A method for determining a safe distance of a target layer of overburden separation grouting

Abstract

The application provides a method for determining a safe distance of a target layer of overburden separation grouting, comprising the following steps: S1, using a rock layer water resistance coefficient method, under the premise that high-pressure slurry does not penetrate the thickness of a protective layer and isolate rock layers, a safe distance H b is calculated and determined to obtain H b1 ; S2, using a rock mass strength discrimination method, under the critical condition that the rock mass in the safe distance is fractured and damaged, the safe distance H b is calculated and determined to obtain H b2 ; S3, using a water-resisting safe rock column setting method, the vertical height H sh of the water-resisting safe rock column should be greater than or equal to the maximum height H li of a water flowing fractured zone plus the safe distance H b3 , so as to determine H b3 ; S4, using a water inrush coefficient method of water-resisting rock layers, the safe distance H b is the sum of the thicknesses of water-resisting layers and rock layers above the water-resisting layers, so as to obtain H b4 ; S5, the safe distances H b1 , H b2 , H b3 and H b4 are analyzed and sorted to obtain a reasonable value range of the safe distance H b : H b2 <H b approx H b3 <H b1 <H b4 . The most suitable safe distance is obtained through scientific calculation and analysis.

Description

Technical Field

[0001] This invention relates to the field of coal mine overburden separation grouting technology, and in particular to a method for determining the safe distance of the target layer for overburden separation grouting. Background Technology

[0002] The most fundamental and core technical requirement of overburden separation grouting technology is technical safety. Since overburden separation grouting and the mining of the underlying coal seam are carried out simultaneously, it is crucial to ensure that the grouting does not pose a safety hazard to the coal mining operations. Therefore, a reasonable grouting technique should be adopted to prevent water inrush and slurry collapse disasters caused by pressurized grouting. Currently, the most commonly used safety measure is to first determine the height of the water-conducting fracture zone and then leave a certain safety distance above it. The distance between the bottom of the grouting borehole and the top interface of the water-conducting fracture zone should be greater than this safety distance. If the distance between the bottom of the borehole and the water-conducting fracture zone is insufficient, under high-pressure grouting, the filling grout is very likely to enter the fracture zone and flow into the working face, leading to a slurry inrush accident.

[0003] In summary, the setting of the safety distance is crucial to the safety of overburden separation and settlement reduction grouting technology and is a critical technical parameter. However, there is currently no scientifically accurate method for setting the safety distance. Generally, a safety distance of 10-20m is set based on past engineering experience, or a safety distance of 4-5 times the mining thickness is set.

[0004] When the safety distance is insufficient, the risk of the bottom of the borehole connecting with the water-conducting fracture zone increases significantly under the action of grouting pressure, which can easily cause water inrush and grout collapse disasters at the working face.

[0005] When the safety distance is set too large, the borehole depth is too shallow, increasing the risk of missing lower groutable exfoliation spaces and reducing the effectiveness of grouting for settlement reduction. Under the influence of grouting and filling of the exfoliation space, the development height of the overburden water-conducting fracture zone generally decreases. Previous projects have often conservatively set safety distances based on the development height of the water-conducting fracture zone before grouting. Furthermore, according to past exfoliation grouting patterns, there is a lag time in reducing surface subsidence (i.e., surface deformation only begins to slow down after a period of grouting). The larger the safety distance, the longer this lag time, and the later the exfoliation grouting settlement reduction effect takes hold. Therefore, setting an excessively large safety distance may not only miss groutable lower exfoliation spaces, reducing the grouting settlement reduction effect, but may also cause an excessively long lag time in surface settlement reduction, leading to incorrect judgments about the effectiveness of exfoliation grouting for settlement reduction.

[0006] Traditional methods rely heavily on engineering experience, and the safety distance is not scientifically calculated, making its rationality unknown. Therefore, establishing a scientifically sound and reasonable safety distance is of significant practical importance for grouting of overburden separation. Summary of the Invention

[0007] The present invention aims to at least partially solve one of the technical problems in the related art.

[0008] To achieve the above objectives, this invention proposes a method for determining the safe distance of the target stratum for overburden separation grouting, comprising the following steps:

[0009] S1. Using the rock layer water resistance coefficient method, under the premise of ensuring that the high-pressure grout does not penetrate the isolation rock layer within the protective layer thickness, the safety distance H is determined. b Calculations were performed to determine H. b1 ;

[0010] S2. Using the rock mass strength discrimination method, under the critical condition that the rock mass fractures and fails within the safe distance, the safe distance H is determined. b Calculations are performed to determine H. b2；

[0011] S3. Using the method of leaving a watertight safety rock pillar, the vertical height H of the watertight safety rock pillar is... sh It should be greater than or equal to the maximum height H of the water-conducting fracture zone. li Plus safety distance H b3 Thus determining H b3 ;

[0012] S4. Using the water inrush coefficient method for impermeable rock layers, the safe distance H is... b H is the sum of the thickness of the impermeable layer and the rock layer above it. b4 ;

[0013] S5, H b1 H b2 H b3 and H b4 The safe distance H is obtained by performing analysis and sorting. b Reasonable range of values ​​for H: b2 <H b ≈H b3 <H b1 <H b4 .

[0014] This invention calculates four different safety distances for overburden separation and settlement reduction grouting projects using four methods. By analyzing the differences between the theoretical values ​​and the actual values ​​in the actual project, the safety distances obtained by each method are conservatively estimated and ranked. The most suitable safety distance for overburden separation and settlement reduction grouting projects is obtained from this ranking.

[0015] Optionally, in step S1, the required safety distance H is calculated based on the water-blocking coefficient of the rock strata corresponding to the safety distance, under the design grouting pressure conditions. b H is calculated using the following formula.b1 :

[0016]

[0017] Among them, H b --Safety distance, in meters; P0-Design grouting orifice pressure, in MPa; γ-Specific density of filling grout, in tons per cubic meter. 3 H k --Designed borehole depth, in meters; δ i --Water resistance coefficient of the i-th rock layer, in MPa / m; h i --Thickness of the i-th rock layer, in meters.

[0018] Furthermore, in the calculation of S1, the design orifice pressure P0 for delamination grouting does not exceed 5.5 MPa, where the water resistance coefficient δ i Due to differences in rock strata properties, the water-blocking coefficients of different rock strata are generally 0.3–0.5 MPa / m for medium-coarse sandstone, 0.3 MPa / m for fine sandstone, 0.2 MPa / m for siltstone, 0.1–0.3 MPa / m for mudstone, and 0.4 MPa / m for limestone. In the fault zone from the water-conducting fracture zone to the fault zone below the delamination, the water-blocking capacity varies greatly due to differences in the properties of the infill material and the degree of cementation or compaction. Considering weak-strength infill material, the water-blocking coefficient of the fault zone is 0.05–0.1 MPa / m.

[0019] Furthermore, in S2, since the rock strata in the bending zone generally do not fracture when delamination grouting is not used, the boundary conditions should be regarded as a fixed state. When analyzing the bending deformation of the rock strata in the bending zone to fracture under the action of additional stress such as grouting pressure, the mechanical calculation model should adopt a beam model with two fixed beams or a thin plate model with four fixed thin plates.

[0020] Furthermore, when using the beam model for calculation, under the action of grouting pressure P0, the maximum tensile stress on the fixed beam reaches the tensile strength of the top stratum, i.e., (σ x ) max =σ t When the thickness is H b When the fixed beam breaks, the thickness of the fixed beam is the safety distance H. b Minimum value:

[0021]

[0022] q=P0+γH k +γ c H c ;

[0023] σ mt =K v ×σt ;

[0024] K v =(v pm / v pr ) 2 ;

[0025] wherein, H b2 represents the height reserved for the safety distance, with a unit of m; L k represents the span of rock stratum, that is, the length of the separated layer space along the dip direction of the working face, with a unit of m, and L k can be obtained through theoretical calculation or on-site drilling measurement; q represents the additional load borne by the rock stratum, that is, the grouting pressure, with a unit of MPa; P0 represents the orifice grouting pressure; γH k represents the slurry column pressure in the borehole; γ c H c represents the self-weight load of the filling body; σ mt represents the tensile strength of the rock mass, with a unit of MPa; K v represents the integrity coefficient of the rock mass; v pm represents the longitudinal wave velocity of the rock mass; v pr represents the longitudinal wave velocity of indoor rock or rock blocks; σ t represents rock strength.

[0026] Further, when adopting a thin plate model, the four-edge fixed supported elastic thin plate structure is in an ultimate exposed state, the maximum tensile stress is located in the middle of the long fixed supported edge, the dimension of the separated layer space along the dip direction of the working face S=2b, and the dimension of the separated layer space along the strike direction of the working face L k =2a, let when 0<k<1, σ max =(σ x ) max , when k>1, σ max =(σ y ) max , it can be obtained that:

[0027]

[0028]

[0029] wherein, σ max represents the maximum tensile stress borne by the rock stratum; σ x represents the stress along the dip direction of the working face; σ y represents the stress along the strike direction of the working face;

[0030] and in the thin plate model, the maximum tensile stress strength theory is adopted as the rock stratum failure criterion, when σ max =σ mtWhen the protective rock strata structure undergoes tensile failure, the thickness h (i.e., the safety distance H) of the rock strata at which fracture failure occurs under an external additional load q can be obtained. b Its calculation formula is:

[0031]

[0032] Furthermore, in the thin plate model, when the longer side dimension of the delamination space is much larger than the shorter side dimension, i.e., when k approaches 0, the simplified H of the thin plate model... b The formula can be obtained From the simplified formula, we can obtain that when the delamination space is elongated, the H obtained from the thin plate model is... b Theoretical value and H obtained from beam structure model b The theoretical values ​​are consistent.

[0033] Furthermore, in S3, when using the water-resistant safety pillar method, the thickness of the loose layer and the cumulative mining thickness are compared under different conditions based on the different overburden lithology, and the safety distance H under different conditions is obtained. b3 This method differs from the traditional engineering empirical method in obtaining H. b The results were similar.

[0034] Furthermore, in S4, if a thick water-resistant layer exists, the safety distance can be appropriately shortened; if there is no complete water-resistant layer at the corresponding location, the safety distance should be appropriately increased. The formula for calculating the water inrush coefficient of the water-resistant rock strata within the safety distance of the coal face roof is set as follows:

[0035] T d =p m / M g ;

[0036] p m =P0+γH k ;

[0037] Among them, T d --Water inrush coefficient of impermeable rock strata, in MPa / m; p m -- Grouting pressure exerted on the impermeable rock layer below the delamination space, in MPa; P0-- Grouting pressure at the wellhead; γH k --Magp column pressure inside the borehole; M g --Thickness of the waterproof layer within the safety distance, in meters;

[0038] In sections where the rock strata are structurally damaged, the water inrush coefficient should not exceed 0.06 MPa / m; in sections where the aquitard is intact and without structural damage, the coefficient should not exceed 0.1 MPa / m. The grouting pressure pm should be calculated based on the maximum pressure at the bottom of the borehole at the end of the grouting stage. Therefore, the safety distance H... b It is the sum of the thickness of the impermeable layer and the rock layer above it.

[0039] Furthermore, in S5, H is respectively... b1 H b2 H b3 and H b4 Analysis:

[0040] In H b1 In the calculation, the calculation idea of ​​this method is reasonable, but the value of the grouting pressure on the rock layer is generally too large in the calculation process, which leads to the calculation results of Method 1 being too conservative.

[0041] In H b2 In the calculations, when using the mechanical model, the thickness of the rock strata within the safety distance is left at a height of H. b When the protective rock layer fractures under the additional load q, and the mechanical calculation model used treats the rock layer within the safety distance as a single rock layer, but in actual engineering, there may be multiple rock layers within the safety distance, therefore, in such multi-layered actual engineering projects, the safety distance H... b Theoretical calculations tend to underestimate the value; therefore, the H calculated using this method... b The safe distance is the minimum height;

[0042] In H b3 In the calculation, this method differs from the traditional engineering empirical method in obtaining H. b The results are similar;

[0043] In H b4 In the calculation, considering the risk of sudden water inrush, the safety is the highest, therefore the calculation result H is... b4 Most conservative;

[0044] After comprehensive consideration, the safe distance H is obtained. b Reasonable range of values ​​for H: b2 <H b ≈H b3 <H b1 <H b4 .

[0045] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0046] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0047] Figure 1 A schematic diagram of the rock strata structure during grouting and filling of overburden separation.

[0048] Figure 2This is a schematic diagram of the method steps for determining the safe distance of the target layer in overburden separation grouting according to the present invention;

[0049] Figure 3 This is a schematic diagram of the beam structure mechanical model and the thin plate structure mechanical model of step S2 of the method for determining the safe distance of the target layer for overburden separation grouting according to the present invention.

[0050] Figure 4 This is a schematic diagram of a waterproof safety column for a water-tight safety rock column retention method according to a method for determining the safety distance of the target layer for grouting of overburden separation according to the present invention.

[0051] Figure 5 The safe distance H of the water-tight safety rock column retention method according to the present invention is a method for determining the safe distance of the target layer for grouting of overburden separation. b Corresponding charts for different overburden lithologies and loose layer thicknesses. Detailed Implementation

[0052] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0053] Studies have shown that, in order to improve the settlement reduction effect of grouting for overburden separation, reference should be made to... Figure 1 In such cases, grouting should be performed to fill the lower separation space as much as possible. However, the lower separation location is close to the water-conducting fracture zone, posing a high risk of communication with the fracture zone. Whether it can be used as a grouting target layer depends crucially on whether the distance between the lower separation and the water-conducting fracture zone is safe enough. Therefore, the establishment of a safe distance is not only related to the production safety of the downhole working face, but also directly affects the grouting and settlement reduction effect. The safe distance for separation grouting is extremely important.

[0054] The necessity of leaving a safety distance: First, due to geological conditions and the thickness of the coal seam being mined, the height of the water-conducting fracture zone changes dynamically along the mining direction. Leaving a certain safety distance from the bottom of the borehole to the water-conducting fracture zone can ensure that even when the water-conducting fracture zone is highly developed in a local stratum, grout can still be prevented from entering the water-conducting fracture zone. Second, in actual engineering, the grouting pressure generally fluctuates, especially at the end of the grouting stage, where the grouting pressure is generally higher. Leaving a safety distance can effectively prevent the bottom of the borehole from penetrating the water-conducting fracture zone under high grouting pressure, thus fully ensuring the safe production of the mine working face.

[0055] This application provides a method for determining the safe distance of the target stratum in overburden separation grouting, which is described below. Figures 2 to 5 To elaborate in detail.

[0056] A method for determining the safe distance of the target layer for overburden separation grouting includes the following steps:

[0057] S1. Using the rock layer water resistance coefficient method, under the premise of ensuring that the high-pressure grout does not penetrate the isolation rock layer within the protective layer thickness, the safety distance H is determined. b Calculations were performed to determine H. b1 ;

[0058] S2. Using the rock mass strength discrimination method, under the critical condition that the rock mass fractures and fails within the safe distance, the safe distance H is determined. b Calculations are performed to determine H. b2；

[0059] S3. Using the method of leaving a watertight safety rock pillar, the vertical height H of the watertight safety rock pillar is... sh It should be greater than or equal to the maximum height H of the water-conducting fracture zone. li Plus safety distance H b3 Thus determining H b3 ;

[0060] S4. Using the water inrush coefficient method for impermeable rock layers, the safe distance H is... b H is the sum of the thickness of the impermeable layer and the rock layer above it. b4 ;

[0061] S5, H b1 H b2 H b3 and H b4 The safe distance H is obtained by performing analysis and sorting. b Reasonable range of values ​​for H: b2 <H b ≈H b3 <H b1 <H b4 .

[0062] In overburden separation and settlement reduction grouting projects, the distance from the bottom of the grouting borehole to the roof of the mined coal seam is equal to the height of the water-conducting fracture zone plus the safety distance. However, due to geological conditions and mining methods, the height of the water-conducting fracture zone is not fixed. In order to fully ensure the safety of separation grouting, the safety distance is often set too large. This application adopts multiple methods such as theoretical calculation, engineering experience, and standard formulas to scientifically and reasonably determine the safety distance for separation grouting.

[0063] This invention calculates four different safety distances for overburden separation and settlement reduction grouting projects using four methods. By analyzing the differences between the theoretical values ​​and the actual values ​​in the actual project, the safety distances obtained by each method are conservatively estimated and ranked. The most suitable safety distance for overburden separation and settlement reduction grouting projects is obtained from this ranking.

[0064] In S1, to prevent communication between the filling delamination zone and the water-conducting fracture zone, a pressure-resistant grout barrier of a certain thickness is required as a safety distance to prevent grout from entering the downhole working face. This is especially important since delamination grouting is high-pressure grouting, and the isolation rock layer must be designed to ensure that water pressure does not penetrate the thickness of the protective layer. Based on the rock layer's water-blocking coefficient corresponding to the safety distance, the required safety distance H is calculated under the design grouting pressure conditions. b H is calculated using the following formula. b1 :

[0065]

[0066] Among them, H b --Safety distance, in meters; P0-Design grouting orifice pressure, in MPa; γ-Specific density of filling grout, in tons per cubic meter. 3 H k --Designed borehole depth, in meters; δ i --Water resistance coefficient of the i-th rock layer, in MPa / m; h i --Thickness of the i-th rock layer, in meters.

[0067] In the S1 method using the rock layer water-blocking coefficient, the design orifice pressure P0 for grouting separation does not exceed 5.5 MPa, where the water-blocking coefficient δ i Due to variations in rock strata properties, according to the "Guidelines for Coal Pillar Retention and Coal Mining in Buildings, Water Bodies, Railways and Main Shafts" (2017 edition), the water-blocking coefficients of different rock strata are generally 0.3–0.5 MPa / m for medium-coarse sandstone, 0.3 MPa / m for fine sandstone, 0.2 MPa / m for siltstone, 0.1–0.3 MPa / m for mudstone, and 0.4 MPa / m for limestone. In the fault zone extending from the water-conducting fracture zone to below the delamination, the water-blocking capacity varies greatly due to differences in the properties of the filling material and the degree of cementation or compaction. Considering weak-strength filling material, the water-blocking coefficient of the fault zone is 0.05–0.1 MPa / m. Calculation example: Grouting hole bottom depth H k Based on a depth of 300m, the slurry bulk density γ is 1.3t / m. 3 If the grout pressure at the bottom of the grouting hole reaches approximately 9.4 MPa, then the isolation rock layer must be able to ensure that the water pressure does not penetrate the thickness of the protective layer. In this example, the rock layer above the top interface of the surface water-conducting fracture zone is an interlayer of medium-fine grained sandstone, silt and mudstone, with a comprehensive water-blocking coefficient of 0.25 MPa / m. Therefore, the thickness of the safe isolation rock layer is 9.4 / 0.25 = 37.6 m.

[0068] The calculation approach of this method is reasonable, but the grouting pressure values ​​applied to the rock strata are generally too high during the calculation process, leading to conservative results for Method 1. Theoretically, the maximum grouting pressure at the bottom of the borehole is the sum of the grouting pressure at the borehole opening and the grout column pressure inside the borehole. However, in reality, the grout is mostly in a non-full-pipe flow state within the borehole, and the actual grouting pressure at the bottom of the borehole is close to the grout column pressure inside the borehole. When the grout is in a full-pipe flow state, as the grout flows downwards along the borehole, it encounters resistance from the borehole wall, and the pressure at the bottom of the borehole is generally less than the sum of the grouting pressure at the borehole opening and the grout column pressure inside the borehole. In summary, although the calculation approach of Method 1 is reasonable, the results are often conservative due to the influence of the values ​​of the calculation parameters.

[0069] In S2, when using the rock mass strength discrimination method, generally speaking, the aquitard within the bending zone will not exhibit through-cracks. However, under the action of additional stresses such as grouting pressure, the aquitard below the delamination space may fracture and fail. In addition, high-pressure grouting may also cause splitting cracks in the rock strata. By obtaining the physical and mechanical parameters of the rock strata through exploration and combining them with the rock strength criterion, the fracture failure conditions of the rock mass within the safety distance are calculated and analyzed. This allows for the determination of whether a rock strata with a thickness of Hb within the safety distance will fracture under a certain grouting pressure.

[0070] Since the rock strata in the bending zone generally do not fracture when delamination grouting is not used, the boundary conditions should be considered as a fixed state. When analyzing the bending deformation and fracture failure of the rock strata in the bending zone under additional stress such as grouting pressure, the mechanical calculation model should use a beam model with beams fixed at both ends or a thin plate model with thin plates fixed at four ends. The reasonable allowable height of the safety distance is calculated below using the beam model and the thin plate model respectively.

[0071] The reasonable height for the safety distance is calculated using a fixed-support beam structure calculation model.

[0072] When using the beam model for calculation, under the action of grouting pressure P0, the maximum tensile stress on the fixed beam reaches the tensile strength of the top stratum, i.e., (σ x ) max =σ t When the thickness is H b When the fixed beam breaks, the thickness of the fixed beam is the safety distance H. b Minimum value:

[0073]

[0074] q=P0+γH k +γ c H c ;

[0075] σ mt =K v ×σ t ;

[0076] K v =(v pm / v pr ) 2 ;

[0077] Wherein, H b2 -- reserved height of safety distance, unit: m; L k -- span of rock strata, i.e., the length of the separated space along the working face tendency, unit: m, and L k can be obtained through theoretical calculation or on-site drilling measurement; q-- additional load on rock strata, i.e., grouting pressure, unit: MPa; P0-- grouting pressure at orifice; γH k -- slurry column pressure in the borehole; γ c H c -- dead weight load of filling body; σ mt -- tensile strength of rock mass, unit: MPa; K v -- integrity coefficient of rock mass; v pm -- longitudinal wave velocity of rock mass; v pr -- longitudinal wave velocity of indoor rock (block); σ t -- rock strength.

[0078] When the rock stratum span L k is measured by on-site drilling, firstly an exploration borehole is constructed above the working face, then a three-dimensional laser scanner is lowered into the borehole to detect the three-dimensional shape of the separated space, so as to obtain the rock stratum span L k .

[0079] When calculating σ mt , rock strength is obtained by coring through borehole and sending samples to laboratory for testing. The tensile strength of rock mass is generally 2~10MPa. Empirical calculation method for tensile strength of rock mass: tensile strength of rock mass = rock strength × rock mass integrity coefficient; the empirical calculation method is the most commonly used method for determining rock mass strength in engineering; the calculation formula is simple and clear; relevant parameters can be easily obtained through laboratory tests and simple on-site tests. After obtaining L k , q, σ mt , H b under the beam model can be calculated, that is, H b2 .

[0080] An elastic thin plate structure calculation model is used to calculate the reasonable reserved height of the safety distance.

[0081] When adopting the thin plate model, the four-sided clamped elastic thin plate structure is in the ultimate exposed state, the maximum tensile stress is located in the middle of the long clamped edge, the dimension of the separated space along the working face tendency S=2b, the dimension of the separated space along the working face strike L k =2a, let when 0<k<1, σ max =(σx ) max When k>1, σ max =(σ y ) max We can obtain:

[0082]

[0083]

[0084] Where, σ max --The maximum tensile stress on the rock strata; σ x --Stress along the direction of the working surface; σ y --Stress along the direction of the working surface;

[0085] Furthermore, in the thin plate model, the maximum tensile stress strength theory is used as the rock stratum failure criterion, when σ max =σ mt When the protective rock strata structure undergoes tensile failure, the thickness h (i.e., the safety distance H) of the rock strata at which fracture failure occurs under an external additional load q can be obtained. b Its calculation formula is:

[0086]

[0087] Furthermore, in the thin plate model, when the longer side dimension of the delamination space is much larger than the shorter side dimension, i.e., when k approaches 0, the simplified H of the thin plate model... b The formula can be obtained From the simplified formula, we can obtain that when the delamination space is elongated, the H obtained from the thin plate model is... b2 Theoretical value and H obtained from beam structure model b2 The theoretical values ​​are consistent.

[0088] Because the rock stratum thickness is reserved at a height of H within the safety distance. b At that time, the protective rock layer fractured and failed under the additional load q. Therefore, the H calculated by this method... b2 This is the minimum height for a safe distance. Furthermore, the mechanical calculation model used treats the rock strata within the safe distance as a single stratum, while in actual engineering, multiple rock strata may exist within the safe distance. Therefore, the safe distance H... b2 Theoretical calculated value compared to actual value H b The answer may be too small.

[0089] In S3, when calculating the safety distance using the method of leaving water-resistant safety rock pillars, the method for leaving water-resistant safety rock pillars in water-conserving mining is referenced from the "Specifications for the Retention of Coal Pillars in Buildings, Water Bodies, Railways and Main Shafts and Coal Mining under Pressure" (2017). The vertical height H of the water-resistant safety rock pillar is... sh It should be greater than or equal to the maximum height H of the water-conducting fracture zone.li Plus safety distance H b ;

[0090] H sh ≥H li +H b ;

[0091] Among them, H sh With H li and H b Relationship reference Figure 4 As shown, the thickness of the loose layer and the cumulative mining thickness are compared under different conditions based on the different overburden lithology, with reference to... Figure 5 Obtain the safe distance H under different conditions b3 The overburden lithology is categorized as hard, medium-hard, weak, and extremely weak. The difference between the loose layer thickness and the cumulative mining thickness falls into four categories: the thickness of the cohesive soil layer at the bottom of the loose layer is greater than the cumulative mining thickness; the thickness of the cohesive soil layer at the bottom of the loose layer is less than the cumulative mining thickness; the total thickness of the loose layer is less than the cumulative mining thickness; and there is no cohesive soil layer at the bottom of the loose layer. For each category and corresponding overburden lithology, the safe distance H under that category and lithology can be obtained. b The height of the enclosure, and Figure 5 The table above is applicable to layered mining of thick coal seams; it is not suitable for fully mechanized longwall mining. The H obtained using this method... b3 H obtained by traditional engineering empirical methods b The results were similar.

[0092] In S4, the safety distance is calculated using the water inrush coefficient method for impermeable rock strata. Whether the safety distance is reasonable depends not only on the allowance height, but also on the impermeability, integrity, and rock mass strength of the overlying lithology at the corresponding location. If a thick impermeable layer exists, the safety distance can be appropriately shortened; if there is no intact impermeable layer at the corresponding location, the safety distance should be appropriately increased.

[0093] In S4, referring to the calculation method of the water inrush coefficient of the floor of the coal mining face in the "Detailed Rules for Water Prevention and Control in Coal Mines" (2018 Edition), the calculation formula for the water inrush coefficient of the water-resistant rock strata within the safe distance of the roof of the coal mining face is set as follows:

[0094] T d =p m / M g ;

[0095] p m =P0+γH k

[0096] Among them, T d --Water inrush coefficient of impermeable rock strata, in MPa / m; p m-- Grouting pressure exerted on the impermeable rock layer below the delamination space, in MPa; P0-- Grouting pressure at the wellhead; γH k --Magp column pressure inside the borehole; M g --Thickness of the waterproof layer within the safety distance, in meters.

[0097] In the calculation, the grouting pressure p borne by the water-impermeable rock layer below the delamination space is considered. m The maximum pressure at the bottom of the hole at the end of the grouting stage should be used for calculation.

[0098] Based on national data, the water inrush coefficient of the aquitard strata in the roof of coal mining faces is no greater than 0.06 MPa / m in areas where the strata are structurally damaged, and no greater than 0.1 MPa / m in areas where the aquitard is intact and without structural damage. The grouting pressure p m The maximum pressure at the bottom of the hole during the final stage of grouting should be used for calculation, then the safety distance H is... b That is, the sum of the thickness of the impermeable layer and the rock layer above it, thus obtaining the safe distance H calculated using the impermeable rock layer water inrush coefficient method. b4 This method offers the highest level of security and the most conservative calculation results.

[0099] In S5, for H b1 H b2 H b3 and H b4 Analysis:

[0100] In H b1 In the calculation, the calculation idea of ​​this method is reasonable, but the value of the grouting pressure on the rock layer is generally too large in the calculation process, which leads to the calculation results of Method 1 being too conservative.

[0101] In H b2 In the calculations, when using the mechanical model, the thickness of the rock strata within the safety distance is left at a height of H. b When the protective rock layer fractures under the additional load q, and the mechanical calculation model used treats the rock layer within the safety distance as a single rock layer, but in actual engineering, there may be multiple rock layers within the safety distance, therefore, in such multi-layered actual engineering projects, the safety distance H... b Theoretical calculations tend to underestimate the value; therefore, the H calculated using this method... b The safe distance is the minimum height;

[0102] In H b3 In the calculation, this method differs from the traditional engineering empirical method in obtaining H. b The results are similar;

[0103] In H b4 In the calculation, considering the risk of sudden water inrush, the safety is the highest, therefore the calculation result H is... b4 Most conservative;

[0104] After comprehensive consideration, the safe distance H is obtained. b Reasonable range of values ​​for H: b2 <H b ≈H b3 <H b1 <H b4 .

[0105] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0106] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0107] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for determining the safe distance of the target stratum for overburden separation grouting, characterized in that, Includes the following steps: S1. Using the rock layer water resistance coefficient method, under the premise of ensuring that the high-pressure grout does not penetrate the isolation rock layer within the protective layer thickness, the safety distance is determined. H b Calculations were performed to determine the first safe distance: H b1 ; S2. Using the rock mass strength discrimination method, under the critical condition that the rock mass fractures and fails within a safe distance, the safe distance is determined. H b Calculations are performed to determine the second safety distance: H b2； S3. Using the method of leaving a watertight safety rock pillar, the vertical height of the watertight safety rock pillar. H sh It should be greater than or equal to the maximum height of the water-conducting fracture zone. H li Plus a safe distance H b Thus, the third safe distance is determined: H b3 ; S4. Using the water inrush coefficient method of water-resistant rock strata, the safe distance... H b The fourth safety distance is the sum of the thickness of the impermeable layer and the rock layer above it. H b4 ; S5, to H b1 , H b2 , H b3 as well as H b4 Analyze and sort to obtain the safe distance. H b Reasonable range of values: H b2 ＜H b ≈H b3 ＜H b1 ＜H b4 .

2. The method for determining the safe distance of the target stratum for overburden separation grouting as described in claim 1, characterized in that, In S2, since the strata in the bending zone do not fracture when delamination grouting is not used, the boundary conditions should be regarded as a fixed state. When analyzing the bending deformation of the strata in the bending zone to fracture under the additional stress of grouting pressure, the mechanical calculation model should adopt a beam model with two fixed beams or a thin plate model with four fixed thin plates.

3. The method for determining the safe distance of the target stratum for overburden separation grouting as described in claim 2, characterized in that, When using a beam model for calculation, the grouting pressure at the orifice... P Under zero stress, when the maximum tensile stress on the fixed beam reaches the tensile strength of the top stratum rock, the thickness is... H b The fixed beam breaks; at this point, the thickness of the fixed beam is the safe distance. H b minimum value H b2 : ； q=P 0 +γH k +γ c H c ； σ mt =K v × σ t ； K v = （ v pm / v pr ） 2 ； in, H b2 --Second safety distance, in meters; --Exposed rock strata span, i.e., the length of the separation space along the strike of the working face, in meters, and Through theoretical calculations or on-site drilling measurements; --Additional load on the rock strata, in MPa; P 0 -- Grouting pressure at the orifice; γH k --Magp column pressure inside the borehole; γ c H c --Self-weight load of the filling material; σ mt --Tensile strength of rock mass, in MPa; K v --Rock mass integrity coefficient; v pm --P-wave velocity of the rock mass; v pr --Longitudinal wave velocity of indoor rocks; σ t --Rock strength.

4. The method for determining the safe distance of the target stratum for overburden separation grouting as described in claim 3, characterized in that, When using a thin plate model, the four-sided fixed elastic thin plate structure is in a state of extreme exposure. The maximum tensile stress is located at the middle of the long fixed side. The delamination space along the working surface has a dimension S=2b, and the delamination space along the working surface has a dimension of [missing value]. =2a, let ,when hour, ,when hour, ,have to: ； ； in, --The maximum tensile stress on the rock strata; --Stress along the direction of the working surface; --Stress along the direction of the working surface; Furthermore, in the thin plate model, the maximum tensile stress strength theory is used as the rock stratum failure criterion. When the protective rock structure undergoes tensile failure, it is found that: with external additional load... The thickness h of the rock strata when fracture and failure occur under the action of the action is the second safety distance. H b2 Its calculation formula is: ； ； in, σ mt --Tensile strength of rock mass, in MPa.

5. The method for determining the safe distance of the target stratum for overburden separation grouting as described in claim 4, characterized in that, In the thin plate model, when the longer side dimension of the delamination space is much larger than the shorter side dimension, i.e., when k approaches 0, the thin plate model is simplified. H b2 The formula yields: From the simplified formula, when the delamination space is elongated, the second safety distance obtained by the thin plate model is... H b2 The theoretical value and the second safety distance obtained from the beam structure model H b2 The theoretical values ​​are consistent.

6. The method for determining the safe distance of the target stratum for overburden separation grouting as described in claim 1, characterized in that, In S3, when using the water-tight safety pillar method, the thickness of the loose layer and the cumulative mining thickness are compared under different conditions based on the different overburden lithology to obtain the third safety distance under different conditions. H b3 This method yields safe distance results similar to those obtained using traditional engineering empirical methods.

7. The method for determining the safe distance of the target stratum for overburden separation grouting as described in claim 1, characterized in that, In S4, if a thick water-resistant layer exists, the safety distance is shortened; if there is no complete water-resistant layer at the corresponding location, the safety distance should be increased. The formula for calculating the water inrush coefficient of the water-resistant rock strata within the safety distance of the coal face roof is as follows: T d =p m / M g ； ； in, T d --Water inrush coefficient of water-resistant rock strata, in MPa / m; p m -- Grouting pressure exerted on the water-resistant rock layer below the delamination space, in MPa; P 0 -- Grouting pressure at the orifice; γH k --Magp column pressure inside the borehole; M g --Thickness of the waterproof layer within the safety distance, in meters; In sections where the rock strata are structurally damaged, the water inrush coefficient should not exceed 0.06 MPa / m; in sections where the aquitard is intact and without structural damage, the water inrush coefficient should not exceed 0.1 MPa / m; grouting pressure... p m The fourth safety distance should be calculated based on the maximum pressure at the bottom of the hole during the final stage of grouting. H b4 It is the sum of the thickness of the impermeable layer and the rock layer above it.

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