A method for predicting key layer and surface deformation in air extraction of overburden separation grouting

Abstract

This invention relates to the field of mine pressure and strata control, and discloses a method for predicting key strata and surface deformation in open-cut mining through overburden separation grouting. The method includes the following steps: establishing a mechanical model of the key strata in open-cut mining, divided into nine sections along the width of the working face, including isolation coal pillar areas; calculating the total deflection curve of the key strata based on the model; calculating and subtracting the benchmark key strata subsidence curve caused by mining at the first working face, obtaining the net increase in key strata subsidence curve due to open-cut mining; finally, integrating the net increase in subsidence curve using the equivalent mining height theory and a probability integral method with activation coefficient correction, to obtain the surface deformation prediction curve. This invention solves the prediction bias problem caused by model simplification and algorithm inapplicability by constructing a more refined nine-segment mechanical model, accurately separating the net increase in deformation due to open-cut mining, and correcting traditional prediction algorithms, thereby improving the accuracy and reliability of surface deformation prediction under open-cut mining conditions.

Description

Technical Field

[0001] This invention relates to the field of mine pressure and strata control, specifically to a method for predicting surface deformation by grouting key layers in overburden separation during open-cut mining. Background Technology

[0002] With the continuous advancement of coal mining activities, the scale and scope of surface movement caused by these activities are constantly expanding. In mining practice, in order to improve the coal resource recovery rate, percutaneous mining is widely used as an efficient mining method. However, during percutaneous mining, the superimposed mining effects of the mined-out area and the working face to be mined lead to a complex redistribution of the stress field of the overlying strata, which in turn triggers severe and asymmetric overlying deformation. This complex deformation will eventually be transmitted to the surface, inducing disasters such as surface subsidence and ground fissures, posing a serious threat to the safety of existing surface buildings and infrastructure, as well as the regional ecological environment. Therefore, accurately predicting the deformation characteristics of key strata under percutaneous mining conditions and understanding the laws of surface movement are of crucial engineering significance for formulating scientific rock strata control measures and protecting surface facilities.

[0003] However, existing prediction technologies for surface deformation caused by mining have significant limitations when dealing with the specific condition of mining under slump conditions, failing to meet the accuracy requirements of engineering practice. Existing research and analysis methods are mostly based on simplified mechanical models, typically designed for single-face mining scenarios. These models fail to fully consider the differences in disturbance experienced by different regions of the overlying rock under the superimposed stress field of mining under slump conditions, thus making it difficult to accurately reflect the complex non-uniform fracture characteristics and spatial deformation trends of the rock strata. Directly applying such traditional models to mining under slump conditions often underestimates the stress evolution in boundary areas and the potential damage range of critical strata.

[0004] Furthermore, existing key stratum segmentation models lack structural adaptability to the conditions of perilous mining. These models generally neglect the crucial isolation coal pillar, a unique feature of perilous mining. This isolation coal pillar is subject to dual mining disturbances from the mined-out area and the working face to be mined, and its bearing characteristics and the supporting stiffness of the underlying foundation differ significantly from those of solid coal areas or ordinary compacted areas. Because existing models fail to include and quantify the mechanical behavior of this core area, they cannot describe the typical asymmetric deformation characteristics of key strata under perilous mining, resulting in significant calculation errors. Consequently, their predictions are insufficient to effectively guide the optimization design of surface structure protection or delamination grouting parameters. Summary of the Invention

[0005] This invention provides a method for predicting the key layer and surface deformation of overburden separation grouting in open-cut mining, aiming to solve the problem of insufficient accuracy in predicting overburden deformation under open-cut mining conditions due to the simplification of mechanical models and lack of adaptability to open-cut mining conditions in existing technologies.

[0006] This invention constructs a key layer mechanical model that conforms to the actual working conditions of near-shore mining, and introduces the equivalent mining height theory and activation coefficient to correct the surface subsidence prediction parameters, thereby achieving accurate prediction of surface deformation under near-shore mining conditions. The specific technical solution is as follows:

[0007] The method of the present invention includes the following steps:

[0008] S1. A mechanical model for the key layer of overburden separation grouting in open-face mining was established. This mechanical model was divided into nine sections along the width of the working face, each with a different subgrade coefficient. The nine sections, from one side of the working face to the other side of the mined-out area, are as follows: solid coal zone, under-compacted zone, compacted zone, under-compacted zone, isolation coal pillar zone, under-compacted zone, compacted zone, under-compacted zone, and solid coal zone.

[0009] S2. Based on the mechanical model of the key layer for grouting under overburden separation in the open-cut mining operation, the total deflection curve of the key layer during open-cut mining is calculated. The total deflection curve is calculated using the initial parameter method, and the solution is obtained based on the boundary conditions at both ends of the mechanical model of the key layer for grouting under overburden separation in the open-cut mining operation. The boundary conditions at both ends of the mechanical model of the key layer for grouting under overburden separation in the open-cut mining operation are determined to be fixed hinge supports, where both the deflection and rotation angle of the fixed hinge supports are zero.

[0010] S3. Calculate the benchmark key stratum subsidence curve caused by the independent mining of the first working face. This benchmark key stratum subsidence curve has a unified coordinate system with the mechanical model of the key stratum for overburden separation grouting in the open-cut mining. Subtract the benchmark key stratum subsidence curve from the total deflection curve to calculate the net increase in key stratum subsidence due to open-cut mining. The benchmark key stratum subsidence curve is obtained by establishing a single-working-face key stratum mechanical model with a unified coordinate system with the mechanical model of the key stratum for overburden separation grouting in the open-cut mining, and by performing calculations based on this single-working-face key stratum mechanical model.

[0011] S4, based on the subsidence curve of the key layer increased by the net increase in the subsidence of the key layer due to the open-cut mining, and combined with the probability integral method of the loose layer subsidence coefficient using the net increase in the subsidence of the key layer due to the open-cut mining, an integral calculation is performed to obtain the surface deformation prediction curve. Step S4 further includes:

[0012] First, using the equivalent mining height theory, the subsidence curve of the key layer resulting from the net increase in the near-shore mining is divided along its length into nine rectangular segments corresponding to the nine sections. The height of each rectangular segment is taken as the equivalent mining height of the corresponding segment for the integral calculation. The height s′i of each rectangular segment can be calculated using the following formula:

[0013]

[0014] In the formula, z(t) is the key layer subsidence curve function of the net increase in the mining of the open-cut area, which represents the net increase in the key layer subsidence after the mining of the second working face;

[0015] dt of z(t) represents the expression for the function z(t) in the i-th segment from t. i-1 to t i The definite integral of the curve z(t) is given by the curve z(t) intersecting the coordinate axes in the interval [t]. i-1 ,t i The area enclosed by the ] represents, in a physical sense, the total spatial volume formed by the sinking of the key layer in the i-th segment;

[0016] t i-1 and t i These are the starting and ending coordinates of the i-th rectangular segment, respectively;

[0017] (t i -t i-1 Let be the width of the i-th rectangular segment. Divide the total spatial area formed by the sinking of the key layer in the i-th segment by the width of the segment to obtain the average sinking height of the segment, i.e., the equivalent mining height, which is used for subsequent probability integral calculation.

[0018] Second, an activation coefficient is introduced to correct the loose layer subsidence coefficient during single-face mining of the benchmark key layer subsidence curve, thus obtaining the loose layer subsidence coefficient for un-mined mining, which is used for the integral calculation. The un-mined loose layer subsidence coefficient q′0 can be calculated by the following formula:

[0019] q′0=(1+a)q0;

[0020] In the formula, a is the activation coefficient, which is used to quantify the degree of change in the properties of the loose layer caused by the mining of the first working face, and reflects the effect of the loose layer’s buffering and expansion capacity being reduced by a single mining operation.

[0021] q0 is the loose layer subsidence coefficient during single-face mining, representing the degree of response of the loose layer to bedrock subsidence in its original state without being affected by mining. By introducing a correction factor greater than 1 (1+a), the original loose layer subsidence coefficient q0 is amplified to obtain the corrected coefficient q′0, which reflects the law that the weakening of the buffering effect of the loose layer leads to a relative increase in surface subsidence.

[0022] Finally, the parameters after the above two improvements are substituted into the probability integral method model for integral calculation, and the surface deformation prediction curve is finally obtained.

[0023] Furthermore, this invention provides an optimization method. By repeatedly executing steps S1 to S4 for different injection-production ratios, a series of surface deformation prediction curves under different injection-production ratios can be obtained. By comparing and analyzing these curves, the injection-production ratio scheme with the optimal effect on controlling surface deformation can be selected.

[0024] This invention provides a method for predicting key layers and surface deformation during grouting for overburden separation in open-cut mining.

[0025] It has the following beneficial effects:

[0026] 1. This invention constructs a technical solution that divides the mechanical model of the key layer for grouting of overburden in open-cut mining into nine sections along the width of the working face, and assigns different foundation coefficients to each section (especially the isolation coal pillar section). Compared with the existing simplified mechanical model, the nine-segment model can more accurately reflect the non-uniform fracture characteristics and asymmetric deformation trend of overburden under open-cut mining conditions, effectively avoiding the problem of insufficient prediction accuracy caused by model simplification, thereby improving the accuracy of key layer deformation calculation.

[0027] 2. This invention calculates the total deflection curve of the key layer during open-cut mining and accurately subtracts the benchmark key layer subsidence curve caused by the single mining of the first working face under a unified coordinate system to calculate the net increase in key layer subsidence curve caused by open-cut mining. This achieves accurate stripping and quantification of the net deformation of the overburden caused by open-cut mining itself, avoiding prediction deviations caused by confusing the influence of the first working face with the influence of open-cut mining, and making the surface deformation prediction results more targeted and accurate.

[0028] 3. In the integral calculation of surface deformation prediction, this invention innovatively combines the equivalent mining height theory to discretize the key layer subsidence curve of the net increase in near-cut mining, and introduces an activation coefficient to correct the subsidence coefficient of the loose layer. These correction measures overcome the applicability limitations of the traditional probability integral method in the complex geological conditions of near-cut mining, ensuring that the prediction model can fully consider the buffering performance of the loose layer changed by the first mining, thereby improving the accuracy and reliability of surface deformation prediction in near-cut mining. Attached Figure Description

[0029] Figure 1 This is the mechanical model of the key layer for grouting of overburden separation in this invention;

[0030] Figure 2 This invention provides a mechanical model for the key layer of grouting in open-cut mining;

[0031] Figure 3 This is a schematic diagram of the mechanical model of the key layer for grouting in open-cut mining according to an embodiment of the present invention;

[0032] Figure 4(a) is a schematic diagram of the key layer subsidence curves under different injection-production ratios according to an embodiment of the present invention;

[0033] Figure 4(b) is a schematic diagram of the surface subsidence prediction curves under different injection-production ratios according to an embodiment of the present invention;

[0034] Figure 5 This is a comparison curve of surface deformation monitoring data and predicted data according to an embodiment of the present invention. Detailed Implementation

[0035] The technical solutions in 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] See attached document Figure 1 To be continued Figure 5 See attached Figure 1 This invention provides a mechanical model for key layers in grouting for overburden delamination and a method for predicting surface deformation in key layers of overburden delamination grouting during open-cut mining. This method may include the following steps:

[0037] Step S1: Establish a mechanical model for the key layer of grouting for overburden separation in open-cut mining. The mechanical model for the key layer of grouting for overburden separation in open-cut mining is divided into nine sections along the width of the working face, and each section has a different foundation coefficient.

[0038] Step S2: Based on the mechanical model of the key layer for grouting of overburden separation in open-cut mining, calculate the total deflection curve of the key layer during open-cut mining;

[0039] Step S3: Calculate the benchmark key layer subsidence curve caused by the mining of the first working face in a coordinate system that is consistent with the mechanical model of the key layer of the overburden separation grouting in the open-cut mining. Then, calculate the net increase in the key layer subsidence curve of the open-cut mining by subtracting the benchmark key layer subsidence curve from the total deflection curve.

[0040] Step S4: Based on the subsidence curve of the key layer increased by the net increase of the key layer by the mining at the open, and combined with the probability integral method of the subsidence coefficient of the loose layer using the subsidence curve of the key layer increased by the mining at the open, perform integral calculation to obtain the surface deformation prediction curve.

[0041] The steps in the embodiments of the present invention will be described in detail below.

[0042] Before proceeding to step S1, to calculate the benchmark key stratum settlement curve required in step S3, a mechanical model of the key stratum for overburden separation grouting in a single working face is first established. The stress and deformation characteristics of the key stratum are equivalent to an elastic foundation beam, where the key stratum bears the load of the overlying rock strata, and the underlying weak rock strata and filling body are equivalent to an elastic foundation. (Refer to Appendix) Figure 1 Based on the different subgrade coefficients below the key layer, the single working face model is divided into five symmetrical sections along the width of the working face, from left to right: solid coal zone, under-compacted zone, compacted zone, under-compacted zone, and solid coal zone.

[0043] Based on a single working face model, the initial parameter method is used to solve for the deflection curve ω(x) of the key layer. The deflection curve of the key layer is a piecewise function, and its expression is:

[0044]

[0045] In the formula, ω(L) i-1 ), θ(L i-1 ), M(L i-1 ), Q(L i-1 ) represents the deflection, rotation angle, bending moment, and shear force at the end of segment i-1, respectively; is the surface moment of inertia; q is the uniformly distributed load overlying the key layer; k is the uniformly distributed load overlying the key layer. i Let be the subgrade coefficient of the i-th segment; φ i2 φ i3 φ i4 Let i be the Krylov function. The value of i ranges from 1 to 5, corresponding to five different segments.

[0046] The equations for rotation angle θ(x), bending moment M(x), and shear force Q(x) are:

[0047]

[0048] By setting the boundary conditions at both ends of the model as fixed hinge supports, i.e., both deflection and rotation are zero, and solving the system of equations, the deflection curve ω(x) of the key layer under single working face mining conditions can be obtained.

[0049] The specific implementation method of step S1 is as follows:

[0050] See attached document Figure 2A mechanical model for the key layer of overburden separation grouting in open-face mining was established. The core difference between this model and the single-face model lies in the division of the key layer into nine sections to accurately describe the dual mining disturbances experienced by the isolation coal pillar section. From one side of the working face to the other side of the mined-out area, these sections are, in sequence: solid coal zone, under-compacted zone, compacted zone, under-compacted zone, isolation coal pillar zone, under-compacted zone, compacted zone, under-compacted zone, solid coal zone. Each section is assigned a different subgrade coefficient k based on its underlying medium (solid coal, fractured rock mass, backfill, isolation coal pillar). i (i=1,2,...,9), thus accurately reflecting the non-uniform distribution characteristics of the supporting force on the key layer under open-cut mining.

[0051] The specific implementation of step S2 is as follows: Based on the nine-segment mechanical model established in step S1, the initial parameter method is also used to calculate the total deflection curve ω′(x) of the key layer during un-mined conditions. At this time, the equations for deflection, rotation angle, bending moment, and shear force are consistent with those of the single-working-face model, but each parameter is replaced with its corresponding value under un-mined conditions. The formula for calculating the total deflection ω′(x) is:

[0052]

[0053] In the formula, ω′(L′ i-1 ), θ′(L′ i-1 ), M′(L′ i-1 ), Q′(L′ i-1 ) represents the deflection, rotation angle, bending moment, and shear force at the end of the (i-1)th segment under unsupported mining conditions; β′ i k is the beam characteristic coefficient of the i-th segment during open-cut mining; i φ is the subgrade coefficient for the i-th segment during open-cut mining; i1 φ i2 φ i3 φ i4 Let i be the corresponding Krylov function. Here, the value of i ranges from 1 to 9.

[0054] Similarly, by setting the boundary conditions at both ends of the model as fixed hinge supports (with zero deflection and rotation), the total deflection curve ω′(x) of the key layer during open-cut mining can be obtained by solving the system of equations using numerical calculation methods (such as Matlab).

[0055] The specific implementation method of step S3 is as follows:

[0056] This step aims to calculate the net subsidence of the key strata resulting from mining the second working face (free face). First, refer to the appendix... Figure 3 The aforementioned deflection curve ω of the key layer of the single working surface *(x) Perform a coordinate transformation to align its coordinate system with the coordinate system of the nine-segment open-cut mining mechanical model established in step S1. After the transformation, the subsidence curve ω of the benchmark key layer is obtained. * (x), whose expression is:

[0057]

[0058] In the formula, i(x) is the deflection curve function of the single working face after coordinate transformation, L′5 is the starting position of the isolated coal pillar section in the un-mined model, H is the coal seam burial depth, and δ is the rock stratum movement angle. Then, the total deflection curve ω′(x) obtained in step S2 is subtracted from the sinking curve ω′(x) of the benchmark key layer. * (x), the subsidence curve z(x) of the key layer with net increase in value due to open-cut mining is obtained by calculation, and its calculation formula is:

[0059] z(x)=ω′(x)-ω * (x);

[0060] The curve z(x) accurately represents the overburden deformation caused solely by mining at the open face, and serves as a direct basis for subsequent surface subsidence prediction.

[0061] The specific implementation of step S4 is as follows: Based on the net increase in key layer subsidence curve z(x) obtained in step S3, integral calculation is performed using the modified probability integral method to obtain the final surface deformation prediction curve. This step includes two key technical processes:

[0062] First, the equivalent mining height theory is adopted. To simplify the integral calculation, the irregular subsidence curve z(x) is divided into nine rectangular segments along its length, corresponding to the nine sections. The height s′i (i.e., the equivalent mining height) of each rectangular segment is calculated using the following formula:

[0063]

[0064] In the formula, s′ i t represents the average subsidence of the key layer within the i-th segment; i-1 and t i These are the starting and ending positions of the i-th rectangle segment, respectively.

[0065] Secondly, an activation coefficient is introduced to correct the subsidence coefficient of the loose layer. Considering that the loose layer has already been affected by a single mining operation before the perforated mining, its buffering capacity is reduced, and the subsidence coefficient q0 of the loose layer during single-face mining needs to be corrected. The calculation formula for the subsidence coefficient q′0 of the loose layer during perforated mining is as follows:

[0066] q′0=(1+a)q0;

[0067] In the formula, a is the activation coefficient, which is used to quantify the degree of change in the properties of the loose layer caused by the first mining operation.

[0068] Finally, substituting the equivalent extraction height s′i and the corrected subsidence coefficient q′0 into the probability integral method formula, we obtain the expression for the final surface deformation prediction curve y′(x):

[0069]

[0070] In the formula, r is the main influence radius, and t is the integration variable. By performing numerical calculations on this formula, an accurate surface deformation prediction curve can be obtained. This symbol is a summation symbol, indicating that the surface subsidence effects subsequently calculated from the nine different sections are linearly superimposed. This reflects the superposition principle of mining-induced effects, namely, the total subsidence at any point on the surface is the sum of the effects of all micro-element mining within the mining area. i is the index number of the section, from 1 to 9. …dt is the definite integral symbol, representing the integration of the core influence function over the width of the i-th segment. Its physical meaning is to calculate the integral over a width of (t… i -t i-1 The subsidence impact on point x on the surface caused by a unit mining section with a height of 1.

[0071] See attached document Figure 2 , attached Figure 2 This is a schematic diagram of a key layer mechanical model for grouting in open-cut mining according to an embodiment of the present invention. Step S1 in the method of the present invention, namely, establishing a key layer mechanical model for grouting in open-cut mining, is specifically implemented as follows:

[0072] To accurately describe the stress and deformation characteristics of key overburden strata under goaf mining conditions, the key strata are equated to elastic foundation beams. Unlike single-face mining, goaf mining involves an isolation coal pillar section between the mined-out area and the working face to be mined. This section is subject to more severe mining impacts than the solid coal section, and the underlying foundation support characteristics differ significantly.

[0073] Therefore, the mechanical model established in this embodiment divides the key layer into nine continuous sections with different mechanical properties along the width of the working face. From one side of the working face to the other side of the mined-out area, the nine sections are sequentially divided as follows: solid coal zone, under-compacted zone, compacted zone, under-compacted zone, isolation coal pillar zone, under-compacted zone, compacted zone, under-compacted zone, solid coal zone. This nine-segment structure can comprehensively reflect the overburden support conditions unique to near-goaf mining.

[0074] In the model, each section is assigned a specific foundation coefficient k. i(The value of i ranges from 1 to 9), this coefficient is used to quantify the support stiffness of the foundation below the key layer in this section. The physical meanings of the foundation coefficients for each section are as follows: the foundation coefficient of the solid coal zone depends on the unmined coal body and stable rock mass below; the foundation coefficient of the undercompacted zone depends on the grouting filling body and the incompletely compacted fractured rock mass below; the foundation coefficient of the compacted zone depends on the grouting filling body and the compacted fractured rock mass below; the foundation coefficient of the isolation coal pillar zone depends on the isolation coal pillar itself and its bearing characteristics after being affected by mining on both sides. An independent foundation coefficient k is set for each of these nine sections with different physical states. i This mechanical model can accurately characterize the non-uniform distribution of supporting forces at the bottom of the key layer under the combined effects of near-hole mining and mining activities. This model provides an accurate mechanical basis for calculating the asymmetric total deflection curve of the key layer in subsequent steps.

[0075] See attached document Figure 2 Step S2 in the method of this invention, which is based on the mechanical model of the key layer for grouting of overburden separation in the nine-segment open-cut mining established in step S1, calculates the total deflection curve of the key layer during open-cut mining, and the specific method is as follows:

[0076] This embodiment employs the initial parameter method to solve the fourth-order differential equation of the segmented elastic foundation beam in the key layer. This method simplifies the complex calculation process when solving multi-segment continuous beams by representing the deflection, rotation, bending moment, and shear force at the beam ends with the corresponding parameters at the beam beginning (i.e., initial parameters).

[0077] During open-cut mining, the total deflection curve ω′(x) of the key layer in any segment i can be calculated using the following expression:

[0078]

[0079] In the formula, ω′(x) is the total deflection at position x; ω′(L′ i-1 ), θ′(L′ i-1 ), M′(L′ i-1 ), Q′(L′ i-1 ) represent the deflection, rotation angle, bending moment, and shear force at the end of segment i-1 (i.e., the beginning of segment i); β′ i Let be the characteristic coefficient of the beam in segment i, and its calculation formula is:

[0080]

[0081] Where k i Let φ be the subgrade coefficient of the i-th segment, E be the elastic modulus of the key layer, I be the moment of inertia of the key layer section, q be the uniformly distributed load overlying the key layer, and φ be the subgrade coefficient of the i-th segment. i1 φ i2 φ i3 φi4 Let be the Krylov function corresponding to the i-th segment.

[0082] Where k i Let φ' be the subgrade coefficient of the i-th segment, E be the elastic modulus of the key layer, I be the moment of inertia of the key layer section, q be the uniformly distributed load overlying the key layer, and φ' be the subgrade coefficient of the i-th segment. 1i , φ′ 2i , φ′ 3i , φ′ 4i Let be the Krylov function corresponding to the i-th segment.

[0083] The equations for the rotation angle θ′(x), bending moment M′(x), and shear force Q′(x) of the key layer are as follows:

[0084]

[0085] Among them, the Krylov function φ′ i The specific expression for (x) is:

[0086]

[0087] To solve the above equations, the boundary conditions of the model are first defined. Since the key strata outside the influence range of the rock strata movement angle are not affected by mining, the boundary conditions at both ends of the model are determined to be fixed hinge supports. For the initial end of the model (x=0), its deflection ω′(θ) and rotation angle θ′(θ) are both zero. At this time, the entire equation system contains only two unknown initial parameters, M′(θ) and Q′(θ).

[0088] The solution process begins with the first step, substituting ω′(θ), θ′(θ), M′(θ), and Q′(θ) into the system of equations, and calculating...

[0089] Calculate the deflection, rotation angle, bending moment, and shear force at the end L1 of the first segment. Then use these values ​​as the initial parameters for the second segment, and calculate them recursively until the expressions for the deflection ω′(L′9) and rotation angle θ′(L′9) at the end L′9 of the ninth segment are obtained.

[0090] Based on the boundary conditions at the other end of the model, the end of the ninth segment is also a fixed hinge support, therefore:

[0091]

[0092] Since the expressions for ω′(L′9) and θ′(L′9) ultimately contain only two unknowns, M′(θ) and Q′(θ), the above boundary conditions constitute a system of two linear equations in two variables, M′(θ) and Q′(θ). Solving this system of equations using numerical computation tools (such as Matlab) determines the unique solution for M′(θ) and Q′(θ). Substituting the obtained values ​​of M′(θ) and Q′(θ) back into the initial system of equations yields the complete total deflection curve ω′(x) of the key layer across all nine sections during un-mined operations.

[0093] See attached document Figure 3 , attached Figure 3 This is a schematic diagram of the mechanical model of the key stratum in the first working face mining according to an embodiment of the present invention. Step S3 in the method of the present invention, namely calculating the net increase in key stratum subsidence curve during un-mined operations, is specifically implemented as follows:

[0094] The core of this step lies in accurately separating the net increase in deformation caused solely by mining from the second working face (i.e., the free-face mining) from the total deflection curve ω′(x) of the free-face mining calculated in step S2. To achieve this, it is necessary to first obtain the benchmark key layer subsidence curve caused solely by mining from the first working face in the same coordinate system.

[0095] Because the single-face mining model and the nine-segment model of unsupported mining used different coordinate systems and segmentation methods in the aforementioned calculations, direct numerical subtraction is not feasible. Therefore, it is necessary to first perform coordinate transformation on the deflection curve of the key layer in single-face mining and establish the coordinates as shown in the attached figure. Figure 3 The mechanical model of the key layer of the single working face shown has a unified coordinate system with the nine-segment open-cut mining model.

[0096] After coordinate transformation, the subsidence curve ω of the benchmark key layer is obtained. * (x). The expression of this curve in a unified coordinate system is a piecewise function:

[0097]

[0098] In the formula, ω * (x) is the subsidence curve of the benchmark key layer; i(x) is the original single working face deflection curve ω(x) after...

[0099] The function expression after coordinate system transformation; L5 is the starting position coordinate of the isolated coal pillar section in the nine-segment model of unsupported mining; H is the coal seam burial depth; δ is the rock stratum movement angle. The physical meaning of this expression is that outside the influence range of the first working face mining, the subsidence of the key strata caused by it is zero.

[0100] The benchmark key layer subsidence curve ω′(x) is obtained in the same coordinate system as the total deflection curve ω′(x).* After (x), by subtracting the two equations, the subsidence curve z(x) of the key layer resulting from the net increase in the yield from the un-mined area can be calculated. The calculation formula is as follows:

[0101] z(x)=ω′(x)-ω * (x);

[0102] In the formula, z(x) is the subsidence curve of the key layer caused by the net increase in mining at the open face; ω′(x) is the total deflection curve of the key layer during mining at the open face calculated in step S2. This curve z(x) excludes the influence caused by the first working face, accurately reflects the amount of overburden deformation added by mining at the open face, and serves as the direct calculation basis for the surface deformation prediction in the subsequent step S4.

[0103] See attached document Figure 5 , attached Figure 5 This is a comparison curve of surface deformation monitoring data and predicted data according to an embodiment of the present invention. Step S4 of the method of the present invention, namely, based on the subsidence curve z(x) of the key layer caused by the near-cut-off mining obtained in step S3, and combined with the modified probability integral method for integral calculation, to obtain the final surface deformation prediction curve, is specifically implemented as follows:

[0104] Since the subsidence curve z(x) of the key layer resulting from near-shore mining is a complex and irregular piecewise function, direct integration is cumbersome. Therefore, this embodiment first employs the equivalent mining height theory to discretize the continuous subsidence curve z(x) into nine rectangular segments, each corresponding to one of the nine mechanical segments defined in step S1. The height of each rectangular segment, i.e., the equivalent mining height s, is... i The calculation is performed using the following formula:

[0105]

[0106] In the formula, s′ i Let be the height of the i-th rectangular segment; z(t) is the key layer subsidence curve function obtained from the net increase in un-mined area calculated in step S3; t i-1 and t i These are the starting and ending coordinates of the i-th rectangular segment. The physical meaning of this calculation is to divide the area enclosed by the irregular sinking curve within the i-th segment (representing the total volume of the sinking space within the segment) by the width of the segment, thereby obtaining an equivalent rectangular height with the same sinking volume.

[0107] Before performing probability integral calculations, the subsidence coefficient of the loose layer needs to be corrected. Because the surface loose layer has already been affected by the first working face mining before the open-face mining, its internal structure has changed, resulting in a different degree of buffering and expansion response under the influence of the second mining operation compared to its original state. To quantify this change, this embodiment introduces an activation coefficient 'a' to adjust the subsidence coefficient 'q0' of the loose layer during single-face mining.

[0108] After correction, the subsidence coefficient q0 of the loose layer in the unexploded orifice is obtained. Its calculation formula is:

[0109] q0 = (1 + a)q0;

[0110] In the formula, q0 is the corrected loose layer subsidence coefficient applicable to unsupported mining conditions; a is the activation coefficient, the value of which is determined according to the on-site geological conditions; and q0 is the original loose layer subsidence coefficient when single-face mining is carried out under these geological conditions.

[0111] Finally, the calculated equivalent elevations for each section, s i and the revised loose layer for open-cut mining

[0112] Substituting the subsidence coefficient q0 into the probability integral method summation formula, the final surface deformation prediction curve y′(x) is calculated. Its calculation expression is:

[0113]

[0114] In the formula, y′(x) represents the surface subsidence caused by un-mining at a distance x from the origin; r is the main influence radius, whose value is determined by the coal seam depth and the tangent of the main influence angle; t is the integration variable, representing the location within the mining area. By performing numerical integration on this formula, a complete surface deformation prediction curve that accurately reflects the impact of un-mining can be obtained.

[0115] To further illustrate the specific application and effects of the method of the present invention, a specific engineering example is given below. This embodiment applies the aforementioned technical solution to the prediction of surface deformation caused by mining in the Xiadian Coal Mine.

[0116] The engineering background of this embodiment is set as Xiadian Coal Mine, where the 3117 working face has been completely mined, with a width of 190m and an injection-to-production ratio of 40%. The 3119 working face to be mined is an unexploded working face with a width of 215m. The purpose of this embodiment is to use the method of the present invention to predict the surface deformation law of the 3119 working face under different injection-to-production ratios, and to determine an optimal injection-to-production ratio accordingly.

[0117] To achieve the above objectives, this embodiment sets up five different injection-production ratio schemes for simulating the 3119 working face, with injection-production ratios of 30%, 35%, 40%, 45%, and 50%, respectively. Based on engineering experience and geological data, the foundation coefficient values ​​required for model calculations under each working condition are set as follows:

[0118] For the 3117 working face (190m wide, injection-to-production ratio 0.40) that has been mined, the subgrade coefficient of the undercompacted zone is 25.43MPa / m, the subgrade coefficient of the compacted zone is 19.30MPa / m, the subgrade coefficient of the coal pillar is 40.00MPa / m, and the subgrade coefficient of the solid coal is 100MPa / m.

[0119] For the 3119 working face (215m wide) to be mined, under the condition of an injection-to-production ratio of 30%, the subgrade coefficient of the undercompacted zone is taken as 6.31MPa / m, and the subgrade coefficient of the compacted zone is taken as 3.35MPa / m.

[0120] With an injection-to-production ratio of 35%, the subgrade coefficient in the undercompacted zone is 10.11 MPa / m, and the subgrade coefficient in the compacted zone is 6.32 MPa / m.

[0121] With an injection-to-production ratio of 40%, the subgrade coefficient in the undercompacted zone is 15.61 MPa / m, and the subgrade coefficient in the compacted zone is 10.87 MPa / m.

[0122] With an injection-to-production ratio of 45%, the subgrade coefficient in the undercompacted zone is 22.81 MPa / m, and the subgrade coefficient in the compacted zone is 17.00 MPa / m.

[0123] With an injection-to-production ratio of 50%, the subgrade coefficient in the undercompacted zone is 31.72 MPa / m, and the subgrade coefficient in the compacted zone is 24.70 MPa / m.

[0124] Under the five working conditions mentioned above in the 3119 working face, the foundation coefficient of the isolation coal pillar is taken as 40.00 MPa / m, and the foundation coefficient of the solid coal is taken as 100 MPa / m.

[0125] By substituting the parameters (including working face width, injection-production ratio, and local foundation coefficient values) and other relevant engineering parameters under the above working conditions into the calculation methods described in steps S1 to S4, numerical calculations can be performed to obtain the key layer subsidence curves and surface subsidence prediction curves under different injection-production ratios, providing a data basis for subsequent determination of the optimal injection-production ratio and field verification.

[0126] Referring to Figures 4(a) and 4(b), Figure 4(a) is a schematic diagram of the subsidence curve of the key layer under different injection-production ratios according to an embodiment of the present invention, and Figure 4(b) is a schematic diagram of the surface subsidence prediction curve under different injection-production ratios according to an embodiment of the present invention.

[0127] The parameters of the five different injection-production ratio schemes (30%, 35%, 40%, 45%, and 50%) from the previous section are substituted into the calculation process of steps S1 to S4 of this invention to perform numerical simulation calculations in order to analyze the influence of the injection-production ratio on the key layer and surface deformation.

[0128] The calculation results of the key stratum subsidence are shown in Figure 4(a). As can be seen from the figure, the total subsidence of the key stratum decreases with increasing injection-production ratio. As the injection-production ratio increases from 30% to 45%, the shape of the key stratum deflection curve gradually changes from a significantly asymmetric shape to a symmetric shape. When the injection-production ratio reaches 45%, the key stratum deflection curve exhibits a basically symmetrical shape, indicating that the key stratum is under uniform stress and the structure is stable.

[0129] The predicted results of surface subsidence are shown in Figure 4(b). The figure shows that the maximum surface subsidence also decreases with increasing injection-production ratio. This indicates that increasing the injection-production ratio can effectively control surface subsidence caused by unexcavated mining.

[0130] Based on the comprehensive analysis of the above calculation results, when the injection-production ratio is 45%, the key stratum achieves symmetrical deformation, indicating that the overburden structure is in a relatively stable state, and the corresponding surface subsidence is also effectively controlled. Although the subsidence is smaller when the injection-production ratio is 50%, from the perspective of the core indicator of key stratum deformation morphology, a 45% injection-production ratio has achieved the technical goal of controlling the symmetrical deformation of the key stratum. Therefore, in this engineering embodiment, 45% is determined as the optimal injection-production ratio scheme, and subsequent field implementation and data verification will be based on this scheme.

[0131] See attached document Figure 5 , attached Figure 5 This is a comparison curve of surface deformation monitoring data and predicted data according to an embodiment of the present invention.

[0132] Based on the optimal injection-production ratio (45%) determined by the aforementioned analysis, the scheme was implemented in the field at the 3119 working face of Xiadian Coal Mine. To verify the prediction accuracy of the method of this invention, an observation line was laid along the surface of the 3119 working face to monitor the surface subsidence in real time.

[0133] The predicted surface deformation curve calculated using the method of this invention under a 45% injection-to-production ratio was compared and analyzed with the surface subsidence data obtained from the 50th field measurement. The comparison results are attached. Figure 5 As shown.

[0134] From the appendix Figure 5 The comparison curves show that the predicted maximum surface subsidence is 637 mm, while the actual measured maximum surface subsidence is 680 mm. The relative error between the two is 6.38%. Furthermore, the predicted and measured maximum subsidence points are basically consistent.

[0135] The error value is within the allowable range for mining engineering. This comparative result verifies that the prediction method provided by this invention has high computational accuracy and engineering applicability.

Claims

1. A method for predicting key layers and surface deformation during grouting for overburden separation in open-cut mining, characterized in that, include: S1: Establish a mechanical model for the key layer of grouting for overburden separation in open-cut mining. The mechanical model for the key layer of grouting for overburden separation in open-cut mining is divided into nine sections along the width of the working face, each section having a different foundation coefficient. The nine sections, from one side of the working face to the other side of the mined-out area, are as follows: solid coal area, under-compacted area, compacted area, under-compacted area, isolation coal pillar area, under-compacted area, compacted area, under-compacted area, solid coal area. S2: Based on the mechanical model of the key layer for grouting in open-cut mining, the total deflection curve of the key layer during open-cut mining is calculated, and the total deflection is... The calculation formula is: ； In the formula, , , , For the first under the condition of open-pit mining Deflection, rotation, bending moment, and shear force at the end of the segment; For the first time when mining in the air Beam characteristic coefficients of the segment; For the first time when mining in the air The subgrade coefficient of the section; , , , For the corresponding Krylov function, The elastic modulus of the key layer, Here, the moment of inertia of the cross section of the key layer is... The value range is from 1 to 9; S3: Calculate the benchmark key layer subsidence curve caused by the mining of the first working face in a coordinate system that is consistent with the mechanical model of the key layer of the overburden separation grouting in the open mining, and calculate the net increase in the key layer subsidence curve of the open mining by subtracting the benchmark key layer subsidence curve from the total deflection curve. S4: Based on the subsidence curve of the key layer with net increase in the amount of mining at the open, and using the probability integral method of the loose layer subsidence coefficient of the key layer with net increase in the amount of mining at the open, the surface deformation prediction curve is obtained; wherein, an activation coefficient is introduced to correct the loose layer subsidence coefficient of the single working face mining of the benchmark key layer subsidence curve, and the loose layer subsidence coefficient of mining at the open is obtained for the integral calculation. The subsidence coefficient of the loose layer in the open-cut mining area Calculated using the following formula: ； In the formula, The activation coefficient is... This is the subsidence coefficient of the loose layer during single-face mining.

2. The method for predicting key layers and surface deformation in overburden separation grouting during open-cut mining according to claim 1, characterized in that, In step S2, the total deflection curve is calculated using the initial parameter method, and the solution is obtained based on the boundary conditions at both ends of the mechanical model of the key layer for grouting of overburden separation in open mining. The boundary conditions at both ends of the mechanical model for the key layer of the overburden separation grouting in the open-cut mining are determined to be fixed hinge supports, with the deflection and rotation angle of the fixed hinge supports both being zero.

3. The method for predicting key layers and surface deformation in overburden separation grouting during open-cut mining according to claim 1, characterized in that, In step S3, the subsidence curve of the key stratum caused by the independent mining of the first working face was obtained in the following way: A single working face key layer mechanical model with a unified coordinate system with the mechanical model of the key layer of the overburden separation grouting in the open-cut mining is established, and calculations are performed based on the single working face key layer mechanical model.

4. The method for predicting key layers and surface deformation in overburden separation grouting during open-cut mining according to claim 1, characterized in that, Step S4 further includes: Using the equivalent mining height theory, the subsidence curve of the key layer caused by the open-cut mining is divided along the length direction into nine rectangular segments corresponding to the nine sections, and the height of each rectangular segment is used as the equivalent mining height of the corresponding segment for the integral calculation.

5. The method for predicting key layers and surface deformation in overburden separation grouting during open-cut mining according to claim 4, characterized in that, Height of each rectangular segment Calculated using the following formula: ； In the formula, This refers to the subsidence curve of the key strata caused by the aforementioned open-cut mining. and The first The start and end positions of the rectangular segment. Represents the first The total spatial volume formed by the sinking of the key layer within a rectangular section.

6. The method for predicting key layers and surface deformation in overburden separation grouting during open-cut mining according to claim 1, characterized in that, Also includes: For different injection-production ratios, steps S1 to S4 are repeated to obtain surface deformation prediction curves under different injection-production ratios, and the optimal injection-production ratio is determined by comparing the surface deformation prediction curves of each region.

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