Roof water inrush risk identification method under mining influence of adjacent working faces

Abstract

The invention discloses a roof water inrush risk identification method under the mining influence of adjacent working faces, and belongs to the technical field of mining engineering.The roof water inrush risk identification method judges whether a roof water inrush risk exists or not under the mining influence of the adjacent working faces by combining a key layer theory and a full mining concept, and specifically comprises the following steps that 1, working face drilling columnar data is collected; step 2, according to a key layer theory, carrying out position identification and key layer identification on a hard rock layer in overlying strata of the working face; step 3, calculating the boundary size of the broken working face of the key layer from bottom to top according to a key layer full mining concept; 4, predicting the maximum development height of the working face water flowing fractured zone based on the composite width of the adjacent working faces and the working face overlying strata structure; and 5, carrying out risk evaluation on two adjacent working surfaces according to the thickness of the protective layer. According to the invention, accurate identification of the roof water inrush risk under adjacent working face mining can be realized.

Description

Technical Field

[0001] The invention belongs to the technical field of mining engineering, and in particular relates to a method for identifying the risk of roof water inrush under the influence of mining on adjacent working faces. Background Art

[0002] After coal seam mining, the stress balance of the original rock is destroyed, and a water-conducting fracture zone is formed in the overlying rock strata of the working face. When the height of the water-conducting fracture zone (hereinafter referred to as the height of the height of the height of the height of the height of the height of the height of the height of the height of the height of the height of the height of the height of the height of the height of the working face) reaches the roof aquifer, a water-conducting channel will be formed, which will increase the amount of water inflow in the mine, cause the loss of groundwater resources, deteriorate the ecological environment of the mining area, and even cause roof water inrush accidents, thereby causing serious personnel and economic losses. The mining of adjacent working faces will lead to the overlap of the overburden rock disturbance area, and there is a risk of abnormal increase in the height of the current mining working face and delayed increase in the height of the height of the mining working face, thereby inducing water inrush accidents. Therefore, the height of the height of the height of the height of the height of the height of the height of the working face has a great significance for the safe production of coal mines.

[0003] In the prior art, there is a method to evaluate the water inrush risk level of the area to be reinforced based on the effective reinforcement area in the area to be reinforced, and another method to evaluate and prevent water inrush risk based on the geological structure and the water-richness change characteristics of the mining catchment. However, the above methods still have shortcomings: too many parameters are required as criteria, and data processing is complicated; the judgment steps are cumbersome and difficult to implement on site; there is no targeted research on the identification of roof water inrush risks under adjacent working face mining. Summary of the invention

[0004] In order to solve the engineering problem of roof water inrush induced by repeated disturbance of overlying strata during mining of adjacent working faces, the present invention proposes a method for identifying the risk of roof water inrush under the influence of mining of adjacent working faces. By combining the key layer theory with the concept of sufficient mining, the height of the water-conducting fracture zone under mining of adjacent working faces is predicted and the risk of roof water inrush is identified.

[0005] The technical solution of the present invention is as follows: A method for identifying the risk of roof water inrush under the influence of adjacent working face mining is provided. By combining the key layer theory and the concept of sufficient mining, it is determined whether there is a risk of roof water inrush under the influence of adjacent working face mining. The method specifically includes the following steps: Step 1: Collect columnar data of drilling holes on the working surface; Step 2: According to the key layer theory, the position and key layer of the hard rock layer in the overburden of the working face are identified; Step 3: Calculate the critical size of the working face where the key layer breaks from bottom to top based on the concept of full mining of the key layer; Step 4: predicting the maximum development height of the water-conducting fracture zone of the working face based on the composite width of adjacent working faces and the overburden structure of the working face; Step 5: Conduct risk assessment on two adjacent working surfaces based on the thickness of the protective layer.

[0006] Furthermore, in step 1, the working face drilling columnar data includes the thickness and burial depth of the working face rock formation, and the comprehensive physical and mechanical parameters of the working face rock formation; the comprehensive physical and mechanical parameters of the working face rock formation include bulk density, elastic modulus, and tensile strength.

[0007] Furthermore, the specific process of step 2 is as follows: Step 2.1, using stiffness identification to obtain the position of the hard rock layer in the overburden of the working face; Step 2.2, identify the key layer based on strength identification; strength identification determines whether the hard rock layer breaks synchronously with the breaking of the underlying key layer by comparing the breaking distance of the hard rock layer. The hard rock layer that does not break with the underlying key layer is the overburden key layer of the working face.

[0008] Furthermore, the specific process of step 2.1 is as follows: Step 2.1.1, use Indicates the number of rock layers from bottom to top, and the position formula for stiffness identification is: (1); In the formula, , Respectively Layer, elastic modulus of the rock layer; , Respectively Layer, The thickness of the rock layer; , Respectively Layer, The bulk density of the rock layer; ; Step 2.1.2: When performing specific stiffness identification, calculate layer by layer starting from the first rock layer above the coal seam. and , when When the rock layer satisfies formula (1), the calculation is no longer upward. The rock layer is the first hard rock layer; Step 2.1.3, starting from the first hard rock layer, continue to determine the position of the second hard rock layer in the same manner as step 2.1.2, and so on, until the top hard rock layer is determined.

[0009] Furthermore, the specific process of step 2.2 is as follows: Step 2.2.1, use Indicates the numbering of hard rock layers from bottom to top, so The breaking distance formula of hard rock layer is: (2); (3); (4); In the formula, For the The breaking distance of the hard rock layer; For the The ultimate span of the hard rock layer; For the The distance between the hard rock layer and the upper surface of the coal seam; It is the rock fracture angle; For the The thickness of the hard rock layer; For the The tensile strength of hard rock layers; For the The load borne by the hard rock layer; For the The elastic modulus of the hard rock layer; ; , These are the numbers of the second-to-last and topmost hard rock layers respectively; For the The bulk density of the hard rock layer; Step 2.2.2, compare the fracture distances of each hard rock layer and identify the key layer; Step 2.2.3: The identified key layers of the working face are numbered from bottom to top as key layer 1, key layer 2, ..., key layer .

[0010] Furthermore, the specific process of step 2.2.2 is as follows: Step 2.2.2.1, numbering The hard rock layer is the lowest hard rock layer, and the lowest hard rock layer is defined as key layer 1; Step 2.2.2.2, number The fracture distances of the hard rock layers are compared; that is, starting from the second hard rock layer, the The fracture distance of the hard rock layer Above it The fracture distance of the hard rock layer For comparison: like , at this time If the hard rock layer does not break with the underlying key layer, then The hard rock layer is the key layer; like , then the The load borne by the first hard rock layer is added to the On the hard rock layer, recalculate the The breaking distance of the hard rock layer; if the recalculated The breaking distance of the first hard rock layer is less than The breaking distance of the hard rock layer is ; Explain that at this time The fracture of the hard rock layer is controlled by the The hard rock layer, Before the hard rock layer breaks, The hard rock layer is not broken. The hard rock layer breaks and its load acts on the layer of hard rock, leading to the The hard rock layer is broken; The hard rock layer is not a critical layer; Step 2.2.2.3: Continue to judge the next hard rock layer according to the process of step 2.2.2.2 until the last hard rock layer. After the judgment is completed, all the key layers are obtained.

[0011] Furthermore, the specific process of step 3 is as follows: Step 3.1, calculate the free space height, the formula is: (5); In the formula, For the Free space below the critical layer; To mine high; The first The residual expansion coefficient of rock in the rock layer; For the The rock formation number of the key layer; Step 3.2, calculate the maximum deflection, the formula is: (6); In the formula, is the maximum deflection; For the The loads borne by the key layers; For the Overhang distance of key layers; For the Elastic modulus of the key layer; For the The moment of inertia of the cross section of the critical layer about the neutral axis; To find the maximum value; The overlying rock The critical layer fracture must meet the following two conditions at the same time: (7); In the formula, For the The limit span of the critical layer; Satisfies the following formula: (8); Step 3.3, calculate the The critical size of the working surface where the rock of the key layer breaks is given by: (9); In the formula, For the The critical size of the working surface where the key layer breaks.

[0012] Furthermore, the specific process of step 4 is as follows: Step 4.1: Calculate the composite width of the front working surface and the rear working surface : ; In the formula, is the width of the front working surface; is the width of the rear working surface; is the width of the coal pillar; Step 4.2: The judgment starts from the key layer layer by layer; the specific judgment rules are: like , explain If the key layer does not fracture, the water-conducting fracture zone will not develop upwards and can only develop to the current key layer. The maximum development height of the water-conducting fracture zone in the working face is the height of the current key layer, and the risk assessment of step 5 is required; like , indicating that the key layer has fractured, and the water-conducting fracture zone continues to develop upward. The maximum development height of the water-conducting fracture zone in the working face is the height of the key layer in the upper part where no fracture has occurred. At this time, it is necessary to Perform the operation of adding 1 and enter the next key layer to continue the judgment until the boundary size of the working face is greater than the composite width, or the main key layer is judged. If the main key layer is also broken, it means that all key layers are broken, and it is directly judged that the risk of water inrush is high; simultaneously judge whether there is a risk of delayed water inrush in the front working face. If and When the mining of the rear working face is repeated, the maximum development height of the water-conducting fracture zone of the front working face will rise to the height of the key layer where no fracture occurs in the upper part. At this time, the front working face is judged to have the risk of delayed water inrush, and the risk assessment of step 5 needs to be carried out.

[0013] Furthermore, in step 5, by comparing the required protective layer thickness of the working face with the actual protective layer thickness of the working face, it is determined whether there is a risk of roof water inrush on the working face; The thickness of the mined coal seam is known in advance, and the required protective layer thickness is a multiple of the mined coal seam thickness; the rule for the multiple relationship is as follows: In the case of hard overburden, if the thickness of the clay layer at the bottom of the loose layer is greater than the cumulative mining thickness, the required protective layer thickness is 4 times the thickness of the mined coal seam; if the thickness of the clay layer at the bottom of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is 5 times the thickness of the mined coal seam; if the total thickness of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is 6 times the thickness of the mined coal seam; if there is no clay layer at the bottom of the loose layer, the required protective layer thickness is 7 times the thickness of the mined coal seam; For the case where the overburden lithology is medium-hard, if the thickness of the clay layer at the bottom of the loose layer is greater than the cumulative mining thickness, the required protective layer thickness is 3 times the thickness of the mined coal seam; if the thickness of the clay layer at the bottom of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is 4 times the thickness of the mined coal seam; if the total thickness of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is 5 times the thickness of the mined coal seam; if there is no clay layer at the bottom of the loose layer, the required protective layer thickness is 6 times the thickness of the mined coal seam; In the case of weak overburden lithology, if the thickness of the clay layer at the bottom of the loose layer is greater than the cumulative mining thickness, the required protective layer thickness is twice the thickness of the mined coal seam; if the thickness of the clay layer at the bottom of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is three times the thickness of the mined coal seam; if the total thickness of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is four times the thickness of the mined coal seam; if there is no clay layer at the bottom of the loose layer, the required protective layer thickness is five times the thickness of the mined coal seam; In the case of extremely weak overburden lithology, if the thickness of the clay layer at the bottom of the loose layer is greater than the cumulative mining thickness, the required protective layer thickness is twice the thickness of the mined coal seam; if the thickness of the clay layer at the bottom of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is twice the thickness of the mined coal seam; if the total thickness of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is three times the thickness of the mined coal seam; if there is no clay layer at the bottom of the loose layer, the required protective layer thickness is four times the thickness of the mined coal seam; The actual protective layer thickness is the bedrock thickness of the working face minus the maximum development height of the water-conducting fracture zone of the working face. The bedrock thickness of the working face is obtained in advance through three-dimensional seismic exploration technology, and the maximum development height of the water-conducting fracture zone of the working face is calculated according to step 4; If the actual protective layer thickness is greater than or equal to the required protective layer thickness, the risk of roof water inrush is judged to be low; if the actual protective layer thickness is less than the required protective layer thickness, the risk of roof water inrush is judged to be high.

[0014] Beneficial technical effects brought by the present invention: Based on the analysis of the results of theoretical research, indoor experiments and numerical simulation methods, the present invention establishes a method for identifying the risk of roof water inrush in adjacent working faces based on the concept of full mining of the key overburden layer. Compared with other methods for identifying the risk of roof water inrush, it can better reflect the complex situation of the stress changes and crack development of the overburden in the actual mining process. Compared with the method for identifying the risk of roof water inrush in a single working face, it is more in line with the complex mining conditions of coal mines. The identification results can be used for roof water inrush risk identification and monitoring and early warning, and have certain practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of the method for identifying the risk of water inrush from roof under the influence of mining on adjacent working faces of the present invention.

[0016] Figure 2 It is a schematic diagram of the key layer position identification result of the 02 working face in an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments: like Figure 1 As shown in the figure, a method for identifying the risk of roof water inrush under the influence of adjacent working face mining is used to judge whether there is a risk of roof water inrush under the influence of adjacent working face mining by combining the key layer theory and the concept of full mining. The method has strong universality, simple steps, and is easy to understand. The specific steps include: Step 1, collect the columnar data of the working face boreholes; the columnar data of the working face boreholes include the thickness and burial depth of the working face rock formation, and the physical and mechanical parameters of the comprehensive rock formation of the working face; the physical and mechanical parameters of the comprehensive rock formation of the working face include bulk density, elastic modulus, tensile strength, etc.

[0018] Step 2: According to the key layer theory and based on the understanding of the key layer breaking sequence, the position and key layer of the hard rock layer in the overburden of the working face are identified. The specific process is: Step 2.1: Use stiffness identification to obtain the location of the hard rock layer in the overburden of the working face. The specific process is: Step 2.1.1, use Indicates the number of rock layers from bottom to top, and the position formula for stiffness identification is: (1); In the formula, , Respectively Layer, Elastic modulus of the rock layer, GPa; , Respectively Layer, Thickness of the rock layer, m; , Respectively Layer, Bulk density of rock layer, KN·m -3 ; .

[0019] Step 2.1.2: When performing specific stiffness identification, calculate layer by layer starting from the first rock layer above the coal seam. and , when When the rock layer satisfies formula (1), the calculation is no longer upward. The rock layer is the first hard rock layer.

[0020] Step 2.1.3, starting from the first hard rock layer, continue to determine the position of the second hard rock layer in the same manner as step 2.1.2, and so on, until the top hard rock layer is determined. By identifying the position of the hard rock layer, the position of the hard rock layer in the overburden of the working face is obtained.

[0021] Step 2.2, identify the key layer based on strength identification; strength identification mainly determines whether the hard rock layer breaks synchronously with the breaking of the underlying key layer by comparing the breaking distance of the hard rock layer. The hard rock layer that does not break with the underlying key layer is the overburden key layer of the working face; the specific working process is: Step 2.2.1: Consider the influence of the height of the rock layer from the coal seam and the rock layer crushing angle, and use Indicates the numbering of hard rock layers from bottom to top, so The breaking distance formula of hard rock layer is: (2); (3); (4); In the formula, For the The breaking distance of the hard rock layer, m; For the The ultimate span of the hard rock layer, m; For the The distance between the hard rock layer and the upper surface of the coal seam, m; is the rock fracture angle, °; For the Thickness of hard rock layer, m; For the Tensile strength of hard rock layer, MPa; For the Load borne by the hard rock layer, MPa; For the Elastic modulus of hard rock layer, GPa; . , These are the numbers of the second-to-last and topmost hard rock layers respectively; For the The bulk density of the hard rock layer; Step 2.2.2: Compare the breaking distances of each hard rock layer according to the following rules. The hard rock layer that does not break with the underlying key layer is the overburden key layer of the working face. The specific rules for identifying the key layer are: Step 2.2.2.1, numbering The hard rock layer is the lowest hard rock layer, and the lowest hard rock layer is defined as key layer 1; Step 2.2.2.2, number The fracture distances of the hard rock layers are compared; that is, starting from the second hard rock layer, the The fracture distance of the hard rock layer Above it The fracture distance of the hard rock layer For comparison: like , at this time If the hard rock layer does not break with the underlying key layer, then The hard rock layer is the key layer; like , then the The load borne by the first hard rock layer is added to the On the hard rock layer, recalculate the The breaking distance of the hard rock layer. The breaking distance of the first hard rock layer is less than The breaking distance of the hard rock layer is . Explain that at this time The fracture of the hard rock layer is controlled by the The hard rock layer, Before the hard rock layer breaks, The hard rock layer is not broken. The hard rock layer breaks and its load acts on the layer of hard rock, leading to the The hard rock layer is broken. The hard rock layer is not a critical layer; Step 2.2.2.3, continue to judge the next hard rock layer according to the process of step 2.2.2.2 until the last hard rock layer. After the judgment is completed, all key layers are obtained; Step 2.2.3: The identified key layers of the working face are numbered from bottom to top as key layer 1, key layer 2, ..., key layer The key layer can be divided into sub-key layer and main key layer. The sub-key layer is the key layer other than the main key layer, which can be referred to as the key layer. The sub-key layer only controls the local rock layer, while the main key layer can control the rock layer from it to the surface. The last key layer is the key layer. is the main key layer, and the other key layers are sub-key layers.

[0022] Step 3. Calculate the critical size of the working face where the key layer breaks from bottom to top based on the concept of full mining. The situation where the state of the key layer does not change with the increase of the working face size is defined as the critical layer being fully mined. When the key layer is in a fully mined state, if the key layer has been broken, it will continue to break as the working face size increases; if the key layer is in an unbroken state, the continued increase in the working face size will not cause the key layer to break. During the mining process of the working face, the key layer is broken from bottom to top in stages. After the shallow key layer is destroyed, the maximum development height of the water-conducting fracture zone will rise to the height of the upper key layer where no fracture occurs. The working face size that meets the destruction of the key layer is defined as the critical size of the working face corresponding to the key layer. The free space formed by the advancement of the working face will be filled by the crushing and swelling characteristics of the coal seam roof rock layer. When the height of the free space below the key layer is less than the maximum deflection, the key layer will remain intact, the water-conducting fracture zone will develop to the maximum height, and the critical size of the working face will be positive infinity. Step 3. The calculation process of the critical working surface size of the key layer is as follows: Step 3.1, calculate the free space height, the formula is: (5); In the formula, For the Free space below the critical layer; is the mining height, m; For the Thickness of the rock layer, m; The first The residual expansion coefficient of rock in the rock layer; , For the The rock layer number of the key layer.

[0023] Step 3.2, Before the first fracture of the key layer, it can be regarded as a fixed-support beam. The rock beam is bent and deformed under the action of the overlying rock layer and itself. The simply supported beam uniformly distributed load mechanical model is used to calculate the maximum deflection. The formula is: (6); In the formula, is the maximum deflection, m; For the Load borne by the key layer, MPa; For the Overhang distance of key layer, m; For the Elastic modulus of the key layer, GPa; For the Moment of inertia of the cross section of the key layer about the neutral axis, m 4 ; To find the maximum value.

[0024] The overlying rock The fracture of the key layer must meet the following two conditions at the same time: first, The overhang distance of the key layer must be greater than the limit span of its initial fracture, that is, the working surface size must be large enough; second, The free space height below the critical layer must be greater than the maximum deflection of the critical layer, that is: (7); In the formula, For the The limit span of the key layer.

[0025] Therefore, when the coal seam mining thickness and the overlying rock lithology and structure are certain, The critical layer of each layer shall satisfy the following conditions: (8); Step 3.3, calculate the The critical size of the working surface where the rock of the key layer breaks is given by: (9); In the formula, For the The critical size of the working surface where the key layer breaks.

[0026] Step 4: Based on the concept of full mining of key layers and the overburden structure of the working face, the maximum development height of the water-conducting fracture zone of the working face is predicted. The maximum development height of the water-conducting fracture zone is calculated by comparing the boundary size of the working face with the The relationship between the composite width of the front working face and the adjacent working face is predicted. It is necessary to determine whether the key layer is broken and its impact on the front working face. Finally, the maximum development height of the water-conducting fracture zone of the working face is predicted and whether the height of the front working face increases under the influence of repeated mining disturbance. The specific prediction process of the maximum development height of the water-conducting fracture zone of the working face is: Step 4.1: First, calculate the composite width of the front working surface and the rear working surface : ; In the formula, is the width of the front working surface; is the width of the rear working surface; is the width of the coal pillar.

[0027] Step 4.2: The judgment starts from the key layer layer by layer; the specific judgment rules are: like , explain If the key layer does not fracture, the water-conducting fracture zone will not develop upwards and can only develop to the current key layer. The maximum development height of the water-conducting fracture zone in the working face is the height of the current key layer, and the risk assessment of step 5 is required; like , indicating that the key layer has fractured, and the water-conducting fracture zone continues to develop upward. The maximum development height of the water-conducting fracture zone in the working face is the height of the key layer in the upper part where no fracture has occurred. At this time, it is necessary to Perform the operation of adding 1 and enter the next key layer to continue the judgment until the boundary size of the working face is greater than the composite width, or the main key layer is judged. If the main key layer is also fractured, the maximum development height of the water-conducting fracture zone of the working face is equal to or greater than the bedrock thickness. At this time, the thickness of the protective layer is 0, which means that all key layers are fractured, and it is directly judged that the risk of water inrush is high. In this process, it is necessary to simultaneously judge whether there is a risk of delayed water inrush in the front working face. If and When the mining of the rear working face is repeated, the maximum development height of the water-conducting fracture zone of the front working face will rise to the height of the key layer where no fracture occurs in the upper part. At this time, the front working face is judged to have the risk of delayed water inrush, and the risk assessment of step 5 needs to be carried out.

[0028] Assume that there are 4 layers, namely key layer 1, key layer 2, key layer 3 and main key layer. According to the judgment logic of step 4.2, first judge the relationship between the working surface boundary size and the composite width of key layer 1. If , indicating that key layer 1 is not broken, so the water-conducting fracture zone can only develop to key layer 1, and then risk assessment is performed according to step 5.

[0029] like , indicating that the key layer 1 is fractured and the water-conducting fracture zone develops upward. Perform the operation of adding 1, and then judge the key layer 2. If , it means that the key layer 2 is broken, and then judge the key layer 3. If , it means that the key layer 3 is also broken, and then judge the main key layer. If , it means that the main key layer is also fractured, which directly determines that the risk of water inrush is high.

[0030] In short, it is to judge layer by layer from the first key layer until the working face boundary size of a certain key layer is larger than the composite width, and then proceed to step 5 risk assessment; or, if the main key layer is broken, it is directly judged as a high risk of water inrush. As for the comparison between the working face boundary size and the width of the preceding working face, it is equivalent to a small branch of the main judgment loop. and This indicates that the maximum development height of the water-conducting fracture zone of the front working face will rise to the height of the key layer where no fracture has occurred in the upper part, which has the risk of inducing delayed water inrush in the front working face. The risk of water inrush must be identified simultaneously.

[0031] Step 5: Conduct risk assessment on two adjacent working faces based on the thickness of the protective layer. By comparing the required protective layer thickness of the working face with the actual protective layer thickness of the working face, it is possible to determine whether there is a risk of roof water inrush on the working face.

[0032] According to the "Specifications for the Retention and Compressed Coal Mining of Coal Pillars in Buildings, Water Bodies, Railways and Main Wells and Lanes", the selection of the thickness of the protective layer needs to comprehensively consider the overall water-richness of the porous aquifer of the loose layer of the Cenozoic Erathem and the development of the clay impermeable layer at the bottom and the thickness of the wind-oxidized zone, and consider them separately according to the strong and medium aquifer water bodies, no bottom impermeable layer and aquifer. In Table 1, A represents the thickness of the mined coal seam.

[0033] Table 1 Thickness of waterproof and safe coal (rock) column protective layer .

[0034] The specific process of determining whether there is a risk of roof water inrush at the working face is as follows: the thickness of the mined coal seam is known in advance, and the required thickness of the protective layer is determined according to Table 1 as several times the thickness of the mined coal seam, and the required thickness of the protective layer can be obtained.

[0035] The definition rule of the protective layer is: for the case of hard overburden rock, if the thickness of the clay layer at the bottom of the loose layer is greater than the cumulative mining thickness, the required protective layer thickness is 4 times the thickness of the mined coal seam; if the thickness of the clay layer at the bottom of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is 5 times the thickness of the mined coal seam; if the total thickness of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is 6 times the thickness of the mined coal seam; if there is no clay layer at the bottom of the loose layer, the required protective layer thickness is 7 times the thickness of the mined coal seam. For the case where the overburden lithology is medium-hard, if the thickness of the clay layer at the bottom of the loose layer is greater than the cumulative mining thickness, the required protective layer thickness is 3 times the thickness of the mined coal seam; if the thickness of the clay layer at the bottom of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is 4 times the thickness of the mined coal seam; if the total thickness of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is 5 times the thickness of the mined coal seam; if there is no clay layer at the bottom of the loose layer, the required protective layer thickness is 6 times the thickness of the mined coal seam. For the case where the overburden lithology is weak, if the thickness of the clay layer at the bottom of the loose layer is greater than the cumulative mining thickness, the required protective layer thickness is 2 times the thickness of the mined coal seam; if the thickness of the clay layer at the bottom of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is 3 times the thickness of the mined coal seam; if the total thickness of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is 4 times the thickness of the mined coal seam; if there is no clay layer at the bottom of the loose layer, the required protective layer thickness is 5 times the thickness of the mined coal seam. In the case of extremely weak overburden lithology, if the thickness of the clay layer at the bottom of the loose layer is greater than the cumulative mining thickness, the required protective layer thickness is twice the thickness of the mined coal seam; if the thickness of the clay layer at the bottom of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is twice the thickness of the mined coal seam; if the total thickness of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is three times the thickness of the mined coal seam; if there is no clay layer at the bottom of the loose layer, the required protective layer thickness is four times the thickness of the mined coal seam; the actual protective layer thickness is the bedrock thickness of the working face minus the maximum development height of the water-conducting fracture zone of the working face. The bedrock thickness of the working face is obtained in advance through three-dimensional seismic exploration technology, and the maximum development height of the water-conducting fracture zone of the working face is calculated according to step 4.

[0036] If the actual protective layer thickness is greater than or equal to the required protective layer thickness, the risk of roof water inrush is judged to be low; if the actual protective layer thickness is less than the required protective layer thickness, the risk of roof water inrush is judged to be high.

[0037] In order to demonstrate the feasibility and superiority of the present invention, the following examples are given.

[0038] Table 2 Lithology and properties of each layer in the 02 working face based on exploration drilling .

[0039] Taking a coal mine in Anhui as an example, the 01 working face and the 02 working face are adjacent working faces, of which the 01 working face is the front working face with a width of about 262m, and the 02 working face is about 270m wide. The mining height of the two working faces is 4m. The combined mining width of the two working faces is 548m, and the width of the coal pillar is 16m. The lithology of the working face roof is mainly sandstone and mudstone, which belongs to the medium-hard roof. The lithology and properties of each layer of the 02 working face based on the exploration drilling are shown in Table 2, and the comprehensive rock stratum physical and mechanical parameters of the 02 working face are shown in Table 3.

[0040] Table 3 Comprehensive rock stratum physical and mechanical parameters of 02 working face .

[0041] According to the key layer identification method in step 2.2 of the present invention, the key layer position of the 02 working face is theoretically identified. The identification result is as follows: Figure 2 As shown, there are 4 key layers in total, which are numbered from bottom to top as sub-key layer 1, sub-key layer 2, sub-key layer 3, and main key layer; Coal 5 is the current mined coal seam. Figure 2 The lithology and thickness of each key layer are included. The lithology of sub-key layer 1 is fine sandstone, with a thickness of 5.4m, and it is 5.48m away from the roof of coal No. 5; the lithology of sub-key layer 2 is fine sandstone, with a thickness of 5.32m, and it is 29.99m away from the roof of coal No. 5; the lithology of sub-key layer 3 is fine sandstone, with a thickness of 3m, and it is 60m away from the roof of coal No. 5; the lithology of the main key layer is siltstone, with a thickness of 8.42m, and it is 102.1m away from the roof of coal No. 5.

[0042] According to the working face boundary size calculation formula (9), the working face boundary size of the key layer of the 02 working face was theoretically calculated. The calculation results are shown in Table 4 below.

[0043] Table 4 02 Working face boundary dimensions of the key layer breaking of the working face .

[0044] Based on the theory of full mining of key layers and referring to the prediction of comprehensive rock stratum physical and mechanical parameters of the working face, when the mining height is 4m, the maximum development height of the water-conducting fracture zone of the 02 working face is 60m, and there is no risk of delayed water inrush from the roof at the 01 working face.

[0045] The thickness of the protective layer is considered as medium-hard roof, and the thickness of the protective layer needs to be 6 times the thickness of the mined coal seam, calculated according to the mining height of 4m, that is, the thickness of the protective layer should not be less than 24m. Based on the three-dimensional seismic exploration, the bedrock thickness around the 02 working face is between 160 and 200m, and the maximum height of the water-conducting fracture zone is predicted to be 60m. The thickness of the protective layer is between 100 and 140m, which is greater than 24m, and the risk of roof water inrush is low.

[0046] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for identifying the risk of water inrush from roof under the influence of mining at adjacent working faces, characterized in that: By combining the key layer theory and the concept of full mining, it is determined whether there is a risk of roof water inrush under the influence of mining at adjacent working faces, which specifically includes the following steps: Step 1: Collect columnar data of drilling holes on the working surface; Step 2: According to the key layer theory, the position and key layer of the hard rock layer in the overburden of the working face are identified; Step 3: Calculate the critical size of the working face where the key layer breaks from bottom to top based on the concept of full mining of the key layer; Step 4: predicting the maximum development height of the water-conducting fracture zone of the working face based on the composite width of adjacent working faces and the overburden structure of the working face; Step 5: Conduct risk assessment on two adjacent working surfaces based on the thickness of the protective layer.

2. The method for identifying the risk of roof water inrush under the influence of adjacent working face mining according to claim 1 is characterized in that: In step 1, the working face drilling columnar data includes the thickness and burial depth of the working face rock formation, and the comprehensive physical and mechanical parameters of the working face rock formation; the comprehensive physical and mechanical parameters of the working face rock formation include bulk density, elastic modulus, and tensile strength.

3. The method for identifying the risk of water inrush from roof under the influence of mining at adjacent working faces according to claim 1, characterized in that: The specific process of step 2 is: Step 2.1, using stiffness identification to obtain the position of the hard rock layer in the overburden of the working face; Step 2.2, identify the key layer based on strength identification; strength identification determines whether the hard rock layer breaks synchronously with the breaking of the underlying key layer by comparing the breaking distance of the hard rock layer. The hard rock layer that does not break with the underlying key layer is the overburden key layer of the working face.

4. The method for identifying the risk of water inrush from roof under the influence of mining at adjacent working faces according to claim 3 is characterized in that: The specific process of step 2.1 is as follows: Step 2.1.1, use Indicates the number of rock layers from bottom to top, and the position formula for stiffness identification is: （1）； In the formula, , Respectively Layer, elastic modulus of the rock layer; , Respectively Layer, The thickness of the rock layer; , Respectively Layer, The bulk density of the rock layer; ; Step 2.1.2: When performing specific stiffness identification, calculate layer by layer starting from the first rock layer above the coal seam. and , when When the rock layer satisfies formula (1), the calculation is no longer upward. The rock layer is the first hard rock layer; Step 2.1.3, starting from the first hard rock layer, continue to determine the position of the second hard rock layer in the same manner as step 2.1.2, and so on, until the top hard rock layer is determined.

5. The method for identifying the risk of roof water inrush under the influence of adjacent working face mining according to claim 4 is characterized in that: The specific process of step 2.2 is as follows: Step 2.2.1, use Indicates the numbering of hard rock layers from bottom to top, so The breaking distance formula of hard rock layer is: （2）； （3）； （4）； In the formula, For the The breaking distance of the hard rock layer; For the The ultimate span of the hard rock layer; For the The distance between the hard rock layer and the upper surface of the coal seam; It is the rock fracture angle; For the The thickness of the hard rock layer; For the The tensile strength of hard rock layers; For the The load borne by the hard rock layer; For the The elastic modulus of the hard rock layer; ; , These are the numbers of the second-to-last and topmost hard rock layers respectively; For the The bulk density of the hard rock layer; Step 2.2.2, compare the fracture distances of each hard rock layer and identify the key layer; Step 2.2.3: The identified key layers of the working face are numbered from bottom to top as key layer 1, key layer 2, ..., key layer .

6. The method for identifying the risk of water inrush from roof under the influence of mining at adjacent working faces according to claim 5, characterized in that: The specific process of step 2.2.2 is as follows: Step 2.2.2.1, numbering The hard rock layer is the lowest hard rock layer, and the lowest hard rock layer is defined as key layer 1; Step 2.2.2.2, number The fracture distances of the hard rock layers are compared; that is, starting from the second hard rock layer, the The fracture distance of the hard rock layer Above it The fracture distance of the hard rock layer For comparison: like , at this time If the hard rock layer does not break with the underlying key layer, then The hard rock layer is the key layer; like , then the The load borne by the hard rock layer is added to the On the hard rock layer, recalculate the The breaking distance of the hard rock layer; if the recalculated The breaking distance of the first hard rock layer is less than The breaking distance of the hard rock layer is ; Explain that this time The fracture of the hard rock layer is controlled by the The hard rock layer, Before the hard rock layer breaks, The hard rock layer is not broken. The hard rock layer breaks and its load acts on the layer of hard rock, leading to the The hard rock layer is broken; The hard rock layer is not a critical layer; Step 2.2.2.3: Continue to judge the next hard rock layer according to the process of step 2.2.2.2 until the last hard rock layer. After the judgment is completed, all the key layers are obtained.

7. The method for identifying the risk of water inrush from roof under the influence of mining at adjacent working faces according to claim 6, characterized in that: The specific process of step 3 is as follows: Step 3.1, calculate the free space height, the formula is: （5）； In the formula, For the Free space below the critical layer; To mine high; The first The residual expansion coefficient of rock in the rock layer; For the The rock formation number of the key layer; Step 3.2, calculate the maximum deflection, the formula is: （6）； In the formula, is the maximum deflection; For the The loads borne by the key layers; For the Overhang distance of key layers; For the Elastic modulus of the key layer; For the The moment of inertia of the cross section of the critical layer about the neutral axis; To find the maximum value; The overlying rock The critical layer fracture must meet the following two conditions at the same time: （7）； In the formula, For the The limit span of the critical layer; Satisfies the following formula: （8）； Step 3.3, calculate the The critical size of the working surface where the rock of the key layer breaks is given by: （9）； In the formula, For the The critical size of the working surface where the key layer breaks.

8. The method for identifying the risk of water inrush from roof under the influence of mining at adjacent working faces according to claim 7, characterized in that: The specific process of step 4 is as follows: Step 4.1: Calculate the composite width of the front working surface and the rear working surface : ； In the formula, is the width of the front working surface; is the width of the rear working surface; is the width of the coal pillar; Step 4.2: The judgment starts from the key layer layer by layer; the specific judgment rules are: like , explain If the key layer does not break, the water-conducting fracture zone will not develop upwards and can only develop to the current key layer. The maximum development height of the water-conducting fracture zone in the working face is the height of the current key layer, and the risk assessment of step 5 is required; like , indicating that the key layer has fractured, and the water-conducting fracture zone continues to develop upward. The maximum development height of the water-conducting fracture zone in the working face is the height of the key layer in the upper part where no fracture has occurred. At this time, it is necessary to Perform the operation of adding 1 and enter the next key layer to continue the judgment until the boundary size of the working surface is greater than the composite width, or the main key layer is judged. If the main key layer is also broken, it means that all key layers are broken, and it is directly judged that the risk of water inrush is high; Simultaneously determine whether there is a risk of delayed water inrush at the front working face. and When the mining of the rear working face is repeated, the maximum development height of the water-conducting fracture zone of the front working face will rise to the height of the key layer where no fracture occurs in the upper part. At this time, the front working face is judged to have the risk of delayed water inrush, and the risk assessment of step 5 needs to be carried out.

9. The method for identifying the risk of water inrush from roof under the influence of mining at adjacent working faces according to claim 8, characterized in that: In step 5, by comparing the required protective layer thickness of the working face with the actual protective layer thickness of the working face, it is determined whether there is a risk of roof water inrush on the working face; The thickness of the mined coal seam is known in advance, and the required protective layer thickness is a multiple of the mined coal seam thickness; the rule for the multiple relationship is as follows: In the case of hard overburden, if the thickness of the clay layer at the bottom of the loose layer is greater than the cumulative mining thickness, the required protective layer thickness is 4 times the thickness of the mined coal seam; if the thickness of the clay layer at the bottom of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is 5 times the thickness of the mined coal seam; if the total thickness of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is 6 times the thickness of the mined coal seam; if there is no clay layer at the bottom of the loose layer, the required protective layer thickness is 7 times the thickness of the mined coal seam; For the case where the overburden lithology is medium-hard, if the thickness of the clay layer at the bottom of the loose layer is greater than the cumulative mining thickness, the required protective layer thickness is 3 times the thickness of the mined coal seam; if the thickness of the clay layer at the bottom of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is 4 times the thickness of the mined coal seam; if the total thickness of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is 5 times the thickness of the mined coal seam; if there is no clay layer at the bottom of the loose layer, the required protective layer thickness is 6 times the thickness of the mined coal seam; In the case of weak overburden lithology, if the thickness of the clay layer at the bottom of the loose layer is greater than the cumulative mining thickness, the required protective layer thickness is twice the thickness of the mined coal seam; if the thickness of the clay layer at the bottom of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is three times the thickness of the mined coal seam; if the total thickness of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is four times the thickness of the mined coal seam; if there is no clay layer at the bottom of the loose layer, the required protective layer thickness is five times the thickness of the mined coal seam; In the case of extremely weak overburden lithology, if the thickness of the clay layer at the bottom of the loose layer is greater than the cumulative mining thickness, the required protective layer thickness is twice the thickness of the mined coal seam; if the thickness of the clay layer at the bottom of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is twice the thickness of the mined coal seam; if the total thickness of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is three times the thickness of the mined coal seam; if there is no clay layer at the bottom of the loose layer, the required protective layer thickness is four times the thickness of the mined coal seam; The actual protective layer thickness is the bedrock thickness of the working face minus the maximum development height of the water-conducting fracture zone of the working face. The bedrock thickness of the working face is obtained in advance through three-dimensional seismic exploration technology, and the maximum development height of the water-conducting fracture zone of the working face is calculated according to step 4; If the actual protective layer thickness is greater than or equal to the required protective layer thickness, the risk of roof water inrush is judged to be low; if the actual protective layer thickness is less than the required protective layer thickness, the risk of roof water inrush is judged to be high.

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