CN110630268A - Method for determining advancing direction offset of upper and lower co-mining working faces of double coal seams - Google Patents
Method for determining advancing direction offset of upper and lower co-mining working faces of double coal seams Download PDFInfo
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Abstract
The invention provides a method for determining the advancing direction offset of an upper and a lower co-mining working faces of double coal seams, which belongs to the technical field of coal mining and comprises the following steps: finding out an ideal offset range; according to the ideal offset range, the maximum depth H of the upper coal seam floor damage area under the condition of the limit bearing pressure is obtained by utilizing a limit bearing capacity calculation formula during rock-soil plastic slippagemaxCalculating a formula to obtain the maximum horizontal distance L of the upper coal seam floor to damage the rock stratummaxCalculating a formula; establishing a pressure stabilizing type and pressure reducing type mechanical model for simultaneously exploiting and advancing working faces of an upper coal seam and a lower coal seam in a double-coal seam mining direction, obtaining the maximum horizontal distance of a bottom plate of the upper coal seam to damage a rock stratum, the stress transmission angle of the bottom plate and the distance between the upper coal seam and the lower coal seam, and determining a stagger calculation formula of the pressure stabilizing type and the pressure reducing type advancing direction; and correcting the calculation result in the step 3. The method can effectively reduce the mine pressure of the working face of the coal seam under simultaneous mining in the overlapped area of the double coal seamsThe strength and the surface damage degree realize the high-efficiency green mining of double coal beds.
Description
Technical Field
The invention belongs to the technical field of coal mining, and particularly relates to a method for determining the advancing direction offset of upper and lower co-mining working faces of double coal seams.
Background
Coal is an important energy source in China, and in order to realize high-efficiency coal mining, coal enterprises begin to change from single-coal-seam mining to double-coal-seam mining simultaneously. The simultaneous mining of double coal seams mainly relates to two technical problems: firstly, the high-strength mining of double coal seams causes the overburden rock to move violently, so that the tensile stress on the earth surface is excessively concentrated, and the ecological environment on the earth surface is seriously damaged; and secondly, areas where the upper coal seam and the lower coal seam are arranged are mined simultaneously, surrounding rock stress of a working face of the lower coal seam is complex and severe, and the propelling speed and safety of the working face of the lower coal seam are seriously influenced.
For a long time, the mining technology and research conclusion of a single coal seam are mature, and the research on the mining of double coal seams mainly relates to the aspects of coal pillar reserving positions, stress concentration influence, mining modes and the like, and less relates to the research on the aspect of simultaneously mining and advancing direction offset of an upper coal seam and a lower coal seam. Under the background of high-efficiency coal mining, green mining and sustainable development, the reasonable offset distance of the advancing direction of the upper coal seam and the lower coal seam in the same mining working face is determined, the mining technology which gives consideration to the simultaneous safe and high-efficiency mining of the double-coal seam working face and the reduction of the ground surface damage is researched, and the method has important theoretical significance and practical value for the double-coal seam mining.
At present, for simultaneous mining of an upper coal seam and a lower coal seam in an overlapped area, a method of stopping mining and avoiding pressure is mostly adopted on site to solve the problems of large-area pressure of a working face of the lower coal seam, support crushing and the like, so that mine mining is continuously tense, and the production efficiency is low. Meanwhile, the high-intensity mining causes serious surface damage and continuous deterioration of the ecological environment. The existing double-coal-bed mining technology can not give consideration to safe and efficient mining and slow down surface damage, and does not research the advancing direction offset of the upper and lower co-mining working faces of the double coal beds.
Therefore, the method for determining the advancing direction offset of the upper and lower co-production working faces of the double coal seams is provided.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a method for determining the advancing direction offset of the upper and lower co-production working faces of double coal seams.
In order to realize the double purposes of safety, high efficiency and ground surface damage alleviation in the simultaneous mining process of the coal layer stacking areas, theoretical analysis and UDEC are applied2D(two-dimensional plane discrete unit method) numerical simulation and physical simulation combined method for analyzing different propulsion of upper and lower coal layer stacking areas on same mining working faceThe method comprises the steps of studying the mutual influence range and the mutual influence degree of the upper coal layer stacking area and the lower coal layer stacking area on the same mining working face in different advancing direction offset, establishing a pressure stabilizing type and pressure reducing type arrangement model of the upper coal layer stacking area and the lower coal layer stacking area on the same mining working face, determining a propelling direction offset calculation formula of 2 arrangement modes, and correcting and comparing 2 calculation results according to field mining practice experiences to obtain a reasonable offset determination method which gives consideration to safe and efficient mining and slows down earth surface damage. The method can effectively reduce the mining pressure intensity and the surface damage degree of the working face of the coal seam under simultaneous mining in the overlapping area of the double coal seams, and can realize the efficient green mining of the double coal seams.
The invention provides the following technical scheme:
a method for determining the advancing direction offset of the upper and lower co-mining working faces of double coal seams comprises the following steps:
the method comprises the following steps:
step 1. use of UDEC2DThe numerical simulation and physical simulation method is used for mastering the surrounding rock stress distribution rule and the surface subsidence rule of the upper and lower co-mining working faces of the double coal seams when the advancing direction of the working face is different in offset distance, analyzing the influence range and degree between the upper and lower working faces during simultaneous mining to obtain an ideal offset distance range, and providing scientific basis for theoretical analysis and model establishment;
step 2, according to the ideal offset range, selecting a calculation formula of the ultimate bearing capacity during rock-soil plastic slippage in the elastoplasticity theory, and obtaining the maximum depth H of the upper coal bed bottom plate damage area under the condition of ultimate bearing pressure by using the calculation formula of the ultimate bearing capacity during the rock-soil plastic slippagemaxCalculating a formula to obtain the maximum horizontal distance L of the upper coal seam floor to damage the rock stratummaxCalculating a formula;
step 3, establishing a pressure stabilizing type and pressure reducing type mechanical model for simultaneously exploiting the advancing direction of the working faces of the upper coal seam and the lower coal seam in the double-coal seam exploitation according to the numerical calculation and mechanical theory analysis results, comprehensively considering the maximum horizontal distance of the upper coal seam bottom plate to damage the rock stratum, the stress transmission angle of the bottom plate and the distance between the upper coal seam and the lower coal seam, and determining a stagger calculation formula of the pressure stabilizing type and the pressure reducing type advancing direction;
and 4, correcting the calculation result in the step 3 according to the practical experience and the actual measurement result of the field mining to obtain the optimal offset distance suitable for the field production in the initial mining stage of the advancing direction of the working faces of the upper coal seam and the lower coal seam and in the normal stoping period.
Preferably, in step 1, it is calculated according to a large number of numerical simulations, when the offset distance in the advancing direction of the upper and lower coal seam is less than 70m, the mining influence of the upper coal seam starts to affect the working face of the lower coal seam, the mining stress superposition gradually increases with the decrease of the offset distance, the peak value of the advanced support pressure of the working face of the lower coal seam continuously increases, when the offset distance arranged edge-to-edge is 0m, the value of the pressure of the lower coal seam over the front support reaches 11.38MPa, the curvature of the surface subsidence curve continuously increases with the decrease of the offset distance, and a decompression area and a pressure stabilization area exist in the mining process of the lower coal seam are obtained through analysis, so that a basis is provided for theoretical analysis and the determination of the strike offset formula.
Preferably, in the step 2, it is obtained that:
length of yield zone of coal wall position of working face:
maximum failure depth of the bottom plate of the upper coal layer:
the maximum horizontal distance for the upper coal bed bottom plate to damage the rock stratum:
wherein, the maximum damage depth point of the upper coal bed bottom plate is away from the horizontal distance of the working surface:
the maximum damage depth of the bottom plate of the upper coal seam is far away from the maximum horizontal distance of the compaction critical point of the goaf:
wherein:the angle of friction in the coal bed is degree; cmThe coal bed cohesion is MPa; m is the coal seam mining height M; k is the maximum stress concentration coefficient; k1Is the triaxial stress coefficient;the angle of friction in the floor strata is degree; gamma-overburden average volume weight; h-coal seam burial depth.
Preferably, the step 3 comprises the steps of:
step 31, establishing pressure stabilizing and pressure reducing mechanical models for mining of the upper working face and the lower working face of the double coal seam according to theoretical analysis results, and determining quantitative influence parameters;
step 32, integrating the mechanical model and the UDEC in the step 312DEstablishing a voltage stabilization type and pressure reduction type stagger calculation formula according to the numerical calculation result;
voltage-stabilizing type offset calculation formula: wmin＝X1+B+hcotα
In the formula: h is the average distance between the upper coal bed and the lower coal bed, m; alpha is the stress influence angle, °; b is the maximum top control distance of the upper coal layer, m; x1The horizontal distance m between the critical point Y of the compaction area of the goaf of the upper coal seam and the hydraulic support; said X1Maximum horizontal distance L of damage of rock stratum by upper coal bed bottom platemaxObtaining;
the pressure reduction type offset calculation formula: j. the design is a squaremax＝Wmin-L0
Jmin＝B+X2+hcotα+S2
In the formula: wminArranging the minimum value of the stagger for a voltage stabilization type, m; l is0The average period caving step distance of the upper coal layer is m; j. the design is a squaremaxMaximum offset for a pressure-reducing arrangement, m;
Jminminimum offset, m, for a pressure relief arrangement; h is the average distance between the upper coal bed and the lower coal bed, m; alpha is the stress influence angle, °; b is upperThe maximum control top distance of the coal seam is m; x2The horizontal distance m between the critical point of the top plate damage area of the lower coal seam and the support of the upper coal working face.
Preferably, in the step 4, the voltage-stabilizing calculation formula is corrected by combining with the field mining experience, so as to obtain an optimal offset calculation formula suitable for a field initial mining stage and a normal stoping stage, and guide the field mining practice;
the correction formula at the initial mining stage is as follows: wC＝Wmin+1.4LC
And (3) correcting a formula in a normal stoping stage: wZ＝Wmin+2LZ
In the formula, LCThe primary caving step of the basic roof, m; l isZIs the fundamental top cycle step size, m.
The method for determining the advancing direction offset of the upper and lower co-mining working faces of the double coal seams has the following beneficial effects:
1. and a pressure-stabilizing arrangement is adopted to lower the coal seam working face, so that safe mining is realized. The high-strength mining of double coal seams, the overlying strata collapse of the working face of the lower coal seam and the mine pressure display rule are different from the single-layer coal mining. In the double-coal-bed mining of the overlapped area, the surrounding rock stress state of the lower coal-bed working face is more complicated and changeable, the mine pressure is severely displayed, and the personnel safety and the equipment utilization rate of the working face are seriously threatened; the working face propulsion direction offset determined by the method avoids simultaneous surrounding rock stress superposition areas of upper and lower coal seams, and ensures the safety of lower coal seam mining personnel and equipment.
2. The uniform settlement of overlying strata is realized, the generation of concentrated tensile stress on the earth surface is avoided, and green mining is realized. The overlying strata collapse violently when the double coal seam overlapping area is mined, due to the coal wall supporting effect, the overlying strata above are not uniformly settled obviously, the internal stress distribution of the overlying strata is greatly differentiated, an obvious concentrated tensile stress area is generated on the earth surface, and an obvious tensile crack is generated on the earth surface. On the basis, by using a method of combining numerical simulation and physical simulation, the overburden rock collapse rule and the ground surface settlement rule when the advancing directions of the upper and lower same mining working faces in the superposition area are different in offset are researched, and the offset for reducing the ground surface damage degree is determined.
3. The difficult problem of on-site connection shortage is solved, and efficient mining of coal mine enterprises is realized. The upper coal seam and the lower coal seam are simultaneously mined in the overlapping area, and the advancing speed of the working face of the lower coal seam is influenced by the mining of the upper coal seam, so that the mine is in tension and the production efficiency is low. By determining the safe offset of the propulsion direction, mining basis is provided for field production, the problem of continuous tension is reasonably avoided, and the aim of high-yield and high-efficiency production is fulfilled.
4. The reasonable offset method of the advancing direction of the upper and lower co-mining working faces of the shallow-buried double coal seam is determined by integrating numerical simulation calculation, theoretical analysis and field mining practical experience, a calculation model is established, quantifiable parameters and a quantification calculation formula in the model are given, field mining can be effectively guided, and efficient mining of the shallow-buried double coal seam is realized.
Drawings
FIG. 1 is a stress diagram of surrounding rock of a working face of a coal seam at different staggers in the advancing direction;
FIG. 2 is a graph of the leading bearing pressure peak for the lower seam face;
FIG. 3 is a time chart sag curve for different staggers in the propulsion direction;
FIG. 4 shows the distribution law of the front and rear bearing pressures of the working face;
FIG. 5 is a pressure-stabilized mechanical model;
FIG. 6 is a mechanical model of reduced pressure;
FIG. 7 is a model of a Steady voltage calculation;
fig. 8 is a decompression type calculation model.
Detailed Description
In order that those skilled in the art will better understand the technical solutions of the present invention and can practice the same, the present invention will be described in detail with reference to the accompanying drawings and specific examples. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
The invention provides a method for determining the advancing direction offset of an upper and a lower co-mining working faces of double coal seams, which comprises the following steps:
step 1: distribution rule of different offset stress in the advancing direction of working face of upper and lower coal seam
For shallow buried doubleThe mining condition of the upper and lower coal mining working faces in the same direction is realized by adopting UDEC2DAnd (3) performing numerical simulation calculation to obtain the distribution rule of the stress of different offset distances in the advancing direction of the upper and lower working faces which are the same in mining, as shown in figure 1.
(1) And (5) the surrounding rock stress distribution rule of the working surface of the lower coal seam.
The surrounding rock stress of the working face of the lower coal seam at different propulsion direction staggers is shown in figure 1, the influence of the mining of the upper coal seam on the rock layer of the bottom plate is distributed in a shape like a Chinese character 'ba', and the surrounding rock stress of the working face of the lower coal seam is influenced by the dual functions of the mining of the coal seam and the caving overlying strata of the upper part. Along with the reduction of the advancing direction offset distance between the working surface of the lower coal seam and the working surface of the upper coal seam, the mining influence of the working surface of the upper coal seam on the working surface of the lower coal seam is more and more obvious. The variation may be based on the ratio of the face advance direction offset l to the seam spacing h (i.e., advance direction offset ratio k) taking into account the effect of the thickness of the intervening strataZ) And (4) showing.
When the advancing direction offset is 100m, namely about 3h, the upper coal seam caving rock stratum behind the goaf is compacted, the working surface of the lower coal seam is similar to single-layer coal mining, and the influence of the mining stress of the upper coal seam is basically avoided.
When the advancing direction offset is 60-70 m, namely 2h, the mining influence of the upper coal seam begins to affect the working surface of the lower coal seam, and the stress superposition is gradually increased.
When the offset of the propelling direction is less than 30m, namely 1h, the surrounding rock stress increasing area of the working surface of the lower coal seam and the surrounding rock stress increasing area of the bottom plate of the working surface of the upper coal seam are completely communicated and overlapped, so that the coal wall of the working surface of the lower coal seam is seriously caving, and the pressure of the support rises sharply.
(2) And the working surface of the lower coal seam leads the pressure peak rule of the support.
According to the calculation result, when the advancing direction offset is 100, 70, 35 and 0m, the advanced support pressure peak values in the front elastic zone of the coal wall of the lower coal seam working face are respectively 5.30, 6.00, 9.23 and 11.38 MPa. The leading support pressure peak of the lower coal seam working face is increased continuously along with the reduction of the advancing direction offset of the working face, as shown in figure 2. It can be seen that the advancing direction offset distance between the lower coal seam working face and the upper coal seam working face should be greater than 2 times of the coal seam distance, that is, 2h is 70 m.
Step 2: ground surface settlement rule of double coal seams with different offset distances in upper and lower mining working faces
The surface subsidence curves at different propulsion direction offsets are shown in fig. 3, and the maximum subsidence values at full surface mining are substantially the same, about 5.1 m. But when the displacement is carried out in different propulsion directions, the difference of the subsidence curvature of the ground surface is large, which shows that the ground surface has obvious difference of the tensile damage degree. When the offset distance in the propulsion direction is less than 1h (h is 35m), the ground surface sinking curvature is large, and the sinking gradient is more than 4 cm/m; when the offset distance in the propelling direction is 2 hours, the subsidence curvature of the ground surface is obviously reduced to 3.7 cm/m; when the advancing direction offset is more than 3h, the ground surface subsidence curvature is small, and the damage to the ground surface is small.
And step 3: theoretical analysis of different offset distances of working faces in the same mining direction at the upper part and the lower part of double coal seams
(1) Distribution law of supporting pressure of working face
The mining of coal seam causes the stress of stope to redistribute, the formed supporting pressure can be divided into decompression area, pressure increasing area and pressure stabilizing area, the range from the peak value of supporting pressure to the coal wall in front of the working face is the limit balance area, and the elastic area is towards the coal body, as shown in figure 4, wherein, a is the pressure increasing area; b-a pressure reduction zone; c-a pressure stabilizing area; gamma-overburden average volume weight; h, coal seam burial depth; k is the maximum stress concentration coefficient.
(2) Law of failure of coal seam mining floor
According to the elasto-plastic mechanics theory, the floor rock stratum is influenced by the supporting pressure and can be divided into 3 areas, namely an active stress limit area, a transition stress limit area and a passive stress limit area. According to a calculation formula of the ultimate bearing capacity during plastic slippage of rock soil, which is provided by A.S.Vesic, a calculation formula of the maximum depth and the length of a damaged area of the bottom plate of the upper coal seam under the condition of ultimate bearing pressure is obtained after correction.
1) Maximum failure depth H of coal seam floormaxDetermining, wherein the length S of the coal seam yielding area is as follows:
wherein:the angle of friction in the coal bed is degree; cmThe coal bed cohesion is MPa; m is the coal seam mining height M; k is the maximum stress concentration coefficient; k1Is the triaxial stress coefficient; gamma-overburden average volume weight; h-coal seam burial depth. Maximum failure depth H of coal seam floormaxComprises the following steps:
in the formula:is the internal friction angle of the floor strata.
2) Maximum horizontal distance L for coal seam floor to damage rock stratummaxCalculating the horizontal distance L between the maximum damage depth point of the bottom plate and the working surface1Comprises the following steps:
maximum horizontal distance L from maximum damage depth of bottom plate to compaction critical point of goaf2Comprises the following steps:
then
And 4, step 4: pressure stabilizing and pressure reducing mechanical model for upper and lower co-mining working faces of double coal seams
UDEC2DThe numerical calculation result provides a basis for selecting a proper mechanical theory. According to UDEC in the invention2DThe numerical calculation result is analyzed and obtained, and a calculation formula of the ultimate bearing capacity during rock-soil plastic slippage in the elastoplasticity mechanics theory is selected to be more appropriate. Obtaining the upper coal seam floor break according to the ultimate bearing capacity calculation formula during rock-soil plastic slippageBad law. Establishing a pressure stabilizing type and pressure reducing type mechanical model for simultaneously mining and advancing directions of working faces of upper and lower coal seams of double-coal-seam mining by taking the spatial superposition relationship of the upper and lower coal seams as the background in the practical process of double-coal-seam mining and combining the damage rule of the bottom plate of the upper coal seam
(1) Voltage stabilizing type mechanical model
The arrangement theory of the pressure stabilizing area considers that the lower coal seam working face is required to be located in the upper coal seam goaf to re-compact the stable area, the lower coal seam is mined after the overlying strata of the upper coal seam working face collapse stably, and the mechanical model is shown in figure 5. In the figure, a Y point is a critical point of compaction of a goaf of an upper coal seam, a goaf top plate on the left side of the Y point collapses and is compacted, the horizontal offset distance between a working surface of a lower coal seam and a working surface of the upper coal seam is larger than the length of the AY segment, and the length of the AY segment can be the maximum horizontal distance L of a rock stratum damaged by a bottom plate of the upper coal seammaxAnd (6) obtaining. Wherein: s1The length of the coal seam yield zone of the working face of the upper coal seam; alpha is a stress influence angle; r is the radius of influence.
(2) Pressure reduction type mechanical model
The arrangement of the pressure reducing area must ensure that the working face of the lower coal seam is positioned in the overlying rock caving arch structure of the upper coal seam, namely the position with relatively small bearing pressure of the top plate. The mechanical model of the pressure reduction zone is shown in FIG. 6. In the figure, point C is the deepest point of the upper coal seam bottom plate damage, the corresponding point P is the critical point of the lower coal seam top plate damage, and the lower coal seam working surface must be arranged on the left side of the point P. The length of the AP segment can be determined by the horizontal distance L from the maximum damage depth point of the bottom plate to the working surface1And (6) obtaining. S2The length of the yield zone of the coal seam of the working face of the lower coal seam.
And 5: reasonable offset calculation formula for advancing direction of upper and lower co-mining working faces of double coal seams
(1) A model of the stabilivolt calculation is shown in fig. 7. X1For the length of AY, the maximum horizontal distance L of the stratum can be destroyed by the bottom plate of the upper coal layermaxAnd (6) obtaining. Therefore, the minimum value W of the reasonable offset distance of the advancing directions of the working faces in the same miningminComprises the following steps:
Wmin＝X1+B+hcotα (6)
in the formula: h is the average distance between the upper coal bed and the lower coal bed, m; alpha is the stress influence angle, °; b is upperThe maximum control top distance of the coal seam is m; x1The horizontal distance m between the critical point Y of the compaction area of the goaf of the upper coal seam and the hydraulic support;
(2) the decompression-type calculation model is shown in fig. 8. According to the decompression type arrangement theory, the working surface of the lower coal seam is arranged in the arch structure of the top plate of the upper coal seam, and the average period collapse step L of the upper coal seam is subtracted from the minimum value of the pressure stabilizing type arrangement offset0Maximum value J of propulsion direction offsetmaxComprises the following steps:
Jmax＝Wmin-L0 (7)
in the formula: wminArranging the minimum value of the stagger for a voltage stabilization type, m; l is0M is the average period of the upper coal seam caving.
The minimum value of the pressure reduction type arrangement offset distance must meet the condition that the working face of the lower coal seam is not influenced by the mining dynamic pressure of the upper coal seam, X2For the length of the AP segment, the horizontal distance L from the maximum damage depth point of the bottom plate to the working surface can be used1And (6) obtaining. Therefore, the advancing direction is offset by JminThe calculation formula is as follows:
Jmin＝B+X2+hcot α+S2 (8)
in the formula: h is the average distance between the upper coal bed and the lower coal bed, m; alpha is the stress influence angle, °; b is the maximum top control distance of the upper coal layer, m; x2The horizontal distance m between the critical point P of the top plate damage area of the lower coal seam and the support of the upper coal working face.
In mining practice, the control is difficult due to the small extent of the pressure reduction zone. The offset obtained by adopting the pressure stabilizing area principle can ensure that the lower coal seam avoids the influence of the superposed stress of the upper coal seam, and is easy to apply on site. Therefore, the reasonable offset calculation of the advancing direction of the upper and lower co-mining working faces in the shallow-buried double-coal-seam mining is preferably realized by adopting a pressure stabilizing formula.
6. Correction of reasonable offset calculation formula of propulsion direction
(1) And (5) a primary mining stage. According to field actual measurement, the step pitch of primary caving of the working face overlying strata is large, and the duration is generally 2-3 d. In the initial mining stage, the influence of the initial caving step of the upper coal seam is considered, and the correction formula is WC＝Wmin+1.4LCWherein L isCIs the primary caving step of the basic roof, m.
(2) During normal recovery. In the normal mining process of the upper coal seam, the influence of the periodically caving mine pressure is considered, and the correction formula is WZ＝Wmin+2LZWherein L isZIs the fundamental top cycle step size, m.
Example 1
The method for determining the advancing direction offset of the upper and lower co-production working faces of the double coal seam provided by the invention is further explained by taking a certain coal mine in northern Shaanxi as an example through a specific embodiment.
According to typical shallow coal seam mining conditions in northern Shaanxi, the application of the method is illustrated by taking mining of upper and lower same mining working faces of double coal seams in the east area of a wing in northern China of a certain mine as an example. The mining area adopts inclined shaft exploitation, a full-height long-arm comprehensive mechanized coal mining method is adopted at one time, and a roof is managed by a full caving method. The dip angle of the coal seam is about 1 degree, and the coal seam is a nearly horizontal coal seam. Now mainly mined 1-2Coal seam and 2-2A coal seam. 1-2Coal seam and 2-2The internal friction angles of the coal seam are respectively 37.5 degrees and 38.5 degrees, the cohesive force is respectively 1.3MPa and 1.4MPa, and 1 degree-2Coal seam and 2-2The average mining heights of the coal beds are 1.89m and 5.00m, 2-2The average stress concentration coefficient of the coal bed is 5.0, and the average volume weight of the overlying strata is 23kN/m3，1-2Coal and 2-2The average buried depth of the coal seam is respectively 110m and 145m, 1-2The internal friction angle of the coal seam floor rock stratum is 42 degrees, the rock stratum collapse angle is 49 degrees and 1 degree-2Coal seam and 2-2The average spacing of coal seams is 35m, 1-2The average period caving step of coal seam mining is 11.8m and 1-2The maximum control top distance of the coal bed is 6 m.
At present in mine 1-2Coal seam and 2-2The coal seam working face mining has large mutual influence 2-2When mining coal bed, in order to avoid 1-2Coal seam mining concentrates stress effects, push mining speed must be limited, 1-2The working surface of the coal seam keeps a certain offset distance, and the mining is stopped and the pressure is avoided. The offset range is determined on site according to mining experience, scientific basis is lacked, and mine production is continuously tense.
According to the occurrence conditions of the coal seam in the mining area, the method is adoptedThe method for determining the advancing direction offset of the upper and lower co-mining working faces of the double coal seams is obviously provided, and the method for determining the advancing direction offset of the upper and lower co-mining working faces of the shallow double coal seams by adopting a voltage stabilization type calculation method is provided. W can be obtained by substituting the above parameters into the formulae (6), (7) and (8)min＝81m，Jmax＝69.2m，Jmin56 m. In mining practice, the control is difficult due to the small extent of the pressure reduction zone. The offset obtained by adopting the principle of the pressure stabilizing area can ensure that the lower coal seam avoids the influence of the superposed stress of the upper coal seam. Therefore, the offset of the northeast region of the north wing in the advancing direction of the working face is determined according to a pressure stabilizing formula, namely the offset is larger than 81 m.
And correcting the advancing direction offset of the upper and lower co-mining working faces of the shallow-buried double coal seam.
1) And (5) a primary mining stage. According to field actual measurement, the step pitch of primary caving of the working face overlying strata is large, and the duration is generally 2-3 d. In the initial mining stage, the influence of the initial caving step of the upper coal seam is considered. The empirical formula is WC＝Wmin+1.4LC，1-2Coal seam primary caving step LC29.7m, initial mining stage 2-2And 1-2The advancing direction offset distance of the coal seam working face is more than 123 m.
2) During normal recovery. In the normal mining process of the upper coal seam, the influence of cycle collapse is considered, and the offset empirical formula of the same mining working face is WZ＝Wmin+2LZ，1-2Coal seam cycle collapse step LZSubstituting 11.8m into the formula can obtain the normal recovery period 2-2Coal seam and 1-2The offset distance of the advancing direction of the coal seam and the working face is larger than 105 m.
Therefore, 2-2Coal seam working face and 1-2The reasonable offset distance of the advancing direction of the coal seam working face is as follows: the stagger of the initial mining stage is more than 123m, and the stagger of the normal stoping stage is more than 105 m.
After the mining method is adopted, 2-2The coal wall of the coal seam working surface is positioned at 1-2In the range of a pressure stabilizing area behind a coal seam goaf, 1 is avoided-2The coal mining working face concentrates the stress influence. The offset determined by the method is easy to realize in-situ mining, the mine is easy to continue, and efficient mining of the shallow-buried double coal seams is realized.
The above-mentioned embodiments are only preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, and any simple modifications or equivalent substitutions of the technical solutions that can be obviously obtained by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (5)
1. A method for determining the advancing direction offset of the upper and lower co-mining working faces of double coal seams is characterized by comprising the following steps:
step 1. use of UDEC2DThe numerical simulation and physical simulation method grasps the surrounding rock stress distribution rule and the surface subsidence rule of the upper and lower co-mining working faces of the double coal seams when the advancing direction of the working face is different in offset distance, and analyzes the influence range and degree between the upper and lower working faces during simultaneous mining to obtain an ideal offset distance range;
step 2, according to the ideal offset range, utilizing a limit bearing capacity calculation formula during rock-soil plastic slippage to obtain the maximum depth H of the upper coal seam bottom plate damage area under the condition of limit bearing pressuremaxCalculating a formula to obtain the maximum horizontal distance L of the upper coal seam floor to damage the rock stratummaxCalculating a formula;
step 3, establishing a pressure stabilizing type and pressure reducing type mechanical model for simultaneously exploiting and advancing working faces of the upper coal seam and the lower coal seam in the double-coal seam exploitation, and synthesizing the maximum horizontal distance L of the bottom plate of the upper coal seam for damaging the rock stratummaxDetermining a stagger calculation formula of a pressure stabilizing type and a pressure reducing type propelling direction according to a stress transfer angle of a bottom plate and the distance between an upper coal layer and a lower coal layer;
and 4, correcting the offset calculation formula in the step 3 to obtain the optimal offset suitable for the initial mining stage of the advancing direction of the working faces of the upper coal seam and the lower coal seam in field production and the normal stoping period.
2. The method for determining the advancing direction offset of the upper and lower co-production working faces of the double coal seam according to claim 1, wherein in the step 1, the advancing direction offset of the upper and lower coal seams is calculated according to a large number of numerical simulations, when the advancing direction offset of the upper and lower coal seams is less than 70m, the mining influence of the upper coal seam starts to affect the lower coal seam working face, the mining stress superposition gradually increases along with the reduction of the offset, the advanced supporting pressure peak value of the lower coal seam working face continuously increases, when the offset arranged edge to edge is 0m, the value of the pressure of the lower coal seam over front supporting reaches 11.38MPa, and the curvature of the surface subsidence curve continuously increases along with the reduction of the offset.
3. The method for determining the advancing direction offset of the upper and lower working faces of the same mining of the double coal seams according to claim 1, wherein in the step 2, the following steps are obtained:
length of yield zone of coal wall position of working face:
maximum failure depth of the bottom plate of the upper coal layer:
the maximum horizontal distance for the upper coal bed bottom plate to damage the rock stratum:
wherein, the maximum damage depth point of the upper coal bed bottom plate is away from the horizontal distance of the working surface:
the maximum damage depth of the bottom plate of the upper coal seam is far away from the maximum horizontal distance of the compaction critical point of the goaf:
wherein:the angle of friction in the coal seam is expressed as degree; cmThe cohesive force of the coal bed is expressed in MPa; m is the coal seam mining height and the unit is M; k is maximum stress concentrationA coefficient; k1Is the triaxial stress coefficient;the internal friction angle of the floor rock stratum is shown as an angle; gamma-overburden average volume weight; h-coal seam burial depth.
4. The method for determining the advancing direction offset of the upper and lower working faces of the same mining of the double coal seams according to claim 3, wherein the step 3 comprises the following steps:
step 31, establishing pressure stabilizing and pressure reducing mechanical models for mining of the upper working face and the lower working face of the double coal seam according to theoretical analysis results, and determining quantitative influence parameters;
step 32, integrating the mechanical model and the UDEC in the step 312DEstablishing a voltage stabilization type and pressure reduction type stagger calculation formula according to the numerical calculation result;
voltage-stabilizing type offset calculation formula: wmin＝X1+B+hcotα
In the formula: h is the average distance between the upper coal bed and the lower coal bed, and the unit is m; alpha is the stress influence angle in degrees; b is the maximum top control distance of the upper coal layer, and the unit is m; x1The horizontal distance between the critical point Y of the compaction area of the goaf of the upper coal seam and the hydraulic support is m; said X1Maximum horizontal distance L of damage of rock stratum by upper coal bed bottom platemaxObtaining;
the pressure reduction type offset calculation formula: j. the design is a squaremax＝Wmin-L0
Jmin＝B+X2+hcotα+S2
In the formula: wminThe minimum value of the voltage stabilization type arrangement offset is m; l is0The average period caving step distance of the upper coal layer is m; j. the design is a squaremaxMaximum offset in m for a reduced pressure arrangement;
Jminminimum offset in m for a depressurisation arrangement; h is the average distance between the upper coal bed and the lower coal bed, and the unit is m; alpha is the stress influence angle in degrees; b is the maximum top control distance of the upper coal layer, and the unit is m; x2Is the critical point of the roof damage area of the lower coal seam and the upper coal seamThe horizontal distance of the working face support is in m.
5. The method for determining the advancing direction offset of the upper and lower co-mining working faces of the double coal seams as claimed in claim 4, wherein in the step 4, the pressure stabilizing formula is corrected by combining the field mining experience to obtain the optimal offset formula suitable for the field initial mining stage and the normal stoping stage, and the field mining practice is guided;
the correction formula at the initial mining stage is as follows: wC＝Wmin+1.4LC
And (3) correcting a formula in a normal stoping stage: wZ＝Wmin+2LZ
In the formula, LCThe step pitch of primary caving of the basic roof is m; l isZThe fundamental top cycle step size is in m.
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