A method for identifying the risk of roof water inrush under the influence of adjacent working face mining

Abstract

The present invention discloses a method for identifying the risk of roof water inrush under the influence of adjacent working face mining, belonging to the technical field of mining engineering. By combining the key stratum theory and the concept of full mining subsidence, it is determined whether there is a risk of roof water inrush under the influence of adjacent working face mining. The specific steps are as follows: Step 1, collect the borehole column data of the working face; Step 2, according to the key stratum theory, identify the position of the hard rock stratum in the overlying strata of the working face and identify the key strata; Step 3, calculate the critical size of the working face at which the key strata break from bottom to top according to the concept of full mining subsidence of the key strata; Step 4, predict the maximum development height of the water-conducting fissure zone of the working face based on the composite width of the adjacent working face and the overlying strata structure of the working face; Step 5, conduct a risk assessment on the adjacent two working faces according to the protective layer thickness. The present invention can accurately identify the risk of roof water inrush under the mining of adjacent working faces.

Description

Technical Field

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

[0002] After coal seam mining, the original rock stress balance is damaged, and a water-conducting fissure zone is formed in the overlying strata of the working face. When the development height of the water-conducting fissure zone (hereinafter referred to as the water-conducting height) reaches the roof aquifer, a water-conducting channel will be formed, increasing the mine water inflow, causing the loss of groundwater resources, deteriorating the mining area ecological environment, and even triggering roof water inrush accidents, thereby causing serious personnel and economic losses. The mining of adjacent working faces will cause the overlapping of the overburden disturbance areas, and there is a risk of abnormal increase in the water-conducting height of the current mining working face and delayed increase in the water-conducting height of the mined-out working face, which may induce water inrush accidents. Therefore, the method for predicting the water-conducting height and identifying the risk of roof water inrush under the influence of adjacent working face mining is of great significance to the safe production of coal mines.

[0003] In the prior art, there is a method for evaluating the water inrush danger level of the area to be reinforced according to the effective reinforcement area in the area to be reinforced, and there is also a method for evaluating and preventing water inrush danger according to the geological structure and the change characteristics of the water richness of the mining water-converging zone. However, the above methods still have deficiencies: too many parameters are required as criteria, and the data processing is relatively complex; the discrimination steps are cumbersome, and the on-site implementation is difficult; there is no targeted research on the identification of the risk of roof water inrush under the influence of 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 in adjacent working face mining, the present invention proposes a method for identifying the risk of roof water inrush under the influence of adjacent working face mining, which predicts the development height of the water-conducting fissure zone under the influence of adjacent working face mining and identifies the risk of roof water inrush by combining the key stratum theory and the concept of full mining.

[0005] The technical solution of the present invention is as follows:

[0006] A method for identifying the risk of roof water inrush under the influence of adjacent working face mining, which determines whether there is a risk of roof water inrush under the influence of adjacent working face mining by combining the key stratum theory and the concept of full mining, specifically including the following steps:

[0007] Step 1: Collect the borehole column data of the working face;

[0008] Step 2: According to the key stratum theory, identify the positions of the medium-hard rock strata and the key strata in the overlying strata of the working face;

[0009] Step 3: Calculate the critical size of the working face at which the key stratum breaks from bottom to top according to the concept of full mining of the key stratum;

[0010] Step 4: Predict the maximum development height of the water-conducting fissure zone of the working face based on the composite width of adjacent working faces and the overlying strata structure of the working face;

[0011] Step 5: Conduct a risk assessment on two adjacent working faces according to the protective layer thickness.

[0012] Furthermore, in the above Step 1, the borehole column data of the working face includes the thickness and burial depth of the strata in the working face and the physical and mechanical parameters of the comprehensive strata in the working face; the physical and mechanical parameters of the comprehensive strata in the working face include unit weight, elastic modulus, and tensile strength.

[0013] Furthermore, the specific process of the above Step 2 is as follows:

[0014] Step 2.1: Use stiffness identification to obtain the position of the medium-hard strata in the overlying strata of the working face;

[0015] Step 2.2: Conduct key stratum identification based on strength identification; strength identification determines whether the hard strata break synchronously with the breakage of the underlying key stratum by comparing the breaking distance of the hard strata. The hard strata that do not break with the breakage of the underlying key stratum are the key strata in the overlying strata of the working face.

[0016] Furthermore, the specific process of the above Step 2.1 is as follows:

[0017] Step 2.1.1: Use to represent the serial number of the strata from bottom to top, then the position formula for stiffness identification is:

[0018] (1);

[0019] In the formula, , are the elastic moduli of the th and th strata respectively; , are the thicknesses of the th and th strata respectively; , are the unit weights of the th and th strata respectively; ;

[0020] Step 2.1.2: When conducting specific stiffness identification, start calculating and layer by layer from the first layer of strata above the coal seam upwards. When the th layer of strata satisfies formula (1), stop calculating upwards. At this time, the th layer of strata is the first layer of hard strata;

[0021] 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 way as in Step 2.1.2, and so on until the topmost hard rock layer is determined.

[0022] Further, the specific process of Step 2.2 is as follows:

[0023] Step 2.2.1: Use to represent the numbering of the hard rock layers from bottom to top. Then, the formula for the breaking distance of the -th hard rock layer is:

[0024] (2);

[0025] (3);

[0026] (4);

[0027] In the formula, is the breaking distance of the -th hard rock layer; is the ultimate span of the -th hard rock layer; is the distance from the -th hard rock layer to the upper surface of the coal seam; is the rock breaking angle; is the number of the -th hard rock layer; is the thickness of the -th hard rock layer; is the tensile strength of the -th hard rock layer; is the load borne by the -th hard rock layer; ; and are the numbers of the second-to-last and the topmost hard rock layers above, respectively; is the number of the -th hard rock layer;

[0028] Step 2.2.2: Compare the breaking distances of each hard rock layer to identify the key layers;

[0029] Step 2.2.3: Number the identified key layers of the overlying strata of the working face from bottom to top as Key Layer 1, Key Layer 2,..., Key Layer .

[0030] Further, the specific process of Step 2.2.2 is as follows:

[0031] Step 2.2.2.1: Number The hard rock layer at the bottom is the bottommost hard rock layer, and the bottommost hard rock layer is defined as key layer 1;

[0032] Step 2.2.2.2. Compare the breakage distances of the hard rock layers numbered ; that is, starting from the second hard rock layer, compare the breakage distance of the th hard rock layer with the breakage distance of the hard rock layer above it:

[0033] If , at this time, the th hard rock layer does not break with the underlying key layer, then the th hard rock layer is the key layer;

[0034] If , then add the load borne by the th hard rock layer to the th hard rock layer and recalculate the breakage distance of the th hard rock layer; if the recalculated breakage distance of the th hard rock layer is less than the breakage distance of the th hard rock layer, then take ; this indicates that at this time, the breakage of the th hard rock layer is controlled by the th hard rock layer, that is, before the th hard rock layer breaks, the th hard rock layer does not break. Once the th hard rock layer breaks, its load acts on the th hard rock, causing the th hard rock to break accordingly; at this time, the th hard rock layer is not the key layer;

[0035] 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.

[0036] Furthermore, the specific process of Step 3 is as follows:

[0037] Step 3.1. Calculate the free space height, and the formula is:

[0038] (5);

[0039] In the formula, is the free space below the th key layer; is the mining height; is the ​Rock residual swelling coefficient of the strata is the stratum number of the key stratum of the

[0040] Step 3.2. Calculate the maximum deflection, and the formula is:

[0041] (6);

[0042] In the formula, is the maximum deflection; is the load borne by the key stratum of the layer; is the overhanging distance of the key stratum of the layer; is the elastic modulus of the key stratum of the layer; is the moment of inertia of the cross-section of the key stratum of the layer about the neutral axis; is to find the maximum value;

[0043] The fracture of the key stratum of the layer in the overlying strata must simultaneously meet the following two conditions:

[0044] (7);

[0045] In the formula, is the limit span of the key stratum of the layer; Satisfies the following formula:

[0046] (8);

[0047] Step 3.3. Calculate the critical size of the working face where the rock of the key stratum of the layer breaks, and the formula is:

[0048] (9);

[0049] In the formula, is the critical size of the working face where the key stratum of the layer breaks.

[0050] Furthermore, the specific process of the said Step 4 is:

[0051] Step 4.1. Calculate the composite width of the pre-working face and the post-working face :

[0052] ;

[0053] In the formula, is the width of the pre-working face; is the width of the rear working face; is the width of the coal pillar;

[0054] Step 4.2: Start judging layer by layer from the th key layer; the specific judgment rule is:

[0055] If , it indicates that the th key layer does not fracture. Then the water-conducting fissure zone will not develop upward and can only develop to the current key layer. The maximum development height of the water-conducting fissure zone of the working face is the height of the current key layer, and the risk assessment in Step 5 needs to be carried out;

[0056] If , it indicates that the key layer fractures, and the water-conducting fissure zone continues to develop upward. The maximum development height of the water-conducting fissure zone of the working face is the height of the upper key layer that has not fractured. At this time, needs to be incremented by 1, and continue to judge in the next key layer until the critical size of the working face is greater than the composite width, or until the main key layer is judged. If the main key layer also fractures, it indicates that all key layers have fractured, and it is directly determined 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 , the repeated disturbance of the mining in the rear working face will cause the maximum development height of the water-conducting fissure zone of the front working face to rise to the height of the upper key layer that has not fractured. At this time, it is determined that the front working face has the risk of delayed water inrush, and the risk assessment in Step 5 needs to be carried out.

[0057] Furthermore, in the above 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 judged whether there is a risk of roof water inrush in the working face;

[0058] The thickness of the mined coal seam is known in advance, and the required protective layer thickness is a multiple of the thickness of the mined coal seam; the rules of the multiple relationship are as follows:

[0059] For the case where the overlying rock lithology is 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 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;

[0060] For the case where the overlying rock lithology is medium-hard, if the thickness of the cohesive soil 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 cohesive soil 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 cohesive soil layer at the bottom of the loose layer, the required protective layer thickness is 6 times the thickness of the mined coal seam;

[0061] For the case where the overlying rock lithology is soft, if the thickness of the cohesive soil 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 cohesive soil 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 cohesive soil layer at the bottom of the loose layer, the required protective layer thickness is 5 times the thickness of the mined coal seam;

[0062] For the case where the overlying rock lithology is extremely soft, if the thickness of the cohesive soil 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 cohesive soil layer at the bottom of the loose layer is less than the cumulative mining thickness, the required protective layer thickness is 2 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 3 times the thickness of the mined coal seam; if there is no cohesive soil layer at the bottom of the loose layer, the required protective layer thickness is 4 times the thickness of the mined coal seam;

[0063] The actual protective layer thickness is the thickness of the working face bedrock minus the maximum development height of the water-conducting fissure zone in the working face. The thickness of the working face bedrock is obtained in advance through three-dimensional seismic exploration technology, and the maximum development height of the water-conducting fissure zone in the working face is calculated according to step 4;

[0064] If the actual protective layer thickness is greater than or equal to the required protective layer thickness, it is determined that the risk of roof water inrush is low; if the actual protective layer thickness is less than the required protective layer thickness, it is determined that the risk of roof water inrush is high.

[0065] The beneficial technical effects brought by the present invention: Based on the result analysis of methods such as theoretical research, laboratory tests, and numerical simulations, the present invention establishes a method for identifying the risk of roof water inrush during the mining of adjacent working faces based on the concept of full mining of key strata in overlying rocks. Compared with other methods for identifying the risk of roof water inrush, it can better reflect the complex conditions of overlying rock stress changes and fissure development during 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 result can be used for the identification and monitoring and early warning of the risk of roof water inrush, and has certain practical application value. Description of the Drawings

[0066] Figure 1It is the flowchart of the roof water inrush risk identification method under the influence of adjacent working face mining of the present invention.

[0067] Figure 2 It is the schematic diagram of the key stratum position identification result of the 02 working face in the embodiment of the present invention. Detailed implementation manners

[0068] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners:

[0069] As Figure 1 shown, a roof water inrush risk identification method under the influence of adjacent working face mining is to judge whether there is a roof water inrush risk under the influence of adjacent working face mining by combining the key stratum theory and the concept of full mining; the method has strong universality, concise steps and is easy to understand. The specific steps include:

[0070] Step 1: Collect the borehole column data of the working face; the borehole column data of the working face includes the thickness and buried depth of the strata in the working face, and the physical and mechanical parameters of the comprehensive strata in the working face; the physical and mechanical parameters of the comprehensive strata in the working face include unit weight, elastic modulus, tensile strength, etc.

[0071] Step 2: Based on the key stratum theory and the understanding of the key stratum fracture sequence, identify the position of the hard strata in the overlying strata of the working face and the key strata. The specific process is as follows:

[0072] Step 2.1: Use stiffness identification to obtain the position of the hard strata in the overlying strata of the working face. The specific process is as follows:

[0073] Step 2.1.1: Use to represent the serial number of the strata from bottom to top, then the position formula for stiffness identification is:

[0074] (1);

[0075] In the formula, , are the elastic moduli of the -th and -th strata respectively, in GPa; , are the thicknesses of the -th and -th strata respectively, in m; , are the unit weights of the -th and -th strata respectively, in KN·m -3 ; .

[0076] Step 2.1.2: When performing specific stiffness identification, start from the first stratum above the coal seam and calculate layer by layer upwards and When the layer of rock stratum satisfies formula (1), the upward calculation will no longer be carried out. At this time, the layer of rock stratum is the first layer of hard rock stratum.

[0077] Step 2.1.3: Starting from the first layer of hard rock stratum, continue to determine the position of the second layer of hard rock stratum in the same way as in Step 2.1.2, and so on until the topmost layer of hard rock stratum is determined. By identifying the position of the hard rock stratum, the position of the hard rock stratum in the overlying strata of the working face is obtained.

[0078] Step 2.2: Conduct key stratum identification based on strength identification; strength identification is mainly to judge whether the hard rock stratum breaks synchronously with the breakage of the underlying key stratum by comparing the breakage distance of the hard rock stratum. The hard rock stratum that does not break with the breakage of the underlying key stratum is the key stratum in the overlying strata of the working face; the specific working process is as follows:

[0079] Step 2.2.1: Considering the influence of the height of the rock stratum from the coal seam and the fracture angle of the rock stratum, use to represent the serial number of the hard rock stratum from bottom to top. Then the breakage distance formula of the layer of hard rock stratum is:

[0080] (2);

[0081] (3);

[0082] (4);

[0083] In the formula, is the breakage distance of the layer of hard rock stratum, m; is the ultimate span of the layer of hard rock stratum, m; is the distance from the layer of hard rock stratum to the upper surface of the coal seam, m; is the fracture angle of the rock stratum, °; is the thickness of the layer of hard rock stratum, m; is the tensile strength of the layer of hard rock stratum, MPa; is the load borne by the layer of hard rock stratum, MPa; is the elastic modulus of the . , are respectively the serial numbers of the second-to-last layer and the topmost layer of hard rock stratum above; is the specific gravity of the

[0084] Step 2.2.2. Compare the break distances of each hard rock layer according to the following rules. The hard rock layer that does not break with the break of the underlying key layer is the key layer of the overlying strata of the working face. The specific rules for key layer identification are as follows:

[0085] Step 2.2.2.1. Numbering The hard rock layer with the number

[0086] is the bottommost hard rock layer, and the bottommost hard rock layer is defined as Key Layer 1; Step 2.2.2.2. Compare the break distances of the hard rock layers with the number That is, starting from the second hard rock layer, compare the break distance of the -th hard rock layer with the break distance of the hard rock layer above it:

[0087] If , at this time, the -th hard rock layer does not break with the break of the underlying key layer, then the -th hard rock layer is the key layer;

[0088] If , then add the load borne by the -th hard rock layer to the -th hard rock layer and recalculate the break distance of the -th hard rock layer. If the recalculated break distance of the -th hard rock layer is less than the break distance of the -th hard rock layer, then take . This indicates that the break of the -th hard rock layer is controlled by the -th hard rock layer, that is, before the -th hard rock layer breaks, the -th hard rock layer does not break. Once the -th hard rock layer breaks, its load acts on the -th hard rock, causing the -th hard rock to break accordingly. At this time, the -th hard rock layer is not the key layer;

[0089] 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;

[0090] Step 2.2.3. Number the identified key layers of the overlying strata of the working face from bottom to top as Key Layer 1, Key Layer 2,..., Key Layer The key strata can be divided into sub-key strata and main key strata. The sub-key strata are the other key strata except the main key strata, which can be simply referred to as key strata; the sub-key strata only control the local rock strata, while the main key strata can control the rock strata from itself to the ground surface. The last key stratum is the main key stratum, and the remaining key strata are sub-key strata. The main key stratum is the last key stratum, and the remaining key strata are sub-key strata.

[0091] Step 3: Calculate the critical size of the working face at which the key stratum breaks from bottom to top according to the concept of full mining. The situation where the state of the key stratum does not change with the increase of the working face size is defined as the full mining of the key stratum. When the key stratum is in the state of full mining, if the key stratum has broken, it will continue to break with the increase of the working face size; if the key stratum is in the unbroken state, the increase of the working face size will not cause the key stratum to break. During the coal face mining process, the key strata break in a ladder-like manner from bottom to top. After the shallow key stratum is damaged, the maximum development height of the water-conducting fissure zone will rise to the height of the upper key stratum that has not fractured. The working face size that satisfies the damage of the key stratum is defined as the critical size of the working face corresponding to the key stratum. The free space formed by the advance of the working face will be filled by the swelling characteristics of the roof rock strata of the coal seam. When the height of the free space below the key stratum is less than the maximum deflection, the key stratum will remain intact, the water-conducting fissure zone will develop to the maximum height, and the critical size of the working face is positive infinity. The calculation process of the critical size of the working face of the nth key stratum is as follows:

[0092] Step 3.1: Calculate the height of the free space, and the formula is:

[0093] (5);

[0094] In the formula, is the free space below the nth key stratum; is the mining height, m; is the thickness of the nth rock stratum, m; is the residual swelling coefficient of the rock of the nth rock stratum above the coal seam; , is the rock stratum number of the nth key stratum.

[0095] Step 3.2: Before the first fracture of the nth key stratum, it can be regarded as a fixed-ended beam. Under the action of the overlying rock strata and itself, the rock beam undergoes bending deformation. By selecting the mechanical model of uniformly distributed load of a simply supported beam, the maximum deflection is calculated, and the formula is:

[0096] (6);

[0097] In the formula, is the maximum deflection, m; is the load borne by the key stratum of the th layer, MPa; is the overhang distance of the key stratum of the th layer, m; is the elastic modulus of the key stratum of the th layer, GPa; is the moment of inertia of the cross-section of the key stratum of the th layer about the neutral axis, m 4 ; is to find the maximum value.

[0098] The fracture of the key stratum of the th layer in the overlying strata must simultaneously meet the following two conditions: First, the overhang distance of the key stratum of the th layer must be greater than its ultimate span at the initial fracture, that is, the working face size must be large enough; Second, the free space height below the key stratum of the th layer must be greater than the maximum deflection of the key stratum, that is:

[0099] (7);

[0100] In the formula, is the ultimate span of the key stratum of the th layer.

[0101] Therefore, when the coal seam mining thickness, the lithology and structure of the overlying strata are certain, for the key stratum of the th layer, its ultimate span should satisfy:

[0102] (8);

[0103] Step 3.3. Calculate the critical size of the working face when the rock of the key stratum of the th layer breaks, and the formula is:

[0104] (9);

[0105] In the formula, is the critical size of the working face when the key stratum of the th layer breaks.

[0106] Step 4. Based on the concept of full mining of the key stratum and the overlying strata structure of the working face, predict the maximum development height of the water-conducting fissure zone of the working face. The maximum development height of the water-conducting fissure zone is obtained by comparing the critical size of the working face It is predicted based on the relationship with the composite width of the front working face and the adjacent working face. It is necessary to determine whether the key stratum breaks and its impact on the front working face. Finally, the maximum development height of the water-conducting fissure zone of the working face is predicted, and it is judged whether the water-conducting height of the front working face increases under the influence of repeated mining disturbances. The specific prediction process of the maximum development height of the water-conducting fissure zone of the working face is as follows:

[0107] Step 4.1: First, calculate the composite width of the front working face and the rear working face :

[0108] ;

[0109] In the formula, is the width of the front working face; is the width of the rear working face; is the width of the coal pillar.

[0110] Step 4.2: Start judging layer by layer from the layer of the key stratum. The specific judgment rule is as follows:

[0111] If , it means that the layer of the key stratum does not fracture. Then the water-conducting fissure zone will not develop upward and can only develop to the current key stratum. The maximum development height of the water-conducting fissure zone of the working face is the height of the current key stratum, and it is necessary to perform the risk assessment in Step 5;

[0112] If , it means that the key stratum fractures and the water-conducting fissure zone continues to develop upward. The maximum development height of the water-conducting fissure zone of the working face is the height of the upper key stratum that has not fractured. At this time, it is necessary to perform an operation of adding 1 to , and enter the next key stratum to continue the judgment until the critical size of the working face is greater than the composite width, or the main key stratum is judged. If the main key stratum also fractures, the maximum development height of the water-conducting fissure zone of the working face is equal to or greater than the bedrock thickness, and the protective layer thickness is 0 at this time, which means that all key strata have fractured, and it is directly judged that the risk of water inrush is high; among them, it is necessary to synchronously judge whether there is a risk of delayed water inrush in the front working face. If and when, the repeated mining disturbance of the rear working face will cause the maximum development height of the water-conducting fissure zone of the front working face to rise to the height of the upper key stratum that has not fractured. At this time, it is judged that the front working face has the risk of delayed water inrush and it is necessary to perform the risk assessment in Step 5.

[0113] Suppose there are a total of 4 key strata, namely key stratum 1, key stratum 2, key stratum 3, and the main key stratum. According to the judgment logic of Step 4.2: First, judge the relationship between the critical size of the working face of key stratum 1 and the composite width. If , it shows that the key stratum 1 does not break, so the water-conducting fissure zone can only develop to the key stratum 1, and then the risk assessment is carried out according to step 5.

[0114] If , it shows that the key stratum 1 has broken and the water-conducting fissure zone has developed upward. Then, is incremented by 1, and then the key stratum 2 is judged. If , it means that the key stratum 2 has broken. Then, the key stratum 3 is judged. If , it means that the key stratum 3 has also broken. Then, the main key stratum is judged. If , it means that the main key stratum has also broken, and the water inrush risk is directly judged to be high.

[0115] In short, it is to judge layer by layer starting from the first key stratum until the critical size of the working face of a certain key stratum is greater than the composite width, and then the risk assessment in step 5 is carried out; or, if the main key stratum breaks, the water inrush risk is directly judged to be high. As for the comparison between the critical size of the working face and the width of the preface working face, it is equivalent to a small branch of the main judgment loop. If and , it shows that the maximum development height of the water-conducting fissure zone of the preface working face will rise to the height of the key stratum that has not broken in the upper part currently, and there is a risk of inducing the delayed water inrush of the preface working face, and the water inrush risk must be judged synchronously.

[0116] Step 5: Carry out risk assessment on two adjacent working faces according to the protective layer thickness. By comparing the required protective layer thickness of the working face with the actual protective layer thickness of the working face, the risk of roof water inrush of the working face is judged.

[0117] According to the "Code for Pillar Setting and Coal Mining Under Buildings, Water Bodies, Railways and Main Roadways", the selection of the protective layer thickness needs to comprehensively consider the overall water-richness of the pore aquifer in the Cenozoic loose layer, the development of the clay aquitard at its bottom, and the thickness of the weathered oxidation zone, and consider them according to strong and medium aquifer water bodies, no bottom aquitard, and aquifer respectively. In Table 1, A represents the thickness of the mined coal seam.

[0118] Table 1 Protective layer thickness of waterproof safety coal (rock) pillar

[0119] .

[0120] The specific process of judging whether there is a risk of roof water inrush in the working face is as follows: The thickness of the mined coal seam is known in advance. According to Table 1, judge how many times the required protective layer thickness is of the thickness of the mined coal seam, and the required protective layer thickness can be obtained.

[0121] The definition rules of the protective layer are as follows: for the case where the overlying rock lithology is hard, if the thickness of the clay layer at the bottom of the loose layer is greater than the cumulative mining thickness, the required thickness of the protective layer 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 thickness of the protective layer 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 thickness of the protective layer 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 thickness of the protective layer is 7 times the thickness of the mined coal seam. For the case where the overlying rock 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 thickness of the protective layer 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 thickness of the protective layer 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 thickness of the protective layer 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 thickness of the protective layer is 6 times the thickness of the mined coal seam. For the case where the overlying rock lithology is soft, if the thickness of the clay layer at the bottom of the loose layer is greater than the cumulative mining thickness, the required thickness of the protective layer 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 thickness of the protective layer 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 thickness of the protective layer 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 thickness of the protective layer is 5 times the thickness of the mined coal seam. For the case where the overlying rock lithology is extremely soft, if the thickness of the clay layer at the bottom of the loose layer is greater than the cumulative mining thickness, the required thickness of the protective layer 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 thickness of the protective layer is 2 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 thickness of the protective layer is 3 times the thickness of the mined coal seam; if there is no clay layer at the bottom of the loose layer, the required thickness of the protective layer is 4 times the thickness of the mined coal seam; the actual thickness of the protective layer is the thickness of the bedrock of the working face minus the maximum development height of the water-conducting fissure zone of the working face. The thickness of the bedrock of the working face is obtained in advance through three-dimensional seismic exploration technology, and the maximum development height of the water-conducting fissure zone of the working face is calculated according to step 4.

[0122] If the actual thickness of the protective layer is greater than or equal to the required thickness of the protective layer, it is determined that the risk of roof water inrush is low; if the actual thickness of the protective layer is less than the required thickness of the protective layer, it is determined that the risk of roof water inrush is high.

[0123] To prove the feasibility and superiority of the present invention, the following embodiments are given.

[0124] Table 2 Lithology and its properties of each layer of the 02 working face based on exploration boreholes

[0125] 。

[0126] Taking a certain coal mine in Anhui as an example, the 01 working face and the 02 working face are adjacent working faces. Among them, the 01 working face is the pre - placed working face with a width of about 262m, the 02 working face has a width of about 270m, and the mining height of both working faces is 4m. The superimposed mining width of the two working faces is 548m, and the coal pillar width is 16m. The lithology of the working face roof is mainly sandstone and mudstone, belonging to medium - hard roof. The lithology and its properties of each layer of the 02 working face based on exploration boreholes are shown in Table 2, and the comprehensive physical and mechanical parameters of the rock strata of the 02 working face are shown in Table 3.

[0127] Table 3 Comprehensive physical and mechanical parameters of the rock strata of the 02 working face

[0128] 。

[0129] According to the key stratum identification method in step 2.2 of the present invention, the theoretical identification of the key stratum position of the 02 working face is carried out, and the identification results are as Figure 2 shown. There are a total of 4 key strata, and the key strata are numbered from bottom to top as sub - key stratum 1, sub - key stratum 2, sub - key stratum 3, and main key stratum in turn; the 5 - coal is the currently mined coal seam. Figure 2 It includes the lithology and thickness of each key stratum. The lithology of sub - key stratum 1 is fine sandstone, with a thickness of 5.4m, and it is 5.48m away from the roof of the 5 - coal; the lithology of sub - key stratum 2 is fine sandstone, with a thickness of 5.32m, and it is 29.99m away from the roof of the 5 - coal; the lithology of sub - key stratum 3 is fine sandstone, with a thickness of 3m, and it is 60m away from the roof of the 5 - coal; the lithology of the main key stratum is siltstone, with a thickness of 8.42m, and it is 102.1m away from the roof of the 5 - coal.

[0130] According to the critical size calculation formula (9) of the working face, the theoretical calculation of the critical size of the working face for the breaking of the key stratum of the 02 working face is carried out, and the calculation results are shown in Table 4 below.

[0131] Table 4 Critical size of the working face for the breaking of the key stratum of the 02 working face

[0132] 。

[0133] Based on the full - mining theory of key strata and referring to the comprehensive physical and mechanical parameters of the working face rock strata for prediction, when the mining height is 4m, the maximum development height of the water - flowing fractured zone of the 02 working face is 60m, and there is no risk of roof water inrush with a lag in the 01 working face.

[0134] Considering the medium - hard roof, the thickness of the protective layer should be taken as 6 times the thickness of the mined - out 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 3D seismic exploration, the thickness of the bedrock around the 02 working face is between 160 - 200m. Predicting the maximum height of the water - flowing fractured zone to be 60m, then the thickness of the protective layer is between 100 - 140m, which is greater than 24m, and the risk of roof water inrush is relatively low.

[0135] Certainly, 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 those skilled in the art within the scope of the essence 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. The specific process 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; For the The thickness of the rock 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 critical layer breaks; It is the rock fracture angle; 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; For the 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; 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 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 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.

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: 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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