Calculation method for separation amount of extremely thick gravel stratum based on similar simulation

Abstract

The present invention provides a method for calculating the separation amount of a super-thick gravel layer based on similar simulation, comprising the following steps: S1, fabricating a plane stress similar simulation test model; S2, conducting a similar simulation test for fully-mechanized caving mining under a super-thick gravel layer; S3, establishing a mechanical model for calculating the separation amount of the super-thick gravel layer; S4, establishing a calculation formula for the separation amount of the super-thick gravel layer based on the mechanical model; the separation amount of the super-thick gravel layer is calculated through the above steps. Based on the results of similar simulation tests and field observations, using the "key stratum" and "thick plate" theories for calculation, the deformation, movement, and separation evolution characteristics of the super-thick gravel layer during fully-mechanized caving mining are studied, a separation and fracture mechanical model of the super-thick gravel layer during fully-mechanized caving mining is established, and a calculation formula for the separation amount is derived. The research conclusion has important guiding significance for ground subsidence reduction and prediction and prevention of underground rock bursts during fully-mechanized caving mining under a super-thick gravel layer.

Description

Technical Field

[0001] The present invention relates to the technical field of coal mine surface subsidence control, in particular to a calculation method for the separation amount of a thick gravel layer based on similarity simulation. Background Art

[0002] Fully-mechanized top coal caving mining is one of the main high-yield and high-efficiency coal mining methods for extra-thick coal seams in China. The thick gravel layer, thick igneous rock layer, and thick hard rock layer overlying the coal seam are characterized by large thickness, good integrity, and long distance from the coal seam. Since the starting cut, as the advancing speed of the fully-mechanized caving face continuously increases, after the first sub-key stratum above the coal seam fractures, the overlying soft rock layer as the follower layer sinks along with it; then the second sub-key stratum shows separation, and so on upwards until the main key stratum (gravel layer) shows separation, instability and caving, and surface subsidence. Before the thick gravel layer fractures and becomes unstable, the separation space at the bottom reaches the maximum. Calculating the separation amount of the thick gravel layer overlying fully-mechanized top coal caving mining can provide a basis for disaster prediction and control technologies such as separation grouting for coal mining under the thick gravel layer.

[0003] After the fully-mechanized caving face is mined, a large-scale hanging roof appears in the high-position thick gravel layer. When the advancing speed of the fully-mechanized caving face under the thick gravel layer exceeds the limit span of the gravel layer, the gravel layer suddenly becomes unstable and collapses. The vibration field formed by the collapse is superimposed on the moving stress field in front of the fully-mechanized caving face, resulting in high stress areas or stress abnormal areas in the coal and rock mass in front of the fully-mechanized caving face or the surrounding rock of the mining roadway, causing large-energy microseismic events (mine tremors) in the front of the working face or the surrounding rock of the mining roadway, and even triggering rock burst accidents. Therefore, studying the separation evolution law of the thick gravel layer overlying thick coal seam mining, especially the separation amount calculation method, is widely used for the implementation of technical measures such as ground separation grouting for subsidence reduction, hydraulic fracturing, and presplitting blasting, effectively reducing the surface subsidence amount, especially in controlling the rock burst disasters induced by the fracture and instability of the thick gravel layer in the underground fully-mechanized caving face.

[0004] At present, the research on the separation amount and separation law of the thick gravel layer overlying extra-thick coal seam mining mainly adopts methods and technologies such as field observation, numerical calculation, similar material simulation test, and theoretical analysis. However, there is still no mature and practical theoretical calculation system for calculating the separation amount of the thick gravel layer.

[0005] When constructing observation holes on the ground or underground and using on-site observation methods such as "drilling core sampling method" and "drilling camera", the actual value of the separation of the gravel layer during coal seam mining is obtained, and the research conclusion is the basis for numerical calculation and theoretical analysis; however, the on-site engineering quantity is huge, laborious and time-consuming, and is greatly affected by the on-site production process, and sometimes even unsatisfactory conclusions cannot be obtained.

[0006] Regarding the fracture step distance of extremely thick gravel strata, a large number of theoretical studies have been carried out using plate theory, beam theory, and key stratum theory. However, there are many influencing factors for the separation amount of overlying strata in fully-mechanized caving mining, and the calculation formula is complex and variable, making it difficult to achieve through a single theoretical calculation method such as elastic, plastic, and large deformation of rock mass engineering. Especially for the separation amount of extremely thick gravel strata overlying extra-thick coal seams, there is no dedicated theoretical calculation formula at present.

[0007] Chinese patent document CN109635357A records a method for predicting the dynamic position of overlying strata separation considering the swelling property of mined rock mass. By considering the differences in the separation mechanical models of different strata caused by the swelling property of rock mass, for the separation below the maximum development height of the caving zone, both the upper and lower rock groups of the separation are simplified as fixed-ended beam models at both ends for analysis and calculation; for the separation above the maximum development height of the caving zone, the upper rock group of the separation is simplified as a fixed-ended beam at both ends, and the lower rock group of the separation is simplified as a Winkler elastic foundation beam for analysis and calculation. Compared with the traditional method, the mechanical model selected in this invention is more reasonable; this invention also gives the criteria for the disappearance of separation in different strata, and can also be used for predicting the dynamic development position of roof separation. Therefore, it can more accurately predict the development position of overlying strata separation corresponding to the face advance, so as to better serve the basic research and prevention work of strata movement and related secondary disasters. However, this method can only predict the dynamic development position of separation, and there is no dedicated theoretical calculation formula, and it cannot study the development status of the separation amount at different times. At the same time, there are no shape characteristics of the collapsed bodies during the first caving and periodic caving of the gravel strata, which is not conducive to further evaluating the prediction of later disasters, and there are defects in use and need to be improved. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a calculation method for the separation amount of gravel strata based on similar simulation, so as to solve the problems that there are many influencing factors for the separation amount of overlying strata in fully-mechanized caving mining, the calculation formula is complex and variable, it is difficult to achieve through a single theoretical calculation method such as elastic, plastic, and large deformation of rock mass engineering, and there is no dedicated theoretical calculation formula.

[0009] To solve the above technical problems, the technical solution adopted by the present invention is: a calculation method for the separation amount of gravel strata based on similar simulation, including the following steps:

[0010] S1. Fabricate a plane stress similar simulation test model;

[0011] S2. Conduct a similar simulation test of fully-mechanized caving mining under extremely thick gravel strata;

[0012] S3. Establish a mechanical model for calculating the separation amount of extremely thick gravel strata;

[0013] S4. Establish a calculation formula for the separation amount of extremely thick gravel strata according to the mechanical model;

[0014] The separation amount of the conglomerate layer is calculated through the above steps.

[0015] In the preferred solution, in step S1, the steps of making a plane stress similarity simulation test model are as follows:

[0016] S11. According to the comprehensive columnar section of the fully-mechanized caving face and the isopach map of the extremely thick conglomerate layer, make a plane stress similarity simulation model according to the similarity ratio;

[0017] S12. Set a fixed support edge at the bottom of the plane stress similarity simulation model, set simply supported edges on both sides of the plane stress similarity simulation model, and set a hydraulic jack at the top of the plane stress similarity simulation model to apply vertical stress;

[0018] S13. On the front of the similarity model, arrange observation lines A, B, C, and D in sequence at the bottom, middle, and top of the extremely thick conglomerate layer, and arrange several other observation lines in the overlying strata of the coal seam and the underlying strata of the extremely thick conglomerate layer;

[0019] S14. Set multiple observation points on observation lines A, B, C, D and other observation lines.

[0020] In the preferred solution, in step S11, there is a parallel unconformity contact soft interlayer between the extremely thick conglomerate layers. The soft interlayer divides the conglomerate layer into an upper conglomerate layer and a lower conglomerate layer. According to the structural characteristics and thickness development characteristics of the conglomerate layer, use surfer software to draw the isopach map of the conglomerate layer in the mine field

[0021] In the preferred solution, the coal and rock layer materials for making the plane stress similarity simulation model in S11 are sand, calcium carbonate, and gypsum. Borax is used as a retarder, talcum powder simulates the bedding plane, and mica simulates the bedding surface.

[0022] In the preferred solution, in S2, conduct a similarity simulation test for fully-mechanized caving mining under the extremely thick conglomerate layer, mine the coal seam, and use a total station to measure the horizontal and vertical displacement coordinates of the observation points of each observation station.

[0023] In the preferred solution, according to the similarity simulation test for fully-mechanized caving mining under the extremely thick conglomerate layer, obtain the relationships between the separation amount and the separation interval length of the conglomerate layer and the advancement of the fully-mechanized caving face respectively, obtain the relationships between the separation rate and the change rate of the separation interval of the conglomerate layer and the advancement of the fully-mechanized caving face respectively, and obtain the shape characteristics of the first caving and periodic caving caving bodies of the extremely thick conglomerate layer.

[0024] In the preferred solution, the calculation formula for the separation rate is: The calculation formula for the change rate of the separation interval is:

[0025] Wherein, v his the separation rate, H i is the amount of separation at the end of the separation stage; H0 is the amount of separation at the beginning of the separation stage; L i is the advancement at the end of the separation stage; L0 is the advancement at the beginning of the separation stage; v L is the change rate of the separation interval; S i is the length of the separation interval at the end of the separation stage; S0 is the length of the separation interval at the beginning of the separation stage.

[0026] In the preferred solution, based on the results of the similar simulation test of the fully-mechanized caving face under the extremely thick conglomerate layer, combined with the theoretical calculations of the "key stratum" and "thick plate", according to the deformation, movement and separation evolution characteristics of the extremely thick conglomerate layer, a mechanical model of separation and fracture for the fully-mechanized caving of the extremely thick conglomerate layer was established.

[0027] In the preferred solution, the mechanical model for calculating the separation of the conglomerate layer from bottom to top is successively: the coal cutting seam of the fully-mechanized caving face, the coal caving seam of the fully-mechanized caving face, multiple rock layers, and the conglomerate layer.

[0028] In the preferred solution, the formula for calculating the amount of separation of the extremely thick conglomerate layer is:

[0029]

[0030] In the formula, S is the maximum amount of separation of the conglomerate layer overlying the coal seam; M0 is the coal cutting height of the fully-mechanized caving face; M1 is the coal caving height of the fully-mechanized caving face; η is the caving rate of the top coal, 70% ≤ η ≤ 90%; K M is the residual swelling coefficient of the top coal, 1.04 ≤ K M ≤ 1.06; h i is the thickness of the i-th rock layer overlying the coal seam; K i is the residual swelling coefficient of the i-th rock layer overlying the coal seam; W o is the maximum deflection at the initial fracture of the conglomerate layer.

[0031] The present invention provides a calculation method for the separation amount of gravel strata based on similar simulation. According to the geological and mining conditions of the fully-mechanized caving face, based on the results of plane stress similar simulation tests, the "key stratum" and "thick plate" theories are used for calculation to study the deformation, movement and separation evolution characteristics of extremely thick gravel strata in fully-mechanized caving mining, establish a separation and fracture mechanics model for extremely thick gravel strata in fully-mechanized caving mining, and derive a formula for calculating the separation amount. The "separation rate" and "change rate of separation interval" are introduced to quantitatively represent the separation evolution law of gravel strata, and the deformation is divided into zones during the separation stage. Through simulation tests, the shape characteristics of the initial caving and periodic caving caving bodies of extremely thick gravel strata are obtained. The initial caving and periodic caving of the lower gravel strata are both caving of the whole layer. The initial caving body is a quadrangular prism with a "positive trapezoid" cross-section, and the periodic caving body is a quadrangular prism with a "quasi-parallelogram" cross-section. The impact of the caving and instability of the caving body of extremely thick gravel strata on the coal and rock mass of the lower fully-mechanized caving face is theoretically calculated, and the influence of the vibration field on the mine tremors of the lower fully-mechanized caving face is explained. The research conclusions have certain theoretical and on-site guiding significance for the safe production of fully-mechanized caving faces and the prevention of rock burst disasters. Further, the research results have important theoretical value and practical guiding significance for the stability and safety assessment of surface tunnel engineering, reservoir dam foundations and highway subgrades in coal mining under the geological conditions of thick and hard rock strata in China, as well as the prediction and prevention of rock burst dynamic disasters in metal mines. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be further described below in conjunction with the drawings and embodiments:

[0033] Figure 1 is a front view of the similar model of the present invention and the roof and floor strata of the coal seam;

[0034] Figure 2 is a linear relationship diagram of the separation of gravel strata and the advance of the working face of the present invention;

[0035] Figure 3 is a schematic diagram of the mechanical model for calculating the separation of gravel strata of the present invention.

[0036] In the figure: gravel stratum 1; upper gravel stratum 101; lower gravel stratum 102; rock stratum 2; fully-mechanized caving coal seam 3; fully-mechanized caving coal layer 4; observation line A 5; observation line B 6; observation line C 7; observation line D 8; other observation lines 9. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] Example 1:

[0038] A calculation method for the separation amount of gravel strata based on similar simulation includes the following steps:

[0039] S1. Fabricate a plane stress similar simulation test model;

[0040] S2. Conduct a similar simulation test for fully-mechanized caving mining under an extremely thick gravel stratum 1;

[0041] S3. Establish a mechanical model for calculating the separation amount of the extremely thick conglomerate layer 1;

[0042] S4. Establish a formula for calculating the separation amount of the extremely thick conglomerate layer 1 based on the mechanical model;

[0043] Calculate the separation amount of the conglomerate layer 1 through the above steps.

[0044] In the preferred solution, in step S1, the steps for fabricating the plane stress similarity simulation test model are as follows:

[0045] S11. According to the comprehensive columnar section of the fully-mechanized caving face and the isopach map of the extremely thick conglomerate layer 1, fabricate a plane stress similarity simulation model according to the similarity ratio;

[0046] S12. Set a fixed support edge at the bottom of the plane stress similarity simulation model, set simply supported edges on both sides of the plane stress similarity simulation model, and set a hydraulic jack at the top of the plane stress similarity simulation model to apply vertical stress;

[0047] S13. On the front of the similarity model, arrange observation lines A 5, B 6, C 7, and D 8 in sequence at the bottom, middle, and top of the extremely thick conglomerate layer 1, and arrange several other observation lines 9 in the overlying strata of the coal seam and the underlying strata 2 of the extremely thick conglomerate layer 1;

[0048] S14. Set multiple observation points on the observation lines A 5, B 6, C 7, D 8, and other observation lines 9.

[0049] In the preferred solution, in step S11, there is a parallel unconformity contact soft interlayer between the extremely thick conglomerate layers. The soft interlayer divides the conglomerate layer into the upper conglomerate layer 101 and the lower conglomerate layer 102. According to the structural characteristics of the conglomerate layer and the development characteristics of the conglomerate layer thickness, use the surfer software to draw the isopach map of the conglomerate layer in the mine field.

[0050] In the preferred solution, the coal and rock layer materials for fabricating the plane stress similarity simulation model in S11 are sand, calcium carbonate, and gypsum. Borax is used as a retarder, talcum powder simulates the bedding plane, and mica simulates the bedding surface.

[0051] In the preferred solution, in S2, conduct a similarity simulation test for fully-mechanized caving mining under the extremely thick conglomerate layer 1, mine the coal seam, and use a total station to measure the horizontal and vertical displacement coordinates of the observation points of each observation station.

[0052] In the preferred solution, based on the similarity simulation test for fully-mechanized caving mining under the extremely thick conglomerate layer, obtain the relationships between the separation amount and the length of the separation interval of the conglomerate layer and the advancement of the fully-mechanized caving face respectively, obtain the relationships between the separation rate and the change rate of the separation interval of the conglomerate layer and the advancement of the fully-mechanized caving face respectively, and obtain the shape characteristics of the first caving and periodic caving caved bodies of the extremely thick conglomerate layer.

[0053] Through simulation tests, the shape characteristics of the first caving and periodic caving caving bodies of the extremely thick conglomerate layer were obtained. The first caving and periodic caving of the lower conglomerate layer are both whole-layer caving. The first caving body is a quadrangular prism with a "regular trapezoid" cross-section, and the periodic caving body is a quadrangular prism with a "quasi-parallelogram" cross-section. The impact of the caving and instability of the extremely thick conglomerate layer caving body on the coal and rock mass of the lower fully-mechanized caving face was theoretically calculated, and the influence of the vibration field on the mine tremors of the lower fully-mechanized caving face was explained.

[0054] Study the impact of the caving and instability of the conglomerate layer at different caving stages on the fully-mechanized caving face. The impact of the first caving and periodic caving instability of the lower conglomerate layer on the working face is significantly higher than that of the first caving of the upper conglomerate layer, and the former is one to two orders of magnitude different from the latter. When the lower conglomerate layer undergoes the first caving instability, the impact on the working face is the most serious, and the energy of the vibration stress wave transmitted to the coal and rock mass of the fully-mechanized caving face reaches 1.8×10 5 J, which is likely to induce a large-energy microseismic event in the coal and rock mass. Therefore, the risk of the lower conglomerate layer caving instability inducing rock bursts in the working face is the highest.

[0055] In the optimal solution, the formula for the separation rate is:

[0056] The formula for the change rate of the separation interval is:

[0057] In the formula, v h is the separation rate, H i is the separation amount at the end of the separation stage; H0 is the separation amount at the beginning of the separation stage; L i is the advance at the end of the separation stage; L0 is the advance at the beginning of the separation stage; v L is the change rate of the separation interval; S i is the length of the separation interval at the end of the separation stage; S0 is the length of the separation interval at the beginning of the separation stage.

[0058] Two new terms, "separation rate" and "change rate of separation interval", are introduced to quantitatively represent the separation evolution law of the conglomerate layer and divide the deformation of the separation stage.

[0059] In the optimal solution, based on the results of the similar simulation test of the fully-mechanized caving face under the extremely thick conglomerate layer, combined with the theoretical calculations of the "key stratum" and "thick plate", according to the deformation, movement and separation evolution characteristics of the extremely thick conglomerate layer, a separation and fracture mechanics model for the fully-mechanized caving of the extremely thick conglomerate layer was established.

[0060] In the optimal solution, the separation calculation mechanics model of the conglomerate layer from bottom to top is: the coal cutting layer 3 of the fully-mechanized caving face, the coal caving layer 4 of the fully-mechanized caving face, multiple rock layers 2, and the conglomerate layer 1.

[0061] In the preferred solution, the calculation formula for the separation amount of the extremely thick gravel layer is as follows:

[0062]

[0063] In the formula, S is the maximum separation amount of the gravel layer overlying the coal seam; M0 is the coal cutting height of the fully mechanized caving face; M1 is the coal caving height of the fully mechanized caving face; η is the caving rate of the top coal, 70% ≤ η ≤ 90%; K M is the residual swelling coefficient of the top coal, 1.04 ≤ K M ≤ 1.06; h i is the thickness of the i-th layer of the overlying strata of the coal seam; K i is the residual swelling coefficient of the i-th layer of the overlying strata of the coal seam; W o is the maximum deflection at the initial fracture of the gravel layer.

[0064] Example 2:

[0065] Further illustrate in combination with Example 1:

[0066] The 13230 fully mechanized caving face of a certain coal mine belongs to the strike longwall fully mechanized caving face. The strike length of the fully mechanized caving face is 971 m, the dip length is 196 m, the length of the return air heading is 1088 m, and the length of the transportation heading is 1087 m. The 13230 fully mechanized caving face mines the 2-3 coal seam, the coal seam thickness is 9.3 - 10.9 m, the average thickness is 10.5 m, the coal seam dip angle is 9° - 13°, and the average dip angle is 11°, belonging to the "soft" gently inclined extra-thick coal seam. The direct floor of the working face is black-gray mudstone, the old floor is fine-grained sandstone, the direct roof is an interlayer of mudstone and sandy mudstone, and the old roof is a fine-grained sandstone layer.

[0067] About 220 m from the roof of the 2-3 coal seam of the 13230 fully mechanized caving face, there is a layer of extremely thick gravel layer with a thickness of 335 m. Between the gravel layer 1 and the ground surface is a relatively thin Quaternary loess layer with a thickness of about 7.85 m. Therefore, when the fully mechanized caving face is mined, the subsidence and movement of the upper extremely thick gravel layer 1 can represent the subsidence and movement of the ground surface.

[0068] Similar simulation test:

[0069] The geometric similarity constant C of the model L = 250, the unit weight similarity constant C γ = 0.56; the strength similarity constant C σ = 0.017; the time similarity constant C t = 15.8; the Poisson's ratio similarity constant C μ = 1. The coal seam floor rock stratum, the 2-3 coal seam, the overlying strata are simulated similar until the extremely thick gravel layer 1, and the length × width × height of the model are 4000 mm × 300 mm × 2072 mm respectively.

[0070] According to the similarity ratio, the similar model coal and rock strata are made of sand, calcium carbonate and gypsum. Borax is used as a retarder. Talcum powder simulates the bedding plane, and mica simulates the bedding surface. The model is made in layers according to the designed similarity ratio, and each rock stratum is fully compacted and consolidated. After the model is completed for 1 - 2 days, the front and rear templates are removed. After the model is naturally dried for 6 - 10 days, four displacement observation lines A, B, C, and D are arranged in sequence at the bottom and top of the lower conglomerate layer 102 and the upper conglomerate layer 101. Starting from the open-off cut, after the coal and rock strata are stable with the coal seam mining, the horizontal and vertical displacement coordinates of each measuring point on the observation line are measured using a total station. The similar model, the observation line and the layout of its observation points are as Figure 3 shown.

[0071] Results of the similarity simulation test:

[0072] During the mining of the fully mechanized top coal caving face, the separation amount and the separation interval length of the conglomerate layer 1 are related to the advancing degree of the fully mechanized top coal caving face, as shown in Table 1 and Figure 3 shown. According to the separation evolution characteristics of the conglomerate layer 1, the whole process of separation evolution is divided into four stages, namely: the gestation stage, the acceleration stage, the slow expansion stage and the stable stage.

[0073] The relationships between the separation rate of the conglomerate layer in the 13230 fully mechanized top coal caving face, the change rate of the separation interval and the advancing degree of the fully mechanized top coal caving face are shown in Table 1.

[0074] Table 1 Separation parameters in different separation stages

[0075]

[0076] The whole process of separation evolution is divided into four stages, namely: the gestation stage, the acceleration stage, the slow expansion stage and the stable stage. The relationships between the gestation stage, the acceleration stage, the slow expansion stage and the stable stage and the separation rate and the change rate of the separation interval are obtained.

[0077] Calculation of separation of the extremely thick conglomerate layer:

[0078] Regarding the geological and mining conditions of the 13230 fully mechanized top coal caving face, the relevant parameters of the overlying strata and the deformation and movement of the extremely thick conglomerate layer, substituting them into the separation amount S calculation formula of the conglomerate layer overlying the coal seam, the maximum separation amount S of the conglomerate layer is calculated:

[0079]

[0080] Therefore, when the extremely thick conglomerate layer collapses, the maximum separation amount of the lower conglomerate layer is 4.70 m, and this value is basically consistent with the separation amount of 4.7 - 5.0 m obtained from the similarity simulation test.

[0081] The above embodiments are only the preferred technical solutions of the present invention and should not be regarded as limitations on the present invention. In the present application, the embodiments and the features in the embodiments can be arbitrarily combined with each other without conflict. The protection scope of the present invention shall be the technical solutions recited in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recited in the claims, that is, the equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A calculation method for the separation amount of a super-thick gravel layer based on similar simulation, characterized by the following steps: S1. Fabricate a plane stress similar simulation test model; S2. Conduct a similar simulation test for fully-mechanized caving mining under the super-thick gravel layer (1); S3. Establish a mechanical model for calculating the separation amount of the super-thick gravel layer (1); S4. Establish a calculation formula for the separation amount of the super-thick gravel layer (1) according to the mechanical model; Calculate the separation amount of the gravel layer (1) through the above steps; Based on the similar simulation test for fully-mechanized caving mining under the super-thick gravel layer, obtain the relationships between the separation amount and the length of the separation interval of the gravel layer and the advancement of the fully-mechanized caving face respectively, obtain the relationships between the separation rate and the change rate of the separation interval of the gravel layer and the advancement of the fully-mechanized caving face respectively, obtain the shape characteristics of the initial caving and periodic caving collapse bodies of the super-thick gravel layer, and conduct deformation zoning for the separation stage; The formula for calculating the delamination rate is: ; The calculation formula for the change rate of the abscission zone is as follows: ; In the formula, is the separation rate, H i is the separation amount at the end of the separation stage; H 0 is the separation amount at the beginning of the separation stage; L i is the advancement degree at the end of the separation stage; L 0 is the advancement degree at the beginning of the separation stage; is the change rate of the separation interval; S i is the separation interval length at the end of the separation stage; S 0 is the separation interval length at the beginning of the separation stage; Based on the results of the similar simulation test for the fully-mechanized caving face under the super-thick gravel layer, combined with the calculation of the "key stratum" and "thick plate" theories, establish a mechanical model for separation and fracture of the super-thick gravel layer in fully-mechanized caving mining according to the deformation movement and separation evolution characteristics of the super-thick gravel layer; The calculation formula for the separation amount of the super-thick gravel layer (1) is: Wherein, S is the maximum separation amount of the overlying conglomerate layer of the coal seam; M 0 is the coal cutting height of the fully-mechanized caving face; M 1 is the coal caving height of the fully-mechanized caving face; is the top coal recovery rate, ; is the residual swelling coefficient of the top coal, ; h i is the thickness of the i th layer of the overlying strata of the coal seam; K i is the residual swelling coefficient of the i th layer of the overlying strata of the coal seam; W o is the maximum deflection at the initial fracture of the conglomerate layer.

2. The calculation method of the separation amount of a huge thick gravel layer based on similar simulation according to claim 1, characterized in that: in In step S1, the steps for fabricating the plane stress similar simulation test model are: S11. According to the comprehensive columnar section of the fully-mechanized caving face and the isopach map of the super-thick gravel layer (1), fabricate a plane stress similar simulation model according to the similar ratio; S12. Set a fixed support edge at the bottom of the plane stress similar simulation model, set simply supported edges on both sides of the plane stress similar simulation model, and set a hydraulic jack at the top of the plane stress similar simulation model to apply vertical stress; S13. On the front of the similar model, arrange observation line A (5), observation line B (6), observation line C (7), and observation line D (8) in sequence at the bottom, middle, and top of the super-thick gravel layer (1), and arrange several other observation lines (9) on the overlying strata of the coal seam and the underlying strata (2) of the super-thick gravel layer (1); S14. Set multiple observation points on observation line A (5), observation line B (6), observation line C (7), observation line D (8), and other observation lines (9).

3. The calculation method of the separation amount of a super-thick gravel layer based on similar simulation according to claim 2, characterized in that: In step S11, there is a parallel unconformity contact soft interlayer between the super-thick gravel layers, and the soft interlayer divides the gravel layer into an upper gravel layer (101) and a lower gravel layer (102). According to the structural and thickness development characteristics of the gravel layer, use surfer software to draw the isopach map of the gravel layer in the mine field.

4. The calculation method of the separation amount of a super-thick gravel stratum based on similar simulation according to claim 2, characterized in that: The coal and rock layer materials for fabricating the plane stress similar simulation model in S11 are sand, calcium carbonate, and gypsum, with borax as a retarder, talcum powder simulating bedding planes, and mica simulating bedding surfaces.

5. The calculation method of the separation amount of the extremely thick gravel layer based on similarity simulation according to claim 1, characterized in that: S2 In the similar simulation test for fully-mechanized caving mining under the super-thick gravel layer (1), mine the coal seam, and use a total station to measure the horizontal and vertical displacement coordinates of the observation points of each observation station.

6. The calculation method of the separation amount of the extremely thick gravel stratum based on similar simulation according to claim 1, characterized in that: The mechanical model for calculating the separation of the gravel layer from bottom to top is successively: the coal layer cut by the fully-mechanized caving face (3), the coal layer caved by the fully-mechanized caving face (4), multiple rock layers (2), and the gravel layer (1).

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