Method for judging layering fracture motion state of thick and hard rock stratum in mining of ultra-thick coal seam

Abstract

The invention discloses a method for discriminating the layering fracture motion state of a thick and hard rock stratum in ultra-thick coal seam mining, and belongs to the technical field of mineral engineering. The method comprises the steps that according to coal seam occurrence and mining conditions, the position of a thick and hard rock stratum, soft and weak interlayer distribution and layered mining thickness are determined by applying a key layer theory; constructing a cantilever beam stress model, analyzing critical conditions of layered movement of the thick and hard rock stratum, and calculating a minimum suspension length L1 required by layering; the periodic fracture step L2 of the thick and hard rock stratum is calculated through theoretical mechanics, L1 and L2 are compared, and whether the thick and hard rock stratum is firstly layered and then fractured or not is judged; if layering occurs, the upper and lower layering loads and the fracture step pitch are recalculated, and the layering fracture motion state is further judged; and finally, analyzing the hinged stability of the broken rock by adopting a masonry beam theory, and determining the range of the rock stratum needing to be controlled. According to the method, the influence of the weak intercalated layer is considered, the layering fracture behavior of the thick and hard rock stratum can be quantitatively judged, a theoretical basis is provided for support model selection and roof control, and the safety of a stope is guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of mining engineering, specifically relating to a method for determining the stratified fracture movement state of thick and hard rock strata during the mining of extremely thick coal seams. Background Technology

[0002] With Xinjiang's transformation into a strategic mineral resource development base, large-scale integrated coalfields such as Zhundong, Yili, Turpan-Hami, and Kubai have entered a stage of large-scale development. All four coalfields contain massive coal seams with a single layer thickness exceeding 20 meters. These massive coal seams are composed of sedimentary rocks, typically 20-30 meters thick, and contain structurally weak planes or soft interlayers along their thickness. During mining, the strata are in a cantilever state, leading to increased internal shear. When the shear exceeds a critical value, the strata stratify. If the thick, hard rock strata, which play a major role in the manifestation of mining pressure, stratify, the load on each stratum changes, causing alterations in the periodic fracture step of the thick, hard rock strata. This can result in sudden changes in the roof pressure at the mining face, severely impacting safe production. Summary of the Invention

[0003] To reduce the impact of the stratification and fracturing of thick, hard rock strata on the degree of mine pressure manifestation in the mining area, this invention proposes a method for determining the stratification and fracturing state of thick, hard rock strata in the mining of very thick coal seams. This method can theoretically analyze the stratification and fracturing state and articulation stability of thick, hard rock strata in advance, determine the range of rock strata that need to be controlled in the mining area, and provide theoretical guidance for support selection and roof control.

[0004] To achieve the above objectives, this invention designs a method for determining the stratified fracture movement state of thick and hard rock strata during mining of extremely thick coal seams, comprising the following steps: Step A. Based on the occurrence and mining conditions of the target thick coal seam, use the key layer theory to determine the location of the thick and hard rock layer and the condition of the supporting rock layer, determine the distribution of the weak interlayers in the thick and hard rock layer and the thickness of the thick coal seam for stratified mining, and then proceed to Step B; Step B. Construct a cantilever beam stress model for thick and hard rock strata, analyze the critical conditions for the stratification of thick and hard rock strata, determine the required exposed length L1 for the stratification of thick and hard rock strata, and then proceed to step C. Step C. The periodic fracture step L2 of the thick and hard rock layer is obtained by theoretical mechanics calculation and compared with L1. When L1 > L2, the thick and hard rock layer does not undergo stratification and fractures directly, proceeding to step E. When L1 < L2, the thick and hard rock layer first undergoes stratification and then fractures as the working face advances, proceeding to step D. Step D. Treat the thick, hard rock layer as two layers, recalculate the loads on the upper and lower layers of the thick, hard rock layer using the critical layer theory, and determine the fracture step distance for each layer. If the fracture step distance of the upper layer is L... up <Lower layer breaking step distance L downBefore fracture, the upper and lower strata act as a whole, with a periodic fracture step of L2. After fracture, the upper and lower strata move independently. If the fracture step of the upper strata is L... up ≥Lower layer breaking step distance L down After the rock beam is stratified, the upper and lower strata are treated as independent rock layers and undergo fracture movement, proceeding to step E; Step E. Based on the above analysis, determine the stratified fracture movement state of the thick and hard rock strata. Then, use the masonry beam theory to analyze the hinged stability of the fractured rock blocks in the thick and hard rock strata and determine the range of rock strata that need to be controlled in the mining area.

[0005] As a preferred embodiment of the present invention, in step B, the calculation method for the exposed length L1 required for the stratification movement of the thick, hard rock layer is as follows: if the thick, hard rock layer does not contain weak interlayers, the minimum exposed length required for the stratification movement of the thick, hard rock layer is calculated according to Formula 1; if the thick, hard rock layer contains weak interlayers, the minimum exposed length required for the stratification movement of the thick, hard rock layer is calculated according to Formula 2, where L1 is the minimum exposed length required for the stratification movement of the thick, hard rock layer, h is the thickness of the thick, hard rock layer, q is the load on the thick, hard rock layer, and R... τ τ1 represents the shear strength of the thick, hard rock layer, [τ1] represents the shear strength of the weak structural surface, and y1 represents the distance from the weak structural surface to the middle layer of the rock beam.

[0006] (1) (2).

[0007] As a preferred technical solution of the present invention, the layered fracture movement state of the thick and hard rock strata in the mining of the thick coal seam is divided into three situations: direct fracture without layering, layering first and then overall fracture, and layering first and then independent fracture.

[0008] As a preferred technical solution of the present invention, during the mining process of the thick coal seam, in addition to the thick and hard rock layer in the middle of the mining area which may be broken in layers again, the roof rock layer on the cut side may also experience tensile and bending failure in the middle due to the increase in the exposed length and rotation angle, resulting in re-fracture.

[0009] The beneficial effects of this invention, a method for determining the stratification and fracture movement state of thick and hard rock strata in the mining of super-thick coal seams, are as follows: it considers the influence of weak interlayers contained in the thick and hard rock strata on the stratification movement and the manifestation of mining pressure in the stope, which can explain the reason for the significant changes in the load on the supports in the early stage of stratified mining of super-thick coal seams; it quantitatively analyzes the conditions for stratification of thick and hard rock strata, which can determine the range of rock strata that need to be controlled in the roof, and can provide theoretical support for the selection of stope supports and roof control in the mining of super-thick coal seams. Attached Figure Description

[0010] The embodiments of the present invention will be further described below with reference to the accompanying drawings: Figure 1 This is a flowchart illustrating the method for determining the fracture movement state of thick, hard rock layers according to the present invention. Figure 2 This is a schematic diagram of the basic top layer fracture movement process during the first mining of a very thick coal seam according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the basic top layer fracture movement process during the mining of the second layer of a very thick coal seam according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the basic top layer fracture movement process during the mining of the third layer of a very thick coal seam according to an embodiment of the present invention; In the diagram, 1-hard rock layer, 2-weak rock layer, 3-basic roof, 31-layer above the basic roof, 32-layer below the basic roof, 4-direct roof, 5-coal seam. Detailed Implementation

[0011] The present invention will be further described below with reference to the accompanying drawings, but this does not limit the invention to the scope of the embodiments described.

[0012] like Figure 1 As shown, this invention designs a method for determining the stratified fracture movement state of thick and hard rock strata in the mining of very thick coal seams. In practical applications, it is first necessary to determine the physical and mechanical parameters of the roof rock strata and the fragmentation coefficient of the fractured rock blocks in the laboratory, and then implement the method according to the following steps.

[0013] Step A. Based on the occurrence and mining conditions of the target thick coal seam, use the key layer theory to determine the location of the thick and hard rock layer and the condition of the supporting rock layer, determine the distribution of the weak interlayers in the thick and hard rock layer and the thickness of the thick coal seam for stratified mining, and then proceed to Step B; Step B. Construct a cantilever beam stress model for thick and hard rock strata, analyze the critical conditions for the stratification of thick and hard rock strata, determine the required exposed length L1 for the stratification of thick and hard rock strata, and then proceed to step C. Step C. The periodic fracture step L2 of the thick and hard rock layer is obtained by theoretical mechanics calculation and compared with L1. When L1 > L2, the thick and hard rock layer does not undergo stratification and fractures directly, proceeding to step E. When L1 < L2, the thick and hard rock layer first undergoes stratification and then fractures as the working face advances, proceeding to step D. Step D. Treat the thick, hard rock layer as two layers, recalculate the loads on the upper and lower layers of the thick, hard rock layer using the critical layer theory, and determine the fracture step distance for each layer. If the fracture step distance of the upper layer is L... up <Lower layer breaking step distance L down Before fracture, the upper and lower strata act as a whole, with a periodic fracture step of L2. After fracture, the upper and lower strata move independently. If the fracture step of the upper strata is L... up ≥Lower layer breaking step distance L downAfter the rock beam is stratified, the upper and lower strata are treated as independent rock layers and undergo fracture movement, proceeding to step E; Step E. Based on the above analysis, determine the stratified fracture movement state of the thick and hard rock strata. Then, use the masonry beam theory to analyze the hinged stability of the fractured rock blocks in the thick and hard rock strata and determine the range of rock strata that need to be controlled in the mining area.

[0014] As a preferred embodiment of the present invention, in step B, the calculation method for the exposed length L1 required for the stratification movement of the thick, hard rock layer is as follows: if the thick, hard rock layer does not contain weak interlayers, the minimum exposed length required for the stratification movement of the thick, hard rock layer is calculated according to Formula 1; if the thick, hard rock layer contains weak interlayers, the minimum exposed length required for the stratification movement of the thick, hard rock layer is calculated according to Formula 2, where L1 is the minimum exposed length required for the stratification movement of the thick, hard rock layer, h is the thickness of the thick, hard rock layer, q is the load on the thick, hard rock layer, and R... τ τ1 represents the shear strength of the thick, hard rock layer, [τ1] represents the shear strength of the weak structural surface, and y1 represents the distance from the weak structural surface to the middle layer of the rock beam.

[0015] (1) (2) As a preferred technical solution of the present invention, the layered fracture movement state of the thick and hard rock strata in the mining of the thick coal seam is divided into three situations: direct fracture without layering, layering first and then overall fracture, and layering first and then independent fracture.

[0016] As a preferred technical solution of the present invention, during the mining process of the thick coal seam, in addition to the thick and hard rock layer in the middle of the mining area which may be broken in layers again, the roof rock layer on the cut side may also experience tensile and bending failure in the middle due to the increase in the exposed length and rotation angle, resulting in re-fracture.

[0017] The beneficial effects of this invention, a method for determining the stratification and fracture movement state of thick and hard rock strata in the mining of super-thick coal seams, are as follows: it considers the influence of weak interlayers contained in the thick and hard rock strata on the stratification movement and the manifestation of mining pressure in the stope, which can explain the reason for the significant changes in the load on the supports in the early stage of stratified mining of super-thick coal seams; it quantitatively analyzes the conditions for stratification of thick and hard rock strata, which can determine the range of rock strata that need to be controlled in the roof, and can provide theoretical support for the selection of stope supports and roof control in the mining of super-thick coal seams.

[0018] Based on the above steps, the stability of the fractured rock blocks in the thick and hard rock strata is analyzed. Combined with the columnar section of the coal-bearing strata, the range of rock strata that need to be controlled in the mining area roof is determined, thereby guiding the selection of mining support and roof control, and ensuring the safety of the mining area.

[0019] Taking the layered mining of a very thick coal seam in a certain mine as a specific example, Table 1 shows the geological conditions of the very thick coal seam in the mine. The total thickness of the very thick coal seam is 70 m, and the layered mining thickness is 10 m.

[0020] Table 1 This invention is applied to determine the fracture movement state of the basic top layer during the layered mining of thick coal seams. Based on the roof conditions of the thick coal seam in this mine, see [reference needed]. Figure 2 and Figure 3 From the bottom up, the coal seam 5 is divided into the direct roof 4, the basic roof 3, the weak rock layer 2, and the hard rock layer 1.

[0021] Specifically as follows: Step A. By analyzing the occurrence and mining conditions of the target super-thick coal seam, it can be seen that above coal seam 5 are the 9.8 m thick immediate roof 4 and the 20 m thick basic roof 3, the middle layer of the basic roof is a weak interlayer, the super-thick coal seam is mined in layers with a thickness of 10 m, proceed to step B; Step B. Through the stress analysis of the cantilever beam of the basic roof, it can be seen that the minimum exposed length L1 of the basic roof 3 with stratification is 5.19 m, proceed to step C; Step C. Through theoretical mechanics calculations, it can be seen that the periodic step L2 of the complete failure of the basic top 3 is 22.76 m, and L1 < L2. Therefore, the basic top 3 first breaks along the middle layer and then breaks as the working face advances, proceeding to step D. Step D. Because the weak interlayer is located in the middle of the main top, the load on the upper layer 31 of the main top is greater than that on the lower layer 32 of the main top. The fracture step distance of the upper layer 31 of the main top is smaller than that of the lower layer 32 of the main top. Therefore, the upper and lower layers of the main top 3 bear the load as a whole before fracture. The periodic fracture step distance is 22.76 m. After fracture, the upper and lower rock layers move independently, and proceed to step E. Step E. Based on the above analysis, determine the stratified fracture movement state of the thick, hard rock strata. During the initial mining of the first layer, the initial fragmentation coefficient of the goaf rock blocks is taken as 1.4. During the mining of the second and third layers, the fragmentation coefficients of the goaf rock blocks during re-mining are taken as 1.2 and 1.1, respectively. The stability of the hinged rock blocks in the fractured thick, hard rock strata is analyzed using masonry beam theory. Figure 2 As shown, during the first layer of mining, the broken rock blocks of the upper layer 31 and the lower layer 32 can form a stable masonry beam structure. During the second layer of mining, such as Figure 3 As shown, the uppermost layer 31 and the lowermost layer 32 move independently, and the load on each layer changes. The lowermost layer 32 fractures into two parts, L5 (14.05 m) and L6 (8.71 m). The uppermost layer 31 undergoes secondary fracture, breaking into two parts, L3 (19.87 m) and L4 (2.89 m). The fractured rock block of the lowermost layer 32 deforms and becomes unstable. See [reference needed]. Figure 3 Region B; the top layered 31 fractured rock blocks are hinged and stable, see [reference]. Figure 3 Area A in the middle; During the third layer of mining, such as Figure 4 As shown, the residual fragmentation coefficient of the collapsed rock blocks in the goaf further decreased, and the deformation and instability of the basically top-layered 31 broken rock blocks were observed, as shown in area C in the figure.

Claims

1. A method for determining the stratified fracture movement state of thick, hard rock strata during mining of extremely thick coal seams, characterized in that, Includes the following steps: Step A. Based on the occurrence and mining conditions of the target thick coal seam, use the key layer theory to determine the location of the thick and hard rock layer and the condition of the supporting rock layer, determine the distribution of the weak interlayers in the thick and hard rock layer and the thickness of the thick coal seam for stratified mining, and then proceed to Step B; Step B. Construct a cantilever beam stress model for thick and hard rock strata, analyze the critical conditions for the stratification of thick and hard rock strata, determine the required exposed length L1 for the stratification of thick and hard rock strata, and then proceed to step C. Step C. The periodic fracture step L2 of the thick and hard rock layer is obtained by theoretical mechanics calculation and compared with L1. When L1 > L2, the thick and hard rock layer does not undergo stratification and fractures directly, proceeding to step E. When L1 < L2, the thick and hard rock layer first undergoes stratification and then fractures as the working face advances, proceeding to step D. Step D. Treat the thick, hard rock layer as two layers, recalculate the loads on the upper and lower layers of the thick, hard rock layer using the critical layer theory, and determine the fracture step distance for each layer. If the fracture step distance of the upper layer is L... up <Lower layer breaking step distance L down Before fracture, the upper and lower strata act as a whole, with a periodic fracture step of L2. After fracture, the upper and lower strata move independently. If the fracture step of the upper strata is L... up ≥Lower layer breaking step distance L down After the rock beam is stratified, the upper and lower strata are treated as independent rock layers and undergo fracture movement, proceeding to step E; Step E. Based on the above analysis, determine the stratified fracture movement state of the thick and hard rock strata. Then, use the masonry beam theory to analyze the hinged stability of the fractured rock blocks in the thick and hard rock strata and determine the range of rock strata that need to be controlled in the mining area.

2. The method for determining the stratified fracture movement state of thick and hard rock strata in the mining of extremely thick coal seams according to claim 1, characterized in that, In step B, the calculation method for the exposed length L1 required for the stratification of the thick, hard rock layer is as follows: If the thick, hard rock layer does not contain weak interlayers, the minimum exposed length required for the stratification of the thick, hard rock layer is calculated according to Formula 1; if the thick, hard rock layer contains weak interlayers, the minimum exposed length required for the stratification of the thick, hard rock layer is calculated according to Formula 2. In the formulas, L1 is the minimum exposed length required for the stratification of the thick, hard rock layer, h is the thickness of the thick, hard rock layer, q is the load on the thick, hard rock layer, and R... τ τ1 represents the shear strength of the thick, hard rock layer, [τ1] represents the shear strength of the weak structural surface, and y1 represents the distance from the weak structural surface to the middle layer of the rock beam. （1） （2）。 3. The method for determining the stratified fracture movement of thick and hard rock strata in the mining of extremely thick coal seams according to claim 1, characterized in that, The fracturing motion of thick and hard rock strata in the mining of thick coal seams can be divided into three situations: direct fracturing of thick and hard rock strata without stratification, fracturing of strata first and then as a whole, and fracturing of strata first and then independently.

4. The method for determining the stratified fracture movement of thick and hard rock strata in the mining of extremely thick coal seams according to claim 1, characterized in that, During the mining of very thick coal seams, in addition to the possibility of the thick and hard rock strata in the middle of the mining area being broken in layers, the roof strata on the cut side may also experience tensile and bending failures in the middle due to the increase in the exposed length and rotation angle, resulting in re-fracture.

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