CN113431577A

CN113431577A - Method for arranging same-direction inward-staggered roadways in ultra-close coal seam mining

Info

Publication number: CN113431577A
Application number: CN202110470097.2A
Authority: CN
Inventors: 张安慎; 田王健; 李溪枝; 孙国强; 王利军; 党其; 刘兆宇; 冯刚; 张亮; 卫伟
Original assignee: Shanxi Coal Transportation And Marketing Group Science And Technology Research Co ltd
Current assignee: Shanxi Coal Transportation And Marketing Group Science And Technology Research Co ltd
Priority date: 2021-04-28
Filing date: 2021-04-28
Publication date: 2021-09-24

Abstract

The invention discloses a method for arranging equidirectional and inward staggered roadways for mining a very close coal seam. And a solid foundation is laid for supporting the roadway and saving the cost.

Description

Method for arranging same-direction inward-staggered roadways in ultra-close coal seam mining

Technical Field

The invention relates to a coal seam mining method, in particular to a method for mining a coal seam in a very short distance by arranging same-direction and inwards staggered roadways.

Background

According to geological specification of No. 11 coal seam four mining areas of Taishan Longan coal industry Co., Ltd, Shanxi coal transportation and marketing group and actual disclosure on site, 11_{On the upper part}The coal seam has the maximum coal seam thickness of 1.9m, the minimum coal seam thickness of 1.38m and the average thickness of 1.66 m; 11_{Lower part}The coal seam has the maximum coal seam thickness of 5.09m, the minimum coal seam thickness of 3.70m and the average thickness of 4.46 m. 11_{On the upper part}And 11_{Lower part}The maximum interlayer spacing of the coal seam is 3.46m, the minimum interlayer spacing is 2.01m, the average interlayer spacing is 2.74m, and the coal seam belongs to a very short-distance mining coal seam.

In the process of short-distance coal seam mining, due to the influence of comprehensive factors such as roadway arrangement, coal pillar reservation, distance between upper and lower mining spacing layers and the like, when a lower layer coal seam is mined, the phenomena of pressure concentration, obvious mine pressure appearance and the like can occur in the aspect of roof disasters, and even large-area roof collapse accidents occur; because the rock strata between the upper and lower layers completely collapse, accumulated water and accumulated gas formed during the mining of the coal strata on the upper layer can be discharged, and water damage and gas accidents are caused; due to the communication of the goaf, after air leakage is formed, spontaneous combustion of the goaf remaining coal is easily formed. In order to ensure safe production of a mine, improve the resource recovery rate of No. 11 coal seams and increase the economic benefit of enterprises, a new mining method is needed.

Disclosure of Invention

In order to overcome the defects and shortcomings of the prior art, the method for mining the coal seam in the extremely close range by arranging the same-direction and inwards staggered roadways can ensure the safe production of a mine, improve the resource recovery rate of the No. 11 coal seam and increase the economic benefit of an enterprise.

The method for the same-direction and inward-staggered roadway arrangement of the ultra-close coal seam mining, which is provided for realizing the purpose of the invention, comprises the following steps:

the first step is as follows: based on the coal seam, the coal quality and the structure exposure condition of the No. 11 coal seam four-mining area and the hydrogeological conditions of the mining area, the No. 11 coal seam four-mining area 11 is subjected to comparison of an internal wrong type arrangement, an external wrong type arrangement and an internal same direction wrong type arrangement method by adopting engineering analogy, theoretical calculation and numerical simulation methods and through the investigation of the geological conditions of mine production_{On the upper part}、11_{Lower part}Determining to adopt a same-direction inward-staggered scheme and a reasonable mining connection sequence by adopting a coal seam working face crossheading arrangement mode;

the second step is that: comprehensively analyzing the mining conditions of the working faces of the adjacent mining areas of the No. 11 coal seam, and specifically determining the technical scheme of the arrangement mode and the connection sequence of the working face roadway of the four mining areas of the No. 11 coal seam;

the third step: respectively carrying out analogy on the conditions of the same type and theoretical calculation on 11 # coal seam four mining areas 11_{On the upper part}、11_{Lower part}Selecting types by coal seam mining and excavating working face equipment, and determining a mining process;

the fourth step: determining the roadway layout, the mining process and the equipment type selection of a first mining working face of No. 11 coal seam four-mining area, and determining 11 coal seam four-mining area 11_{On the upper part}First-hand working face, i.e. 11_{On the upper part}401 arrangement of the working surfaces.

As a further improvement of the above scheme, the theoretical calculation and numerical simulation method in the first step specifically includes analysis of destructive behavior of the mined-out floor of the upper coal seam, analysis of stability of the coal pillar between the crossheading, and the analysis of destructive behavior of the mined-out floor of the upper coal seam includes 11_{On the upper part}Research on maximum damage depth of bottom plate in coal seam mining, 11_{On the upper part}And (3) analyzing the stress under the coal pillar of the coal bed, wherein the stability analysis of the coal pillar between the crossheading comprises the calculation of the width of a plastic zone of a stoping coal pillar and the reasonable width of the coal pillar.

As a further improvement of the scheme, in the first step, the four mining areas 11 of No. 11 coal seams_{On the upper part}、11_{Lower part}The method for determining the arrangement of the coal seam working face crossheading adopts a 'same-direction inward-staggered' scheme, and specifically comprises 11_{Lower part}Coal seam roadway arrangement mode and quality factor comparisonMining area 11_{Lower part}And (3) carrying out numerical simulation on the arrangement scheme of the coal seam area mining roadway and the arrangement scheme of the mining roadway.

As a further improvement of the above scheme, the arrangement mode of the working face roadway of the No. 11 coal seam four mining area in the second step specifically includes: comprises 11_{On the upper part}Coal seam working face layout, 11_{Lower part}And arranging a coal seam working surface.

As a further improvement of the above scheme, the engagement sequence comprises 11_{On the upper part}Coal seam mining sequence, 11_{Lower part}Coal seam mining sequence, 11_{On the upper part}、11_{Lower part}And (4) alternately mining coal beds.

As a further improvement of the above solution, said 11_{On the upper part}The theoretical analysis of the research on the maximum damage depth of the bottom plate in coal seam mining is as follows:

when the pressure applied to the rock stratum under the bottom plate of the goaf exceeds the maximum value capable of being borne by the rock stratum, the rock stratum of the bottom plate can generate plastic deformation in a certain range; when the pressure on the bottom plate rock stratum is continuously increased, the bottom plate rock stratum is completely crushed, and then plastic zones in the pressure influence range are connected into a whole, so that bottom bulging of a goaf is caused, the plastic zone rock mass moves in the goaf to gradually form a continuous slip surface, and the goaf bottom plate rock stratum is influenced by maximum damage;

according to the floor rock stratum slip line field theory, the damage depth of the goaf floor, which is affected by the supporting pressure, can be obtained by calculation: the yield failure depth h of the bottom plate is as follows:

by

Calculating to obtain the maximum damage depth h of the upper coal seam mining to the bottom plate_max：

According to the formula:

obtaining the width x of the plastic zone of the coal pillar when one side is mined by applying the limit balance theory₀Comprises the following steps:

x in the above formula₀Substituting to obtain the maximum damage depth h of the upper group coal seam mining to the bottom rock layer_max：

Wherein:

m is the mining height, and M is the mining height,

k-stress concentration factor (from empirical formula K1 + 0.23L)_x ^0.47，L_xFor working face length)

Gamma-the average volume force of the overburden,

h, mining depth;

c-coal bed cohesion;

-an internal angle of friction of the coal seam;

f is the friction coefficient of the coal bed and the top and bottom plates;

xi-the triaxial stress coefficient,

-floor formation internal friction angle;

p_i-resistance of the support to the coal slope;

combining the geological data of the mine and the mechanical parameters of the surrounding rock, wherein the values of all the parameters are as follows: m is 1.90M, and M is equal to 1.90M,

p_i＝0，ξ＝2.846，H＝290m，

γ＝25KN/m³k is 4.02, C is 1.3MPa, and f is 0.2; substituting each parameter into formula (2-5), calculating to obtain 11_{On the upper part}The maximum damage depth of the coal seam mining to the bottom plate is 2.45 m; consider that 11_{On the upper part}Caving and mine pressure phenomena during the hard roof extraction of the coal seam, therefore 11_{On the upper part}The damage depth of the coal seam mining to the bottom plate can reach more than 2.45m, and the arrangement 11 is arranged_{Lower part}When the coal seam mining roadway and the roadway support parameters are selected, 11 need to be considered_{On the upper part}The destructive influence of coal seam mining on the floor.

As a further improvement of the above, in the first step 11_{On the upper part}The stress analysis under the coal bed coal pillar is as follows:

the mining of the coal bed causes the stress of surrounding rocks of the mining space to be redistributed, so that concentrated stress is formed on coal pillars around the mining space, and the concentrated stress can be transferred and diffused to the bottom plate; the stress distribution rule of the coal pillar in the bottom rock stratum (the top plate of the lower coal stratum) is researched, and the stress state and the ore pressure display of the roadway of the lower rock stratum are masteredThe method comprises the following steps of (1) performing characterization, wherein the reasonable position of a lower coal (rock) layer roadway is determined, and the selection of support parameters has a guiding function; according to the fact that a coal (rock) body is a homogeneous elastic body, the stress component sigma of a concentrated load q at any point in a semi-infinite plane body is applied by an elastic theory_x、σ_y、τ_xyThe stress distribution condition of concentrated load in the bottom plate is shown in figure 3, the simplified load on the coal pillar bottom plate can be regarded as the combination of two load distribution forms of linear and uniform distribution, the stress distribution form of the uniform load in the bottom plate is shown in figure 4, the stress distribution form of the linear load in the bottom plate is shown in figure 5, the generated stress components are respectively calculated, and then the stress components of any point in the rock stratum of the bottom plate can be obtained by superposition; setting distributed force on a starting boundary AB section of a semi-plane body, wherein the concentration of the semi-plane body at each point is P; and the distance between the AB section and the origin O is xi, the stress of any point M is as follows under the action of a small load q (xi) d xi of the semi-infinite body under the plane strain condition:

to determine the stresses due to the total distribution force, it is only necessary to add all the stresses due to the individual small concentration forces, i.e., integrate the above three equations from ξ ═ b to ξ ═ a, resulting in:

when the formula (2-7) is applied, the concentration q of the distribution force is expressed as a function of xi and then is integrated; the calculation formulas of the uniformly distributed load and the linearly distributed load are given as follows:

② evenly distributing the load

Wherein the formulas (2-7) and (2-8) are simultaneously rewritable as follows:

② linearly distributing the load

In the same way, the formulas (2-7) and (2-10) are rewritten as follows:

the load form of the residual section coal pillar after the mining of the upper coal seam in the close range is very complicated, and the two types of the load form are simplified; load is evenly distributed and linearly distributed; and (3) assuming that the coal pillars are uniformly loaded, under the condition of giving the width of the coal pillars, providing stress distribution curves of the concentrated stress of the coal pillars at different depths of the bottom plate, and further analyzing the transfer and diffusion rules of the concentrated stress of the coal pillars on the bottom plate.

As a further improvement of the above scheme, the analysis of the width of the plastic zone of the coal pillar produced in the first step is specifically as follows:

the stress state of the coal body at the edge of the goaf can be changed due to the action of lateral supporting pressure on the rear coal pillar along with the propulsion of the stope face of the upper coal layer; elastic state-plastic state-fracture state development. The width of the coal pillar is B, and the range of the action of the supporting pressure on one side of the coal pillar is L₀And then the elastic-plastic deformation zone of the roadway-protecting coal pillar is left in the upper coal layer goafThe vertical stress distribution is as follows:

first, assume that all the pillars around the gob are elastically deformed. When the distance between the vertical stress and the edge of the goaf coal pillar is increased continuously, the vertical stress is decreased progressively with a negative index. Under the action of high stress, a cracking zone, a plastic zone, an elastic zone and an original stress zone appear from the edge of the coal pillar to the deep part of the coal body once. Within a certain width from the edge of the coal column body, the bearing capacity and the supporting pressure of the coal column body are in a limit equilibrium state, and the formula is known as follows: the maximum value of the pillar support pressure and the distance of the pillar edge can be expressed as:

from the above formula, the factors affecting the width of the plastic zone of the coal pillar include: layer thickness, coal pillar supporting pressure, coal bed cohesion and internal friction angle, friction coefficient of the coal bed and the contact surface of the top and bottom plates and the like.

The research and analysis on the width of the plastic zone of the coal pillar can show that the stable and reasonable width of the coal pillar has important influence significance on the load acting on the coal pillar. The width x of the plastic zone in the process of coal pillar side mining is obtained by the analysis₀A theoretical calculation formula of (2), and x₀The size of the coal seam is influenced by various factors such as mining thickness, mining depth, layer thickness, coal pillar supporting pressure, coal seam cohesion, internal friction angle, friction coefficient of a contact surface of the coal seam and a top floor plate and the like. When the sum of pillar both sides plastic zone width is greater than the pillar and stays to establish the width, then the plastic zone that is located the pillar both sides will take place to link up, and this will directly make the pillar all be the plastic failure state, and its stability also reduces thereupon, and the width that the last pillar of coal seam all got into the plastic yield state after stoping is: l is less than or equal to 2x₀。

Prerequisites for the coal pillar to maintain its stable state are: when the two sides of the coal pillar are in a plastic deformation state, an elastic core with a certain width is formed in the center of the coal pillar, and the minimum width of the elastic core is 1-2 times of the height of the coal pillar. Therefore, the minimum width B that keeps the pillar stable can be expressed as:

B＝2x₀+(1～2)M

substituting the formula, namely:

as a further improvement of the scheme, the reasonable width calculation of the coal pillar in the first step is specifically as follows:

(1)11_{on the upper part}Coal bed pillar set-up calculation

From the geological data of the mine and the rock physical mechanical test parameters, 11_{On the upper part}The values of all parameters of the coal bed are as follows: m is 1.60M, and M is a linear,

p_i＝0，ξ＝2.846，H＝229m，γ＝25KN/m₃k is 4.02, C is 1.3MPa, and f is 0.2; the width x of the plastic zone of the coal pillar when one side is mined₀Comprises the following steps:

according to the calculation formula of the width of the coal pillar plastic zone proposed by A.H.Wilson, the following can be known:

x₀＝0.00492MH＝1.80m

substituting the above parameters into the above formula to obtain x₀1.86m and 1.80m respectively, so that x is taken₀1.86m, the minimum width of the coal pillar in a stable state can be obtained according to the formula: 6.92m, 11_{On the upper part}The width of the coal pillar of the working face of the coal bed can be stable when being more than 6.92 m; 11_{On the upper part}When the width of the coal pillar on the working surface of the coal bed is reserved to be 15m, the requirement for forming a stable coal pillar is met; thus, the upper coal seam 11_{On the upper part}The probability of overall instability and damage of the remaining coal pillar in the goaf after the coal seam is recovered is very low, and the stable coal pillar will damage the lower coal seam 11_{Lower part}The arrangement of coal seam mining roadways and the selection of support parameters have important influences;

(2)11_{lower part}Coal bed pillar set-up calculation

From the geology of the mineData and rock physical mechanical test parameters can be known, 11_{Lower part}The values of all parameters of the coal bed are as follows: m is 4.50M, and M is the same as the total weight of the alloy,

p_i＝0，ξ＝2.49，H＝231.7m，γ＝25KN/m³k is 3.84, C is 1.5MPa, and f is 0.2; the width x of the plastic zone of the coal pillar when one side is mined₀Comprises the following steps:

the calculation formula of the width of the coal pillar plastic zone proposed by A.H.Wilson can be obtained as follows:

x₀＝0.00492MH＝5.11m

the formula can be used to obtain: x is the number of₀Respectively as follows: 4.75m, 5.11m, so x₀Taking 5.11m, the minimum width of the coal pillar in a stable state can be obtained according to the formula: 14.72m, determined 11 taking into account a certain safety factor_{Lower part}The size of a reasonable stable coal pillar on the working surface of the coal bed is 20 m;

11_{lower part}The arrangement of coal pillars on the working face of the coal seam needs to be considered 11_{On the upper part}Coal seam pair 11_{Lower part}The influence of the working surface of the coal seam is ensured to be 11_{Lower part}Normal recovery and effective connection of the coal seam working face; thus by proposing 11_{Lower part}The coal seam mining roadway layout scheme is simulated and compared through numerical simulation software, and then a reasonable roadway layout mode and a reasonable coal pillar reserved width are determined

The invention has the beneficial effects that:

compared with the prior art, the method for the same-direction inward-staggered roadway layout in the ultra-close coal seam mining is realized by the following steps:

the first step is as follows: the method is characterized in that the coal seam, the coal quality and the structure exposure condition of the No. 11 coal seam four mining area and the hydrogeological condition of the mining area are used, the No. 11 coal seam four mining area is subjected to the comparison of an internal wrong type arrangement method, an external wrong type arrangement method and an internal same direction wrong type arrangement method through the geological condition investigation, the engineering analogy, the theoretical calculation and the numerical simulation method of mine productionFour-mining-area coal seam 11_{On the upper part}、11_{Lower part}Determining that a same-direction inward-staggered scheme is adopted for the crossheading arrangement of the coal seam working face, and determining a reasonable mining connection sequence;

the fourth step: determining the roadway layout, the mining process and the equipment type selection of a first mining working face of No. 11 coal seam four-mining area, and determining 11 coal seam four-mining area 11_{On the upper part}First-hand working face, i.e. 11_{On the upper part}401 arrangement of the working surfaces. The invention can ensure the safe production of the mine, improve the resource recovery rate of the No. 11 coal bed and increase the economic benefit of enterprises.

Drawings

The following detailed description of embodiments of the invention is provided in conjunction with the appended drawings, in which:

FIG. 1 is a bottom rock formation slip line field and bottom rock formation yield failure depth;

FIG. 2 is a distribution diagram of the plastic zone of the lower plate at different lengths of the working surface, wherein (a), (b), (c) and (d) are respectively schematic diagrams of the working surface at lengths of 150m, 180m, 210m and 240 m;

FIG. 3 is a simplified diagram of the distribution of concentrated stress of coal pillars on a bottom plate;

FIG. 4 is a schematic diagram of the calculation of uniform load distribution;

FIG. 5 is a linear load calculation diagram;

FIG. 6 is a stress diffusion cloud chart of coal pillar base plates with different widths, wherein (a), (b), (c) and (d) are schematic diagrams of coal pillars with widths of 5m, 8m, 12m and 15m respectively;

FIG. 7 is a staggered arrangement;

FIG. 8 is a staggered arrangement;

FIG. 9 is a co-directional staggered arrangement;

FIG. 10 is a numerical calculation model;

fig. 11 is a cloud chart of vertical stress distribution in different roadway layout schemes, wherein (a), (b), and (c) are schematic diagrams of a first scheme, a second scheme, and a third scheme, respectively;

FIG. 12 is a cloud of shear stress distributions for different roadway layout scenarios; wherein (a), (b) and (c) are respectively schematic diagrams of a scheme I, a scheme II and a scheme III;

FIG. 13 is a plastic zone profile for different roadway layout schemes; wherein (a), (b) and (c) are respectively schematic diagrams of a scheme I, a scheme II and a scheme III;

FIG. 14 is a cloud chart of vertical stress distribution of surrounding rocks at different internal offset distances; wherein (a), (b), (c) and (d) are schematic diagrams of different stagger distances of 10m, 12m, 15m and 20m respectively;

FIG. 15 is a cloud chart of horizontal stress distribution of surrounding rock at different internal offset distances, wherein (a), (b), (c), and (d) are schematic diagrams of different offset distances of 10m, 12m, 15m, and 20m, respectively;

FIG. 16 is a cloud chart of vertical stress distribution of surrounding rock under different coal pillar widths, wherein (a), (b), (c) and (d) are respectively schematic diagrams of different coal pillar widths of 10m, 15m, 20m and 25 m.

Detailed Description

According to the invention, through a theoretical calculation and numerical simulation comprehensive method, the damage influence of different working face lengths on the bottom plate, the diffusion influence range of coal pillars with different widths on the bottom plate and three different roadway arrangement schemes are analyzed and researched, and the roadway arrangement parameters are selected. And a solid foundation is laid for supporting the roadway and saving the cost.

Analysis of destructive bottom plate after mining of upper coal seam

In the short-distance coal seam downward mining sequence, the coal pillars left after the upper group of coal seams are mined can destroy and influence the bottom rock layer, and further the top plate of the coal pillars is influenced by the mining of the upper group of coal seams when the lower group of coal seams are mined, so that when a reasonable arrangement mode of a stoping roadway of the lower group of coal seams is selected, the damage depth of the coal pillars left in the goaf of the upper group of coal seams on the bottom plate and the stress distribution characteristics of surrounding rocks below the coal pillars need to be analyzed at first.

1、11_{On the upper part}Depth grinding for maximum damage of bottom plate in coal seam miningIs especially suitable for the treatment of diabetes

(1) Theoretical calculation of

During the stoping period of the working face of the upper group of coal seams, the initial stress balance in the bottom plate of the coal seams is influenced by the mining of the working face, so that shearing and stretching damage is generated, and the research on the damage depth and range of the bottom plate rock stratum of the goaf provides a theoretical basis for the stoping roadway arrangement and surrounding rock control of the lower group of coal seams.

When the pressure applied to the rock stratum under the bottom plate of the goaf exceeds the maximum value which can be borne by the rock stratum, the bottom plate rock stratum can generate plastic deformation in a certain range. When the pressure borne by the bottom plate rock stratum continues to increase, the bottom plate rock stratum is completely broken, and then the plastic zones in the pressure influence range are connected into a whole, so that bottom bulging of the goaf is caused, the plastic zone rock mass moves in the goaf, a continuous slip surface is gradually formed, and the goaf bottom plate rock stratum is influenced by maximum damage. The sliding line field and the damage depth of the floor generated by the floor of the goaf of the upper group of coal seams under the influence of the supporting pressure are shown in figure 1.

The slip line field of the rock mass inside the bottom plate in fig. 1 is divided into three areas: an active limit zone (I), a transition zone (II) and a passive limit zone (III). After the upper group of coal seams are mined, the rock stratum of the bottom plate of the goaf is under the action of supporting pressure, and when the supporting pressure exceeds the ultimate strength of a rock body in an active ultimate region, the rock stratum of the bottom plate can generate plastic deformation; the bottom plate rock stratum receives fore-and-aft supporting pressure effect, and then causes horizontal inflation, produces the rock mass in the passive limit district of expanded rock mass extrusion, and the passive limit district is transferred to stress simultaneously, and the transition region produces the squeezing action through stress transfer law to the rock mass in the passive limit district. The rock mass in the transition region and the passive limit region is under the action of the rock mass in the active limit region, so that the rock mass in the transition region and the passive limit region extends and expands towards the direction of the goaf, and the process is the extension pressure action of the bottom plate rock mass.

by

According to the formula:

Wherein:

m is mining height;

γ — average volume force of overburden;

h, mining depth;

c-coal bed cohesion;

-an internal angle of friction of the coal seam;

f is the friction coefficient of the coal bed and the top and bottom plates;

xi-the triaxial stress coefficient,

-floor formation internal friction angle;

p_i-resistance of the support to the coal slope.

p_i＝0，ξ＝2.846，H＝290m，

γ＝25KN/m³k is 4.02, C is 1.3MPa, and f is 0.2. Substituting each parameter into formula (2-5), calculating to obtain 11_{On the upper part}The maximum damage depth of the coal seam mining to the bottom plate is 2.45 m. Consider that 11_{On the upper part}Caving and mine pressure phenomena during the hard roof extraction of the coal seam, therefore 11_{On the upper part}The damage depth of the coal seam mining to the bottom plate can reach more than 2.45m, and the arrangement 11 is arranged_{Lower part}When the coal seam mining roadway and the roadway support parameters are selected, 11 need to be considered_{On the upper part}The destructive influence of coal seam mining on the floor.

(2) Numerical simulation

Using numerical simulation software, for 11_{On the upper part}And (3) carrying out numerical calculation analysis on the damage depth of the bottom plate after the mining of the 401 working face under the condition of different working face lengths. The simulation scheme is thatUnder the same conditions, the working face lengths were selected to be 150m, 180m, 210m, and 240 m. The range of damage to the floor after recovery is shown in fig. 2(a) to 2 (d).

As is clear from FIGS. 2(a) to 2(d), 11_{On the upper part}After the recovery of the 401 working face is finished, the plastic area is integrally distributed in a U shape along the inclined direction of the working face, and the damage depth of the bottom plate along the length of the working face is gradually increased. When the length of the working surface is 150m, the damage depth of the bottom plate is 0.8-1.2 m, and the average depth is 0.95 m; when the length of the working surface is 180m, the damage depth of the bottom plate is 0.8-1.4 m, and the average damage depth is 1.05 m; when the length of the working surface is 210m, the damage depth of the bottom plate is 1.2-1.98 m, and the average damage depth is 1.54 m; when the length of the working surface is 240m, the damage depth of the bottom plate is 1.25-2.23 m, and the average damage depth is 1.89 m; the distance between coal seams in the four mining areas is 3.46m at the maximum, 2.01m at the minimum and 2.74m on average, so that the mining of the upper coal seam damages a bottom plate rock stratum, and the anchoring and supporting of a top plate of a lower coal mining roadway are difficult, so that the damage to the bottom plate can be reduced by selecting the reasonable length of the working surface of the upper coal group, and the maintenance of the lower coal roadway is facilitated. Comprehensive consideration determination 11_{On the upper part}The length of the working face of the four mining areas is 180-240 m, and the specific length is determined according to actual geological conditions in construction.

2、11_{On the upper part}Analysis of stress under coal pillar

(1) Theoretical analysis

The mining of the coal bed causes the stress of surrounding rocks of the mining space to be redistributed, so that concentrated stress is formed on coal pillars around the mining space, and the concentrated stress can be transferred and diffused to the bottom plate. The stress distribution rule of the coal pillar in the bottom rock stratum (the top plate of the lower coal seam) is researched, and the method has a guiding function for mastering the stress state and the mine pressure display characteristic of the lower rock stratum roadway, determining the reasonable position of the lower coal (rock) stratum roadway and selecting support parameters.

For longwall face mining, the roof is managed by a natural caving method, and the overlying rock stratum of the goaf periodically collapses along with the forward advance of the working face. Overburden on the whole working face of longwall mining is characterized by stage, subsection, migration and collapse. The overlying rock stratum in the middle of the working face is broken and collapsed to fill the goaf, and the overlying rock strata in the goaf at two ends are extended into the coal pillar and the coal body in front of the working face, and part of the overlying rock stratum is in a hinged suspension state, so that part of the self weight and the load of the overlying rock stratum are transferred into the coal pillar and the coal body of the working face in front of the coal pillar, and a supporting pressure area higher than the stress of the original rock is formed. For the plastic coal pillar, the bearing capacity of the coal pillar will change due to the greatly reduced stability of the coal pillar, and the concentration degree of the stress transferred to the coal (rock) layer of the bottom plate is obviously reduced correspondingly. When the width of the coal pillar is larger than the minimum width of the plastic coal pillar, an elastic nuclear area exists in the center of the coal pillar, the concentration degree of stress transmitted from the coal pillar to the bottom plate is increased, and correspondingly, a stress increasing area with a large influence range exists in a bottom plate coal (rock) layer below the coal pillar. The width of the coal pillar and the lithology of the coal bed and the top floor rock stratum have direct influence on the distribution range of the concentrated stress of the coal pillar on the bottom floor rock stratum.

According to the fact that a coal (rock) body is a homogeneous elastic body, the stress component sigma of a concentrated load q at any point in a semi-infinite plane body is applied by an elastic theory_x、σ_y、τ_xyThe calculation can be carried out according to the condition that the semi-infinite body bears normal uniformly distributed loads on the boundary, the simplified loads on the coal pillar bottom plate can be regarded as the combination of two load distribution forms of linear and uniform distribution, the generated stress components are respectively calculated, and then the stress components of any point in the bottom plate rock stratum can be obtained through superposition. The semi-plane body is provided with distributed force on the starting boundary AB section, and the concentration of the distributed force at each point is P. And the distance between the AB section and the origin O is xi, the stress of any point M is as follows under the action of a small load q (xi) d xi of the semi-infinite body under the plane strain condition:

when applying equation (2-7), the concentration q of the distribution force must be expressed as a function of ξ, which is then integrated. The calculation formulas of the uniformly distributed load and the linearly distributed load are given as follows:

③ evenly distributing the load

Wherein the formulas (2-7) and (2-8) are simultaneously rewritable as follows:

② linearly distributing the load

In the same way, the formulas (2-7) and (2-10) are rewritten as follows:

the load form of the residual section coal pillar after the mining of the upper coal seam in the close range is very complicated, and the two types of the load form are simplified; load is evenly distributed and linearly distributed. And (3) assuming that the coal pillars are uniformly loaded, under the condition of giving the width of the coal pillars, providing stress distribution curves of the concentrated stress of the coal pillars at different depths of the bottom plate, and further analyzing the transfer and diffusion rules of the concentrated stress of the coal pillars on the bottom plate.

(2) Numerical simulation

And according to the mine production geological report, establishing a model for carrying out numerical simulation calculation, and analyzing the diffusion of the coal pillar stress in the bottom plate. At 11 with_{On the upper part}401 working face and 11_{On the upper part}And 403, analyzing the stress diffusion rule of the bottom plate under different coal pillar widths by taking the coal pillar at the working surface section as an example. The simulation scheme is as follows: under the same other conditions, coal pillars with the widths of 5m, 8m, 12m and 15m are respectively selected for calculation. The calculation results are shown in fig. 6(a) to (d).

The distribution rule of the stress of the coal pillars with different widths on the bottom plate is summarized as follows:

the vertical stress transferred from the concentrated stress of the coal pillar to the coal (rock) layer of the bottom plate is diffused to the two sides of the coal pillar according to a certain angle. On the horizontal cross sections of the bottom plate with different depths, the closer the load is to the uniform distribution of the coal pillars, the smaller the distribution range of the stress is, and the larger the influence program is. On the contrary, the farther the load is uniformly distributed from the coal pillar, the larger the distribution range of the stress is, and the smaller the influence degree is.

Secondly, on horizontal cross sections of the bottom plate at different depths, two peak values are formed by the vertical stress from the center of the coal pillar, then the two peak values gradually attenuate along with the distance from the center of the coal pillar, and the attenuation speed is maximum at the edge of the coal pillar.

And thirdly, in a certain range, along with the gradual increase of the width of the coal pillar, the vertical stress peak value of the lower coal seam is gradually reduced, the position of the vertical stress peak value gradually moves towards the center of the coal pillar, and the vertical stress distribution curve is changed from the original 'unimodal' into the 'saddle shape', which indicates that the width of the coal seam has great influence on the vertical stress distribution of the lower coal seam.

(II) analysis of stability of coal pillars between crosswalks

The stability of the coal pillar left in the goaf after the coal seam is mined and the distribution rule of the stress of surrounding rocks are influenced by mining, stress concentration is formed on the coal pillar in the goaf left section of the working face, and the analysis of the stability of the coal pillar has important significance for researching the influence and damage rule of the concentrated stress in the coal pillar on the bottom plate. If the coal pillar is in a plastic yield state, the bearing capacity of the coal pillar can be obviously reduced, and the coal pillar can release a part of bearing pressure borne by the coal pillar, so that the stress concentration degree on the coal pillar is reduced, and the stability analysis of the upper coal layer left coal pillar has a good guiding function on the affected state of a top plate, the arrangement of a stoping roadway and the stability analysis of the lower coal layer coal pillar during the exploitation of the lower coal layer.

1. Width of plastic zone of coal pillar

Along with the propulsion of the stope face of the upper coal layer, the stress state of the coal body at the edge of the goaf can be changed due to the lateral supporting pressure effect of the rear coal pillar; elastic state-plastic state-fracture state development. The width of the coal pillar is B, and the range of the action of the supporting pressure on one side of the coal pillar is L₀And then the elastic-plastic deformation area and the vertical stress distribution of the coal pillar of the upper coal layer gob leaving roadway protection are as follows:

The research and analysis on the width of the plastic zone of the coal pillar can show that the stable and reasonable width of the coal pillar has important influence significance on the load acting on the coal pillar. The width x of the plastic zone in the process of coal pillar side mining is obtained by the analysis₀A theoretical calculation formula of (2), and x₀The size of the coal seam is influenced by various factors such as mining thickness, mining depth, layer thickness, coal pillar supporting pressure, coal seam cohesion, internal friction angle, friction coefficient of a contact surface of the coal seam and a top floor plate and the like. When the plastic area width of the two sides of the coal pillarAnd be greater than the coal pillar and reserve when establishing the width, then lie in the plastic zone of coal pillar both sides and will take place to link up, this will directly make the coal pillar all be the plastic destruction state, its stability also reduces thereupon, the width that the coal pillar of leaving over after the coal seam recovery all got into the plastic yield state is: l is less than or equal to 2x₀。

B＝2x₀+(1～2)M

substituting the formula, namely:

2. calculation of reasonable width of coal pillar

(1)11_{On the upper part}Coal bed pillar set-up calculation

p_i＝0，ξ＝2.846，H＝229m，γ＝25KN/m³k is 4.02, C is 1.3MPa, and f is 0.2. The width x of the plastic zone of the coal pillar when one side is mined₀Comprises the following steps:

x₀＝0.00492MH＝1.80m

substituting the above parameters into the above formula to obtain x₀1.86m and 1.80m respectively, so that x is taken₀1.86m, the minimum width of the coal pillar in a stable state can be obtained according to the formula:6.92m，11_{on the upper part}The width of the coal pillar of the working face of the coal seam can be stable when being more than 6.92 m. 11_{On the upper part}When the width of the coal pillar on the working surface of the coal bed is set to be 15m, the requirement for forming the stable coal pillar is met. Thus, the upper coal seam 11_{On the upper part}The probability of overall instability and damage of the remaining coal pillar in the goaf after the coal seam is recovered is very low, and the stable coal pillar will damage the lower coal seam 11_{Lower part}The arrangement of coal seam mining roadways and the selection of support parameters have important influences.

(2)11_{Lower part}Coal bed pillar set-up calculation

From the geological data of the mine and the rock physical mechanical test parameters, 11_{Lower part}The values of all parameters of the coal bed are as follows: m is 4.50M, and M is the same as the total weight of the alloy,

p_i＝0，ξ＝2.49，H＝231.7m，γ＝25KN/m₃k is 3.84, C is 1.5MPa, and f is 0.2. The width x of the plastic zone of the coal pillar when one side is mined₀Comprises the following steps:

x₀＝0.00492MH＝5.11m

the formula can be used to obtain: x is the number of⁰Respectively as follows: 4.75m, 5.11m, so x⁰Taking 5.11m, the minimum width of the coal pillar in a stable state can be obtained according to the formula: 14.72m, determined 11 taking into account a certain safety factor_{Lower part}The reasonable stable coal pillar size of the coal seam working face is 20 m.

11_{Lower part}The arrangement of coal pillars on the working face of the coal seam needs to be considered 11_{On the upper part}Coal seam pair 11_{Lower part}The influence of the working surface of the coal seam is ensured to be 11_{Lower part}Normal recovery and effective connection of the coal seam working face. Thus by proposing 11_{Lower part}And (3) a coal seam stoping roadway arrangement scheme is adopted, and simulation comparison is carried out through numerical simulation software, so that a reasonable roadway arrangement mode and a reasonable coal pillar reserved width are determined.

11 determination of layout plan of coal seam roadway

(I) 11_{Lower part}Coal seam roadway arrangement mode and comparison of good and bad factors

According to the spatial relationship between the mining roadway of the lower group of coal seams and the upper group of coal seams, the arrangement mode of the mining roadway of the lower group of coal seams is generally considered to be an internal staggered mode and an external staggered mode. Three roadway distribution scheme modes are designed according to the scheme:

1. staggered arrangement

11_{Lower part}The coal seam mining roadway is arranged at 11_{On the upper part}The inner offset distance is generally 3-5 m below the working surface of the coal bed;

2. staggered arrangement

11_{Lower part}The coal seam mining roadway is arranged at 11_{On the upper part}The outer offset distance of the coal seam stope face below the left coal pillar is generally 5-7 m;

3. in the same direction arranged in a staggered manner

11_{Lower part}The working faces of the coal seam are staggered in the same direction and are arranged below two different working face goafs of the upper coal seam, and the offset distance is more than 15 m.

Comparing the advantages and the disadvantages of the three arrangement modes: the staggered type roadway is easy to maintain and high in stability, but coal pillars between working faces are reserved greatly, the working faces are shortened, and the recovery rate is low; the staggered type roadway can ensure the length of a stope face and high stope rate to the maximum extent, but the roadway has large deformation and is difficult to maintain; the same-direction internal staggered arrangement integrates the advantages of the two arrangement modes, and in view of the two arrangement modes:

1. two crossroads of a lower coal seam are arranged below two different goafs of an upper coal seam in the same direction, and two roadways are positioned in a low stress area, so that the excavation and support difficulty of the roadways is reduced, and the maintenance is easy;

2. the coal pillar reserved between the working faces of the lower coal seam is not restricted by the mining of the upper coal seam, so that the reasonable deployment of the mining of the lower coal seam is liberated, and the coal loss caused by the overlarge reserved coal pillar is completely avoided;

3. the offset distance in the lower coal seam roadway is more flexible, and the influence of concentrated stress transfer and diffusion of residual coal pillars in the upper coal seam on the lower coal seam roadway can be completely avoided by adopting larger offset distance.

4. The width of the coal pillar for mining the lower coal seam can be greatly reduced by reserving the coal pillar, and even a way of reserving a narrow coal pillar for protecting the roadway can be adopted, so that the recovery rate of a mining area can be obviously improved, and the reasonable and sustainable mining of coal resources is realized.

(II) four-mining area 11_{Lower part}Coal seam area stoping roadway arrangement scheme

In view of the foregoing, reference 11_{On the upper part}Distribution rule of stress under bottom plate of coal pillar left after stoping on working face 11_{Lower part}The physical and mechanical properties of the top and bottom rock layers of the coal seam and the stability of surrounding rocks of the mining roadway of the upper and lower coal seams are classified, and three different types of 11 are provided_{Lower part}The arrangement scheme of the coal seam mining roadway is specifically shown in fig. 7-9.

The first scheme is as follows:

11_{lower part}The 401 working face return air channel is arranged at 11_{On the upper part}401 under a goaf; 11_{Lower part}The 401 working face haulage roadway is arranged at 11_{On the upper part}Under the gob 401, the internal dislocation is 11_{On the upper part}401 face side, staggered.

In this scheme, 11_{Lower part}The 401 working face transportation lane and the return airway are both arranged at 11_{On the upper part}In the stress reduction zone under the 401 goaf, the stress of surrounding rock is relatively small, and 11_{On the upper part}The coal bed coal pillar has reasonable stagger distance and relatively low stress imbalance degree, 11_{Lower part}The size of the coal pillar reserved on the 401 working face section is larger, 11_{On the upper part}The length of the working surface of the coal bed is reduced, and the extraction rate of coal resources is low.

Scheme II:

11_{lower part}401 working face haulage roadway and 11_{Lower part}The 401 working face return airway is all arranged at 11_{On the upper part}Under the 401 face coal pillar, the external fault is 11_{On the upper part}401 face coal pillar edges are some distance apart.

In the scheme, the difficulty of controlling the surrounding rock of the roadway is easily increased during the working face extraction period, 11_{Lower part}The length of the working face with reasonable width reserved on the 401 working face section coal pillar meets the production requirement, and the coal extraction rate is high.

The third scheme is as follows:

11_{lower part}401 face haulage roadway arrangementAt the boundary of the well field, 11_{Lower part}The 401 working face return airway is arranged at 11_{On the upper part}Below the 401 face gob, 11_{Lower part}The 401 working face air inlet lane is arranged at 11_{On the upper part}Below the 401 face gob, i.e. "equidirectional stagger in" 11_{On the upper part}401 working surface arrangement.

In this scheme, 11_{Lower part}The 401 working face transportation lane and the return airway are both arranged in the stress reduction area, so that the tunnel driving is facilitated, the length of the working face is prolonged, the coal extraction rate is high, but the phenomenon of stress concentration is easily caused during the extraction of the anchoring working face without a stable rock stratum on the upper portion of the tunnel, and the difficulty in maintaining the tunnel is increased.

In order to further determine the reasonable arrangement mode of the short-distance coal seam mining roadway of the Taishan Longan coal industry company, the proposed three schemes need to be simulated and calculated through numerical simulation software, so that the arrangement mode of the roadway is determined, and finally, the arrangement parameters such as the reasonable offset of the roadway are determined.

(III) numerical simulation of mining roadway layout scheme

From the above, 11 is proposed_{Lower part}Three arrangement schemes of coal seam mining laneway, wherein FLAC is adopted^3DNumerical simulation software pair 11_{Lower part}Carrying out numerical simulation research on the stress distribution characteristic, the plastic region damage depth and the damage characteristic of the roadway when the coal seam mining roadway has different internal offset distances, initially selecting the lower coal seam mining roadway layout scheme, and finally determining the reasonable internal offset distance of the lower coal seam mining roadway which is 11_{Lower part}The reasonable width of the coal pillar on the working face of the coal seam is reserved for providing reference.

1. Establishment of numerical model

According to the engineering geological conditions of No. 11 coal seam four mining areas, FLAC is utilized^3DThe numerical calculation platform establishes a numerical calculation model, comprehensively considers influence factors of all aspects, divides the model into 10 layers, and selects the size of the numerical model: 500 multiplied by 100 multiplied by 200m, the numerical model is divided into 315000 units, 354860 nodes, the displacement in the horizontal direction is limited by the four boundaries of the model, the displacement in the vertical direction is limited by the bottom of the model, the vertical load is applied to the top of the model by 5.53MPa, and the numerical calculation model is shown in FIG. 10.

The numerical calculation model calculation process is as follows:

(1) after the initial model applies load, starting calculation until the stress in the initial model is balanced;

(2) the model after the initial stress field is balanced is excavated and the upper coal seam 11 is mined_{On the upper part}401, extracting 5m in each cycle of the working face, and calculating until the model is balanced;

(3) in order to further arrange 11 mining roadways of a lower coal seam_{On the upper part}Deep analysis and calculation are carried out under the 401 working face goaf, and 11 pairs of the models are calculated under the state of model balance in the step (2)_{On the upper part}Corresponding physical and mechanical parameters are assigned to the overlying rock stratum and the collapsed waste rock of the goaf on the 401 working face, namely the elastic structure filling of the goaf is calculated to be balanced;

(4) beginning to excavate the lower coal seam 11_{Lower part}401 working face stoping lane, according to it and 11 respectively_{On the upper part}And (3) excavating the 401 working face at different staggered distances.

2. Numerical simulation result analysis of different roadway arrangement schemes

Aiming at three roadway arrangement schemes provided by the front section, FLAC is adopted^3DAnd performing numerical simulation calculation on the three schemes in different arrangement modes by software. The calculation results were analyzed as follows:

(1) roadway surrounding rock stress distribution characteristic result analysis

11_{Lower part}The vertical stress distribution of different arrangement schemes of the mining roadway of the 401 working face is shown in fig. 11(a) - (c).

As shown in FIG. 11(a), the first embodiment 11_{Lower part}The maximum vertical stress of a mining roadway of a 401 working face is 1.5MPa, and the area where the roadway is located is a stress reduction area; as shown in FIG. 11(b), the second embodiment 11_{Lower part}The 401 working face stoping roadway is influenced by concentrated stress of the coal pillars left on the upper coal seam, and the maximum vertical stress reaches 12 MPa; as shown in FIG. 11(c), the third embodiment 11_{Lower part}Most of the 401 working face stoping lane is located in a vertical stress reduction area, only the side close to the coal pillar left on the upper coal seam is still affected by concentrated stress, the maximum vertical stress is 2.5-5 MPa, but the whole stoping lane is still located in the stress reduction area, the roadway stress environment is good, and the maintenance is easy.

11_{Lower part}Different cloth of 401 working face mining roadwayThe shear stress distribution under the mounting is shown in fig. 12(a) to (c).

As can be seen from FIG. 12(a), embodiment I11_{Lower part}The 401 working face stoping roadway is in a stress reduction area, and the maximum value of the shear stress is 2.5 MPa; as shown in FIG. 12(b), the second embodiment 11_{Lower part}The 401 working face stoping roadway is in a section with higher stress, and the maximum shearing stress reaches 5 MPa; as shown in FIG. 12(c), the third embodiment 11_{Lower part}The 401 working face stoping roadway is in a stress reduction area, and the shear stress is 3.5 MPa; and the roadway surrounding rock is less damaged in the first and third arrangement modes, and the maintenance is easy.

11_{Lower part}The damage ranges of plastic zones of different arrangement schemes of the mining roadway of the 401 working face are shown in 13(a) to (c),

as can be seen from FIG. 13(a), embodiment I11_{Lower part}The damage depth of the plastic zone on the side of the working face stoping roadway close to the upper coal seam remaining coal pillar is 1-3 m, and the upper coal seam goaf upper rock stratum gradually tends to a stable state after caving, 11_{Lower part}The bottom plate and two sides of the 401 working face transportation roadway are not obviously subjected to yield failure, and the roadway maintenance is facilitated; as can be seen from FIG. 13 (b), embodiment two 11_{Lower part}Staggered coal seam 11 of 401 face stoping roadway_{On the upper part}In the 401 working face goaf, the failure depth of the plastic zones on two sides exceeds 3m, and shear failure and tensile failure occur, and the failure depth range of the top plate is 11_{On the upper part}The destruction ranges of the surrounding rocks of the 401 working face are connected into a whole to make 11_{Lower part}The maintenance difficulty of the 401 working face transportation lane is increased, and the purpose of safe and efficient production is not facilitated; as can be seen from FIG. 13 (c), scheme III 11_{Lower part}401 working face conveying lane is uniformly arranged at 11_{On the upper part}Under the 401 working face goaf, the shearing failure and the stretching failure of the roadway bottom plate and two sides are lighter, and the failure depth of the top plate reaches 11_{On the upper part}The 401 working face haulage roadway surrounding rock damage range is through, the whole roadway is located in the stress reduction area, and the influence of the coal pillar on the coal seam is not easy to receive, so that the control of the roadway surrounding rock is facilitated.

In summary, combine the mine production practice with 11_{Lower part}The method comprises the following steps of carrying out classification research on the stability of surrounding rocks of a coal seam mining roadway, analyzing the stress distribution rule and the plastic region damage range of the surrounding rocks under different roadway arrangement schemes, and preliminarily determining miningAnd (5) performing roadway arrangement by using a scheme III, namely 'equidirectional inward staggering'.

3. Numerical simulation analysis of different-offset mining roadway

The analysis results are integrated, and a 'same-direction and internal-error' arrangement mode is adopted to establish 11_{Lower part}And (3) respectively simulating the stress distribution rules and characteristics of the mining roadway of the 401 working face under different staggers (10m, 12m, 15m and 20m) and analyzing the calculation results to determine the reasonable arrangement stagger of the mining roadway of the lower coal seam.

The analysis of the stress distribution characteristic results of the surrounding rock of the roadway is shown in fig. 14(a) to (d):

from fig. 14(a) - (d), it can be seen that the maximum value of the vertical stress of the mining roadway is 15MPa when the offset is 10m, and the influence of the side wall rock close to the coal pillar is serious; the maximum vertical stress of the mining roadway is 8MPa when the offset is 12 m; when the offset distance is 15m, the maximum value of the vertical stress of the mining roadway is 6 MPa; when the offset is 20m, the maximum value of the vertical stress of the mining roadway is 5.8MPa, and after the offset exceeds 15m, the stress of surrounding rock of the roadway is stable and is in a lower stress range, so that the roadway is easy to maintain.

The horizontal stress distribution diagrams of the surrounding rock at different internal offset distances are shown in fig. 15(a) to (d).

As can be seen from fig. 15(a) - (d), the maximum horizontal stress of the roadway is 5MPa when the offset is 10m, and the influence of the side wall rock close to the pillar is severe; the maximum value of the horizontal stress of the roadway is 4.2MPa when the offset is 12 m; when the offset distance is 15m, the maximum value of the vertical stress of the mining roadway is 3 MPa; when the offset is 20m, the maximum value of the vertical stress of the mining roadway is 2.8MPa, and after the offset exceeds 15m, the surrounding rock of the roadway is in a lower stress range, so that the roadway is easy to maintain.

4. Numerical simulation analysis of different coal pillar extraction roadways

The above analysis results are combined to establish 11_{Lower part}The method comprises the steps of respectively simulating the stress distribution law and characteristics of a 401 working face stoping roadway under different coal pillar widths, analyzing and comparing the calculation results, and determining the reasonable width of the coal pillar of the lower coal face stoping roadway by combining theoretical analysis.

From fig. 16(a) to (d), it is understood that the maximum value of the vertical stress of the surrounding rock is 5MPa when the coal pillar width is 10m, and the influence of the surrounding rock is serious; when the width of the coal pillar is 15m, the maximum value of the vertical stress of the surrounding rock is 3.8MPa, and the whole surrounding rock of the roadway is in a stress reduction area; when the width of the coal pillar is 20m, the maximum value of the vertical stress of the surrounding rock is 3.6 MPa; when the width of the coal pillar is 25m, the maximum value of the vertical stress of the surrounding rock is 3.6MPa, after the width of the coal pillar exceeds 15m, the stress of the surrounding rock of the roadway is in a lower stress range, the change degree is not large, and the whole body is in a stable state.

By combining the analysis, the advantages of the roadway arrangement mode of 'equidirectional inward dislocation' are obvious, the maintenance of the surrounding rock of the roadway is facilitated, the working face is lengthened, the recovery rate of coal resources is improved, and the equidirectional inward dislocation is determined to be 20m and 11m_{Lower part}The width of the coal pillar at the working face section is 20m, and specific parameters are adjusted according to the actual pressure condition in construction.

The working face roadway layout specifically comprises the following steps:

(I) 11_{On the upper part}Coal seam face arrangement

11_{On the upper part}The coal seam is provided with 5 working faces which are respectively 11_{On the upper part}401 work surface, 11_{On the upper part}403 work surface, 11_{On the upper part}405 work surface, 11_{On the upper part}407 working face, 11_{On the upper part}409 work surface.

11_{On the upper part}409 working face length 76m, and the other working face lengths are 240 m; 11_{On the upper part}401 working face air inlet along groove distance well field boundary safety coal pillar 15m, 11_{On the upper part}409 the distance between the return air crossheading of the working face and the boundary line of the third mining area and the fourth mining area is 5 m; the rest coal pillars between the crossheading of each working face are all 15 m.

(II) 11_{Lower part}Coal seam face arrangement

11_{Lower part}The coal seam is provided with 5 working faces which are respectively 11_{Lower part}401 work surface, 11_{Lower part}403 work surface, 11_{Lower part}405 work surface, 11_{Lower part}407 working face, 11_{Lower part}409 work surface.

11_{Lower part}409 working face length 162m, and the length of each of the other working faces is 215 m; 11_{Lower part}409 working face return air crossheading inner dislocation 11_{On the upper part}409 return air crossheading of the stope face is 5 m; 11_{Lower part}401 air intake crossheading channel outside stagger 11_{On the upper part}Air inlet of 401 working surfaceThe groove 15m is arranged along the security coal pillar at the boundary of the well field; 11_{Lower part}401 working face return air crossheading and 11_{Lower part}403 air intake runner arranged at 11_{On the upper part}Below the 401 face gob, 11 of which_{Lower part}401 return air crossheading for working face 11_{On the upper part}401 return air crossheading 47.5 m; 11_{Lower part}403 working face air inlet crossheading inner error 11_{On the upper part}401, the working face return air crossheading is 22.5 m; all the other working faces are arranged at 11 in a staggered way along the same direction_{On the upper part}The internal staggered distance is 25-40 m below the goaf of the adjacent working face of the coal seam, and the coal pillars between the crossheading are 20 m; comprehensively considering the factors of large span of open-off cut tunnel of working face, difficult support and the like, 11_{Lower part}The cutting holes of each working face of the coal seam are staggered 11 times_{On the upper part}And 15m of coal seam open-off cuts.

To reduce 11 to the maximum_{On the upper part}401 goaf coal pillar support pressure and lateral bearing pressure pair 11_{Lower part}Influence of 401 face air intake crossheading, mining 11_{On the upper part}When the working face is 401, roof cutting and pressure relief measures such as directional presplitting blasting, deep hole hydraulic fracturing and the like are taken for the working face air inlet crossheading, and the top plate at the end of the crossheading is promoted to fully collapse.

The mining linking sequence specifically comprises:

determination of interval between mining of coal seam 11 and coal seam 11

When the short-distance coal seam is mined downwards, after the upper coal seam is mined, the surrounding rock stress is secondarily balanced under the mining influence, the decisive factors of the re-stabilization time of the goaf and the rock layer above the goaf are complex, and the decisive factors mainly include factors in geological occurrence aspects such as the thickness of a covering layer, the thickness of a coal rock layer, the properties of the surrounding rock, geological structures, underground water and the like, and also include the influences of other factors such as a coal mining method, roadway arrangement, final mining time and the like.

The mining situation in the industry is analyzed comprehensively and preliminarily determined 11_{Lower part}The coal seam roadway tunneling time is corresponding to 11_{On the upper part}The construction can be started at least over 12 months after the coal seam mining is finished, and the construction time is 11_{On the upper part}The coal seam is separated by 2 working face strips.

Second, the mining linking sequence

The back mining is adopted in the No. 11 coal seam mining area of the four mining areas, and the comprehensive examination is carried outThe overall mining engagement and production requirements of the mine, 11_{On the upper part}、11_{Lower part}Alternate stoping of the coal seam working face is carried out in the following sequence:

(I) 11_{On the upper part}Coal seam mining sequence

11_{On the upper part}401 work surface → 11_{On the upper part}403 work surface → 11_{On the upper part}405 work surface → 11_{On the upper part}407 working face → 11_{On the upper part}409 work surface.

(II) 11_{Lower part}Coal seam mining sequence

11_{Lower part}401 work surface → 11_{Lower part}403 work surface → 11_{Lower part}405 work surface → 11_{Lower part}407 working face → 11_{Lower part}409 work surface.

(III) 11_{On the upper part}、11_{Lower part}Coal seam alternate mining sequence

11_{On the upper part}401 work surface → 11_{On the upper part}403 work surface → 11_{On the upper part}405 work surface → 11_{Lower part}401 work surface → 11_{On the upper part}407 working face → 11_{Lower part}403 work surface → 11_{On the upper part}409 working face → 11_{Lower part}405 work surface → 11_{Lower part}407 working face → 11_{Lower part}409 work surface.

The above embodiments are not limited to the technical solutions of the embodiments themselves, and the embodiments may be combined with each other into a new embodiment. The above embodiments are only for illustrating the technical solutions of the present invention and are not limited thereto, and any modification or equivalent replacement without departing from the spirit and scope of the present invention should be covered within the technical solutions of the present invention.

Claims

1. A method for arranging equidirectional and inward staggered roadways in ultra-close coal seam mining is characterized by comprising the following steps: the method comprises the following steps:

2. The method for arranging the equidirectional and inwards staggered roadways for the mining of the coal seams in the extremely close range according to claim 1, wherein the method comprises the following steps: the theoretical calculation and numerical simulation method in the first step specifically comprises the destructive analysis of the mined bottom plate of the upper coal seam and the stability analysis of the coal pillar between the crossheading, wherein the destructive analysis of the mined bottom plate of the upper coal seam comprises 11_{On the upper part}Research on maximum damage depth of bottom plate in coal seam mining, 11_{On the upper part}And (3) analyzing the stress under the coal pillar of the coal bed, wherein the stability analysis of the coal pillar between the crossheading comprises the calculation of the width of a plastic zone of a stoping coal pillar and the reasonable width of the coal pillar.

3. The method for arranging the equidirectional and inwards staggered roadways for the mining of the coal seams in the extremely close range according to claim 1, wherein the method comprises the following steps: in the first step, the No. 11 coal seam four mining areas 11 are subjected to_{On the upper part}、11_{Lower part}The method for determining the arrangement of the coal seam working face crossheading adopts a 'same-direction inward-staggered' scheme, and specifically comprises 11_{Lower part}Coal seam roadway arrangement mode, comparison of good and bad factors and four mining areas 11_{Lower part}And (3) carrying out numerical simulation on the arrangement scheme of the coal seam area mining roadway and the arrangement scheme of the mining roadway.

4. According to the rightThe method for arranging the equidirectional and inwards staggered roadways for mining the coal seams in the extremely close range according to claim 1, is characterized in that: the working face roadway layout mode of the No. 11 coal seam four-mining area in the second step is as follows: comprises 11_{On the upper part}Coal seam working face layout, 11_{Lower part}And arranging a coal seam working surface.

5. The method for arranging the equidirectional and inwards staggered roadways for the mining of the coal seams in the extremely close range according to claim 1, wherein the method comprises the following steps: the said connection sequence includes 11_{On the upper part}Coal seam mining sequence, 11_{Lower part}Coal seam mining sequence, 11_{On the upper part}、11_{Lower part}And (4) alternately mining coal beds.

6. The method for arranging the equidirectional and inwards staggered roadways for the mining of the coal seams in the extremely close range according to claim 2, wherein the method comprises the following steps: the 11 is_{On the upper part}The theoretical analysis of the research on the maximum damage depth of the bottom plate in coal seam mining is as follows:

by

According to the formula:

Wherein:

m is the mining height, and M is the mining height,

Gamma-the average volume force of the overburden,

h, mining depth;

c-coal bed cohesion;

-an internal angle of friction of the coal seam;

f is the friction coefficient of the coal bed and the top and bottom plates;

xi-the triaxial stress coefficient,

-floor formation internal friction angle;

p_i-resistance of the support to the coal slope;

p_i＝0，ξ＝2.846，H＝290m，

7. An extremely close range according to claim 1The method for mining the same-direction staggered roadway from the coal seam is characterized by comprising the following steps of: in the first step 11_{On the upper part}The stress analysis under the coal bed coal pillar is as follows:

the mining of the coal bed causes the stress of surrounding rocks of the mining space to be redistributed, so that concentrated stress is formed on coal pillars around the mining space, and the concentrated stress can be transferred and diffused to the bottom plate; the stress distribution rule of the coal pillars in the bottom rock layer (the top plate of the lower coal layer) is researched, and the method has a guiding function for mastering the stress state and the mine pressure display characteristics of the lower rock layer roadway and determining the reasonable position of the lower coal (rock) layer roadway and the selection of support parameters;

according to the fact that a coal (rock) body is a homogeneous elastic body, the stress component sigma of a concentrated load q at any point in a semi-infinite plane body is applied by an elastic theory_x、σ_y、τ_xyThe calculation can be carried out according to the condition that the semi-infinite body bears normal uniformly distributed loads on the boundary, the simplified loads on the coal pillar bottom plate can be regarded as the combination of two load distribution forms of linear and uniform distribution, the generated stress components are respectively calculated and then superposed to obtain the stress component of any point in the bottom plate rock stratum; setting distributed force on a starting boundary AB section of a semi-plane body, wherein the concentration of the semi-plane body at each point is P; and the distance between the AB section and the origin O is xi, the stress of any point M is as follows under the action of a small load q (xi) d xi of the semi-infinite body under the plane strain condition:

evenly distributing load

Wherein the formulas (2-7) and (2-8) are simultaneously rewritable as follows:

② linearly distributing the load

In the same way, the formulas (2-7) and (2-10) are rewritten as follows:

8. The method for arranging the equidirectional and inwards staggered roadways for the mining of the coal seams in the extremely close range according to claim 1, wherein the method comprises the following steps: the analysis of the width of the plastic zone of the coal pillar recovered in the first step is specifically as follows:

the stress state of the coal body at the edge of the goaf can be changed due to the action of lateral supporting pressure on the rear coal pillar along with the propulsion of the stope face of the upper coal layer; elastic state-plastic state-rupture state develops. The width of the coal pillar is B, and the range of the action of the supporting pressure on one side of the coal pillar is L₀And then the elastic-plastic deformation area and the vertical stress distribution of the coal pillar of the upper coal layer gob leaving roadway protection are as follows:

The research and analysis on the width of the plastic zone of the coal pillar can show that the stable and reasonable width of the coal pillar has important influence significance on the load acting on the coal pillar. The width x of the plastic zone in the process of coal pillar side mining is obtained by the analysis₀A theoretical calculation formula of (2), and x₀The size of the coal seam is influenced by various factors such as mining thickness, mining depth, layer thickness, coal pillar supporting pressure, coal seam cohesion, internal friction angle, friction coefficient of a contact surface of the coal seam and a top floor plate and the like. When the sum of the widths of the plastic zones at the two sides of the coal pillar is larger than that of the coal pillarWhen reserving the width, then lie in the plastic zone of coal pillar both sides and will take place to link up, this will directly make the coal pillar all be the plastic failure state, its stability also reduces thereupon, the width that the last coal seam was retrieved the whole plastic yield state that gets into of the left over coal pillar of back is: l is less than or equal to 2x₀。

B＝2x₀+(1～2)M

substituting the formula, namely:

9. the method for arranging the equidirectional and inwards staggered roadways for the mining of the coal seams in the extremely close range according to claim 1, wherein the method comprises the following steps: the reasonable width calculation of the coal pillar in the first step is specifically as follows:

(1)11_{on the upper part}Coal bed pillar set-up calculation

p_i＝0，ξ＝2.846，H＝229m，γ＝25KN/m³k is 4.02, C is 1.3MPa, and f is 0.2; the width x of the plastic zone of the coal pillar when one side is mined₀Comprises the following steps:

x₀＝0.00492MH＝1.80m

(2)11_{lower part}Coal bed pillar set-up calculation

x₀＝0.00492MH＝5.11m

11_{lower part}The arrangement of coal pillars on the working face of the coal seam needs to be considered 11_{On the upper part}Coal seam pair 11_{Lower part}The influence of the working surface of the coal seam is ensured to be 11_{Lower part}Coal seam operationNormal extraction and effective connection of the faces; thus by proposing 11_{Lower part}And (3) a coal seam stoping roadway arrangement scheme is adopted, and simulation comparison is carried out through numerical simulation software, so that a reasonable roadway arrangement mode and a reasonable coal pillar reserved width are determined.