A method for water conservation exploitation of fissure zone in aquifer in-situ protection

Abstract

This invention discloses a method for in-situ protection of aquifers through cemented backfilling in fractured zones, belonging to the field of water-conserving mining technology. By acquiring the geological and mining technical conditions of the coal face, the key bearing strata are determined based on the key layer theory. The development height of the caving zone and the water-conducting fracture zone is calculated. When a key bearing stratum exists within 1 / 3 to 2 / 3 of the height of the water-conducting fracture zone, a fixed-stratum backfilling mode is adopted, determining the bottom of the key bearing stratum as the backfilling layer and using a fixed cemented backfilling step distance. When no key bearing stratum exists within this range, a variable-stratum backfilling mode is adopted. The backfilling layer is determined according to the evolution law of the water-conducting fracture zone, and the choice between fixed cemented backfilling step distance or no fixed cemented backfilling step distance is determined based on the coal seam thickness. This invention achieves adaptive selection of backfilling modes and quantitative determination of backfilling parameters, reducing the risk of hydraulic connectivity between the water-conducting fracture zone and the overlying aquifer, and realizing in-situ protection of the aquifer.

Description

Technical Field

[0001] This invention relates to the field of water-conserving mining technology, and in particular to a method for in-situ protection of aquifers through cemented backfilling in fracture zones for water-conserving mining. Background Technology

[0002] However, different water-retaining coal mining technologies have certain applicable conditions. Traditional backfilling mining has low backfilling efficiency, and mining and backfilling interfere with each other, making it unsuitable for large mines. Overburden separation grouting requires a relatively thick critical rock layer, and the aquifer must be above the critical rock layer, which greatly limits its applicability, generally focusing on surface subsidence reduction. Aquifer freezing water-retaining technology does not address water resource loss after mining. Mining deployment optimization is a protective technology based on the mining source; since it does not change the properties of the rock strata themselves, its applicability is relatively limited. Rock strata modification achieves stability of the aquifer by thickening the water-retaining rock layer, which is common in in-situ protection of floor water, but maintaining the stability of the grouting layer after multi-face mining is difficult.

[0003] Publication No. CN121162281A discloses a method for water conservation in coal mining. This patent controls the development height of fracture zones by regulating the filling height to achieve a balance between mine water inflow and domestic water use in the mining area. This method is based on the water-determined mining approach proposed by traditional filling mining. However, traditional filling mining is inefficient, and large domestic water use in the mining area can severely damage the aquifer. Publication No. CN120830538A discloses a method for water conservation in coal seam sandstone roof mining based on mining-induced fracture grouting. This patent achieves the goal of water conservation mining by repairing the fractured aquitard. This method is a method of damaging the aquifer first and then treating it. The repaired aquitard may fail again during the self-stabilization process of rock strata settlement, leading to the failure of water conservation mining. Publication No. CN115030722A discloses a highly efficient water conservation mining method for goaf delayed filling. This patent uses directional drilling to grout the voids in the caving zone before compaction, thereby reducing the impact range of mining. This method only considers the compaction effect of the caving zone and is suitable for rock strata with a large coefficient of caving expansion in the roof.

[0004] Existing water-retaining mining methods lack systematic technical solutions for determining the spatial relationship between key bearing strata and water-conducting fracture zones, selecting filling layers, controlling the timing of filling, and quantifying the amount of filling material. In particular, existing technologies have not provided effective solutions for how to scientifically determine the filling layer under different geological conditions, how to dynamically adjust filling parameters based on the evolution characteristics of water-conducting fracture zones, and how to maximize filling efficiency and optimize material usage while ensuring water retention. Therefore, there is an urgent need to propose a water-retaining mining method that is widely applicable, highly efficient, and allows for quantitative determination of filling parameters. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for in-situ protection of aquifers by cemented backfilling in fracture zones for water-conserving mining. By establishing a spatial relationship discrimination criterion between key bearing rock layers and water-conducting fracture zones, and combining the evolution characteristics of water-conducting fracture zones with the advance distance, the invention enables adaptive selection of two cemented backfilling modes: fixed stratum and variable stratum. Furthermore, it quantitatively determines the backfilling stratum, backfilling step distance, and backfilling amount to reduce the risk of hydraulic connectivity between the water-conducting fracture zones and the overlying aquifers, thereby achieving in-situ protection of the aquifers.

[0006] To achieve the above objectives, this invention provides a method for in-situ protection of aquifers through cemented backfilling in fractured zones for water-retaining mining, comprising the following steps: Step S1, obtaining the geological conditions and mining technical conditions of the coal face, including coal seam thickness, coal seam depth, working face length, distance between the coal seam and the protected aquifer, lithology of each rock stratum, thickness of each rock stratum, volumetric force of each rock stratum, elastic modulus of each rock stratum, and uniaxial compressive strength of each rock stratum; determining the critical bearing rock stratum position and fracture step between the coal seam and the aquifer based on the critical stratum theory, wherein the determination process is based on the first critical bearing rock stratum position of the coal seam roof. The calculation begins with the first rock layer, and the key bearing rock layer is determined by cyclically comparing the loads exerted on the first rock layer by adjacent rock layers.

[0007] Step S2: Calculate the development height of the caving zone based on the geological and mining technical conditions, and obtain the rock fragmentation coefficient using the standard sand volume replacement method; calculate the development height of the water-conducting fracture zone using a multivariate nonlinear fitting method based on the mathematical statistics of the height of the water-conducting fracture zone under similar geological conditions, where the fitting method involves the coal seam burial depth, the coal seam thickness, the working face length, and the hard rock ratio coefficient; determine the cementitious filling stratum pattern of the fracture zone based on the spatial relationship between the development height of the water-conducting fracture zone and the key bearing rock stratum.

[0008] Step S3: Determine the filling layer, filling timing, and filling step distance according to the cemented filling layer pattern of the fracture zone. Form the main hole and secondary inclined hole through ground directional drilling, construct directional drilling and arrange filling pipelines, use expansive cementitious material to fill the fracture zone, and implement the process in a cycle with the mining operation.

[0009] Furthermore, in step S1, the process of determining the key bearing strata based on the key stratum theory includes: taking the first coal seam roof as the key bearing stratum... The first layer is the first rock layer. If the second layer is the first layer, then the third layer is the first layer. Load of layer on first layer Less than the Load of layer on first layer Then determine the first The layer is the first The key bearing rock layer, and the first The first layer is the key upper layer determined by the cyclic determination; the calculation expression for the load is as follows:

[0010] ;

[0011] ;in, For the first The elastic modulus of the rock strata For the first The elastic modulus of the rock strata For the first The elastic modulus of the rock strata For the first The elastic modulus of the rock strata, in units of ; For the first Thickness of rock layers, For the first Thickness of rock layers, For the first Thickness of rock layers, For the first Thickness of rock layers, in units of ; For the first Density of rock layers For the first Density of rock layers For the first Density of rock layers For the first Unit weight of the rock layer, in units ;Breaking step distance The calculation formula is: ;in, The breaking step distance is expressed in units of... ; The tensile strength of the key rock strata, in units of ; The load on the key rock strata, in units of ; The thickness of the key rock strata is given in units of 1. .

[0012] Furthermore, in step S2, the development height of the landslide zone... The calculation formula is: ;in, Coal seam thickness, in units of ; Rock fragmentation coefficient; rock fragmentation coefficient Volume after fragmentation calculated using the standard sand volume replacement method Volume before fragmentation The ratio is determined by taking the coal seam thickness. The average value of the rock fragmentation coefficient within a multiple of 1.

[0013] Furthermore, in step S2, the hard rock proportion coefficient is determined by the uniaxial compressive strength being greater than 1 in step S1. The ratio of rock layer thickness to total thickness is obtained; the method for determining the cementitious filling layer pattern in the fracture zone is as follows: when the water-conducting fracture zone... to When the critical bearing stratum exists within the height range, the cemented filling stratum pattern of the fracture zone is a fixed-stratum fracture zone cemented filling pattern; when the water-conducting fracture zone... to When the critical bearing rock layer is not present within the height range, the cementitious filling layer pattern of the fracture zone is the variable layer fracture zone cementitious filling pattern.

[0014] Furthermore, in step S3, when the cemented filling layer mode in the fracture zone is a fixed-layer fracture zone cemented filling mode, the filling layer is fixed at the bottom of the low-lying key bearing stratum, and the distance between the filling layer and the coal seam is... The working face advance distance corresponding to the first filling. The formula for determining it is: ;in, The distance the working face advances from the development of the water-conducting fracture zone to the corresponding filling layer is expressed in units of... ; This represents the working face advance distance corresponding to the point where the critical rock strata reach a point of instability, expressed in units of... ; The calculation formula is: ;in, The critical rock strata fracture step distance, in units of ; The distance between the filling layer and the coal seam is expressed in units of 1. ; The angle of collapse of the rock strata, in units of To advance the distance The periodic filling interval is used for the cycle of mining and fracture zone filling operations.

[0015] Furthermore, in step S3, under the fixed-layer fracture zone cementitious filling mode, the volume of grouting material in a single cycle is... The calculation formula is: ;in, This represents the volume of fracture development, in units of... ; The volume of pores within the collapse zone; unit: ; The calculation formula is: ;in, The length of the working face, in units of ; This represents the working face advance distance corresponding to the first filling, in units of... ; The distance between the filling layer and the coal seam is expressed in units of 1. ; The elevation of the landslide zone is expressed in units of [missing information]. ; The porosity of the fractured region is taken as a value. to ; The calculation formula is: ;in, The porosity of the caving zone is calculated using the following formula: , is the rock fragmentation coefficient.

[0016] Furthermore, in step S3, when the cemented filling layer mode of the fracture zone is the variable layer cemented filling layer mode of the fracture zone, the evolution characteristics of the water-conducting fracture zone under different advance distances of the working face are determined, and the development of the water-conducting fracture zone to its maximum value is recorded. of The corresponding propulsion distance And the propulsion distance corresponding to the maximum height of the water-conducting fracture zone. Normalized value based on the height of the water-conducting fracture zone The vertical axis represents the distance traveled. By fitting parameters to the horizontal axis, the relationship is obtained. The corresponding advance distance during the first filling is The first grouting layer is The grouting layer position is dynamically adjusted as the working face advances further; the evolution characteristics of the water-conducting fracture zone under different working face advance distances are determined by measured data from adjacent working faces or by numerical calculation methods.

[0017] Furthermore, in step S3, under the gelation filling mode of the variable-stratum fracture zone, when the coal seam thickness is less than... At that time, a continuous filling method without fixed gelling spacing was adopted, and gelling filling was carried out immediately when the crack developed to the position of the filling pipeline; the advancing distance Grouting layer under the conditions The calculation formula is: ;in, The correction factor is based on the coal seam thickness. Value: When hour, Value to ;when hour, Value to ; This represents the maximum value of the development of water-conducting fracture zones, in units of ; The distance the working face advances is expressed in units of... ; This is a functional relationship between the normalized height of the water-conducting fracture zone and the advance distance of the working face, determined based on measured data. It specifically represents a fitting function model, such as, but not limited to, a linear function, a quadratic polynomial, an exponential function, or a logarithmic function, the specific form of which is determined by the distribution characteristics of the measured data.

[0018] Furthermore, in step S3, under the gel filling mode of the variable-stratum fracture zone, when the coal seam thickness is greater than or equal to... At that time, the cementitious filling step distance was fixed at... Grouting layer The corrected formula is: ;in, This refers to the number of cycles of gelling filling. ; The correction factor is based on the coal seam thickness. Value: When hour, Value to ;when hour, Value to ; For the water-conducting fracture zone to develop to its maximum value The corresponding propulsion distance, in units of ; This is a functional relationship between the normalized height of the water-conducting fracture zone and the working face advancement distance, determined based on measured data. It specifically represents a fitted function model, such as, but not limited to, a linear function, a quadratic polynomial, an exponential function, or a logarithmic function, the specific form of which is determined by the distribution characteristics of the measured data; the volume of grouting material injected each time... The calculation formula is: ;in, This represents the volume of fracture development, in units of... The calculation formula is: ; The volume of pores within the collapse zone, in units of The calculation formula is: ; The length of the working face, in units of ; This refers to the grouting layer, in units of... ; The elevation of the landslide zone is expressed in units of [missing information]. ; The porosity of the fractured region is taken as a value. to ; The porosity of the caving zone is calculated using the following formula: , is the rock fragmentation coefficient.

[0019] Furthermore, in step S3, the drilling spacing in the middle of the working face is... to The spacing between the boreholes on both sides of the working face is to .

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention establishes a spatial relationship discrimination criterion between key bearing rock layers and water-conducting fracture zones, thereby realizing the adaptive selection of two cementation filling modes: fixed stratum and variable stratum. When key bearing rock layers exist within 1 / 3 to 2 / 3 of the height of the water-conducting fracture zone, the fixed stratum mode is adopted, utilizing the bearing capacity of the key rock layers to form stable support at its bottom, effectively controlling the upward development of the fracture zone. When key bearing rock layers do not exist within 1 / 3 to 2 / 3 of the height of the water-conducting fracture zone, the variable stratum mode is adopted, and the filling stratum is dynamically adjusted as the advance distance increases, realizing the process tracking and sealing of the water-conducting fracture zone as it moves with mining and evolves in stages, avoiding the problems of leakage sealing and re-fracture caused by single-height filling. This method makes the filling stratum no longer dependent on experience selection, but scientifically determined based on quantitative spatial relationships, enhancing the applicability and controllability under different overburden combinations, different coal thicknesses and different working face scales, overcoming the shortcomings of the existing technology's narrow applicability and arbitrary selection of filling stratum.

[0021] (2) In the fixed-layer filling mode, this invention calculates the working face advancement distance corresponding to the development of the water-conducting fracture zone to the filling layer and the working face advancement distance corresponding to the instability distance of the key rock layer. The smaller value between the former and 2 / 3 of the latter is taken as the first filling time, and this value is used as the periodic filling step distance, thus achieving precise control of the filling time. This method ensures timely filling before the water-conducting fracture zone develops to the filling layer and before the key rock layer is broken, so that the cementitious material solidifies and forms effective support before the key rock layer becomes unstable, preventing the fractures from penetrating the aquifer after the key rock layer breaks.

[0022] (3) By calculating the volume of crack development and the volume of pores in the collapse zone, this invention determines that the volume of grouting material in a single cycle is the sum of 20% to 30% of the volume of pores in the collapse zone and the volume of crack development. This realizes the quantification of cementitious material usage and the predictability of engineering, avoiding the cost waste and secondary disturbance risk caused by blindly increasing the injection volume.

[0023] (4) In the variable-layer filling mode, this invention fits the relationship between the normalized value of the water-conducting fracture zone height and the advance distance. Based on the coal seam thickness, it adopts a continuous filling method without fixed filling step distance and a periodic filling method with fixed step distance, and introduces a correction coefficient to dynamically adjust the grouting layer position. When the coal seam thickness is less than 5 meters, the fracture develops to the position of the filling pipeline and is immediately filled to achieve continuous tracking and sealing. When the coal seam thickness is greater than or equal to 5 meters, a periodic filling method with fixed step distance is adopted. The correction coefficient is segmented according to the coal seam thickness. The larger the coal seam thickness, the larger the correction coefficient. This fully considers the difference in the range of mining influence under different coal thickness conditions, making the filling layer position more reasonable and the water retention effect more significant.

[0024] (5) This invention achieves a filling operation method that does not interfere with downhole production by forming a main hole and secondary inclined holes through surface directional drilling to enter the filling layer and then constructing directional boreholes and laying filling pipelines. Expansive cementitious materials are used for filling. The borehole spacing in the middle of the working face is 15 to 20 meters, and the borehole spacing on both sides of the working face is 30 to 50 meters. The borehole layout is optimized according to the differences in mining impact at different locations, ensuring both filling effect and reducing construction costs. It has strong field feasibility and promotional value. Attached Figure Description

[0025] Figure 1 This is a flowchart of the water-retaining mining method for in-situ protection of aquifers in fracture zones using cementitious backfilling, according to the present invention.

[0026] Figure 2 This is a plan view of the arrangement of the cementitious filling boreholes in this invention.

[0027] Figure 3 This is a schematic diagram of fixed-layer gel filling in this invention.

[0028] Figure 4 This is a diagram illustrating the effect of fixed-layer cementitious backfilling for water-retaining coal mining in this invention.

[0029] Figure 5 This is a graph showing the relationship between the normalized value of the water-conducting fracture zone height and the propulsion distance in this invention.

[0030] Figure 6 This is a schematic diagram of the initial gelling and filling of the variable-layer fixed-distance step in this invention.

[0031] Figure 7 This is a schematic diagram of the second gel filling with fixed step distance and variable layer position in this invention.

[0032] Figure 8 This is a diagram illustrating the effect of water-retaining coal mining using variable-stratum fixed-step cementitious backfilling in this invention.

[0033] The following are included: 1. Surface directional drilling; 2. Main borehole; 3. Secondary inclined borehole; 4. Directional drilling; 5. Coal seam; 6. Aquifer; 7. Initial cementing backfilling zone; 8. Periodic cementing backfilling zone; 9. Zone awaiting cementing backfilling; 10. Backfilling step distance; 11. Collapse zone; 12. Water-conducting fracture zone; 13. Cementing backfilling material; 14. Uncemented backfilled estimated water-conducting fracture zone. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0035] Unless otherwise specifically stated, the relative arrangement, expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. Techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and apparatus should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0036] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist, for example... and / or , can represent existence alone , coexisting and Existing alone These are the three cases. Additionally, the character " / " in this article generally indicates that the objects before and after it have an "or" relationship.

[0037] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0038] like Figure 1 As shown, this invention provides a method for in-situ protection of aquifers through cemented backfilling in fractured zones for water-retaining extraction. The method includes the following steps: First, the geological and mining technical conditions of the coal face are obtained, including parameters such as coal seam thickness, coal seam depth, working face length, distance between the coal seam and the protected aquifer, lithology, thickness, volumetric force, elastic modulus, and uniaxial compressive strength of each rock stratum. Geological conditions are obtained through a combination of on-site core drilling and laboratory testing to ensure the accuracy and reliability of the parameters.

[0039] Based on the critical stratum theory, the critical bearing stratum and its fracture step distance between coal seam 5 and aquifer 6 were determined. The determination process began with the first stratum of the coal seam roof as the first stratum, and the critical bearing stratum was determined cyclically by comparing the loads exerted on the first stratum by adjacent strata. If the... Layer-to-first-floor loads Less than the Load of layer on first layer Then determine the first The first layer is the key bearing rock layer, and the second layer is the first layer. The first rock stratum is used to determine the upper key rock stratum in a cyclical analysis. The load calculation adopts the elastic thin plate theory, comprehensively considering the elastic modulus, thickness, and unit weight of each rock stratum. The fracture step distance is calculated based on the mechanical parameters of the key rock stratum, and the tensile strength of the key rock stratum is taken as 1 / 20 of its compressive strength.

[0040] step The development height of the caving zone is calculated based on geological conditions and mining technology. The development height of the caving zone is determined using the formula... Calculations, including the thickness of the coal seam. The rock fragmentation coefficient was obtained from actual measurements. The volume after fragmentation was determined by the standard sand volume displacement method. Volume before fragmentation The ratio was determined by taking the average value of the rock fragmentation coefficient within 6 times the coal seam thickness to reflect the overall fragmentation characteristics of the rock within the caving zone 11.

[0041] The calculation of the development height of the water-conducting fracture zone is based on mathematical and statistical results under similar geological conditions. A multivariate nonlinear fitting method is used to establish the relationship between the height of the water-conducting fracture zone and the coal seam depth, coal seam thickness, working face length, and hard rock proportion coefficient. The hard rock proportion coefficient is obtained by comparing the thickness of rock strata with a uniaxial compressive strength greater than 50 MPa to the total thickness, reflecting the distribution characteristics of hard rock in the overburden. Establishing the fitting equation requires collecting sufficient measured data of the water-conducting fracture zone under similar geological conditions. The average error rate between the fitted prediction and the measured results should not exceed 10% to ensure that the prediction accuracy meets the requirements of engineering applications.

[0042] The cementitious infilling stratum pattern of the fracture zone was determined based on the spatial relationship between the development height of the water-conducting fracture zone and the key bearing strata. When a key bearing stratum exists within 1 / 3 to 2 / 3 of the height of the water-conducting fracture zone 12, the cementitious infilling stratum pattern is a fixed-stratum fracture zone cementitious infilling pattern. When no key bearing stratum exists within 1 / 3 to 2 / 3 of the height of the water-conducting fracture zone 12, the cementitious infilling stratum pattern is a variable-stratum fracture zone cementitious infilling pattern. The selection of the 1 / 3 to 2 / 3 height range is based on the fracture density distribution pattern during the development of the water-conducting fracture zone 12, as this area is the key control zone where fracture development is most concentrated.

[0043] step Based on the determined cementitious filling layer pattern in the fractured zone, the corresponding filling layer positions, filling timing, and filling spacing (10) are formulated. For example... Figure 2 The diagram shows the borehole layout for cementitious filling. A main borehole (2) is formed by drilling 1 using a surface directional drill, followed by a secondary directional drilling technique to construct a horizontal directional borehole (4) at the target stratum, where the filling pipeline is laid out. Considering the significant mining impact in the central part of the working face, the borehole spacing is 15m to 20m. Since the mining impact on the sides of the working face is relatively smaller, the borehole spacing can be increased to 30m to 50m, achieving an optimized borehole layout. An expansive cementitious material is used for filling. During the curing process, the filling material generates a certain expansion pressure, which is beneficial for the dense filling and sealing of fractures.

[0044] For the fixed-layer fracture zone cemented filling mode, the filling layer is fixed at the bottom of the low-lying key bearing stratum. The working face advance distance corresponding to the first filling is... Through formula Confirmed, among which This represents the working face advance distance from the development of water-conducting fracture zone 12 to the filling layer. The formula for calculating the working face advance distance corresponding to the loss of stability in the key rock strata is as follows: . The determination of this requires obtaining the development characteristics of the water-conducting fracture zone 12 with the advance distance through measured data or numerical calculation methods near the working face. The advance distance... The cyclic filling step distance is used for mining and fracture zone filling operations to ensure that when the working face advances to the key rock layer and reaches the loss of the step distance, the grout has been completely gelled and solidified to form an effective load-bearing structure.

[0045] Volume of grouting material per cycle Pore ​​volume within the collapse zone 20% to 30% of the volume of fracture development The sum of the volumes of fracture development. The calculation formula is Porosity in the fractured region Values ​​range from 5% to 10%. Pore volume within the caving zone. The calculation formula is Porosity of the collapse zone The formula is calculated using the coefficient of fragmentation: The volume of the grouting material is taken as 20% to 30% of the sum of the pore volume and the fracture volume, which is determined based on a comprehensive consideration of the diffusion and filling characteristics of the grout in the fracture network and economic efficiency.

[0046] For the gel-filling mode of the fracture zone with varying strata, the evolution characteristics of the water-conducting fracture zone 12 under different advance distances of the working face are first determined. The evolution characteristics of the water-conducting fracture zone 12 can be determined by measured data from adjacent working faces or by numerical calculation methods, recording the development of the water-conducting fracture zone 12 to its maximum value. The propulsion distance corresponding to 1 / 2 .like Figure 5 As shown, the normalized value is based on the height of the water-conducting fracture zone 12. The vertical axis represents the distance traveled. By fitting parameters to the horizontal axis, the relationship is obtained. The propulsion distance corresponding to the first filling is... The first grouting layer is The grouting layer position is dynamically adjusted as the working face advances further.

[0047] When the coal seam thickness is less than 5m, a continuous filling method without fixed gelling filling step distance is adopted. Gelation filling is immediately carried out when the fracture develops to the filling pipeline position, achieving real-time tracking and sealing of fracture development. Only the initial filling step distance needs to wait for a period of time after the gelling filling operation is completed before pushing and mining can proceed. Advance distance Grouting layer under the conditions The calculation formula is ,in The correction factor is based on the coal seam thickness. Take the value when At m, The value ranges from 0.05 to 0.1, when 2m At m, The value ranges from 0.1 to 0.2.

[0048] When the coal seam thickness is greater than or equal to 5m, due to the large impact range of mining and the large amount of cementitious filling in the fracture zone, the cementitious filling step distance is fixed. Grouting layer The corrected formula is ,in This refers to the number of cycles of gelling filling. , The correction factor is based on the coal seam thickness. Value, when 5m At m, The value ranges from 0.2 to 0.3. At m, The value ranges from 0.3 to 0.5. This represents the volume of grouting material injected each time. The calculation formula is ,in The volume of fracture development is calculated using the following formula: , The formula for calculating the pore volume within the collapse zone is: Each cycle requires waiting for a certain period after the gelling and backfilling operation is completed before proceeding with mining. The specific time can be further adjusted according to the characteristics of the backfilling material.

[0049] The present invention will now be described in detail with reference to specific embodiments.

[0050] Example 1

[0051] This embodiment illustrates the application of a cementitious filling method for fracture zones at fixed strata. For example... Figure 3 The diagram shown is a schematic of fixed-layer cementitious filling.

[0052] step To obtain the geological conditions and mining technology conditions of the coal mining face, and the coal seam thickness. The coal seam is 4m deep. The length of the working face is 200m. The distance between coal seam 5 and the protected aquifer is 150m. The depth is 134m. Parameters such as lithology, thickness, volumetric force, elastic modulus, and uniaxial compressive strength of each rock layer were obtained through core drilling and laboratory tests. Based on the critical stratum theory, the key bearing stratum and fracture step between coal seam 5 and aquifer 6 were determined. Specific parameters and calculation results are shown in Table 1.

[0053] Table 1

[0054]

[0055] According to the critical stratum identification criteria, the calculation begins with the first stratum of the coal seam roof as the first stratum. By comparing the load of adjacent strata on the first stratum, coarse-grained sandstone was identified as the critical bearing stratum, with a thickness of 10m and a distance of 32m from coal seam 5. The tensile strength of the critical stratum is taken as 1 / 20 of its compressive strength of 100MPa, i.e., 5MPa. Based on the formula for calculating the fracture step distance, the calculated fracture step distance is 34.65m.

[0056] step The development height of caving zone 11 and fracture zone in the coal mining face is calculated. The caving zone height is given by the formula... Calculation. Based on the standard sand volume replacement method, the fragmentation coefficient of each rock stratum within 6 times the thickness of the coal seam was measured. Table 2 shows the measurement results of the fragmentation coefficient of each rock stratum within 6 times the thickness of the coal seam.

[0057] Table 2

[0058]

[0059] The coefficients of fragmentation for each rock stratum are 1.2, 1.3, 1.4 and 1.3, respectively. Taking the average value of 1.3 as the coefficient of fragmentation, the height of the collapse zone is calculated to be 13.30m.

[0060] The height of the water-conducting fracture zone and the depth of the coal seam Coal seam thickness Working face length Hard rock ratio coefficient This is relevant. By collecting and measuring data on water-conducting fracture zones under similar geological conditions at the demonstration working face, Table 3 shows the statistical results of the height of water-conducting fracture zones under 30 groups of similar geological conditions.

[0061] Table 3

[0062]

[0063] Using a multivariate nonlinear fitting method, the relationship between water-conducting fracture zone 12 and coal seam burial depth was established. Coal seam thickness Working face length Hard rock ratio coefficient The fitting equation is The average error rate between the fitted prediction results and the measured results was 9.06%, which meets the accuracy requirement of no more than 10%. The coal seam depth of the demonstration working face was 200m, the thickness was 4m, the working face length was 150m, and the hard rock ratio coefficient was 0.27. This value was obtained by using the ratio of the thickness of rock strata with a uniaxial compressive strength greater than 50MPa to the total thickness. Substituting this value into the equation, the height of the water-conducting fracture zone was determined to be 68.87m.

[0064] Based on the height of the water-conducting fracture zone (68.87m) and the caving zone (13.30m), the calculated height range corresponding to 1 / 3 to 2 / 3 of the height of water-conducting fracture zone 12 is 31.82m to 50.35m. The key bearing stratum is 32m away from the coal seam, located within the 1 / 3 to 2 / 3 height range of water-conducting fracture zone 12, and a fixed-position fracture zone cementitious filling mode is adopted.

[0065] step The filling layer is fixed at the bottom of the low-lying key bearing rock layer, with a distance of [missing information] from the coal seam. It is 32m. For example... Figure 2As shown, the main borehole 2 and secondary inclined borehole 3 are formed by drilling 1 on the ground. After entering the filling layer, horizontal directional borehole 4 is constructed and filling pipelines are laid. Considering that the mining impact in the middle of the working face is relatively large, the borehole spacing in the middle of the working face is 20m, and the borehole spacing on both sides of the working face is 40m, for a total of 5 directional boreholes 4.

[0066] Based on the development characteristics of the water-conducting fracture zone 12 during the mining of adjacent working faces, the working face advance distance corresponding to the development of the water-conducting fracture zone 12 to the filling layer was determined by numerical simulation. The angle of rock strata collapse is 40m. The angle is 66°, and the critical rock stratum fracture step distance is 34.65m. The working face advance distance corresponding to the critical rock stratum reaching the loss of step distance is calculated. The distance is 63.65m. This represents the working face advance distance during the initial filling. m, ensuring that the grout has completely gelled and solidified when the working face advances to the key rock strata and reaches the point of instability.

[0067] The working face continues to advance, using the aforementioned advance distance of 40m as the periodic filling step distance to ensure the stability of key rock strata. Repeated cycles of mining and fracture zone filling are performed until mining is completed. Figure 4 The image shown is an illustration of the effect of fixed-layer cemented backfilling for water retention in coal mining.

[0068] The volume of material required for a single grouting cycle Volume of fracture development With 20% of the caving zone internal pore volume The sum of the porosity in the fractured region. Take 5% for porosity in the collapse zone The volume of material required for a single grouting cycle is calculated. 9281m 3 To ensure the effective filling of the cracked area, an expansive cementitious material was used for filling. The expansion pressure generated during the curing process of the filling material effectively improved the crack sealing effect.

[0069] Example 2

[0070] This embodiment demonstrates the application of a cementitious filling mode in fractured zones with varying strata. When the coal seam thickness is greater than or equal to 5m, a fixed-step periodic filling method is used. For example... Figure 6 The diagram shown is a schematic of the first cementitious filling with a fixed step distance at a variable layer position. Figure 7 The diagram shown is a schematic of the second cementitious filling with a fixed step distance at a variable layer position.

[0071] step To obtain the geological conditions and mining technology conditions of the coal mining face, and the coal seam thickness. The coal seam is 6m deep. The length of the working face is 250m. The distance between the coal seam and the protected aquifer is 150m. The depth is 180m. Parameters such as lithology, thickness, volumetric force, elastic modulus, and uniaxial compressive strength of each rock layer were obtained through core drilling and laboratory tests. Based on the critical stratum theory, the key bearing stratum and fracture step between coal seam 5 and aquifer 6 were determined. Specific parameters and calculation results are shown in Table 4.

[0072] Table 4

[0073]

[0074] Calculations determined that the fine-grained sandstone was the key bearing stratum, with a thickness of 8m and a distance of 8m from the coal seam. The tensile strength of the key stratum was taken as 1 / 20 of its compressive strength of 60MPa, i.e., 3MPa, and the calculated fracture step distance was 27.08m.

[0075] step The development height of caving zone 11 and fracture zone in the coal mining face is calculated. The caving zone height is given by the formula... Calculation. Based on the standard sand volume replacement method, the fragmentation coefficient of each rock stratum within 6 times the thickness of the coal seam was determined. Table 5 shows the results of the fragmentation coefficient determination of each rock stratum within 6 times the thickness of the coal seam.

[0076] Table 5

[0077]

[0078] The coefficients of fragmentation for each rock stratum are 1.5, 1.2, 1.4, 1.5, and 1.4, respectively. Taking the average value of 1.4 as the coefficient of fragmentation, the height of the collapse zone is calculated to be 15m.

[0079] The height of the water-conducting fracture zone and the depth of the coal seam Coal seam thickness Working face length Hard rock ratio coefficient This is relevant. By collecting and measuring data on water-conducting fracture zones under similar geological conditions at the demonstration working face, Table 6 shows the statistical results of the height of water-conducting fracture zones under 25 similar geological conditions.

[0080] Table 6

[0081]

[0082] Using a multivariate nonlinear fitting method, the relationship between water-conducting fracture zone 12 and coal seam burial depth was established. Coal seam thickness Working face length Hard rock ratio coefficient The fitting equation is The average error rate between the fitted prediction and the measured results was 5.66%, meeting the accuracy requirement of no more than 10%. The coal seam depth of the demonstration working face was 250m, the thickness was 6m, the working face length was 150m, and the hard rock ratio coefficient was 0.23. This value was obtained by using the ratio of the thickness of rock strata with a uniaxial compressive strength greater than 50MPa to the total thickness. Substituting this value into the equation, the height of the water-conducting fracture zone was determined to be 65.88m.

[0083] Based on the height of the water-conducting fracture zone (65.88m) and the caving zone (15m), the calculated height range corresponding to 1 / 3 to 2 / 3 of the height of water-conducting fracture zone 12 is 31.96m to 48.92m. The key bearing stratum is 8m away from the coal seam and is not located within the 1 / 3 to 2 / 3 height range of water-conducting fracture zone 12; therefore, a variable-stratum fracture zone cementitious filling mode is adopted.

[0084] step Based on measured data from adjacent working faces, the evolution characteristics of water-conducting fracture zone 12 under different advance distances were determined. The development of water-conducting fracture zone 12 to its maximum value was recorded. The advance distance corresponding to 1 / 2 of 65.88m It is 38m. For example... Figure 5 As shown, the normalized value is based on the height of the water-conducting fracture zone. The vertical axis represents the distance traveled. By fitting parameters to the horizontal axis, the relationship is obtained. .

[0085] The corresponding propulsion distance during the first filling The first grouting layer is 38m long. The depth is 32.94m. The grouting layer depth gradually increases with the advancing distance, but remains unchanged when the advancing distance exceeds 150m. Figure 2 As shown, the main hole 2 and secondary inclined hole 3 are formed by drilling 1 through ground directional drilling. The long-distance directional drilling hole 4 is used to construct the cement filling hole and arrange the filling pipeline.

[0086] Because the coal seam thickness is 6m or greater than or equal to 5m, the mining impact area is relatively large, and the amount of cementitious filling in the fracture zone is large. The cementitious filling step distance is fixed at 38m. Subsequent grouting layers are determined according to the formula. calculate, This refers to the number of cycles of gelling filling. Based on the coal seam thickness of 6m falling within the range of 5m to 8m, a correction factor is applied. The value is 0.29.

[0087] The volume of material required for a single grouting cycle Volume of fracture development With the pore volume within the collapse zone 20% of the sum. Among them, the porosity of the fractured region... Take 6% for porosity in the collapse zone Table 7 shows the filling layers and filling material volumes corresponding to different cycles of gelled filling.

[0088] Table 7

[0089]

[0090] As shown in Table 7, the filling level gradually rises with the increase of the number of cycles. The first filling level is 32.94m, the second is 38.59m, the third is 41.07m, the fourth is 42.72m, and the filling level remains unchanged at 42.72m from the fifth cycle onwards, because the corresponding advance distance has exceeded 150m. The volume of the filling material increases with the increase of the filling level, from 111005.6m in the first cycle. 3 Increased to 143963.5m for the 4th time and subsequent times. 3 Within each cycle, mining should only proceed after a certain period has elapsed following the completion of the gelling and backfilling operation. The specific timing can be adjusted based on the solidification characteristics of the backfill material to ensure the backfill body has formed effective load-bearing capacity before proceeding to the next mining step. To ensure the effectiveness of gelling and backfilling in fracture zones, expansive gelling materials are used. For example... Figure 8 The diagram shows the effect of water-retaining coal mining with fixed-step cemented backfilling in variable-stratum areas. It can be seen that the cemented backfilling zone 8 gradually expands upward in each cycle, the estimated fracture zone 14 without cemented backfilling is effectively controlled, and the aquifer 6 is protected in situ.

[0091] Example 3

[0092] This embodiment describes the application of a gel-filling mode in a fractured zone with varying strata. When the coal seam thickness is less than 5m, a continuous filling method without a fixed filling step distance is adopted.

[0093] step and steps Similar to Example 2, geological conditions were obtained and the development height of the collapse zone 11 and the water-conducting fracture zone 12 was calculated to determine the adoption of the cementitious filling mode for the fracture zone with variable strata.

[0094] step When the coal seam thickness is less than 5m, the impact range of mining is relatively small, and the fracture development rate is relatively fast. Therefore, a continuous filling method without fixed gelling filling step distance is adopted. When the fracture develops to the position of the filling pipeline, gelling filling is carried out immediately to achieve real-time tracking of fracture development, that is, uninterrupted filling. Only after the gelling filling operation is completed for a period of time during the first filling step distance should pushing mining be carried out.

[0095] Advance distance Grouting layer under the conditions The calculation formula is ,in This is a correction factor. It is based on the coal seam thickness. Different values, correction coefficient Segmentation is determined, when When less than 2m, The value ranges from 0.05 to 0.1, reflecting the characteristic of rapid fracture development but relatively slow height growth under thin coal seam conditions; when 2m ≤ When less than 5m, The value ranges from 0.1 to 0.2, reflecting the increased rate of fracture height growth under medium-thickness coal seam conditions.

[0096] like Figure 2 As shown, a main hole 2 and a secondary inclined hole 3 are formed by drilling 1 on the ground. A long-distance directional drilling hole 4 is then used to construct a cementitious filling borehole and lay filling pipelines to achieve continuous tracking and filling of fracture development. This method can promptly seal newly formed fractures, effectively preventing the rapid penetration of the water-conducting fracture zone 12 under thin coal seam mining conditions, and ensuring the in-situ protection of the aquifer 6.

[0097] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for in-situ protection of aquifers through cemented backfilling in fractured zones for water-retaining extraction, characterized in that, Includes the following steps: Step S1: Obtain the geological conditions and mining technology conditions of the coal mining face. These include coal seam thickness, coal seam depth, working face length, distance between the coal seam and the protected aquifer, lithology of each rock stratum, thickness of each rock stratum, volumetric force of each rock stratum, elastic modulus of each rock stratum, and uniaxial compressive strength of each rock stratum. Based on the key stratum theory, determine the critical bearing stratum position and fracture step between the coal seam and the aquifer. The determination process is based on the first critical bearing stratum of the coal seam roof. The calculation begins with the first rock layer, and the key bearing rock layer is determined by comparing the loads exerted on the first rock layer by adjacent rock layers in a cyclical manner. Step S2: Calculate the development height of the caving zone based on the geological and mining technical conditions, and obtain the rock fragmentation coefficient using the standard sand volume replacement method; calculate the development height of the water-conducting fracture zone using a multivariate nonlinear fitting method based on the mathematical statistics of the height of the water-conducting fracture zone under similar geological conditions, where the fitting method involves the coal seam burial depth, the coal seam thickness, the working face length, and the hard rock ratio coefficient; determine the cementitious filling stratigraphic pattern of the fracture zone based on the spatial relationship between the development height of the water-conducting fracture zone and the key bearing rock strata. Step S3: Determine the filling layer, filling timing, and filling step distance according to the cemented filling layer pattern of the fracture zone. Form the main hole and secondary inclined hole through ground directional drilling, construct directional drilling and arrange filling pipelines, use expansive cementitious material to fill the fracture zone, and implement the process in a cycle with the mining operation.

2. The method for in-situ protection of aquifers through cemented backfilling and water-retaining extraction in fracture zones according to claim 1, characterized in that, In step S1, the process of determining the key bearing strata based on the key stratum theory includes: taking the first coal seam roof as the key bearing stratum. The first layer is the first rock layer. If the second layer is the first layer, then the third layer is the first layer. Load of layer on first layer Less than the Load of layer on first layer Then determine the first The layer is the first The key bearing rock layer, and the first The first layer is the key upper layer determined by the cyclic determination; the calculation expression for the load is as follows: ； ； in, For the first The elastic modulus of the rock strata For the first The elastic modulus of the rock strata For the first The elastic modulus of the rock strata For the first The elastic modulus of the rock strata, expressed in Pa. For the first Thickness of rock layers, For the first Thickness of rock layers, For the first Thickness of rock layers, For the first Thickness of rock strata, in meters; For the first Density of rock layers For the first Density of rock layers For the first Density of rock layers For the first Unit weight of rock strata, in N / m³; fracture step distance The calculation formula is: ； in, The breaking step distance is expressed in meters. The tensile strength of the key rock strata is expressed in Pa. This represents the load on the key rock strata, expressed in Pa. The thickness of the critical rock strata is expressed in meters (m).

3. The method for in-situ protection of aquifers through fracture zone cemented backfilling and water-retaining extraction according to claim 1, characterized in that, In step S2, the development height of the landslide zone... The calculation formula is: ； in, This refers to the coal seam thickness, in meters (m). Rock fragmentation coefficient; rock fragmentation coefficient Volume after fragmentation calculated using the standard sand volume replacement method Volume before fragmentation The ratio is determined by taking the coal seam thickness. The average value of the rock fragmentation coefficient within a multiple of 1.

4. The method for in-situ protection of aquifers through cemented backfilling and water-retaining extraction in fracture zones according to claim 1, characterized in that, In step S2, the hard rock proportion coefficient is obtained by the ratio of the thickness of rock layers with a uniaxial compressive strength greater than 50 MPa to the total thickness in step S1; the method for determining the cementitious filling layer pattern in the fracture zone is: when the water-conducting fracture zone... to When the critical bearing stratum exists within the height range, the cemented filling stratum pattern of the fracture zone is a fixed-stratum fracture zone cemented filling pattern; when the water-conducting fracture zone... to When the critical bearing rock layer is not present within the height range, the cementitious filling layer pattern of the fracture zone is the variable layer fracture zone cementitious filling pattern.

5. The in-situ protection method for water-retaining mining in fractured zones according to claim 4, characterized in that, In step S3, when the cemented filling layer mode in the fracture zone is the fixed-layer fracture zone cemented filling mode, the filling layer is fixed at the bottom of the low-level key bearing stratum, and the distance between the filling layer and the coal seam is [missing information]. The working face advance distance corresponding to the first filling. The formula for determining it is: ； in, The distance the working face advances from the development of the water-conducting fracture zone to the corresponding filling layer is expressed in meters. The working face advance distance corresponding to the critical rock strata reaching the point of instability, in meters; The calculation formula is: ； in, The critical rock stratum fracture step distance is expressed in meters. The distance between the filling layer and the coal seam is expressed in meters (m). The angle of rock strata collapse is expressed in degrees; the distance traveled is the angle of rock strata collapse. The periodic filling interval is used for the cycle of mining and fracture zone filling operations.

6. The method for in-situ protection of aquifers through cemented backfilling and water-retaining extraction in fracture zones according to claim 5, characterized in that, In step S3, under the fixed-layer fracture zone gel filling mode, the volume of grouting material in a single cycle is... The calculation formula is: ； in, This represents the volume of fracture development, expressed in m³. The volume of pores within the collapse zone is expressed in m³. The calculation formula is: ； in, The length of the working surface is in meters (m). This represents the working face advance distance during the initial filling, in meters (m). The distance between the filling layer and the coal seam is expressed in meters (m). The height of the landslide zone is expressed in meters (m). The porosity of the fractured region is 5% to 10%. The calculation formula is: ； in, The porosity of the caving zone is calculated using the following formula: , is the rock fragmentation coefficient.

7. The method for in-situ protection of aquifers through cemented backfilling and water-retaining extraction in fracture zones according to claim 4, characterized in that, In step S3, when the cemented filling layer mode of the fracture zone is the variable layer cemented filling layer mode, the evolution characteristics of the water-conducting fracture zone under different advance distances of the working face are determined, and the development of the water-conducting fracture zone to its maximum value is recorded. of The corresponding propulsion distance And the propulsion distance corresponding to the maximum height of the water-conducting fracture zone. Normalized value based on the height of the water-conducting fracture zone The vertical axis represents the distance traveled. By fitting parameters to the horizontal axis, the relationship is obtained. The corresponding advance distance during the first filling is The first grouting layer is The grouting layer position is dynamically adjusted as the working face advances further; the evolution characteristics of the water-conducting fracture zone under different working face advance distances are determined by measured data from adjacent working faces or by numerical calculation methods.

8. The method for in-situ protection of aquifers and fracture zone cementitious backfilling for water retention mining according to claim 7, characterized in that, In step S3, under the gel filling mode for the variable-stratum fracture zone, when the coal seam thickness is less than 5 m, a continuous filling method without a fixed gel filling step distance is adopted. Gelation filling is immediately carried out when the fracture develops to the position of the filling pipeline; the advancing distance... Grouting layer under the conditions The calculation formula is: ； in, The correction factor is based on the coal seam thickness. Value: When At m, Values ​​range from 0.05 to 0.1; when m At m, Values ​​range from 0.1 to 0.2; This represents the maximum value of the water-conducting fracture zone development, expressed in meters (m). The distance the working face advances is expressed in meters (m). This is a functional relationship between the normalized height of the water-conducting fracture zone and the working face advance distance, determined based on measured data.

9. A method for in-situ protection of aquifers through cemented backfilling and water-retaining extraction in fracture zones, as described in claim 7, is characterized in that... In step S3, under the gelatinous filling mode for the variable-stratum fracture zone, when the coal seam thickness is greater than or equal to 5 m, the gelatinous filling step distance is fixed at [value missing]. Grouting layer The corrected formula is: ； in, This refers to the number of cycles of gelling filling. ; The correction factor is based on the coal seam thickness. Value: When m At m, Values ​​range from 0.2 to 0.3; when At m, Values ​​range from 0.3 to 0.5; For the water-conducting fracture zone to develop to its maximum value of The corresponding propulsion distance, in meters; This is a functional relationship between the normalized height of the water-conducting fracture zone and the working face advancement distance, determined based on measured data; the volume of grouting material injected each time. The calculation formula is: ； in, The volume of fracture development is expressed in m³, and the calculation formula is as follows: ； The volume of pores within the collapse zone is expressed in m³, and the calculation formula is as follows: ； The length of the working surface is in meters (m). This refers to the grouting layer, in meters (m). The height of the landslide zone is expressed in meters (m). The porosity of the fractured region is 5% to 10%. The porosity of the caving zone is calculated using the following formula: , is the rock fragmentation coefficient.

10. The method for in-situ protection of aquifers through cemented backfilling and water-retaining extraction in fracture zones according to claim 1, characterized in that, In step S3, the drilling spacing in the middle of the working face is 15m to 20m, and the drilling spacing on both sides of the working face is 30m to 50m.

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