A method for distinguishing overburden separation considering horizontal stress and mining unloading effect

Abstract

The present application relates to the field of overburden movement and damage after coal mining, and relates to a method for distinguishing overburden separation considering horizontal stress and mining unloading effect, which comprises: determining the limit natural balance arch height of overburden after coal mining according to the mining thickness of coal seam; numbering the rock layers from bottom to top starting from the immediate roof of coal seam (i = 1, 2, 3…). Calculating the natural balance arch height according to the mining distance of working face, determining the actual length l of each rock layer in the natural balance arch i ; regarding each rock layer in the natural balance arch as a rock beam, calculating the deflection of the midpoint of each rock layer under the action of horizontal stress and vertical stress; distinguishing separation based on the deflection of the midpoint of each rock layer. Starting from the top of the balance arch, comparing the deflection values of the midpoints of the adjacent two rock beams from top to bottom, if δ 上 <δ 下 , it is determined that there is separation between the two rock layers. The present application fully considers the horizontal stress of rock layer and the mining unloading effect, and the obtained separation distinguishing result is more similar to the actual situation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of overburden movement and damage after coal mining, and particularly relates to an overburden separation layer discrimination method considering horizontal stress and mining unloading effect. BACKGROUND

[0002] Coal resources account for a large proportion in energy consumption in China. In the past decade, with the exhaustion of shallow coal resources, coal mining gradually develops to deep part. Due to the increasing ground stress, a series of disasters such as water inrush and gas outburst in working face frequently occur. Especially for the working face located under the loose aquifer, water inrush accident is the main safety threat, and many such water inrush accidents have occurred in the country since 2000. No doubt, these water inrush accidents are related to the movement and damage of overburden after coal mining, and the existence of overburden separation layer will change the stress distribution of overburden, which will inevitably affect the overburden damage. Therefore, discrimination of overburden separation layer is the key to prevent such water inrush accidents.

[0003] In the prior art, discrimination methods of overburden separation layer mainly include field monitoring, theoretical calculation, simulation test (numerical simulation, similar test) and the like. Among them, the discrimination of separation layer by field monitoring method is the most reliable method, but the arrangement range of monitoring points is usually small, which is difficult to cover the entire roof rock layer, and is also time-consuming and laborious. When the simulation method is used to discriminate the separation layer, the discrimination result is related to the model size, material parameters and boundary conditions, etc., which may lead to large deviation, and is often verified by other discrimination methods. The theoretical method is a commonly used separation layer discrimination method, among which the separation layer discrimination formula derived by Qian Minggao according to the combined beam theory is the most classical, and many scholars have optimized and improved the formula. However, the existing theoretical method often ignores the effect of horizontal stress on the combined beam and lacks consideration of the unloading effect in the vertical direction of the natural balance arch after coal mining. Therefore, the length of each rock beam is controlled by the shape of the natural balance arch.

[0004] Due to the above limitations, the existing theoretical method can only roughly discriminate the overburden separation layer, and it is difficult to obtain an accurate discrimination result, which may be greatly deviated from the actual situation, or even completely opposite. SUMMARY

[0005] To solve the technical problems proposed in the background art, the present application provides an overburden separation layer discrimination method considering horizontal stress and mining unloading effect.

[0006] The application adopts the following technical scheme to achieve the method for distinguishing the separation layer of overburden strata considering the horizontal stress and mining unloading effect, which comprises the following steps:

[0007] S1: determining the limit natural balance arch height of overburden strata after coal seam mining according to the mining thickness of the coal seam.

[0008] S2: numbering the rock layers from bottom to top starting from the immediate roof of the coal seam (i (i=1, 2, 3…)). Calculating the natural balance arch rise according to the mining distance of the working face, and determining the actual length l of each rock layer in the natural balance arch. i .

[0009] S3: regarding each rock layer in the natural balance arch as a rock beam, calculating the deflection of the midpoint of each rock layer under the action of horizontal stress and vertical stress.

[0010] S4: distinguishing the separation layer based on the deflection of the midpoint of each rock layer. Starting from the top of the balance arch, comparing the deflection values of the midpoints of the adjacent two rock beams from top to bottom. 上 <δ 下 If δ

[0011] S5: based on the separation layer distribution in step S4, checking whether the maximum tensile stress of each rock layer exceeds its tensile strength, and if yes, considering that the rock layer is broken, and the rock layers below the rock layer are also broken.

[0012] S6: determining the final distribution of the overburden strata separation layer according to the breaking condition of the rock layer.

[0013] Optionally, the step S1 comprises:

[0014] calculating the limit height of the natural balance arch by the formula: M-(H-h)·(η-1)=0, wherein M is the mining thickness; H is the limit height of the natural balance arch; h is the height of the water flowing fractured zone; and η is the average dilatancy coefficient of the water flowing fractured zone.

[0015] Optionally, the step S2 comprises:

[0016] S201: for a certain coal seam mining distance a, describing the shape of the natural balance arch by the formula: wherein b1 is the natural balance arch rise; f is the Protodyakonov coefficient; λ is the lateral pressure coefficient; K is the arch foot stability safety state coefficient; and a1 is a parameter related to the stability of the roadway rock, which is equal to the half-span length a / 2 of the mining distance when the two side rocks are stable.

[0017] S202: Determine the safety factor K at the arch foot of the naturally balanced arch. Considering that the shape of the naturally balanced arch is similar to the distribution of the overburden fracture lines, and the angle between the overburden fracture lines and the coal seam after mining is approximately between 60° and 64°, tan62° is taken as the slope of the arch curve at y = b1 / 2. In the arch curve equation... After differentiating with respect to x, the point Substituting into the equation, we obtain the value of the arch foot safety factor K as 18.6.

[0018] S203: Use the formula: Calculate the corresponding natural equilibrium arch height for different mining distances, and calculate the critical mining distance at this time from the limit natural equilibrium arch height obtained in step S1.

[0019] S204: Based on the value of b1, the distance from the midpoint of each rock layer in the vertical direction to the crown is taken as y. i (i = 1, 2, 3…), calculate the length l of each rock layer located within the arch at this time based on the curve equation of the arch. i =2x i (i = 1, 2, 3...).

[0020] Optionally, step S3 includes:

[0021] Calculate the bending moment and midpoint deflection of the rock strata using a beam-column model with fixed ends;

[0022] Using the formula: Calculate the bending moment at the end of the rock stratum.

[0023] Using the formula: Calculate the midpoint deflection of the rock strata under self-weight stress and horizontal stress;

[0024] Where q i E is the self-weight load of the rock strata. i I i Let be the bending stiffness of the beam; p i M represents the horizontal stress of the rock strata. 0,i The bending moment at the beam end is the moment under the action of self-weight load and horizontal stress.

[0025] Optionally, step S4 includes:

[0026] S401: Begin the first round of delamination detection, comparing the rock strata deflection from top to bottom of the arch. If the first layer at the arch is numbered i, and δ... i,l / 2 >δ i-1,l / 2 If δ i,l / 2 <δ i-1,l / 2 If so, it is determined that there is a delamination between the i-th layer and the (i-1)-th layer, that is, starting from the (i-1)-th layer, the deflection is compared with that of the (i-2)-th layer.

[0027] S402: When the i-th floor and the (i-1)-th floor are determined to be a composite beam, calculate the midpoint deflection δ of the composite beam. A,l / 2 The deflection δ at the midpoint of the (i-2)th rock layer i-2,l / 2 Comparison, if δ A,l / 2 <δ i-2,l / 2 If δ is the deflection of the composite beam, then layers i to i-2 are determined to be composite beams, and the deflection of the composite beams at this time is calculated. A,l / 2 <δ i-2,l / 2 If a delamination exists between the (i-1)th and (i-2)th rock layers, the deflection of the (i-3)th and (i-4)th rock layers is compared. This process continues until the rock layer numbered 1 is reached, at which point the first round of delamination detection ends.

[0028] S403: Based on the results of the first round of judgment, compare the midpoint deflection between adjacent composite beams from top to bottom. If there is a case where the deflection of the upper composite beam is greater than that of the lower composite beam, then the adjacent composite beams form a new composite beam with the sum of the two in terms of the number of layers, and calculate the midpoint deflection value of the new composite beam. This is the second round of judgment.

[0029] S404: If the results of a certain round of delamination judgment are all that the deflection of the upper rock layer is less than that of the lower rock layer, then the delamination judgment is terminated.

[0030] Optionally, the deflection calculation of the composite beam in step S402 includes two cases: the midpoint deflection calculation of a composite beam composed of two rock layers and a composite beam composed of three or more rock layers.

[0031] When the composite beam consists of two rock layers:

[0032] Assume the rock strata are numbered i and i-1 from top to bottom;

[0033] The bending moment at the midpoint of the i-th rock layer is calculated using the formula Calculate, where q i,i-1 The interaction force between the i-th layer and the (i-1)-th layer;

[0034] The midpoint bending moment of the i-1th rock layer and the deflection of the composite beam are calculated according to the following steps:

[0035] Using the formula: Calculate the midpoint bending moment of the (i-1)th rock layer under its own weight and horizontal stress.

[0036] Using the formula: Calculate the interaction force q of the (i-1)th rock layer. i,i-1 and beam end bending moment under horizontal stress Where, a=(l i-1 -l i ) / 2, b=(li-1 + i ) / 2;

[0037] Using the formula: Calculate the midpoint bending moment of the i-1 layer rock under the action of interaction force q i,i-1 and horizontal stress

[0038] Using the formula: Calculate the total midpoint bending moment M l / 2,i-1 of the i-1 layer rock

[0039] Using the formula: Solve the interaction force q i,i-1 between the two rocks

[0040] Using the formula: Calculate the deflection δ A,l / 2 of the composite beam

[0041] When the three-layer and three-layer composite beam:

[0042] Assume that there are s (s≥3) layers of rock to form a composite beam, and the rock is numbered from top to bottom as i, i-1, …, i-s+1;

[0043] The midpoint bending moment of the i layer rock is calculated by the formula ;

[0044] The midpoint bending moment of the i-s+1 layer rock is calculated by the following steps:

[0045] Using the formula: Calculate the midpoint bending moment of the i-s+1 layer rock under the action of self-weight load and horizontal stress

[0046] Using the formula: Calculate the beam end bending moment of the i-s+1 layer rock under the action of interaction force q i-s+2,i-s+1 and horizontal stress Where a=(l i-s+1 -l i-s+2 ) / 2, b=(l i-s+1 +l i-s+2 ) / 2;

[0047] Using the formula: Calculate the midpoint bending moment of the i-s+1 layer rock under the action of interaction force q i-s+2,i-s+1 and horizontal stress

[0048] Using the formula: Calculate the total midpoint bending moment M l / 2,i-s+1 of the i-1 layer rock

[0049] Taking the i-1 layer as an example, the midpoint bending moment of the i-1 layer to the i-s+2 layer is calculated by the following steps:

[0050] The midpoint bending moment of the i-1 layer under the action of the self-weight load, the horizontal stress and the force q i-1,i-2 of the i-2 layer is calculated by the formula: The beam end bending moment of the i-1 layer under the action of the force q i,i-1 and the horizontal stress is calculated by the formula:

[0051] The midpoint bending moment of the i-1 layer under the action of the force q i,i-1 and the horizontal stress is calculated by the formula:

[0052] The total midpoint bending moment M l / 2,i-1 of the i-1 layer is calculated by the formula:

[0053] The midpoint bending moment expressions of the i-1 layer to the i-s+2 layer are obtained by repeating the above steps, and the force q i,i-1 , q i-1,i-2 ,..., q i-s+2,i-s+1 are solved by the formula:

[0054] The deflection δ A,l / 2 of the composite beam is calculated by the formula:

[0055] Optionally, the step S5 comprises: S501: The maximum tensile stress σ of the rock layer (composite beam) is calculated by the formula:

[0056]

[0057] S502: The tensile strength [σ] of the rock layer is taken as the failure criterion, if σ>[σ], the rock layer is damaged, when the bottom rock layer of the composite beam reaches the damage condition, it is considered that the composite beam is damaged as a whole. When a certain layer of rock layer is damaged, it is considered that the rock layers below the rock layer have been damaged, and the rock layers below the rock layer do not develop delamination.

[0058] Compared with the prior art, the beneficial effects of the present application are:

[0059]

[0060] ​​​​​​​1. When the coal seam mining overburden separation is distinguished by the application, the range of the overburden natural balance arch after mining is calculated, and the length of each rock layer in the balance arch is determined at different mining distances, and the separation is fully considered to develop in the natural balance arch. In addition, the separation in the overburden is a continuous development and evolution process with the increase of the mining distance, and the obtained distinguishing result is more reliable. The beam-column theory shows that when the horizontal stress is large enough, even if the vertical load is small, the rock layer will also have a large deflection. The separation distinguishing model in the application is based on the beam-column theory, and the horizontal stress of the rock layer is considered, so that the deficiency of the existing separation distinguishing model is made up, and therefore the distinguishing result is more close to the actual situation.

[0061] 2. The application has clear thought structure, simple operation, and is convenient to program and suitable for practical application, and provides a new method and thought for distinguishing the separation in the overburden of the coal seam mining. BRIEF DESCRIPTION OF DRAWINGS

[0062] Figure 1 A flowchart of a separation distinguishing method of overburden considering horizontal stress and mining unloading effect is provided. DETAILED DESCRIPTION

[0063] In the following, the application is further described in combination with the drawings and specific embodiments, and it should be noted that the following described embodiments or technical features can be combined to form new embodiments without conflict.

[0064] Embodiment 1:

[0065] Please combine Figure 1 A separation distinguishing method of overburden considering horizontal stress and mining unloading effect, comprising the following steps:

[0066] Step S1: according to the thickness of the coal seam mining, the limit natural balance arch height of the overburden after the coal seam mining is determined.

[0067] Step S2: the rock layers are numbered from bottom to top starting from the immediate roof of the coal seam (i=i, 2, 3…). The natural balance arch vector height is calculated according to the mining distance of the working face, and the actual length li of each rock layer in the natural balance arch is determined.

[0068] Step S3: each rock layer in the natural balance arch is regarded as a rock beam, and the deflection of the midpoint of each rock layer under the action of horizontal stress and vertical stress is calculated.

[0069] Step S4: the separation is distinguished based on the midpoint deflection of each rock layer. Starting from the top of the balance arch, the midpoint deflection values of the adjacent two rock beams are compared from top to bottom, and if δ 上 <δ 下If the value of the formula is greater than 0, it is determined that there is a separation between the two rock layers.

[0070] Step S5: Based on the separation distribution in step S4, it is calculated whether the maximum tensile stress of each rock layer exceeds its tensile strength. If yes, it is considered that the rock layer is broken, and the rock layers below the rock layer are also broken.

[0071] Step S6: The final distribution of the overburden separation is determined according to the breaking of the rock layers.

[0072] Optionally, the step S1 comprises:

[0073] The limit height of the natural equilibrium arch is calculated by the formula: M-(H-h)·(η-1)=0, wherein M is the mining thickness; H is the limit height of the natural equilibrium arch; h is the height of the water flowing fractured zone; and η is the average dilatancy coefficient of the water flowing fractured zone.

[0074] Optionally, the step S2 comprises:

[0075] S201: For a certain coal seam mining distance a, the formula: The shape of the natural equilibrium arch is described, wherein b1 is the sagitta of the natural equilibrium arch; f is the Protodyakonov coefficient; λ is the lateral pressure coefficient; K is the arch foot stability safety state coefficient; and a1 is a parameter related to the stability of the roadway rock, which is equal to the half-span length a / 2 of the mining distance when the two sides of the rock are stable.

[0076] S202: The arch foot safety coefficient K of the natural equilibrium arch is determined. Considering that the shape of the natural equilibrium arch is similar to the distribution of the overburden fracture line, the angle between the overburden fracture line after mining and the coal seam is about 60°-64°, and tan62° is taken as the slope of the arch curve at y=b1 / 2. In the arch curve equation After derivation of x, the point is substituted into the equation, and the value of the arch foot safety coefficient K is 18.6.

[0077] S203: The formula: is used to calculate the corresponding natural equilibrium arch height of different mining distances, and the critical mining distance at this time is calculated from the limit natural equilibrium arch height obtained in step S1.

[0078] S204: According to the value of b1, the distance from the midpoint position of each rock layer in the vertical direction to the arch top is taken as y i (i=1, 2, 3…), and the rock layer length l i inside the arch at this time is calculated according to the arch curve equation. i (i=1, 2, 3…).

[0079] Optionally, the step S3 comprises:

[0080] Calculate the bending moment and midpoint deflection of the rock strata using a beam-column model with fixed ends;

[0081] Using the formula: Calculate the bending moment at the end of the rock stratum.

[0082] Using the formula: Calculate the midpoint deflection of the rock strata under self-weight stress and horizontal stress;

[0083] Where q i E is the self-weight load of the rock strata. i I i Let be the bending stiffness of the beam; p i M represents the horizontal stress of the rock strata. 0,i The bending moment at the beam end is the moment under the action of self-weight load and horizontal stress.

[0084] Optionally, step S4 includes:

[0085] S401: Begin the first round of delamination detection, comparing the rock strata deflection from top to bottom of the arch. If the first layer at the arch is numbered i, and δ... i,l / 2 >δ i-1,l / 2 If δ i,l / 2 <δ i-1,l / 2 If so, it is determined that there is a delamination between the i-th layer and the (i-1)-th layer, that is, starting from the (i-1)-th layer, the deflection is compared with that of the (i-2)-th layer.

[0086] S402: When the i-th floor and the (i-1)-th floor are determined to be a composite beam, calculate the midpoint deflection δ of the composite beam. A,l / 2 The deflection δ at the midpoint of the (i-2)th rock layer i-2,l / 2 Comparison, if δ A,l / 2 <δ i-2,l / 2 If δ is the deflection of the composite beam, then layers i to i-2 are determined to be composite beams, and the deflection of the composite beams at this time is calculated. A,l / 2 <δ i-2,l / 2 If a delamination exists between the (i-1)th and (i-2)th rock layers, the deflection of the (i-3)th and (i-4)th rock layers is compared. This process continues until the rock layer numbered 1 is reached, at which point the first round of delamination detection ends.

[0087] S403: Based on the results of the first round of judgment, compare the midpoint deflection between adjacent composite beams from top to bottom. If there is a case where the deflection of the upper composite beam is greater than that of the lower composite beam, then the adjacent composite beams form a new composite beam with the sum of the two in terms of the number of layers, and calculate the midpoint deflection value of the new composite beam. This is the second round of judgment.

[0088] S404: If the results of a certain round of delamination judgment are all that the deflection of the upper rock layer is less than that of the lower rock layer, then the delamination judgment is terminated.

[0089] Optionally, the deflection calculation of the composite beam in S402 includes two cases: the midpoint deflection calculation of the composite beam composed of two rock layers and the composite beam composed of three or more rock layers.

[0090] When the composite beam is composed of two rock layers: assume that the rock layers are numbered i and i-1 from top to bottom;

[0091] The bending moment at the midpoint of the i-th rock layer is calculated using the formula Calculate, where q i,i-1 The interaction force between the i-th layer and the (i-1)-th layer;

[0092] The midpoint bending moment of the i-1th rock layer and the deflection of the composite beam are calculated according to the following steps:

[0093] Using the formula: Calculate the midpoint bending moment of the (i-1)th rock layer under its own weight and horizontal stress.

[0094] Using the formula: Calculate the interaction force q of the (i-1)th rock layer. i,i-1 and beam end bending moment under horizontal stress Where, a=(l i-1 -l i ) / 2, b=(l i-1 +l i ) / 2;

[0095] Using the formula: Calculate the interaction force q of the (i-1)th rock layer. i,i-1 Midpoint bending moment under horizontal stress

[0096] Using the formula: Calculate the total midpoint bending moment M of the i-1th rock layer. l / 2,i-1 ;

[0097] Using the formula: Solve for the interaction force q between the two rock layers i,i-1 ;

[0098] Using the formula: Calculate the deflection δ of the composite beam A,l / 2 ;

[0099] For composite beams with three or more layers:

[0100] Assume there are s (s≥3) rock layers forming a composite beam, and the rock layers are numbered from top to bottom as i, i-1, ..., i-s+1;

[0101] The bending moment at the midpoint of the i-th rock layer is calculated using the formula Compute;

[0102] The mid-point bending moment of the i-s+1 layer is calculated as follows:

[0103] Using the formula: Compute the mid-point bending moment of the i-s+1 layer under the action of the self-weight load and the horizontal stress

[0104] Using the formula: Compute the beam end bending moment of the i-s+1 layer under the action of the interaction force q i-s+2,i-s+1 and the horizontal stress where a = (l i-s+1 -l i-s+2 ) / 2, b = (l i-s+1 +l i-s+2 ) / 2;

[0105] Using the formula: Compute the mid-point bending moment of the i-s+1 layer under the action of the interaction force q i-s+2,i-s+1 and the horizontal stress

[0106] Using the formula: Compute the total mid-point bending moment M l / 2,i-s+1 of the i-1 layer;

[0107] Taking the i-1 layer as an example, the mid-point bending moments of the i-1 to i-s+2 layers are calculated as follows:

[0108] Using the formula: Compute the mid-point bending moment of the i-1 layer under the action of the self-weight load, the horizontal stress, and the action force q i-1,i-2 of the i-2 layer

[0109] Using the formula: Compute the beam end bending moment of the i-1 layer under the action of the interaction force q i,i-1 and the horizontal stress

[0110] Using the formula: Compute the mid-point bending moment of the i-1 layer under the action of the interaction force q i,i-1 and the horizontal stress

[0111] Using the formula: Compute the total mid-point bending moment M l / 2,i-1 of the i-1 layer;

[0112] Repeat the above steps to obtain the expression of the mid-point bending moments of the i-1 to i-s+2 layers, using the formula: Solve q i,i-1 q i-1,i-2 q i-s+2,i-s+1 ;

[0113] Using the formula: Calculate the deflection δ of the composite beam A,l / 2 ;

[0114] Optionally, the step S5 comprises:

[0115] S501: Using the formula: Calculate the maximum tensile stress σ of the rock stratum (composite beam), wherein M0 is the end moment of the rock stratum (if it is a composite beam, the value of the bottommost rock stratum is calculated);

[0116] S502: Take the tensile strength [σ] of the rock stratum as the failure criterion, if σ>[σ], the rock stratum is damaged, when the bottommost rock stratum of the composite beam reaches the failure condition, it is considered that the composite beam as a whole is damaged. When a certain layer of rock stratum is damaged, it is considered that the rock strata below the rock stratum have also been damaged, and the rock strata below the rock stratum do not develop separation.

[0117] The present application takes a working face as an example, Table 1 is the overburden structure of the working face, the overburden lithology is medium-hard, the working face mines 9 coal, the mining height is 3.5m, according to the empirical formula in the “Specification for Coal Pillar Retaining and Pressure Coal Mining of Buildings, Water Bodies, Railways and Main Roadways”, the height of the water flowing fractured zone is about 43.6m. The rock dilatancy coefficient is taken as 1.05, which is substituted into the formula M-(H-h)·(η-1)=0, and the limit natural equilibrium arch height of the overburden after coal mining is calculated as 113.6m.

[0118] Table 1

[0119] No. Lithology Thickness Depth 16 Mudstone 42.6 381.4 15 Siltstone 0.8 424.0 14 Mudstone 14.7 424.8 13 Sandstone 8.0 439.4 12 Mudstone 18.0 447.5 11 Sandstone 4.7 465.5 10 Mudstone 20.7 470.2 9 Sandstone 1.0 490.9 8 Mudstone 10.5 491.9 7 71 Coal 1.2 502.3 6 Sandstone 4.0 503.5 5 72 Coal 2.5 507.5 4 Mudstone 7.5 510.0 3 Siltstone 6.6 517.5 2 Mudstone 7.5 524.1 1 Siltstone 4.5 531.6 9 Coal 3.5

[0120] The rock strata are numbered i (i=1, 2, 3…) from the bottom to the top starting from the immediate roof of the coal seam. The natural equilibrium arch height is calculated according to the working face mining distance, and the actual length l of each rock stratum in the natural equilibrium arch is determined i .

[0121] The limit natural equilibrium arch height is 113.6m, so according to Table 2, the corresponding critical mining distance is 225.4m. When the working face mining distance is 50m, 100m, 150m, 200m and 300m respectively, the corresponding natural equilibrium arch height is also shown in Table 2.

[0122] The length l of each rock stratum in the arch under different mining distances i =2x i (i=1, 2, 3…) as shown in Table 2.

[0123] Table 2

[0124]

[0125] The deflection of the midpoint of each rock layer under the action of horizontal stress and vertical stress is calculated.

[0126] The end bending moment M corresponding to each mining distance 0,i and the midpoint deflection δ of the rock layer i,l / 2 As shown in Table 3.

[0127] Based on the midpoint deflection of each rock layer, the separation of layers is distinguished. Starting from the top of the balanced arch, the midpoint deflection values of the adjacent two rock beams are compared from top to bottom. If δ 上 <δ 下 , it is determined that there is separation between the two rock layers.

[0128] The deflection of the rock layer is compared from the top of the arch to the bottom. The first layer number at the top of the arch is i. If δ i,l / 2 >δ i-1,l / 2 , it is determined that the i-th layer and the i-1-th layer are combined beams. If δ i,l / 2 <δ i-1,l / 2 , it is determined that there is separation between the i-th layer and the i-1-th layer.

[0129] When the i-th layer and the i-1-th layer are determined to be combined beams, the midpoint deflection δ A,l / 2 of the combined beam is calculated and compared with the midpoint deflection δ i-2,l / 2 of the i-2-th layer, until the layer numbered 1, and the first round of separation discrimination ends. The first round of discrimination results and the corresponding midpoint deflection are shown in Table 4.

[0130] Table 3

[0131]

[0132] Table 4

[0133]

[0134] Therefore, when the mining length is 50m, 100m and 150m, the obtained rock layer deflection is increasing from top to bottom, and the separation discrimination ends.

[0135] When the mining length is 200m and 300m, there is a case that the deflection of the upper rock layer is greater than that of the lower rock layer, and the second round of separation discrimination is needed, and the results are shown in Table 5.

[0136] Table 5

[0137]

[0138] Based on the delamination distribution in step S4, the maximum tensile stress of each rock layer is checked to see if it exceeds its tensile strength (the tensile strength of the composite beam is the tensile strength of the rock layer at the bottom of the composite beam). If so, the rock layer is considered to have fractured, and all rock layers below that rock layer have fractured. The calculation results of the tensile stress of each rock layer at different mining distances and whether it has fractured are shown in Table 6.

[0139] Finally, the distribution of the overlying strata was determined based on the fracture characteristics of the rock layers.

[0140] When a rock stratum fractures below a certain point, no delamination occurs below it. Therefore, when the working face advances 50m, delamination only occurs between the 3rd and 2nd layers. When the working face advances 100m, delamination occurs between the 4th and 3rd layers, the 6th and 5th layers, and the 8th and 7th layers. When the working face advances 150m, delamination occurs between the 10th and 9th layers, and between the 8th and 7th layers. When the working face advances 200m, delamination occurs between the 13th and 12th layers. When the working face advances 300m, delamination occurs between the 14th and 13th layers.

[0141] Table 6

[0142]

[0143] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for identifying overburden delamination considering horizontal stress and mining-induced unloading effects, characterized in that, Includes the following steps: S1: Determine the ultimate natural equilibrium arch height of the overlying strata after coal seam mining based on the coal seam thickness. S2: Number the rock strata i (i=1,2,3…) from bottom to top, starting from the immediate top of the coal seam; calculate the natural equilibrium arch rise based on the mining distance of the working face, and determine the actual length li of each rock stratum within the natural equilibrium arch; S3: Treat each rock layer in the natural equilibrium arch as a rock beam and calculate the deflection at the midpoint of each rock layer under horizontal and vertical stress. S4: Delamination is determined based on the deflection at the midpoint of each rock layer; starting from the top of the balance arch, the deflection values ​​at the midpoints of two adjacent rock beams are compared from top to bottom. If δupper < δlower, it is determined that there is a delamination between the two rock layers. S5: Based on the delamination distribution in step S4, check whether the maximum tensile stress of each rock layer exceeds its tensile strength. If so, it is considered that the rock layer has broken, and all the rock layers below the rock layer have broken. S5: Determine the final distribution of the overlying strata based on the fracture characteristics of the rock strata.

2. The overburden separation discrimination method considering horizontal stress and mining-induced unloading effect as described in claim 1, characterized in that, Step S1 includes: Using the formula: Calculate the limit height of the natural equilibrium arch, where M is the mining thickness; H is the limit height of the natural equilibrium arch; h is the height of the water-conducting fracture zone; and η is the average fracture expansion coefficient of the water-conducting fracture zone.

3. The overburden separation discrimination method considering horizontal stress and mining-induced unloading effect as described in claim 1, characterized in that, Step S2 includes: S201: For a mining distance 'a' in a certain coal seam, using the formula: , describes the morphology of a natural equilibrium arch, where b1 is the natural equilibrium arch rise; f is the Protodyakonov coefficient; λ is the lateral pressure coefficient; K is the arch foot stability safety state coefficient; a1 is a parameter related to the stability of the roadway rock, which is equal to half the mining distance a / 2 when the rocks on both sides are stable; S202: Determine the safety factor K at the arch foot of the naturally balanced arch; considering that the shape of the naturally balanced arch is similar to the distribution of the overburden fracture lines, the angle between the overburden fracture lines and the coal seam after mining is approximately between 60° and 64°, tan62° is taken as the slope of the arch curve at y=b1 / 2; in the arch curve equation After differentiating with respect to x, the point Substituting into the equation, the value of the arch foot safety factor K is 18.6; S203: Utilize the formula: Calculate the corresponding natural equilibrium arch height for different mining distances, and calculate the critical mining distance at this time from the limit natural equilibrium arch height obtained in step S1. S204: Based on the value of b1, the distance from the midpoint of each rock layer in the vertical direction to the crown is taken as y. i (i=1,2,3…), calculate the length l of each rock layer located inside the arch at this time according to the curve equation of the arch. i =2x i (i=1,2,3…).

4. The overburden separation discrimination method considering horizontal stress and mining-induced unloading effect as described in claim 1, characterized in that, Step S3 includes: Calculate the bending moment and midpoint deflection of the rock strata using a beam-column model with fixed ends; Using the formula: Calculate the bending moment at the end of the rock stratum; Using the formula: Calculate the midpoint deflection of the rock strata under self-weight stress and horizontal stress; Where q i E is the self-weight load of the rock strata. i I i Let be the bending stiffness of the beam; p i M represents the horizontal stress of the rock strata. 0,i The bending moment at the beam end is the moment under the action of self-weight load and horizontal stress.

5. The overburden separation discrimination method considering horizontal stress and mining-induced unloading effect as described in claim 1, characterized in that, Step S4 includes: S401: Begin the first round of delamination detection, comparing rock strata deflection from top to bottom of the arch; if the first layer at the arch is numbered i, if... > If the i-th floor and the (i-1)-th floor are determined to be composite beams; if < If so, it is determined that there is a delamination between the i-th layer and the (i-1)-th layer, that is, starting from the (i-1)-th layer, the deflection is compared with the (i-2)-th layer. S402: When the i-th floor and the (i-1)-th floor are determined to be a composite beam, calculate the midpoint deflection of the composite beam. The deflection at the midpoint of the (i-2)th rock layer If a comparison is made, < If the i-th to i-2-th layers are determined to be composite beams, the deflection of the composite beams at this time is calculated; if < If a delamination exists between the (i-1)th and (i-2)th rock layers, continue comparing the deflection of the (i-3)th and (i-4)th rock layers until the rock layer numbered 1 is reached, at which point the first round of delamination detection ends. S403: Based on the results of the first round of judgment, compare the midpoint deflection between adjacent composite beams from top to bottom. If there is a case where the deflection of the upper composite beam is greater than that of the lower composite beam, then the adjacent composite beams form a new composite beam with the sum of the two in terms of the number of layers, and calculate the midpoint deflection value of the new composite beam; this is the second round of judgment. S404: If the results of a certain round of delamination judgment are all that the deflection of the upper rock layer is less than that of the lower rock layer, then the delamination judgment is terminated.

6. The overburden separation discrimination method considering horizontal stress and mining-induced unloading effect as described in claim 5, characterized in that, The deflection calculation of the composite beam in S402 includes two cases: the midpoint deflection calculation of the composite beam composed of two rock layers and the composite beam composed of three or more rock layers. When the composite beam consists of two rock layers: Assume the rock strata are numbered i and i-1 from top to bottom; The bending moment at the midpoint of the i-th rock layer is calculated using the formula Calculate, where q i,i-1 The interaction force between the i-th layer and the (i-1)-th layer; The midpoint bending moment of the i-1th rock layer and the deflection of the composite beam are calculated according to the following steps: Using the formula: Calculate the midpoint bending moment of the (i-1)th rock layer under its own weight and horizontal stress. ; Using the formula: Calculate the interaction force q of the (i-1)th rock layer. i,i-1 and beam end bending moment under horizontal stress , where a = (l i-1 -l i ) / 2, b= (l i-1 +l i ) / 2; Using the formula: Calculate the interaction force q of the (i-1)th rock layer. i,i-1 Midpoint bending moment under horizontal stress ; Using the formula: Calculate the total midpoint bending moment of the i-1th rock layer. ; Using the formula: Solve for the interaction force q between the two rock layers. i,i-1 ; Using the formula: Calculate the deflection of the composite beam. ; For composite beams with three or more layers: Assume there are s (s≥3) rock layers forming a composite beam, and the rock layers are numbered from top to bottom as i, i-1, ..., i-s+1; The bending moment at the midpoint of the i-th rock layer is calculated using the formula calculate; The bending moment at the midpoint of the (i-s+1)th rock layer is calculated using the following steps: Using the formula: Calculate the midpoint bending moment of the i-s+1th rock layer under its own weight and horizontal stress. ; Using the formula: Calculate the interaction force q of the i-s+1th rock layer. i-s+2,i-s+1 and beam end bending moment under horizontal stress , where a = (l i-s+1 -l i-s+2 ) / 2, b= (l i-s+1 +l i-s+2 ) / 2; Using the formula: Calculate the interaction force q of the i-s+1th rock layer. i-s+2,i-s+1 Midpoint bending moment under horizontal stress ; Using the formula: Calculate the total midpoint bending moment of the i-1th rock layer. ; Taking the (i-1)th layer as an example, the bending moment at the midpoint of the rock strata from the (i-1)th layer to the (i-s+2)th layer is calculated as follows: Using the formula: Calculate the force q of the (i-1)th rock layer under its own weight, horizontal stress, and the force q of the (i-2)th rock layer. i-1,i-2 Midpoint bending moment ; Using the formula: Calculate the interaction force q of the (i-1)th rock layer. i,i-1 and beam end bending moment under horizontal stress ; Using the formula: Calculate the interaction force q of the (i-1)th rock layer. i,i-1 Midpoint bending moment under horizontal stress ; Using the formula: Calculate the total midpoint bending moment of the i-1th rock layer. ; Repeat the above steps to obtain the midpoint bending moment expression for rock layers i-1 to i-s+2. Using the formula: Solve ; Using the formula: Calculate the deflection of the composite beam. .

7. The overburden separation discrimination method considering horizontal stress and mining-induced unloading effect as described in claim 1, characterized in that, Step S5 includes: S501: Utilize the formula: Calculate the maximum tensile stress σ of the rock strata or composite beam, where M0 is the bending moment at the end of the rock strata. If it is a composite beam, the value of the bottom rock strata is used for calculation. S502: The tensile strength [σ] of the rock strata is used as the failure criterion. If σ>[σ], the rock strata are considered to be damaged. When the bottom rock strata of the composite beam reaches the failure condition, the composite beam is considered to be damaged as a whole. When a certain rock stratum is damaged, it is considered that all rock strata below that rock stratum have been damaged, and no more delamination will develop below that rock stratum.

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