting is arranged in the two roadways and in front of the working face towards the inner side of the coal pillar, wherein the construction parameters of the blast holes arranged from the two roadways towards the inner side of the coal pillar are the same as those when the stability state of the coal pillar is type II, the blast holes arranged from the front of the working face towards the inner side of the coal pillar are arranged in three holes, denoted as holes 4#, 5# and 6#, the inclination angles are 60°, 45° and 30° respectively, the final hole positions are located at the top of the immediate roof, at 2 / 3 of the thickness of the immediate roof and at 1 / 2 of the thickness of the immediate roof respectively, the hole depths are L4, L5 and L6 respectively, the charging lengths are L4 / 2, L5 / 2 and L6 / 2 respectively, and the charging amounts are all 3 kg / m; pressure relief drilling holes are additionally drilled in the coal pillar floor, the hole diameter is φ3≥150 mm, one group is three holes, denoted as holes 7#, 8# and 9#, hole 7# is arranged at the outer corner of the slope, towards the outside at an angle of 60° to the horizontal direction, hole 9# is arranged at the inner corner of the slope, towards the inside at an angle of 60° to the horizontal direction, and hole 8# is arranged at the center of the floor, perpendicular to the horizontal direction, the group spacing is 2±0.2 m, and the final hole positions are all at the coal seam floor, if the coal seam thickness is large, the length of each pressure relief drilling hole is arranged as 15 m.

[0085] Step eight, according to the conditions determined in steps six and seven, different pressure relief measures are combined to release pressure in different zones for the coal pillar: when the stability state of the coal pillar at a position is type I, large-diameter drilling is constructed to release pressure; when the stability state of the coal pillar at a position is type II, large-diameter drilling is first constructed to release pressure, and then roof deep-hole blasting is constructed to release pressure; when the stability state of the coal pillar at a position is type III, large-diameter drilling and roof deep-hole blasting are combined to release pressure for the coal pillar in the current region, and then pressure relief drilling holes are additionally drilled in the coal pillar floor, so as to complete the zoned and combined pressure relief based on the stability safety factor of the coal pillar.

[0086] Test proves that:

[0087] A certain mine in Gansu, 25011, 25021 and 25031 working faces, use the method of the present application for test, the above three working faces in the end of mining stage, between the adjacent panel goaf is irregularly left large roadway coal pillar. In the process of working face advancing, two roadway high energy microseismic events occur frequently, and multiple times cause impact dynamic appearance; with the working face gradually advancing to the large roadway, the impact danger of the coal pillar area gradually increases. Irregular coal pillar setting conditions are shown as Figure 2 .

[0088] The stress distribution characteristics acting on the coal pillar and the limited coal pillar occurrence conditions, the method obtains the coal pillar occurrence data according to the mine exploration results, which is used to calculate the normal stress and shear stress acting on the coal pillar, and further analyze the stress state of the coal pillar; the coal pillar occurrence data is shown in Table 1:

[0089] Table 1

[0090]

[0091] Because the size of the coal pillar is irregular, the minimum coal pillar width is taken for calculation in this example. Among them, the minimum width of 25011, 25021 and 25031 coal pillars is 52m, 146m and 130m respectively. According to the formula (1), the normal stress σ Figure 3 acting on the coal pillar before the working face is mined is obtained: n and the shear stress τ:

[0092] 25011 coal pillar:

[0093]

[0094] 25021 coal pillar:

[0095]

[0096] 25031 coal pillar:

[0097]

[0098] The normal stress σ p and the shear stress τ p acting on the coal pillar are:

[0099] 25011 coal pillar:

[0100] 25021 coal pillar:

[0101] 25031 coal pillar: According to the formula (4), the ultimate strength of the coal pillar is solved:

[0102] 25011 coal pillar: 25021 coal pillar: 25031 coal pillar: According to the formula (5), the load bearing of the coal pillar is solved:

[0103] 25011 coal pillar:

[0104] 25021 coal pillar:

[0105] 25031 coal pillar: According to the formula (6), the safety factor of the coal pillar is solved:

[0106] 25011 coal pillar:

[0107] 25021 coal pillar:

[0108] 25031 coal pillar:

[0109] According to the occurrence conditions of the coal pillars, the width of the coal pillars changes irregularly, wherein the width of the coal pillar 25011 changes in the range of 52-158 m, the width of the coal pillar 25021 changes in the range of 146-328 m, and the width of the coal pillar 25031 changes in the range of 130-334 m. Other factors affecting the safety factor of the coal pillar remain unchanged, and details are shown in Table 1. Therefore, the safety factor of the coal pillar 25011, 25021 and 25031 under the influence of the width of the coal pillar is mainly discussed, so as to divide the stability state of the coal pillar. The safety factor of the coal pillar 25011, 25021 and 25031 under the influence of the width of the coal pillar is shown in Table 2, and the change trend is shown in Figure 4 .

[0110] Table 2

[0111]

[0112] According to Figure 4 , the fitting relationship between the width of the coal pillar and the safety factor of the coal body is obtained:

[0113] The coal pillar 25011: y1=0.0061x1-0.2602

[0114] The coal pillar 25021: y2=0.0111x2-1.0217

[0115] The coal pillar 25031: y3=0.0106x3-0.9318

[0116] According to the fitting relationship between the width of the coal pillar and the safety factor of the coal pillar above, it can be known that:

[0117] For the coal pillar 25011, when the width of the coal pillar x1=124.6 m, the safety factor of the coal pillar y1=0.5;

[0118] For the coal pillar 25021, when the width of the coal pillar x2=182.1 m, the safety factor of the coal pillar y2=1.0;

[0119] For the coal pillar 25031, when the width of the coal pillar x3=182.2 m, the safety factor of the coal pillar y3=1.0.

[0120] In summary, according to the width range of the 25011 coal pillar, the stability state of the coal pillar with a width ranging from 52m to 125m is classified as type III, and the stability state of the coal pillar with a width ranging from 125m to 158m is classified as type II; according to the width range of the 25021 coal pillar, the stability state of the coal pillar with a width ranging from 146m to 182m is classified as type II, and the stability state of the coal pillar with a width ranging from 182m to 328m is classified as type I; according to the width range of the 25031 coal pillar, the stability state of the coal pillar with a width ranging from 130m to 182m is classified as type II, and the stability state of the coal pillar with a width ranging from 182m to 334m is classified as type I; the classification of the stability state of each coal pillar is shown in Figure 5

[0121] According to the different stability states of the coal pillars, a combined pressure relief scheme of large-diameter drilling, roof deep-hole blasting, and floor drilling is formulated, and the specific arrangement of the three pressure relief methods is shown in Figure 6 Figure 6 (a) represents the arrangement of large-diameter drilling pressure relief, Figure 6 (b) represents the arrangement of roof deep-hole blasting pressure relief, Figure 6 (c) represents the arrangement of floor drilling pressure relief. The detailed arrangement parameters of each pressure relief method are shown in Table 3,

[0122] Table 3

[0123]

[0124] According to the above classification of the stability states of the 25011, 25021, and 25031 coal pillars at different width positions, different combinations of pressure relief measures are adopted for each coal pillar for partitioned pressure relief: when the stability state of a coal pillar at a certain position is type I, large-diameter drilling pressure relief is constructed; when the stability state of a coal pillar at a certain position is type II, large-diameter drilling pressure relief is first constructed, and then roof deep-hole blasting pressure relief is constructed; when the stability state of a coal pillar at a certain position is type III, large-diameter drilling and roof deep-hole blasting are combined for pressure relief of the coal pillar in the current area, and then floor drilling pressure relief is supplemented, thereby completing the partitioned and combined pressure relief based on the stability safety factor of the coal pillar.

[0125] After the pressure relief construction of the 25011, 25021, and 25031 coal pillars is completed, microseismic data during the end-mining period of the working face is collected for pressure relief effect test and analysis, wherein the time range of the microseismic data of each working face is selected as follows:

[0126] 25011 working face: August to September 2015 (the working face was completed in September 2015);

[0127] 25021 working face: April to May 2018 (the working face was completed in May 2018);

[0128] ​​25031 working face: June to July 2022 (the working face was completed in July 2022).

[0129] The microseismic source distribution of the coal pillar area is as shown in Figure 7 The microseismic frequency and energy level of the 25011, 25021 and 25031 coal pillars are shown in Table 4.

[0130] Table 4

[0131]

[0132] From the above data, it can be seen that after the irregular coal pillars left after the working face mining are relieved by the partition combination relief, the degree of elastic energy accumulation in the coal pillars is reduced, and during the end mining of the working face, no energy level exceeding 10 4 J microseismic events occur in the coal pillar area, indicating that the partition combination relief effect is good, and the irregular coal pillar impact risk level is significantly reduced; thereby proving the relief effect of the present application.

[0133] The above is only the preferred embodiment of the present application, and it should be pointed out that for ordinary skilled persons in the art, some improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered within the protection scope of the present application.

Claims

1. A method for partition combination pressure relief based on coal pillar stability safety factor, characterized in that, The specific steps are: Step one, collecting coal pillar occurrence data; Step two, establishing a calculation formula for calculating the normal stress and shear force of the coal pillar, which is used to obtain the stress distribution characteristics of the coal pillar at different positions, specifically: The normal stress and shear stress in the coal seam before mining are obtained according to formula (1) and formula (2) respectively. （1） In the formula, γ is the overburden density of the coal seam; H is the coal seam depth; α is the coal seam inclination; k is the pressure measurement coefficient; After the working face is mined, the relationship between the coal pillar width and the two side goaf should be considered, and the coal pillar stress is analyzed according to the dependent area method, and the area recovery ratio r is introduced and expressed as: （2） In the formula, b is the width of the goaf on both sides of the coal pillar; a is the width of the coal pillar; The ratio of the area of the coal pillar to the area of the coal seam, the normal stress acting on the coal pillar The shear stress Is expressed as: （3） Thus, the calculation formula for calculating the normal stress and shear force of the coal pillar is established; Step three, according to the calculation formula established in step two, the Mohr-Coulomb criterion is combined to establish a calculation formula for the stability safety factor of the coal pillar, specifically: Coal pillar ultimate strength is represented as: （4） In the formula, σc is the uniaxial compressive strength of coal; h is the height of coal pillar. According to normal stress and shear stress acting on the coal pillar : （5） Assuming that the coal pillar failure under load conforms to the Mohr-Coulomb criterion, the above establishes the analytical expression of the stability safety factor of the coal pillar under the joint action of normal stress and shear stress: （6） Thus, the calculation formula for the stability safety factor of the coal pillar is established; Step four, setting the coal pillar stability state to include type I, type II and type III, and setting the corresponding coal pillar stability safety factor range for each type of coal pillar stability state; Step five, according to the calculation formula for the stability safety factor of the coal pillar obtained in step three, the influence of different factors on the stability state of the coal pillar is analyzed; Step six, the coal pillar occurrence data collected in step one is substituted into the stability safety factor of the coal pillar at different positions obtained in step three, and the obtained stability safety factor is identified using step four to obtain the stability state classification of the coal pillar at different positions; Step seven, according to the stability state classification of the coal pillar at different positions obtained in step six, different unloading measures and unloading parameters are formulated according to different classification situations; Step eight, according to the determination in steps six and seven, different unloading measures are combined to partition and unload the coal pillar: when the stability state of the coal pillar at a certain position is type I, large-diameter drilling is used for pressure relief; when the stability state of the coal pillar at a certain position is type II, large-diameter drilling is first used for pressure relief, and then roof deep hole blasting is used for pressure relief; when the stability state of the coal pillar at a certain position is type III, large-diameter drilling and roof deep hole blasting are combined to unload the coal pillar in the current area, and then additional coal pillar floor pressure relief drilling is added, thereby completing the partition and combination unloading based on the stability safety factor of the coal pillar.

2. The method according to claim 1, wherein, The coal pillar occurrence data in step one includes working face mining data and coal and rock stratum parameters.

3. The method of claim 1, wherein the method is characterized by, The step four specifically is: If the coal pillar stability safety factor F s 1, indicating that the load intensity acting on the coal pillar is small, and the coal pillar is in a stable stress state. The coal pillar stability state type is recorded as type I; If the coal pillar stability safety factor is 0.5 < F < 1, it indicates that the load strength acting on the coal pillar is large, which reduces the stability of the coal pillar, and the coal pillar stability state type is recorded as type II. s If the coal pillar stability safety factor is 0.5 < F < 1, it indicates that the load strength acting on the coal pillar is large, which reduces the stability of the coal pillar, and the coal pillar stability state type is recorded as If the coal pillar stability safety factor 0 < F < 1, it indicates that the coal pillar bearing ultimate strength is greater than the load acting on the coal pillar, and the coal pillar will not be broken. The coal pillar stability state type is recorded as type II. s If the coal pillar stability safety factor F > 1, it indicates that the coal pillar bearing ultimate strength is greater than the load acting on the coal pillar, and the coal pillar will not be broken. The coal pillar stability state type is recorded as type I. If the coal pillar stability safety 4. The method of claim 1, wherein the method is characterized by, The step five specifically is: According to the formula of the safety factor of the coal pillar established in step three, it is concluded that the safety factor of the coal pillar is determined by the ultimate strength of the coal pillar and the load acting on the coal pillar, wherein the ultimate strength of the coal pillar is related to the uniaxial compressive strength of the coal body , the height h of the coal pillar, the buried depth H of the coal seam and the width a of the coal pillar; the load acting on the coal pillar is related to the area mining ratio r, the buried depth H of the coal seam, the inclination of the coal seam and the lateral pressure coefficient k; and the influence of different factors on the safety factor of the coal pillar is analyzed through the control of a single variable method.

5. The method of claim 1, wherein the method is characterized by, The step seven specifically is: If the stability state of the coal pillar at a certain position is type I, large-diameter drilling is used to unload the coal pillar, the large-diameter drilling is arranged vertically along the roadway sides, parallel to the coal seam, the hole diameter φ1 is greater than or equal to 150 mm; the hole spacing is 1±0.1 m; the hole depth is 25 m; in order to facilitate construction, the drilling distance from the coal seam floor is 1.5 m; If the stability state of the coal pillar at a certain position is type II, large-diameter borehole pressure relief and roof deep-hole blasting are combined to relieve pressure of the coal pillar, wherein the construction parameters of the large-diameter borehole are the same as those when the stability state of the coal pillar is type I; the roof blasting holes are arranged by three holes in two roadways towards the inside of the coal pillar, with a hole diameter of φ2=65 mm; the inclination angles of the holes 1#, 2# and 3# are 60°, 45° and 30° respectively; the final hole positions of the holes 1#, 2# and 3# are located at the top of the immediate roof, at 2 / 3 thickness of the immediate roof and at 1 / 2 thickness of the immediate roof respectively; the depths of the holes 1#, 2# and 3# are L1, L2 and L3 respectively, the charging lengths are L1 / 2, L2 / 2 and L3 / 2 respectively, and the charging amounts are all 3 kg / m; If the stability state of the coal pillar at a certain position is type III, large-diameter borehole, roof deep-hole blasting and floor borehole are combined to relieve pressure, wherein the construction parameters of the large-diameter borehole are the same as those when the stability state of the coal pillar is type I; the roof deep-hole blasting is arranged in two roadways and in front of the working face towards the inside of the coal pillar, wherein the construction parameters of the blasting holes arranged by two roadways towards the inside of the coal pillar are the same as those when the stability state of the coal pillar is type II, the blasting holes arranged by three holes in front of the working face towards the inside of the coal pillar are recorded as holes 4#, 5# and 6#, with inclination angles of 60°, 45° and 30° respectively, final hole positions located at the top of the immediate roof, at 2 / 3 thickness of the immediate roof and at 1 / 2 thickness of the immediate roof respectively, hole depths of L4, L5 and L6 respectively, charging lengths of L4 / 2, L5 / 2 and L6 / 2 respectively, and charging amounts of all 3 kg / m; pressure relief boreholes are additionally drilled in the coal pillar floor, with a hole diameter of φ3≥150 mm, one group of three boreholes, recorded as 7#, 8# and 9#, hole 7# arranged at the outer corner of the slope, towards the outside at an angle of 60° to the horizontal, hole 9# arranged at the inner corner of the slope, towards the inside at an angle of 60° to the horizontal, and hole 8# arranged in the center of the floor, perpendicular to the horizontal, with a group spacing of 2±0.2 m, and the final hole positions are all the coal floor.

Images