Large-dip-angle coal seam gob-side entry driving small coal pillar reasonable setting size determination method

Abstract

The invention relates to a large-dip-angle coal seam gob-side entry driving small coal pillar reasonable setting size determination method, which comprises the following steps of 1, calculating to obtain a large-dip-angle coal seam gob-side entry driving small coal pillar setting size based on a key block fracture theory; 2, based on a lateral bearing pressure distribution rule, calculating to obtain a large-dip-angle coal seam gob-side entry driving small coal pillar reserving size; and 3, sorting and summarizing calculation results based on a key block fracture theory and a lateral bearing pressure distribution rule, and finally accurately determining the reasonable setting size of the gob-side entry driving small coal pillar of the large-dip-angle coal seam. By calculating the position of the fracture line of the key block B and judging the critical minimum value of the width of the reserved coal pillar, when the fracture position is located above the coal pillar and the key block B sinks stably, a small part of the load above the key block B is borne by the coal pillar, a large part of the load is borne by goaf gangue, and at the moment, the influence on the gob-side roadway is minimum; the integrity of the coal pillar close to one side of the roadway is well maintained, and roadway supporting is better facilitated.

Description

Technical Field

[0001] The invention relates to the field of coal mining, and in particular to a method for determining the reasonable size of small coal pillars in gob-side tunneling in a steeply inclined coal seam. Background Art

[0002] Coal is the main energy source in my country. With the continuous development of the coal industry in recent years, coal still occupies a dominant position in my country's energy structure, accounting for 76% and 69% of primary energy production and consumption respectively. Due to the continuous mining of near-horizontal or gently inclined coal seams with good storage conditions, the recoverable reserves of near-horizontal or gently inclined coal seams are getting smaller and smaller. Therefore, many mines have begun to turn to complex high-angle or steeply inclined coal seam mining. The high-angle coal seams are recognized as complex and difficult to mine at home and abroad due to their large coal seam inclination, surrounding rock damage and complex stress distribution, and low resource recovery rate.

[0003] In the current mining process of the working face, in order to ensure that the mining of the two adjacent working faces is not affected, a certain size of segmental coal pillars is usually left as coal pillars to protect the lane. In this case, if the size of the segmental coal pillars is insufficient, it is easy to cause the coal pillars along the empty side to spall and serious deformation of the surrounding rock of the mining lane, which cannot ensure the safe and efficient mining of the working face; and if the size of the segmental coal pillars is too large, it will cause a waste of coal resources. Therefore, in order to take into account both the safe mining of the working face and the efficient recovery of coal resources, the reasonable size of the segmental coal pillars should be studied and determined according to the actual geological conditions of each mine.

[0004] During the mining process of steeply inclined coal seams, due to the asymmetry of the working face roof mechanics, the fracture and migration rules of the overlying strata in the coal seams, the destruction characteristics of the segmented coal pillars and the mining tunnels are different from those in gently inclined coal seams.

[0005] In view of the above problems, it is urgent to propose a method for determining the section coal pillar retention that is suitable for the mining conditions of steep-angle coal seams, so as to ensure the safe and efficient mining of steep-angle coal seams and improve the recovery rate of coal resources. Summary of the invention

[0006] In order to overcome the problem that due to the asymmetry of the working face mining roof mechanics, the fracture and migration rules of the overlying rock strata of the coal seam, the destruction characteristics of the segmented coal pillars and the mining tunnels are different from those of the gently inclined coal seams, the present invention provides a method for determining the segmented coal pillars suitable for mining conditions of steep-angle coal seams, so as to ensure the safe and efficient mining of steep-angle coal seams and improve the recovery rate of coal resources.

[0007] The technical solution of the present invention is: a method for determining the reasonable size of small coal pillars in gob-side roadway driving in a steeply inclined coal seam, comprising the following steps:

[0008] Step 1: Based on the critical block fracture theory, calculate the size of small coal pillars in gob-side roadway excavation in steeply inclined coal seams;

[0009] Step 2: Based on the lateral support pressure distribution law, calculate the size of the small coal pillar set in the gob-side roadway in the steeply inclined coal seam;

[0010] Step 3: Organize and summarize the calculation results based on the key block fracture theory and the lateral support pressure distribution law, and finally accurately determine the reasonable size of small coal pillars in the goaf-side excavation of steeply inclined coal seams.

[0011] Specifically, in step 1, the calculation results based on the key block fracture theory are obtained by the following steps:

[0012] Step 1: Construct the mechanical model of the key block B: According to the mechanical model of the overburden structure at the end of the goaf of the upper section working face, simplify the arc-shaped triangular key block into an isosceles triangle, and establish the mechanical model of the basic top key block B;

[0013] Step 2: Calculate the length of the key block B along the advancing direction of the working face: It can be known from field practice that the length of the key block B along the strike is the same as the periodic pressure step; since the length of the mining working face along the dip is much longer than the exposed span of the basic roof, the basic roof can be regarded as a fixed beam supported by the solid coal of the working face at one end and by the boundary coal pillar at the other end; the normal stress expression of any point in the beam is σ = My / J, M is the bending moment of the section where the point is located, and the maximum bending moment M is taken max =qL1 2 / 2; y is the distance from the point to the neutral axis of the cross section, y = h / 2; J is the cross section distance of the symmetric neutral axis, J = h 3 / 12, the ultimate span expression of the cantilever beam is obtained as:

[0014]

[0015] Where: h-basic top rock layer thickness, m;

[0016] q0- load per unit area of ​​basic top, MPa;

[0017] R T - Ultimate tensile strength of basic top, MPa;

[0018] L1- basic top period pressure step, m;

[0019] Step 3: Calculate the lateral length of the key block B: According to the yield line analysis method of the plate, the lateral length L2 of the key block B is related to L1 and the working surface length S, which can be calculated by the following formula:

[0020]

[0021] Step 4: Determination of the thickness h of the key block B: The thickness h of the arc-shaped triangular block B is the thickness of the basic top rock layer;

[0022] Step 5: Determine the fracture line position of key block B: When the basic roof fracture position is located above the solid coal, the overburden stratum load acts on the coal pillar and the solid coal at the same time. The two sides of the roadway are subject to a large stratum load, resulting in increased displacement of the two sides and more difficult roadway maintenance; when the basic roof fracture position is located above the roadway along the goaf, after the goaf is stable, the lower goaf is compacted by gangue, and the overburden stratum load is transmitted to the direct roof and coal pillar. The coal pillar is subjected to excessive load and will be severely damaged. , the tunnel surrounding rock stability of the coal pillar is weaker, and the tunnel is difficult to maintain; when the basic roof fracture position is above the coal pillar, after the key block B sinks and stabilizes, a small part of the load above it is borne by the coal pillar, and most of the load is borne by the goaf gangue. At this time, the impact on the goaf tunnel is minimal, and the integrity of the coal pillar close to the tunnel side is better maintained, which is more conducive to the support of the tunnel; since the basic roof fracture position is generally at the elastic-plastic junction of the coal body, the distance from the basic roof fracture line to the narrow coal pillar close to the goaf side of the upper section is:

[0023]

[0024] Where: m-coal seam thickness, m;

[0025] A-lateral pressure coefficient, A = μ / 1-μ, μ is Poisson's ratio;

[0026] φ0-internal friction angle of coal rock, °;

[0027] C0-cohesion at the coal layer, MPa;

[0028] k-stress concentration factor;

[0029] γ-average bulk density of rock formation, MN / m 3 ;

[0030] H-tunnel burial depth, m;

[0031] p x - Anchor support resistance to coal seam, MPa;

[0032] Therefore, based on the critical block fracture theory, the calculated size of the small coal pillar in gob-side roadway excavation should be larger than L3.

[0033] Specifically, the calculation result of the lateral support pressure distribution law in step 2 is obtained by the following steps:

[0034] Step 1: Calculate the distance between the peak value of the lateral support pressure of the goaf and the boundary of the goaf in the upper section:

[0035] The distance between the peak value of the lateral support pressure of the goaf and the boundary of the goaf in the upper section can be determined by the following formula:

[0036]

[0037] Where: M-coal seam mining thickness, m;

[0038] x1-limit equilibrium zone width, m;

[0039] α-coal seam inclination, °;

[0040] σ x -x-direction stress, MPa;

[0041] σ y -y-direction stress, MPa;

[0042] σ y1 -Peak stress of coal pillar, MPa;

[0043] τ xy - Shear force between coal seam and rock layer, MPa;

[0044] P x -Horizontal restraint force of the goaf on the coal pillar, MPa;

[0045] φ0-internal friction angle, °;

[0046] C0-cohesion, MPa;

[0047] According to the on-site engineering practice and the distribution law of the lateral support pressure of the working face, it is approximately considered that the pressure value in the lateral support pressure reduction zone is linearly related to the distance between the lateral support pressure peak value and the boundary of the goaf, and the correlation coefficient is 0.5. Then the maximum width of the lateral support pressure reduction zone should satisfy the following formula:

[0048] x0=0.5Kx1

[0049] Where: x0-maximum width of lateral support pressure reduction zone, m.

[0050] K-safety factor, take 1.05~1.1.

[0051] Step 2: Determine the upper limit of the width of the coal pillar: The small coal pillar along the gob roadway should be distributed in the stress reduction zone of the upper section working face and should meet the following requirements:

[0052] a1=x0-bc

[0053] Where: x0-maximum width of lateral support pressure reduction zone, m;

[0054] a-small coal pillar width, m;

[0055] b - roadway width of driving along gob, m;

[0056] c - length of rib bolt, m;

[0057] Step 3: Determine the lower limit of the width of the coal pillar reserved: To ensure the stability of the coal pillar, in addition to the loosened and broken areas on both sides of the coal pillar, there should also be a relatively stable area in the middle of the coal pillar. The lower limit of the small coal pillar width should satisfy the following formula:

[0058] a2 = d1 + d2 + d3

[0059] Where: d1 - width of the loosened area on the gob side of the coal pillar, m;

[0060] d2 - safety factor of the coal pillar, taking 0 - 0.5(d1 + d3);

[0061] d3 - width of the loosened area on the gob - side roadway of the coal body, m;

[0062] Among them, d1 and d3 can be determined according to the results of borehole peeping, etc. The width of the loosened areas on both sides of the small coal pillar in the coal seam is generally 1 - 2 m; d2 should be selected considering factors such as the integrity of the small coal pillar coal body, the coal body reinforcement measures taken, the anchoring requirements of bolts (cables), and the range of the reduced side - supporting pressure area in the gob of the adjacent working face;

[0063] When d1 + d3 ≤ 2, the integrity of the small coal pillar coal body is good, and the range of surrounding - rock fragmentation is small. d2 takes 0.3 - 0.5(d1 + d3), and the small coal pillar can meet the requirements of isolating the gob and bolt anchoring;

[0064] When 2 < d1 + d3 ≤ 4, the integrity of the small coal pillar coal body is average, but it can maintain its own stability and meet the requirement of isolating the gob. To make the bolts (cables) have good anchoring performance, d2 takes 0.2 - 0.3(d1 + d3);

[0065] When d1 + d3 > 4, the integrity of the small coal pillar coal body is poor, and the range of surrounding - rock fragmentation is large. Measures such as grouting reinforcement and strengthening support should be taken to ensure the anchoring performance of bolts and improve the stability of the coal pillar. To make the gob - side roadway within the range of the reduced side - supporting pressure area of the adjacent working - face gob, d2 takes 0 - 0.2(d1 + d3); On the premise of ensuring the long - term stability of the small coal pillar and the requirements of isolating the gob, in principle, the width of the small coal pillar should be as small as possible;

[0066] Step 4: Calculate the distance between the boundary of the original rock stress area of the side - supporting pressure in the gob and the boundary of the upper - section gob:

[0067] The distance between the boundary of the original rock stress area of the side - supporting pressure in the gob and the boundary of the upper - section gob can be determined by the following formula:

[0068]

[0069] Where: x2-lateral support pressure influence range, m;

[0070] x1-limit equilibrium zone width, m;

[0071] λ-lateral pressure coefficient;

[0072] M-coal seam thickness, m;

[0073] α-coal seam inclination, °;

[0074] φ0-internal friction angle, MPa;

[0075] k-stress concentration factor;

[0076] Therefore, based on the calculation of the coal pillar size according to the distribution law of lateral support pressure, the width of the narrow coal pillar should be in the range of a2 to a1 or greater than x2.

[0077] Specifically, in step 3, the reasonable size of small coal pillars in gob-side roadway driving in steeply inclined coal seams is comprehensively and accurately determined by the following steps:

[0078] Step 1: When L3≤a2, the width of the narrow coal pillar should be in the range of a2~a1 or greater than x2. Taking into account the utilization rate of coal resources, the width of the narrow coal pillar is finally determined to be in the range of a2~a1;

[0079] Step 2: When a2≤L3≤a1, the width of the narrow coal pillar should be in the range of L3~a1 or greater than x2. Taking the utilization rate of coal resources into consideration, the width of the narrow coal pillar is finally determined to be in the range of L3~a1;

[0080] Step 3: When cL3≥a1, the width range of the final narrow coal pillar should be determined to be greater than x2.

[0081] Beneficial effects: 1. By calculating the fracture line position of the key block B, the critical minimum value of the width of the coal pillar is determined, so that the fracture position is above the coal pillar. After the key block B sinks and stabilizes, a small part of the load above it is borne by the coal pillar, and most of the load is borne by the goaf gangue. At this time, the impact on the goaf roadway is minimal, and the integrity of the coal pillar close to the roadway side is better maintained, which is more conducive to the support of the roadway.

[0082] 2. By analyzing the distribution law of lateral support pressure in goaf, the distance between the peak value of lateral support pressure in goaf and the boundary of goaf in upper section and the distance between the original rock stress zone and the boundary of goaf in upper section are calculated, and the range of lateral support pressure reduction zone and original rock stress zone in goaf are determined. The coal pillars left along the goaf should be distributed in the stress reduction zone or original rock stress zone within the lateral support pressure of the working face in upper section, so as to improve the safety and stability of the roadway, and thus the upper and lower limits of the width of coal pillars left in the roadway are obtained, and the range of coal pillar width is determined.

[0083] 3. The two methods can ultimately accurately determine the reasonable width of the coal pillar to be left along the goaf, which can effectively improve the problem of difficult tunnel support, reduce the waste of coal resources, and achieve safe and efficient production in the mine. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Figure 1 It is a schematic diagram of the position of the basic top fracture above the solid coal in the present invention;

[0085] Figure 2 It is a schematic diagram of the position of the basic top fracture above the gob-side tunnel in the present invention;

[0086] Figure 3 It is a schematic diagram of the position of the basic top fracture above the coal pillar in the present invention;

[0087] Figure 4 A schematic diagram of a calculation model for setting an upper limit on the size of a small coal pillar in the present invention;

[0088] Figure 5 A schematic diagram of a calculation model for setting a lower limit on the size of a small coal pillar in the present invention;

[0089] Figure 6 is a flow chart of the present invention;

[0090] Markings in the figure are: 1- goaf of the upper section working face; 2- coal pillar; 3- tunnel along the goaf; 4- key block B; 51- the fracture line is located above the solid coal; 52- the fracture line is located above the tunnel along the goaf; 53- the fracture line is located above the coal pillar; 6- solid coal; 7- peak value of lateral support pressure. DETAILED DESCRIPTION

[0091] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments, but the protection scope and application scope of the present invention are not limited.

[0092] A method for determining the reasonable size of small coal pillars in gob-side roadway excavation in a steeply inclined coal seam mainly comprises the following steps:

[0093] Step 1: Based on the critical block fracture theory, the size of the small coal pillar 2 in the gob-side tunneling 3 of the steeply inclined coal seam is calculated;

[0094] Step 2: Based on the lateral support pressure distribution law, the size of the small coal pillar 2 in the gob-side tunneling 3 of the steeply inclined coal seam is calculated;

[0095] Step three, organize and summarize the calculation results based on the key block fracture theory and the lateral support pressure distribution law, and finally accurately determine the reasonable size of the small coal pillar 2 in the goaf-side tunneling 3 in the steep coal seam.

[0096] Specifically, in step 1, the calculation results based on the key block fracture theory are obtained by the following steps:

[0097] Step 1, constructing the mechanical model of the key block B4: according to the mechanical model of the overburden structure at the end of the goaf 1 of the upper section working face, simplify the arc-shaped triangular key block into an isosceles triangle, and establish the mechanical model of the basic top key block B4;

[0098] Step 2, calculate the length of the key block B4 along the advancing direction of the working face: Through field practice, it is known that the length of the key block B4 along the strike is the same as the periodic pressure step. Since the length of the mining working face along the dip is much longer than the exposed span of the basic roof, the basic roof can be regarded as a fixed beam supported by the solid coal of the working face at one end and the boundary coal pillar at the other end. The normal stress expression of any point in the beam is σ = My / J, M is the bending moment of the section where the point is located, and the maximum bending moment M is taken. max =qL1 2 / 2; y is the distance from the point to the neutral axis of the cross section, y = h / 2; J is the cross section distance of the symmetric neutral axis, J = h 3 / 12, the ultimate span expression of the cantilever beam is obtained as:

[0099]

[0100] Where: h-basic top rock layer thickness, m;

[0101] q0- load per unit area of ​​basic top, MPa;

[0102] R T - Ultimate tensile strength of basic top, MPa;

[0103] L1- basic top period to press step length, m.

[0104] Step 3, calculate the lateral length of the key block B4: According to the yield line analysis method of the plate, the lateral length L2 of the key block B4 is related to L1 and the working surface length S, which can be calculated by the following formula:

[0105]

[0106] Step 4, determination of the thickness h of the key block B4: The thickness h of the key block B4 is the thickness of the basic top rock layer.

[0107] Step 5, determine the fracture line position of the key block B4: when the basic roof fracture position 51 is located above the solid coal 6, the overburden stratum load acts on the coal pillar 2 and the solid coal 6 at the same time, and the two sides of the tunnel 3 are subject to a large stratum load, resulting in increased displacement of the two sides and difficult tunnel maintenance; when the basic roof fracture position 52 is located above the tunnel 3 along the goaf, after the goaf 1 is stable, since the lower goaf 1 is compacted by gangue, the overburden stratum load is transmitted to the direct roof and the coal pillar 2, the load on the coal pillar is too large, the coal pillar will be severely damaged, the tunnel surrounding rock stability of the coal pillar side is weaker, and the tunnel is difficult to maintain; when the basic roof fracture position 53 is above the coal pillar 2, after the key block B4 sinks and stabilizes, a small part of the load above it is borne by the coal pillar 2, and most of the load is borne by the gangue in the goaf 1. At this time, the impact on the tunnel 3 along the goaf is minimal, and the integrity of the coal pillar 2 close to the side of the tunnel 3 is better maintained, which is more conducive to the support of the tunnel. Since the basic roof fracture position is generally at the elastic-plastic interface of the coal body, the distance from the narrow coal pillar 2 near the upper section goaf 1 to the basic roof fracture line is:

[0108]

[0109] Where: m-coal seam thickness, m;

[0110] A-lateral pressure coefficient, A = μ / 1-μ, μ is Poisson's ratio;

[0111] φ0-internal friction angle of coal rock, °;

[0112] C0-cohesion at the coal layer, MPa;

[0113] k-stress concentration factor;

[0114] γ-average bulk density of rock formation, MN / m 3 ;

[0115] H-tunnel burial depth, m;

[0116] p x -Anchor support resistance to coal seam, MPa.

[0117] Therefore, based on the critical block fracture theory, the calculated size of the small coal pillar 2 in the gob-side tunneling 3 should be larger than L3.

[0118] Specifically, the calculation result of the lateral support pressure distribution law in step 2 is obtained by the following steps:

[0119] Step 1, calculate the distance between the peak value 7 of the lateral support pressure of goaf 1 and the boundary of goaf 1:

[0120] The distance between the peak value 7 of the lateral support pressure of goaf 1 and the boundary of goaf 1 in the upper section can be determined by the following formula:

[0121]

[0122] Where: M-coal seam mining thickness, m;

[0123] x1-limit equilibrium zone width, m;

[0124] α-coal seam inclination, °;

[0125] σ x -x-direction stress, MPa;

[0126] σ y -y-direction stress, MPa;

[0127] σ y1 -Peak stress of coal pillar, MPa;

[0128] τ xy - Shear force between coal seam and rock layer, MPa;

[0129] P x -Horizontal restraint force of the goaf on the coal pillar, MPa;

[0130] φ0-internal friction angle, °;

[0131] C0 - cohesion, MPa.

[0132] According to the on-site engineering practice and the distribution law of the lateral support pressure of the working face, it is approximately considered that the pressure value in the lateral support pressure reduction zone is linearly related to the distance from the lateral support pressure peak value 7 to the boundary of the goaf 1, and the correlation coefficient is 0.5. The maximum width of the lateral support pressure reduction zone should meet the following requirements:

[0133] x0=0.5Kx1

[0134] Where: x0-maximum width of lateral support pressure reduction zone, m.

[0135] K-safety factor, take 1.05~1.1.

[0136] Step 2, the upper limit of the width of the coal pillar 2 is determined, and the small coal pillar 2 along the gob roadway 3 should be distributed in the stress reduction area of ​​the upper section working face and should meet the following requirements:

[0137] a1=x0-bc

[0138] Where, x0-maximum width of lateral support pressure reduction zone, m;

[0139] a-small coal pillar width, m;

[0140] b- width of gob-side tunneling, m;

[0141] c- Anchor rod length, m.

[0142] Step 3, determining the lower limit of the width of coal pillar 2. To ensure the stability of coal pillar 2, in addition to the loosened and broken areas on both sides of coal pillar 2, there should also be a relatively stable area in the middle of coal pillar 2. The lower limit of the width of coal pillar 2 should satisfy the following formula:

[0143] a2 = d1 + d2 + d3

[0144] In the formula: d1 - the width of the loosened area on the goaf side of the coal pillar, m;

[0145] d2 - the safety factor of the coal pillar, taking 0 - 0.5d1 + d3;

[0146] d3 - the width of the loosened area on the gob-side entry side of the coal body, m.

[0147] Among them, d1 and d3 can be determined according to the results of borehole peephole, etc. The width of the loosened areas on both sides of the small coal pillar 2 in the coal seam is generally 1 - 2 m. d2 should be selected considering factors such as the integrity of the coal body of the small coal pillar 2, the coal body reinforcement measures taken, the requirements for bolt and cable anchorage, and the range of the reduced side abutment pressure area of the goaf 1 of the adjacent working face.

[0148] When d1 + d3 ≤ 2, the integrity of the coal body of the small coal pillar 2 is good, the broken range of the surrounding rock is small, d2 takes 0.3 - 0.5(d1 + d3), and the small coal pillar 2 can meet the requirements of isolating the goaf 1 and bolt anchorage;

[0149] When 2 < d1 + d3 ≤ 4, the integrity of the coal body of the small coal pillar 2 is average, but it can maintain its own stability and meet the requirements of isolating the goaf. In order to make the bolt (cable) have good anchorage performance, d2 takes 0.2 - 0.3(d1 + d3);

[0150] When d1 + d3 > 4, the integrity of the coal body of the small coal pillar 2 is poor, the broken range of the surrounding rock is large, measures such as grouting reinforcement and enhanced support should be taken to ensure the anchorage performance of the bolt (cable) and improve the stability of the coal pillar. In order to make the gob-side entry 3 within the range of the reduced side abutment pressure area of the goaf 1 of the adjacent working face, d2 takes 0 - 0.2(d1 + d3). On the premise of ensuring the long-term stability of the small coal pillar 2 and the requirements of isolating the goaf, in principle, the width of the small coal pillar 2 should be as small as possible.

[0151] Step 4, calculating the distance from the original rock stress area of the side abutment pressure of the goaf 1 to the boundary of the upper panel goaf:

[0152] The distance from the boundary of the original rock stress area of the side abutment pressure of the goaf 1 to the boundary of the upper panel goaf can be determined by the following formula:

[0153]

[0154] In the formula: x2 - the influence range of the side abutment pressure, m;

[0155] x1-limit equilibrium zone width, m;

[0156] λ-lateral pressure coefficient;

[0157] M-coal seam thickness, m;

[0158] Α-coal seam inclination, °;

[0159] φ0-internal friction angle, MPa;

[0160] k-stress concentration factor.

[0161] Therefore, based on the calculation of the coal pillar size according to the lateral support pressure distribution law, the width of the narrow coal pillar 2 should be in the range of a2 to a1 or greater than x2.

[0162] Specifically, the reasonable size of the small coal pillar 2 in the gob-side roadway 3 of the steeply inclined coal seam determined comprehensively and accurately in step 3 is obtained by the following steps:

[0163] Step 1: When L3≤a2, the width of the narrow coal pillar 2 should be in the range of a2 to a1 or greater than x2. Taking the utilization rate of coal resources into consideration, the width of the narrow coal pillar 2 is finally determined to be in the range of a2 to a1.

[0164] Step 2, when a2≤L3≤a1, the width range of the narrow coal pillar 2 should be L3~a1 or greater than x2. Taking the utilization rate of coal resources into comprehensive consideration, finally, the width range of the narrow coal pillar 2 is determined to be L3~a1.

[0165] Step 3: When L3≥a1, the width range of the narrow coal pillar 2 should be determined to be greater than x2.

[0166] The above description of the disclosed embodiments enables those skilled in the art to implement and use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit and scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest range consistent with the principles and novel features disclosed herein.

Claims

1. A method for determining the reasonable size of small coal pillars in gob-side roadway driving in steeply inclined coal seams, characterized in that: The following steps are involved: Step 1: Based on the critical block fracture theory, the size of the small coal pillar (2) in the gob-side tunneling (3) of the steeply inclined coal seam is calculated; Step 2: Based on the lateral support pressure distribution law, the size of the small coal pillar (2) in the gob-side tunneling (3) of the steeply inclined coal seam is calculated; Step 3: Summarize the calculation results based on the key block fracture theory and the lateral support pressure distribution law, and finally accurately determine the reasonable size of the small coal pillar (2) in the gob-side tunneling (3) of the steep coal seam.

2. A method for determining the reasonable size of small coal pillars in gob-side roadway driving in a steeply inclined coal seam as claimed in claim 1, characterized in that: In step 1, the calculation results based on the critical block fracture theory are obtained by the following steps: Step 1: Construct the mechanical model of the key block B (4): According to the mechanical model of the overburden structure at the end of the goaf of the upper section working face, simplify the arc-shaped triangular key block into an isosceles triangle, and establish the mechanical model of the basic top key block B (4); Step 2: Calculate the length of the key block B (4) along the working face advancement direction: It is known from field practice that the length of the key block B along the strike direction is the same as the periodic pressure step distance; since the length of the mining working face along the dip direction is much longer than the exposed span of the basic roof, the basic roof can be regarded as a fixed beam supported by the solid coal of the working face at one end and by the boundary coal pillar at the other end; The normal stress expression of any point in the beam is σ = My / J, where M is the bending moment of the section where the point is located. The maximum bending moment M is taken as max =qL1 2 / 2; y is the distance from the point to the neutral axis of the cross section, y = h / 2; J is the cross section distance of the neutral axis of symmetry, J = h 3 / 12, the ultimate span expression of the cantilever beam is obtained as: Where: h-basic top rock layer thickness, m; q0- load per unit area of ​​basic top, MPa; R T - Ultimate tensile strength of basic top, MPa; L1- basic top period pressure step, m; Step 3: Calculate the lateral length of the key block B (4): According to the yield line analysis method of the plate, the lateral length L2 of the key block B (4) is related to L1 and the working surface length S, and can be calculated by the following formula: Step 4: Determination of the thickness h of the key block B: The thickness h of the arc-shaped triangular block B is the thickness of the basic top rock layer; Step 5: Determine the fracture line position of the key block B (4): When the basic roof fracture position (51) is located above the solid coal (6), the overburden stratum load acts on the coal pillar (2) and the solid coal (6) at the same time, and the two sides of the tunnel (3) are subject to a large stratum load, resulting in increased displacement of the two sides and more difficult tunnel maintenance; when the basic roof fracture position (52) is located above the goaf-side tunnel (3), after the goaf (1) is stabilized, the lower goaf (1) is compacted by gangue, and the overburden stratum load is transmitted to the direct roof and coal pillar (2). The coal pillar is subjected to excessive load, and the coal pillar will have a more serious The roadway surrounding rock stability is weaker due to the destruction of the coal pillar, and the roadway is difficult to maintain. When the basic roof fracture position (53) is above the coal pillar (2), after the key block B (4) sinks and stabilizes, a small part of the load above it is borne by the coal pillar (2), and most of the load is borne by the gangue in the goaf (1). At this time, the impact on the roadway (3) along the goaf is minimal, and the integrity of the coal pillar (2) close to the side of the roadway (3) is better maintained, which is more conducive to the support of the roadway. Since the basic roof fracture position is generally at the elastic-plastic junction of the coal body, the distance between the narrow coal pillar (2) close to the upper section goaf (1) and the basic roof fracture line is: Where: m-coal seam thickness, m; A-lateral pressure coefficient, A = μ / 1-μ, μ is Poisson's ratio; φ0-internal friction angle of coal rock, °; C0-cohesion at the coal layer, MPa; k-stress concentration factor; γ-average bulk density of rock formation, MN / m 3 ; H - roadway burial depth, m; p x - Anchor support resistance to coal seam, MPa; Therefore, based on the key block fracture theory, the size of the small coal pillar (2) reserved for driving along the goaf (3) calculated should be greater than L3.

3. A method for determining the reasonable size of small coal pillars in gob-side roadway driving in a steeply inclined coal seam as claimed in claim 2, characterized in that: Specifically, the calculation results of the lateral abutment pressure distribution law in step two are obtained through the following steps: Step 1: Calculate the distance from the peak value of the lateral abutment pressure (7) in the goaf (1) to the boundary of the goaf (1): The distance from the peak value of the lateral abutment pressure (7) in the goaf (1) to the boundary of the upper panel goaf (1) can be determined by the following formula: In the formula: M - coal seam thickness, m; x1 - width of the limit equilibrium zone, m; α - coal seam dip angle, °; σ x -x-direction stress, MPa; σ y -y-direction stress, MPa; σ y1 -Peak stress of coal pillar, MPa; τ xy - Shear force between coal seam and rock layer, MPa; P x -Horizontal restraint force of goaf on coal pillar, MPa; φ0 - internal friction angle, °; C0 - cohesion, MPa; According to on-site engineering practice and combined with the lateral abutment pressure distribution law of the working face, it is approximately considered that within the range of the lateral abutment pressure reduction zone, the pressure value has a linear relationship with the distance from the peak value of the lateral abutment pressure (7) to the boundary of the goaf (1), and the correlation coefficient is taken as 0.

5. Then, the maximum width of the lateral abutment pressure reduction zone should satisfy the following formula: x0 = 0.5Kx1 In the formula: x0 - maximum width of the lateral abutment pressure reduction zone, m. K - safety factor, taken as 1.05 - 1.

1. Step 2: Determine the upper limit of the reserved width of the coal pillar (2). The small coal pillar (2) driving-along-goaf roadway (3) should be distributed within the stress reduction zone of the upper panel working face and should satisfy the following requirements: a1 = x0 - b - c In the formula: x0 - maximum width of the lateral abutment pressure reduction zone, m; a - small coal pillar width, m; b - width of the driving-along-goaf roadway, m; c - length of the rib bolt, m; Step 3: Determine the lower limit of the reserved width of the coal pillar (2). To ensure the stability of the coal pillar (2), in addition to the loosening and broken areas on both sides of the coal pillar (2), there should also be a relatively stable area in the middle of the coal pillar (2). The lower limit of the small coal pillar (2) width should satisfy the following formula: a2 = d1 + d2 + d3 In the formula: d1 - width of the loosening zone on the goaf side of the coal pillar, m; d2 - safety factor of the coal pillar, taken as 0 - 0.5(d1 + d3); d3 - width of the loosening zone on the driving-along-goaf roadway side of the coal body, m; Among them, d1 and d3 can be determined according to the results of borehole peeping, etc. The width of the loosening zones on both sides of the small coal pillar (2) of the coal seam is generally 1 - 2 m; d2 should be selected considering factors such as the integrity of the small coal pillar (2) coal body, the coal body reinforcement measures taken, the anchoring requirements of bolts (cables), and the range of the lateral abutment pressure reduction zone of the adjacent working face goaf (1); When d1 + d3 ≤ 2, the integrity of the small coal pillar (2) coal body is good, and the surrounding rock fragmentation range is small. d2 is taken as 0.3 - 0.5(d1 + d3), and the small coal pillar (2) can meet the requirements of isolating the goaf (1) and bolt anchoring; When 2 < d1 + d3 ≤ 4, the integrity of the small coal pillar (2) coal body is general, but it can maintain its own stability and meet the requirements of isolating the goaf (1). In order to make the bolts (cables) have good anchoring performance, d2 is taken as 0.2 - 0.3(d1 + d3); When d1+d3>4, the integrity of the coal body of the small coal pillar (2) is poor, and the surrounding rock is broken to a large extent. Grouting reinforcement and strengthening support measures should be taken to ensure the anchor bolt solidity and improve the stability of the coal pillar (2). In order to make the goaf-side tunnel within the lateral support pressure reduction zone of the adjacent working face goaf (1), d2 is set to 0-0.2 (d1+d3); under the premise of ensuring the long-term stability of the small coal pillar (2) and isolating the goaf, in principle, the width of the small coal pillar (2) should be as small as possible; Step 4: Calculate the distance between the boundary of the original rock stress zone of the lateral support pressure of the goaf (1) and the boundary of the goaf in the upper section: The distance between the boundary of the original rock stress zone of the lateral support pressure of the goaf (1) and the boundary of the goaf in the upper section can be determined by the following formula: Where: x2-lateral support pressure influence range, m; x1-limit equilibrium zone width, m; λ-lateral pressure coefficient; M-coal seam thickness, m; α-coal seam inclination, °; φ0-internal friction angle, MPa; k-stress concentration factor; Therefore, based on the calculation of the size of the coal pillar reserved according to the distribution law of the lateral support pressure, the width of the narrow coal pillar (2) should be in the range of a2 to a1 or greater than x2.

4. A method for determining the reasonable size of small coal pillars in gob-side roadway driving in a steeply inclined coal seam as claimed in claim 3, characterized in that: In step 3, the reasonable size of the small coal pillar (2) in the roadway along the goaf (3) of the steeply inclined coal seam is comprehensively and accurately determined by the following steps: Step 1: When L3≤a2, the width of the narrow coal pillar (2) should be in the range of a2 to a1 or greater than x2. Taking the utilization rate of coal resources into consideration, the width of the narrow coal pillar (2) is finally determined to be in the range of a2 to a1; Step 2: When a2≤L3≤a1, the width of the narrow coal pillar (2) should be in the range of L3 to a1 or greater than x2. Taking the utilization rate of coal resources into consideration, the width of the narrow coal pillar (2) is finally determined to be in the range of L3 to a1. Step 3: When cL3≥a1, the width range of the final narrow coal pillar (2) should be determined to be greater than x2.

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