Method for determining space volume of separation layer under thick sandstone

Abstract

The invention relates to a method for determining the space volume of a lower separation layer of thick sandstone. The method comprises the following steps: carrying out precondition assumption on development simulation of the lower separation layer of the thick sandstone; according to the advancing process of the mining working face below the thick sandstone, formation and development stage conditions of the separation layer are researched, the starting distance of development of the separation layer and the distance of height limit development of the middle of the separation layer are determined, and then the development condition of the separation layer is judged according to the two distances and size data of advancing of the working face; determining the middle height of the separation layer according to the difference between the subsidence values of the lower rock stratum and the upper rock stratum of the separation layer; and determining the separation layer space volumes of the separation layer lower rock stratum in different sinking stages by combining the separation layer development stage and the separation layer middle height in the previous two steps.

Description

Technical Field

[0001] This invention belongs to the field of underground delamination data measurement technology, specifically relating to a method for determining the volume of delamination space under thick sandstone. Background Technology

[0002] Delamination occurs due to the relatively uneven settlement movement between underground coal seams and overlying strata caused by mining. Allowing delamination to develop unchecked poses significant risks, potentially leading to underground rock collapse. Currently, the main method for addressing delamination is delamination grouting, which involves drilling holes on the surface and then high-pressure-transmitting a high-concentration fly ash or coal gangue slurry into the delamination. The ground pressure causes the slurry to bleed water and compact, supporting the overlying strata, mitigating ground subsidence, and protecting surface structures. During delamination grouting, estimating the volume of the delamination is fundamental to the design of the grouting project. Existing projects often estimate this volume using the injection-production ratio. However, the injection-production ratio varies depending on geological and mining conditions, and rough figures are often given based on experience, resulting in large estimation errors and an inability to dynamically estimate the volume during the delamination development process. Summary of the Invention

[0003] To address the above problems, the present invention provides a method for determining the volume of the delamination space beneath thick sandstone, comprising:

[0004] S1: Prerequisite assumptions for simulating the development of delamination beneath thick sandstone;

[0005] S2: Based on the advancement of the mining face beneath the thick sandstone, study the formation and development stages of the delamination, determine the starting distance for delamination development and the distance for the extreme development of the middle height of the delamination, and then judge the delamination development based on these two distances and the size data of the working face advancement.

[0006] S3: The height of the middle part of the ablation is determined by the difference in subsidence between the lower and upper rock layers.

[0007] S4: Combining the delamination development stage in step S2 and the height of the middle part of the delamination in step S3, determine the volume of the delamination space when the lower rock strata are in different subsidence stages.

[0008] Optionally, in step S1, the specific assumptions are as follows:

[0009] (1) The delamination space is unique, that is, the fractures along the bedding plane in the upper and lower rock layers where delamination has developed have been compacted, and there is only one delamination space.

[0010] (2) As the degree of impact from mining increases, the coefficient of collapse and swelling of the overlying rock gradually decreases;

[0011] (3) The upper rock layer of the delamination is always in a suspended state, and the subsidence value of the upper rock layer is much smaller than that of the lower rock layer;

[0012] (4) The determination of the area and volume of the separation space is based on an approximate equivalent calculation.

[0013] Optionally, in step S2, the step of studying the formation and development stages of the delamination based on the advancement of the mining face beneath the thick sandstone layer is as follows: starting from the cut-out position, the working face advances along the direction of advancement. When it reaches the first position, a delamination begins to form beneath the thick sandstone layer. As the working face advances, the height of the middle part of the delamination gradually increases. When it continues to advance to the second position, the height of the middle part of the delamination reaches its maximum. After that, as the working face continues to advance, the height of the middle part of the delamination remains constant and no longer increases.

[0014] Further optionally, the starting distance for delamination development is the distance from the opening of the cut hole to the first position in the working face advancing direction, and the distance for the extreme development of the middle height of the delamination is the distance from the opening of the cut hole to the second position in the working face advancing direction.

[0015] Further optionally, the initiation distance L of the delamination development 启 Determined by the following formula:

[0016] L 启 =2h 离 / tanδ 离

[0017] Among them, L 启 The initiation distance for ablation development is m; h 离 δ represents the vertical height of the separation from the coal seam roof, in meters (m); 离 The delamination development angle is in degrees.

[0018] Further optionally, the distance L at the height limit of the delamination midpoint development 极 Determined by the following formula:

[0019] L 极 =2h 离 / tanδ 极

[0020] Among them, L 极 δ represents the distance at which the mid-layer of the ablation zone reaches its maximum development, in meters (m); 极 The maximum development angle at the middle of the delamination layer is , in degrees.

[0021] Optionally, in step S2, the method for determining the development stage of the delamination layer is: L 短 The shorter of the length and width of the working surface, in meters (m); L 长 L is the longer of the length and width of the working surface, in meters (m). 极 Always greater than L 启 ;

[0022] When L 短 <L启 At that time, regardless of L 长 Regardless of size, no delamination is developed under thick sandstone;

[0023] When L 短 =L 启 At that time, a delamination layer had just developed beneath the thick sandstone, regardless of L 长 Regardless of size, the delamination volume is approximately 0;

[0024] When L 启 <L 短 <L 极 And L 启 <L 长 <L 极 At that time, the height of the middle part of the delamination increases with the increase of the length or width of the working surface, and the volume of the delamination space increases at an accelerated rate with the increase of the length or width.

[0025] When L 启 <L 短 <L 极 And L 长 ≥L 极 At that time, the height of the middle part of the delamination only increases with the increase of the short side of the working face, and does not change with the increase of the long side of the working face. The volume of the delamination space increases rapidly with the increase of the short side, and increases at a constant rate with the increase of the long side.

[0026] When L 短 =L 极 At that time, the height at the middle of the delamination reaches its maximum value;

[0027] When L 短 >L 极 At that time, the height of the middle part of the delamination remains constant as the length or width of the working surface increases, while the volume of the delamination space increases uniformly as the length or width of the working surface increases.

[0028] Optionally, in step S3, the height L at the center of the delamination... 离 Determined by the following formula:

[0029] L 离 =L 下 -L 上 =M-(k-1)×h 垮 -w

[0030] Among them, L 离 The height at the midpoint of the delamination, in meters (m); L 下 The subsidence of the underlying rock strata is expressed in meters (m); the subsidence value of the underlying rock strata is expressed in liters (L). 上 ρ is the subsidence of the overlying strata, m; M is the coal seam thickness, m; k is the coefficient of caving and swelling of the overlying strata in the goaf, which decreases with the compaction of the caving gangue; w is the deflection of the overlying strata in the middle of the delamination, m; h 垮 The height of the collapsed overburden in the goaf, in meters (m).

[0031] Optionally, in step S4, when neither the lower rock strata in the length nor width direction of the working face advance has reached stable subsidence, there exists a unique maximum delamination height, and this location is at the center of the delamination space. At this time, the projection of the subsidence space of the lower and upper rock strata is simplified to two quadrangular pyramids with the same base area but different heights. The difference in volume between the two quadrangular pyramids is the volume of the delamination space, which is determined by the following formula:

[0032] V 离 =1 / 3×(L) 推 -L 启 (L) 宽 -L 启 )×L 离

[0033] Among them, V 离 Let m be the volume of the separated space. 3 L 宽 The width of the working surface is in meters (m).

[0034] Optionally, in step S4, when the lower rock strata of the delamination in one direction of the working face's advance direction have reached their ultimate settlement value and there are multiple maximum settlement points, while the lower rock strata of the delamination in another direction have only one maximum settlement point, a straight bottom-shaped delamination space is formed. In this case, the settlement space of the upper rock strata of the delamination is determined according to the elasticity plate bending theory, and the volume of the delamination space is determined by the following formula:

[0035] V 离 =1 / 2×(L) 推 -L 启 (L) 宽 -L 启 )L 下 -1 / 3×(L 宽 -L 启 )L 下 ×1 / 2(L 极 -L 启 ).

[0036] Optionally, in step S4, when the lower rock strata in the length and width directions of the working face advancement have reached a stable subsidence state, forming a planar bottom-shaped delamination space, and the subsidence at multiple points reaches the ultimate subsidence value, forming a subsidence plane, the subsidence space of the lower rock strata is simplified to a truncated quadrangular prism. The subsidence space of the upper rock strata is determined according to the elasticity plate bending theory. At this time, the volume of the delamination space is determined by the following formula:

[0037] V 离 =1 / 3×L 下 ×[(L 推 -L 启 (L)宽 -L 启 )+(L 推 -L 极 (L) 宽 -L 启 )).

[0038] By combining the advance speed of the coal mine working face with the method described in this invention, the volume of the delamination space can be dynamically determined, which can support the precise control of the delamination grouting and settlement reduction project. The dynamic real-time acquisition of the delamination space volume plays a decisive supporting role in calculating and adjusting parameters such as grouting volume, grouting speed, grouting pressure, and grouting concentration. Attached Figure Description

[0039] Figure 1 A schematic diagram of the delamination development process (I);

[0040] Figure 2 Schematic diagram of the delamination development process (II);

[0041] Figure 3 A schematic diagram for determining the height of the middle of the delamination;

[0042] Figure 4 This is a schematic diagram of a four-sided pyramidal exfoliated space;

[0043] Figure 5 A schematic diagram of a straight-bottomed separation space;

[0044] Figure 6 A schematic diagram of a frustum-shaped delamination space;

[0045] Figure 7 The figure shows a comparison curve between the delamination space volume determined in the example and the numerical simulation results.

[0046] In the attached diagram, 1 represents the first position, 2 represents the second position, and 3 represents the incision site. Detailed Implementation

[0047] This embodiment provides a method for determining the volume of the exfoliation space beneath thick sandstone, including:

[0048] S1: Prerequisite assumptions for simulating the development of delamination beneath thick sandstone;

[0049] S2: Based on the advancement of the mining face beneath the thick sandstone, study the formation and development stages of the delamination, determine the starting distance for delamination development and the distance for the extreme development of the middle height of the delamination, and then judge the delamination development based on these two distances and the size data of the working face advancement.

[0050] S3: The height of the middle part of the ablation is determined by the difference in subsidence between the lower and upper rock layers.

[0051] S4: Combining the delamination development stage in step S2 and the height of the middle part of the delamination in step S3, determine the volume of the delamination space when the lower rock strata are in different subsidence stages.

[0052] Optionally, in step S1, the specific assumptions are as follows:

[0053] (1) The delamination space is unique, that is, the fractures along the bedding plane in the upper and lower rock layers where delamination has developed have been compacted, and there is only one delamination space.

[0054] (2) As the degree of impact from mining increases, the coefficient of collapse and swelling of the overlying rock gradually decreases;

[0055] (3) The upper rock layer of the delamination is always in a suspended state, and the subsidence value of the upper rock layer is much smaller than that of the lower rock layer;

[0056] (4) The determination of the area and volume of the separation space is based on an approximate equivalent calculation.

[0057] Beneath the thick sandstone lies the mining area, which can be simplified as a cuboid. Initially, the mining face has a width equal to the distance in the advancing direction and a height equal to the vertical distance from the top of the coal seam to the bottom of the thick sandstone. The length of the working face is horizontal and perpendicular to the width. Delamination gradually forms during the working face's advancement. After the working face advances a certain distance, the mining effects transmit to the underlying strata of the thick sandstone, causing a series of movements and deformations in these strata until both the thick sandstone and the underlying strata have settled and stabilized, and the delamination space has also stabilized. Thereafter, as the working face advances further, the delamination morphology essentially extends outward from the center of the delamination without undergoing further morphological changes.

[0058] The analysis is based on the premise that the thick sandstone is not fractured due to the limitations of the mining size. Affected by mining, the lower strata, with the bottom of the thick sandstone layer as the boundary, experience non-uniform settlement. The thick sandstone and the upper strata undergo uniform settlement, both equal to the deflection of the thick sandstone. This deflection is much smaller than the settlement of the lower strata and can be ignored, i.e., the settlement of the upper strata can be disregarded. The lower strata gradually subside due to mining, leading to a continuous increase in the separation height. When the goaf size reaches the limit of movement of the upper and lower strata, the height in the middle of the separation space remains stable. As the working face advances further, the separation volume increases linearly.

[0059] like Figure 1 As shown, the above assumptions are based on the following delamination development process:

[0060] a. Delamination incubation stage: This stage begins with the advancement of the working face and continues until a differential settlement occurs between the thick sandstone and the underlying strata. During this stage, the effects of mining begin to spread, and delamination begins to occur at the interface between the hard upper and soft lower strata near the goaf. Then, delamination occurs in the overlying strata of the goaf. Due to the effects of mining, the thick sandstone and the underlying strata undergo stress and strain adjustments, resulting in stress and strain concentration at the strata interface. However, the degree of stress and strain change at the interface between the thick sandstone and the underlying strata has not yet exceeded the interlayer interaction limit, and delamination has not yet developed between the thick sandstone and the underlying strata.

[0061] b. Accelerated growth stage of delamination space: This stage begins with delamination occurring below the thick sandstone and continues until uniform subsidence occurs in the middle of the rock strata below the delamination. As the working face advances, delamination between the thick sandstone and the goaf continues to develop. The voids in the fractured and collapsed rocks are compressed, and the delamination space below the thick sandstone grows rapidly, that is, the planar range and development height of the delamination both increase.

[0062] c. Uniform growth stage of delamination space: This stage begins with uniform subsidence in the middle of the lower rock strata of the delamination and continues until the working face is mined out; the area of ​​the delamination space remains stable on the cross section where the working face width is located, and the increase in delamination volume is linearly related to the working face advance distance. The thick sandstone and the rock strata in the goaf are already in the state of compression limit.

[0063] During the delamination incubation stage, multiple delamination regions may develop in the overlying strata of the goaf, but macroscopically, all delamination regions show a gradual upward migration trend. During the uniform growth stage of the delamination space, the increase in delamination space is proportional to the migration space.

[0064] Then, the direction of advance of the mining face is changed to the aforementioned length direction, while the height remains unchanged, the height at the middle of the separation remains unchanged, and the volume of the separation space increases at a constant rate.

[0065] Optionally, in step S2, the step of studying the formation and development stages of the delamination based on the advancement of the mining face beneath the thick sandstone specifically includes: Figure 2 As shown, the working face starts from the opening position 3 and advances along the direction of advancement. When it reaches the first position 1, a delamination begins to form below the thick sandstone layer. As the working face advances, the height of the middle part of the delamination gradually increases. When it continues to advance to the second position 2, the height of the middle part of the delamination reaches its maximum, that is, L. 离max After that, the working face continued to advance, and the height of the middle of the delamination remained constant and did not increase further.

[0066] The starting distance for delamination development is the distance from the cutting eye 3 to the first position 1 in the working face advancing direction, and the distance for the maximum height development of the middle part of the delamination is the distance from the cutting eye 3 to the second position 2 in the working face advancing direction.

[0067] The cutting position refers to the location where coal mining begins.

[0068] Further optionally, the initiation distance L of the delamination development 启 Determined by the following formula:

[0069] L 启 =2h 离 / tanδ 离

[0070] Among them, L 启 The initiation distance for ablation development is m; h 离 δ represents the vertical height of the separation from the coal seam roof, in meters (m); 离 The delamination development angle is in degrees.

[0071] Further optionally, the distance L at the height limit of the delamination midpoint development 极 Determined by the following formula:

[0072] L 极 =2h 离 / tanδ 极

[0073] Among them, L 极 δ represents the distance at which the mid-layer of the ablation zone reaches its maximum development, in meters (m); 极 The maximum development angle at the middle of the delamination layer is , in degrees.

[0074] Optionally, in step S2, the method for determining the development stage of the delamination layer is: L 短 The shorter of the length and width of the working surface, in meters (m); L 长 L is the longer of the length and width of the working surface, in meters (m). 极 Always greater than L 启 ;

[0075] When L 短 <L 启 At that time, regardless of L 长 Regardless of size, no delamination is developed under thick sandstone;

[0076] When L 短 =L 启 At that time, a delamination layer had just developed beneath the thick sandstone, regardless of L 长 Regardless of size, the delamination volume is approximately 0;

[0077] When L 启 <L 短 <L 极 And L 启 <L 长 <L 极 At that time, the height of the middle part of the delamination increases with the increase of the length or width of the working surface, and the volume of the delamination space increases at an accelerated rate with the increase of the length or width.

[0078] The above three stages correspond to Figure 4 The situation shown;

[0079] When L 启 <L 短 <L 极 And L 长 ≥L 极 At that time, the height of the middle part of the delamination only increases with the increase of the short side of the working face, and does not change with the increase of the long side of the working face. The volume of the delamination space increases rapidly with the increase of the short side, and increases at a constant rate with the increase of the long side.

[0080] When L 短 =L 极 At that time, the height at the middle of the delamination reaches its maximum value;

[0081] The above two stages correspond to Figure 5 The situation shown;

[0082] When L 短 >L 极 At this stage, the height of the delamination center remains constant as the length or width of the working surface increases, while the volume of the delamination space increases uniformly with the increase of the length or width of the working surface. This stage corresponds to... Figure 6 The situation is shown below.

[0083] Optionally, in step S3, such as Figure 3 As shown, the height L at the middle of the delamination 离 Determined by the following formula:

[0084] L 离 =L 下 -L 上 =M-(k-1)×h 垮 -w

[0085] Among them, L 离 The height at the midpoint of the delamination, in meters (m); L 下 The subsidence of the underlying rock strata is expressed in meters (m); the subsidence value of the underlying rock strata is expressed in liters (L). 上 ρ is the subsidence of the overlying strata, m; M is the coal seam thickness, m; k is the coefficient of caving and swelling of the overlying strata in the goaf, which decreases with the compaction of the caving gangue; w is the deflection of the overlying strata in the middle of the delamination, m; h 垮 The height of the collapsed overburden in the goaf, in meters (m).

[0086] Based on the assumptions of step S1: the upper rock stratum of the ablation is always in a suspended state, and the subsidence of the upper rock stratum is much smaller than that of the lower rock stratum. Therefore, the deformation of the upper rock stratum in the middle of the ablation is not considered, i.e., the deformation of the upper rock stratum is 0, L 上 =w=0, that is, L 离 =L 下 .

[0087] Optionally, in step S4, based on the characteristics of the formation and development process of the delamination space and the subsidence characteristics of the lower rock layer, the volume models of the delamination space corresponding to the following conditions are established: when the lower rock layer has not reached stable subsidence, when it has reached the ultimate subsidence value, and when it has reached a stable subsidence state.

[0088] like Figure 4 As shown, when the lower strata of the delamination in both the length and width directions of the working face advance have not reached stable subsidence, there exists a unique maximum delamination height, and this location is situated at the center of the delamination space. Figure 4 When the projections along the length and width directions overlap, the subsidence spaces of the lower and upper rock layers are respectively equivalent to two geometric bodies with the same base area but different heights, resembling square pyramids. The difference in volume between the two pyramid-like geometric bodies is the volume of the delamination space, which is determined by the following formula:

[0089] V 离 =1 / 3×(L) 推 -L 启 (L) 宽 -L 启 )×L 离

[0090] Among them, V 离 Let m be the volume of the separated space. 3 L 宽 The width of the working surface is in meters (m).

[0091] like Figure 5 As shown, when the lower strata of the delaminated rock in one direction of the working face's advance direction have reached their ultimate subsidence value and there are multiple maximum subsidence points, while the lower strata of the delaminated rock in the other direction have only one maximum subsidence point, this indicates that the lower strata of the delaminated rock in the length direction have reached their ultimate subsidence state, while the lower strata of the delaminated rock in the width direction have not reached or have just reached their ultimate subsidence state. Figure 5 The projections along the length and width directions overlap, forming a straight-line bottom-shaped delamination space. The subsidence space of the underlying rock strata at this point is equivalent to... Figure 5 The geometry in the upper left corner, the subsidence space of the upper rock layer above the delamination, is determined according to the elasticity plate bending theory. The volume of the delamination space is then determined by the following formula:

[0092] V 离 =1 / 2×(L) 推 -L 启 (L) 宽 -L 启 )L 下 -1 / 3×(L 宽 -L 启 )L 下 ×1 / 2(L极 -L 启 ).

[0093] like Figure 6 As shown, when the lower rock strata in both the length and width directions of the working face have reached a stable subsidence state, forming a planar bottom-shaped delamination space, the subsidence at multiple points reaches the ultimate subsidence value. Figure 6 The projections along the length and width directions overlap to form a sinking plane. At this point, the sinking space of the lower stratum below the delamination is simplified to a truncated pyramid. The sinking space of the upper stratum above the delamination is determined according to the elasticity theory of plate bending. The volume of the delamination space is then determined by the following formula:

[0094] V 离 =1 / 3×L 下 ×[(L 推 -L 启 (L) 宽 -L 启 )+(L 推 -L 极 (L) 宽 -L 启 )).

[0095] Here is a specific example:

[0096] The vertical height h of the location of the delamination development from the top of the coal seam 离 =220m, delamination angle δ 离 =66°, the limiting angle δ at the middle of the delamination layer. 极 =64°, L is obtained from step S2 启 It is 77.58m, L 极 It is 142.96m;

[0097] Working surface width L 宽 =250m, working face advance length L 推 From 0m to 300m, according to the method for determining the delamination development stage in step S2, when the advancing length is less than the working face width, L 宽 For L 长 L 推 For L 短 When L 推 When the depth is <77.58m, no delamination develops beneath the thick sandstone; when L 推 When 77.58 m = L, delamination has just developed beneath the thick sandstone, and the delamination volume is approximately 0; when 77.58 m < L 推 <142.96m and L 宽When the value is greater than 142.96, the height of the middle part of the delamination increases only with the increase of the short side of the working face (i.e., the advancing length), and the volume of the delamination space increases at an accelerated rate with the increase of the short side; the volume of the delamination space in the above three stages is calculated using a simplified geometric method similar to a square pyramid.

[0098] When L 推 When the height reaches 142.96m, the height of the middle part of the delamination reaches its maximum value. The volume of the delamination space at this stage is simplified into a straight-bottom delamination space.

[0099] When L 推 When the height is greater than 142.96m, the height of the middle part of the delamination remains constant as the length of the working face increases, while the volume of the delamination space increases uniformly as the length of the working face increases. The volume of the delamination space at this stage is calculated using a simplified geometric method based on a truncated quadrangular prism.

[0100] In summary, delamination can develop under this working condition, and when the advancing length reaches 142.96m, the underlying rock strata below the delamination reach stable subsidence, and a plane appears at the bottom of the delamination. Thereafter, as the working face advances further, the delamination volume will enter a stage of uniform growth. In step S3, the height h of the collapsed overburden in the goaf... 垮 =20m, the coefficient of collapse of the overlying rock in the goaf is k=1.02, and the coal seam thickness is M=3m.

[0101] The specific numerical value of the delamination space volume determined by the method provided by the present invention is as follows: Figure 7 The numerical values ​​determined by the theory in the text.

[0102] 3Dimension Distinct Element Code (3DEC) software can use the discrete element method to study the interactions between blocks. The object under study is treated as a rigid body, and then discretized into a series of small element blocks using joints and fissures. Constitutive relations are assigned to the element blocks and the contacts between them. By simulating the motion and contact interactions between the small blocks, the motion and deformation of the entire block are obtained. This example uses the discrete element method of the existing 3DEC software for numerical simulation, and the simulated delamination volume data is as follows: Figure 7 The numerical values ​​in the numerical simulation.

[0103] like Figure 7 As shown, the theoretical value of the delamination space volume obtained by the method provided by this invention is not much different from the result obtained by numerical simulation, and the agreement is good.

Claims

1. A method for determining the volume of the exfoliation space beneath thick sandstone, characterized in that, include: S1: Prerequisite assumptions for simulating the development of delamination beneath thick sandstone; S2: Based on the advancement of the mining face beneath the thick sandstone, study the formation and development stages of the delamination, determine the starting distance for delamination development and the distance for the extreme development of the middle height of the delamination, and then judge the delamination development based on these two distances and the size data of the working face advancement. S3: The height of the middle part of the ablation is determined by the difference in subsidence between the lower and upper rock layers. S4: Combining the delamination development stage in step S2 and the height of the middle part of the delamination in step S3, determine the volume of the delamination space when the lower rock strata are in different subsidence stages.

2. The method for determining the volume of the delamination space beneath thick sandstone according to claim 1, characterized in that, In step S1, the specific assumptions are as follows: (1) The delamination space is unique, that is, the fractures along the bedding plane in the upper and lower rock layers where delamination has developed have been compacted, and there is only one delamination space. (2) As the degree of impact from mining increases, the coefficient of collapse and swelling of the overlying rock gradually decreases; (3) The upper rock layer of the delamination is always in a suspended state, and the subsidence value of the upper rock layer is much smaller than that of the lower rock layer; (4) The determination of the area and volume of the separation space is based on an approximate equivalent calculation.

3. The method for determining the volume of the delamination space beneath thick sandstone according to claim 1, characterized in that, In step S2, the process of studying the formation and development stages of the delamination based on the advancement of the mining face beneath the thick sandstone is as follows: starting from the opening position, the working face advances along the direction of advancement. When it reaches the first position, a delamination begins to form beneath the thick sandstone layer. As the working face advances, the height of the middle part of the delamination gradually increases. When it continues to advance to the second position, the height of the middle part of the delamination reaches its maximum. After that, as the working face continues to advance, the height of the middle part of the delamination remains constant and no longer increases.

4. The method for determining the volume of the exfoliation space beneath thick sandstone according to claim 3, characterized in that, The starting distance for delamination development is the distance from the opening of the cut hole to the first position in the working face advancing direction, and the distance for the maximum height development of the middle part of the delamination is the distance from the opening of the cut hole to the second position in the working face advancing direction.

5. The method for determining the volume of the exfoliation space beneath thick sandstone according to claim 4, characterized in that, The initiation distance for delamination development is determined by the following formula: L 启 =2h 离 / tanδ 离 Among them, L 启 The initiation distance for ablation development is m; h 离 δ represents the vertical height of the separation from the coal seam roof, in meters (m); 离 The delamination development angle is in degrees. The distance at which the height of the delamination reaches its maximum development is determined by the following formula: L 极 =2h 离 / tanδ 极 Among them, L 极 δ represents the distance at which the mid-layer of the ablation zone reaches its maximum development, in meters (m); 极 The maximum development angle at the middle of the delamination layer is , in degrees.

6. The method for determining the volume of the exfoliation space beneath thick sandstone according to claim 5, characterized in that, In step S2, the method for determining the development stage of the delamination layer is: L 短 The shorter of the length and width of the working surface, in meters (m); L 长 L is the longer of the length and width of the working surface, in meters (m). 极 Always greater than L 启 ; When L 短 <L 启 At that time, regardless of L 长 Regardless of size, no delamination is developed under thick sandstone; When L 短 =L 启 At that time, a delamination layer had just developed beneath the thick sandstone, regardless of L 长 Regardless of size, the delamination volume is approximately 0; When L 启 <L 短 <L 极 And L 启 <L 长 <L 极 At that time, the height of the middle part of the delamination increases with the increase of the length or width of the working surface, and the volume of the delamination space increases at an accelerated rate with the increase of the length or width. When L 启 <L 短 <L 极 And L 长 ≥L 极 At that time, the height of the middle part of the delamination only increases with the increase of the short side of the working face, and does not change with the increase of the long side of the working face. The volume of the delamination space increases rapidly with the increase of the short side, and increases at a constant rate with the increase of the long side. When L 短 =L 极 At that time, the height at the middle of the delamination reaches its maximum value; When L 短 >L 极 At that time, the height of the middle part of the delamination remains constant as the length or width of the working surface increases, while the volume of the delamination space increases uniformly as the length or width of the working surface increases.

7. The method for determining the volume of the exfoliation space beneath thick sandstone according to claim 6, characterized in that, In step S3, the height L at the middle of the delamination 离 Determined by the following formula: L 离 =L 下 -L 上 =M-(k-1)×h 垮 -w Among them, L 离 The height at the midpoint of the delamination, in meters (m); L 下 The subsidence of the underlying rock strata is expressed in meters (m); L 上 ρ is the subsidence of the overlying strata, m; M is the coal seam thickness, m; k is the coefficient of caving and swelling of the overlying strata in the goaf, which decreases with the compaction of the caving gangue; w is the deflection of the overlying strata in the middle of the delamination, m; h 垮 The height of the collapsed overburden in the goaf, in meters (m).

8. The method for determining the volume of the exfoliation space beneath thick sandstone according to claim 7, characterized in that, In step S4, when the lower strata of the delamination in both the length and width directions of the working face advance have not reached stable subsidence, there exists a unique maximum delamination height, and this location is at the center of the delamination space. At this time, the projection of the subsidence space of the lower and upper strata of the delamination is simplified to two square pyramids with the same base area but different heights. The difference in volume between the two square pyramids is the volume of the delamination space, which is determined by the following formula: V 离 <1 / 3×(L 推 -L 启 )(L 宽 -L 启 )×L 离 Among them, V 离 Let m be the volume of the separated space. 3 L 宽 The width of the working surface is in meters (m).

9. The method for determining the volume of the delamination space beneath thick sandstone according to claim 7, characterized in that, In step S4, when the lower strata of the delamination in one direction of the working face's advance direction have reached their ultimate settlement value and there are multiple maximum settlement points, while the lower strata of the delamination in another direction have only one maximum settlement point, a straight bottom-shaped delamination space is formed. The settlement space of the upper strata of the delamination at this time is determined according to the elasticity plate bending theory, and the volume of the delamination space is determined by the following formula: V 离 <1 / 2×(L 推 -L 启 )(L 宽 -L 启 )L 下 -1 / 3×(L 宽 -L 启 )L 下 ×1 / 2(L 极 -L 启 )。 10. The method for determining the volume of the delamination space beneath thick sandstone according to claim 7, characterized in that, In step S4, when the lower rock strata in the length and width directions of the working face advance have reached a stable subsidence state, forming a planar bottom-shaped delamination space, and the subsidence at multiple points reaches the ultimate subsidence value, forming a subsidence plane, the subsidence space of the lower rock strata is simplified as a truncated pyramid. The subsidence space of the upper rock strata is determined according to the elasticity plate bending theory. At this time, the volume of the delamination space is determined by the following formula: V 离 <1 / 3×L 下 ×[(L 推 -L 启 )(L 宽 -L 启 )+(L 推 -L 极 )(L 宽 -L 启 )]。

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