Construction method for cutting off key layer based on directional blasting

Abstract

The invention discloses a construction method for cutting off a key layer based on directional blasting, which specifically comprises the following steps of: firstly, sampling rock strata and analyzing lithology to obtain physical and mechanical parameters of each rock strata, then determining the position of the key layer in the rock strata, and then establishing a rock strata movement deformation diagram; based on the position of a key layer in the rock stratum and the rock stratum movement deformation graph, the position of the key layer after rock stratum movement deformation is determined, directional blasting is carried out, the overlying rock stratum settles under the influence of blasting to form a compacted separation layer, whether the settlement value reaches the standard or not is verified, finally, filling and reinforcing are carried out on the rock stratum and a goaf, and road or railway construction is carried out after filling and reinforcing are completed. According to the method, rock stratum settlement and separation layer compaction are completed, unstable factors are eliminated, the settled rock stratum forms a whole and is not influenced by movement of other rock stratums, the stability of the rock stratum below a highway or a railway is improved, the grouting workload is greatly reduced, the construction period is greatly shortened, and the construction efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of municipal roads, and in particular to a construction method based on directional blasting to cut off a key layer, which is suitable for the rapid construction of highways and railways. Background Art

[0002] Rock subsidence refers to the phenomenon that the rock layers in the earth's crust sink due to various natural or human factors. It is a common geological engineering problem, especially in mines after underground mining, which is often accompanied by rock movement and surface subsidence. The main reason is that after the minerals are mined, the original mechanical equilibrium state of the rock mass around the mining area is destroyed, causing the rock layers to move, deform and be destroyed. The rock layers that were originally tightly fitted are separated by gravity, which will aggravate the rock subsidence. When the rock layers subside again, it will not only cause ground deformation and cracking, but in severe cases it may also affect the stability and safety of the road, and even cause geological disasters;

[0003] Taking highway construction as an example, the traditional method of dealing with rock subsidence after underground mining is to calculate the boundary angle or movement angle of the surface movement based on the coal pillars left in buildings, water bodies, railways and main shafts. Specifically, the boundary angle is the angle between the boundary point (10mm sinking point) on the main section of the moving basin and the boundary of the goaf and the horizontal line on one side of the coal pillar under full or near full mining conditions; the movement angle is the outermost critical deformation of the surface on the main section of the moving basin under full or near full mining conditions (horizontal deformation ε = +2mm / m, inclination i = ±3mm / m, curvature K = +0.2×10 -3 / m) and the goaf boundary point and the horizontal line on one side of the coal wall; in actual construction, the boundary angle is calculated for special structures such as super-large bridges on expressways and airport runways, and the moving angle is calculated for other structures such as expressways and highways below level one, and integral grouting or pile foundation reinforcement is carried out within the boundary angle or moving angle;

[0004] Although traditional construction methods can solve the problem to a certain extent, the number of grouting stations and the volume of slurry required for grouting reinforcement during the construction process are large, which results in high costs and long construction periods, and cannot meet the requirements of rapid construction. In addition, when underground mining causes large-scale rock formation settlement, there are many unstable factors in the rock formation. The traditional construction method mainly involves grouting reinforcement of detached layers and goaf areas. This type of grouting reinforcement cannot compact detached layers and goaf areas, causing some rock formations to remain in an unstable state. The surface continues to slowly sink, damaging highway or railway facilities, and posing a threat to road traffic safety in severe cases. Summary of the invention

[0005] The purpose of the present invention is to provide a construction method based on directional blasting to cut off the key layer, which not only completes the settlement of rock strata, delamination compaction, and eliminates unstable factors, so that the settled rock strata form a whole and are not affected by the movement of other rock strata, thereby improving the stability of the rock strata under the highway or railway, but also greatly reduces the grouting workload, greatly shortens the construction period, and improves construction efficiency.

[0006] To achieve the above purpose, the present invention provides a construction method for cutting off the key layer based on directional blasting, which specifically includes the following steps:

[0007] S1, sampling and lithology analysis of rock layers to obtain the physical and mechanical parameters of each rock layer;

[0008] S2, determining the position of the key layer in the rock formation according to the physical and mechanical parameters of the rock formation in step S1;

[0009] S3, predicting the movement and deformation of the rock formation after mining, and establishing a rock formation movement and deformation map;

[0010] S4, based on the position of the key layer in the rock formation in step S2 and the rock formation movement deformation diagram in step S3, determine the position of the key layer after the rock formation movement and deformation and perform directional blasting, the overlying rock formation settles under the influence of blasting to form a compacted delamination, and verify whether the settlement value meets the standard;

[0011] S5, fill and reinforce the rock layer and mined-out area, and then carry out road or railway construction after completion.

[0012] In some examples of the present invention, in step S2, the rock layers are defined from bottom to top as layers 1 to n based on the goaf where the coal seam is located, and the rock layers are subjected to a uniformly distributed load q, and the load q(n) formed by the influence of the nth layer on the ith layer (1≤i≤n) is calculated. i , and its calculation formula is:

[0013]

[0014] Among them, E i 、E i+1 …E n is the elastic modulus of each rock layer from the i-th layer upwards, in Pa;

[0015] h i 、h i+1 …h n is the thickness of each rock layer from the i-th layer upwards, in meters;

[0016] r i 、r i+1 …r n is the bulk density of each rock layer starting from the i-th layer, in N / m 3 ;

[0017] Determine the position of the key layer, based on the load q(n) formed by the influence of the nth layer on the ith layer i The calculation formula is used to compare the loads of the upper and lower adjacent rock layers. When the load q(n) of the i-th layer is i Greater than the load q(n) of the i+1th layer i+1 When , the i-th layer is determined to be the key layer.

[0018] In some examples of the present invention, in step S3, multiple prediction points are set at each rock layer after mining, and the deformation at the prediction point is obtained by calculating the vertical displacement and horizontal displacement at the prediction point;

[0019] Multiple prediction points in the same layer are fitted to predict the movement and deformation of the i-th rock layer, thereby establishing a rock layer movement and deformation map.

[0020] In some examples of the present invention, the vertical displacement S(x, z i ) is calculated as:

[0021]

[0022] The horizontal displacement U(x,z i ) is calculated as:

[0023]

[0024] Among them, m is the mining thickness of the coal seam, a i is the ground subsidence coefficient of the i-th layer, R i is the main influence radius of the i-th layer;

[0025] L is the advancing distance of the coal seam, d1 is the offset of the turning point on the left side of the goaf, and d2 is the offset of the turning point on the right side of the goaf;

[0026] x' is the horizontal coordinate of the prediction point in the local coordinate system, z i is the ordinate of the predicted point in the i-th layer in the global coordinate system.

[0027] In some examples of the present invention, in step S4,

[0028] When C s When <C1, it means that the settlement has not reached the standard;

[0029] When C s When ≥C1, it means that the settlement meets the standard;

[0030] Among them, C s To measure the height of ground subsidence;

[0031] C1 is the theoretical value of settlement height, and the calculation formula is:

[0032] C1=0.83K Z

[0033] Among them, K Z =K0+K1+K2+…+K m

[0034] K0 is the thickness of goaf 4, K1, K2, ..., K m is the thickness of each delamination layer.

[0035] In some examples of the present invention, in step S5, a grouting station is used to fill and reinforce the rock formation and the goaf;

[0036] The number of grouting stations is the integer of W / 50, where W is the width of the road / railway and its protection zone.

[0037] In some examples of the present invention, in step S5, the calculation formula of the grouting amount V of the grouting station is:

[0038] V=P2(D3-d)·WN

[0039] Among them, P2 is the porosity of the rock in the goaf after the directional blasting settlement of the rock layer;

[0040] D3 is the thickness of goaf 4;

[0041] d is the settlement thickness of goaf 4;

[0042] W is the width of the road / railway and its protection zone;

[0043] N is the length of the road / railway.

[0044] In some examples of the present invention, in step S5, a plurality of grouting stations are arranged at a distance of 25 m from the center of the highway / railway, and the plurality of grouting stations are arranged at intervals of 50 m along the length direction of the highway / railway.

[0045] Compared with the prior art, the construction method based on directional blasting to cut off the key layer obtains the physical and mechanical parameters of each rock layer under the actual construction environment through rock layer sampling and lithology analysis, determines the position of the key layer in the rock layer, calculates the movement and deformation of the rock layer, accurately locates the separation area, and performs directional blasting on the position of the key layer after the rock layer moves and deforms, cuts off the connection between the key layers, thereby completing the rock layer settlement and separation compaction, eliminating unstable factors, making the rock layer after settlement form a whole, not affected by the movement of other rock layers, and improving the stability of the rock layer under the highway or railway;

[0046] When performing backfill reinforcement, compared with the traditional overall grouting reinforcement within the boundary angle or moving angle, this method of reinforcement only needs to be carried out in the rock layer and the broken and expanded rock layer area in the goaf below it, which greatly reduces the grouting workload and significantly shortens the construction period; at the same time, since the surface forms a basin as the rock layer settles, the earth excavation workload is reduced, which greatly improves the construction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the present invention without underground mining;

[0048] Figure 2 It is a schematic diagram of the formation of separation layer and goaf area after underground mining in the present invention;

[0049] Figure 3 It is a schematic diagram of blasting points when directional blasting is performed in the present invention;

[0050] Figure 4 It is a schematic diagram of rock formation settlement after directional blasting according to the present invention;

[0051] Figure 5 This is a schematic diagram of grouting in the delamination layer and goaf area of ​​a traditional highway / railway at the boundary angle (movement angle);

[0052] Figure 6 It is the principle diagram for estimating vertical displacement of predicted points in rock formation;

[0053] In the figure: 1. Coal seam; 2. Separation layer; 3. Highway / railway; 4. Goaf; 5. Blasting point. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solution and advantages of the technical solution of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described in conjunction with the drawings of specific embodiments of the present invention. The same figure marks in the drawings represent the same parts. It should be noted that the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] Unless otherwise defined, the technical terms or scientific terms used herein shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar words used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one" or "one" do not necessarily indicate a quantity limitation. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0056] like Figures 1 to 4 As shown, the present invention is a construction method based on directional blasting to cut off the key layer, which specifically includes the following steps:

[0057] S1, sampling and lithology analysis of rock layers to obtain the physical and mechanical parameters of each rock layer;

[0058] Specifically, a drilling rig is used to perform drilling and sampling on the upper surface of the goaf 4, and after sampling, the rock samples are stored in a sample box in order, and the rock samples are subjected to lithology analysis in a laboratory, and a lithology column chart is further drawn;

[0059] According to the lithology analysis, the parameters of each rock layer are obtained, including the elastic modulus, thickness and bulk density of the rock layer;

[0060] As explained, in the laboratory, standard cylindrical specimens can be specified for typical rock samples in accordance with the "Methods for Determination of Physical and Mechanical Properties of Coal and Rock", and the specimens can be tested for uniaxial compressive strength, tensile strength and shear strength, and a rock formation parameter comparison table can be compiled, and a lithology columnar diagram can be drawn;

[0061] S2, determining the position of the key layer in the rock formation according to the physical and mechanical parameters of the rock formation in step S1;

[0062] Specifically, based on the physical and mechanical parameters of the rock formation in step S1, the load borne by the key layer is determined. In addition to its own gravity load, the key layer also bears the load transmitted by the upper rock formation;

[0063] According to the drawn lithology columnar diagram, the corresponding rock layers are defined from bottom to top based on the goaf 4 where the coal seam 1 is located, that is, set from 1 to n layers, and the rock layers are subjected to a uniformly distributed load of q. The load q(n) formed by the influence of the nth layer on the ith layer (1≤i≤n) is calculated.i , and its calculation formula is:

[0064]

[0065] Among them, E i 、E i+1 …E n is the elastic modulus of each rock layer from the i-th layer upwards, in Pa, h i 、h i+1 …h n is the thickness of each rock layer from the i-th layer upwards, in m; r i 、r i+1 …r n is the bulk density of each rock layer starting from the i-th layer, in N / m 3 ;

[0066] Determine the position of the key layer, based on the load q(n) formed by the influence of the nth layer on the ith layer i The calculation formula is to compare the loads of the upper and lower adjacent rock layers. When the load q(n) of the i-th layer is i Greater than the load q(n) of the i+1th layer i+1 When q(n) i >q(n) i+1 , then the i-th layer is determined to be the key layer;

[0067] Determine the location of the key layer to provide a basis for determining the blasting location information;

[0068] S3, predicting the movement and deformation of the rock formation after mining, and establishing a rock formation movement and deformation map;

[0069] Specifically, a prediction point is set at each rock layer, and the underground subsidence and horizontal movement of each rock layer are calculated, that is, the vertical displacement and horizontal displacement at the prediction point are obtained by integrating the left and right inflection points of the i-th rock layer;

[0070] Based on the mechanical model integrated geometric method, a rock movement calculation model based on influence function is introduced to facilitate calculation, such as Figure 6 As shown, the origin of the OX coordinate system is defined at the left edge of the working surface, and the horizontal coordinate of the predicted point in the global coordinate system is x, the horizontal coordinate of the predicted point in the local coordinate system is x', and the vertical coordinate of the predicted point in the i-th layer in the global coordinate system is z i ;

[0071] The calculation formula of the vertical displacement influence function of the prediction point of the i-th rock layer is:

[0072]

[0073] The calculation formula of the horizontal displacement influence function of the prediction point of the i-th rock layer is:

[0074]

[0075] S max (z i ) is the maximum displacement of the predicted point at the i-th layer that may settle, and the calculation formula is:

[0076] S max (z i )=m·a i ,i=1,2,···,n

[0077] Among them, R i is the main influence radius of the i-th layer;

[0078] m is the mining thickness of coal seam 1, a i is the ground subsidence coefficient of the i-th layer;

[0079] By integrating the horizontal coordinate x' of the prediction point in the local coordinate system, the calculation formulas for the vertical and horizontal displacements of the prediction point can be obtained;

[0080] When the horizontal coordinate of the predicted point in the global coordinate system is x, the horizontal coordinate of the predicted point in the local coordinate system is x', and the vertical coordinate of the predicted point in the i-th layer in the global coordinate system is z i When the integral is performed in the interval of the left turning point offset d1 and the right turning point offset d2 of the goaf, the integral domain is L s =[d1-x,L-d2-x], where L is the advancement distance of coal seam 1;

[0081] Therefore, the vertical displacement S(x,z i ) is calculated as:

[0082]

[0083] The horizontal displacement U(x,z i ) is calculated as:

[0084]

[0085] As shown in the figure, the integral value of the influence function of the predicted horizontal displacement in the integral region, after the introduction of the local coordinate system, since the horizontal displacement of the rock formation has a directionality relative to the mining unit, a negative sign should be added in front of the horizontal displacement influence function, which indicates that the direction of the horizontal displacement is the negative direction of the x-axis, that is, moving from the right side of the working face to the left side of the working face, and the horizontal displacement U(x,z i )for Figure 6 The shaded area;

[0086] After obtaining the vertical displacement and horizontal displacement at the prediction point, the deformation at the prediction point is further obtained. Multiple prediction points can be set for the same layer of rock, and the displacement calculation of the prediction points is performed to obtain the corresponding deformation. Multiple prediction points in the same layer can be fitted to predict the movement deformation of the i-th layer of rock, and establish a rock movement deformation map; based on the rock movement deformation map, the position of the rock separation layer 2 is analyzed and determined, the movement law of the rock layer is deduced, and the separation layer 2 information is visualized, so as to provide positioning for the directional blasting settlement rock layer, and provide a basis for the blasting parameter design and verification of the settlement effect;

[0087] S4, based on the position of the key layer in the rock formation in step S2 and the rock formation movement deformation diagram in step S3, determine the position of the key layer after the rock formation movement and deformation and perform directional blasting, the overlying rock formation settles under the influence of blasting to form a compacted separation layer 2, and verify whether the settlement value meets the standard;

[0088] Specifically, holes are drilled in the rock layer below the boundary of the highway / railway 3 protection zone and explosives are preset, that is, according to the position of the key layer in the rock layer and the predicted rock layer movement and deformation, the position of the key layer after the rock layer movement and deformation is determined, holes are drilled at the boundary of the highway / railway 3 protection zone to the final key layer position, and explosives are buried in the key layer to form blasting points 5, and the key layer above the separation layer 2 in the rock layer below the boundary line of the protection zone is directionally blasted to cut off the continuity of the key layer;

[0089] After directional blasting, cracks of predetermined direction and range will be formed inside the rock layer, which can be precisely controlled and moved in the expected direction, effectively destroying the unstable factors in the original rock layer structure, eliminating separation 2, accelerating the rock layer settlement progress, saving construction time, and the rock layer after settlement forms a more compact and stable whole, which is not affected by the movement of other rock layers, significantly improving the geological stability of the mining area;

[0090] The overlying rock strata settle due to the blasting, i.e. the ground surface settles as the rock strata move and compacts the strata 2;

[0091] Based on the information of separation layer 2 in the rock movement deformation map, the thickness of the goaf 4 and the separation layer 2 above it is counted, and the sum of all the thicknesses of separation layer 2 and goaf 4 is K Z for

[0092] K Z =K0+K1+K2+…+K m

[0093] Among them, K0 is the thickness of goaf 4, K1, K2, ..., K m is the thickness of each separation layer 2;

[0094] When directional blasting is carried out, there is a crushing and swelling effect in the rock layer. The theoretical value of the surface settlement height after blasting is C1=0.83KZ , measure the surface subsidence height C s , when the measured surface settlement height is less than the theoretical value of settlement height, that is, C s <C1, it means that the settlement has not reached the standard, and repeat this step, perform drilling and directional blasting again, until C s When ≥C1, it means that the settlement meets the standard and proceed to the next step;

[0095] S5, filling and reinforcing the rock layer and the goaf 4, and then constructing the road or railway after completion;

[0096] Specifically, the filling and reinforcement mainly relies on a grouting station. For example, a grouting station is set up 25m away from the center of the highway / railway 3. There are multiple grouting stations, which are set up every 50m along the length of the highway / railway 3. Concrete is used to reinforce the rock layer after blasting, and the crushed and expanded rock in the goaf 4 is filled and reinforced. This method can improve the overall stability of the rock layer and prevent further settlement of the rock layer and the occurrence of delamination.

[0097] The rock layer will settle in a directional manner due to the blasting, and a foundation pit will be formed on the surface where Highway / Railway 3 is located, which will reduce the amount of foundation pit excavation work. After the excavation is completed, the construction will be carried out in an orderly manner according to the construction specifications of Highway / Railway 3;

[0098] In order to solve the problem that the rock strata move and delamination 2 occur during the mining process, resulting in the instability of the rock strata and affecting the construction effect, this invention provides a construction method based on directional blasting to cut off the key layer. Through rock strata sampling and lithology analysis, the mechanical parameters of the materials of each rock stratum under the actual construction environment are obtained to determine the position of the key layer in the rock stratum; the amount of rock stratum movement and deformation is calculated, the delamination 2 area is accurately located, and directional blasting is carried out on the position of the key layer after the rock stratum moves and deforms, so as to cut off the connection between the key layers, thereby realizing the settlement of the rock strata, compacting the delamination 2, eliminating unstable factors, and making the settled rock strata form a whole, which is not affected by the movement of other rock strata, thereby improving the stability of the rock strata under the highway or railway; in addition, when performing filling reinforcement, reinforcement only needs to be carried out in the rock stratum and the rock stratum area of ​​the goaf 4 below it, which greatly reduces the workload of grouting and greatly shortens the construction period; at the same time, since the surface forms a basin as the rock stratum settles, the workload of earth excavation is reduced, so that the construction efficiency is greatly improved.

[0099] In some examples of the present invention, in step S5, the number of grouting stations is an integer of W / 50, where W is the width of the road / railway 3 and its protection zone;

[0100] Specifically, the number of grouting stations in this example is related to the width of the highway / railway 3 and its protection zone;

[0101] However, the number of grouting stations in some grouting reinforcement methods is not only related to the road / railway3 and the width of its protection zone, but also to the boundary angle or movement angle, and the depth of the goaf4;

[0102] Correspondingly, in terms of the amount of grouting, the theoretical calculation formula for the amount of grouting in this construction method is:

[0103] V=P2(D3-d)·WN

[0104] Among them, P2 is the porosity of the crushed and expanded rock in goaf 4 after directional blasting of the settled rock layer;

[0105] D3 is the thickness of goaf 4;

[0106] d is the settlement thickness of the goaf 4, W is the width of the road / railway 3 and its protection zone, and N is the length of the road / railway 3;

[0107] The calculation of the amount of grouting in the traditional construction method is also related to the thickness and depth of each separation layer 2, the boundary angle or movement angle, and the porosity of the rock in the goaf 4 before the directional blasting settlement rock layer.

[0108] like Figure 5 As shown, the grouting reinforcement area of ​​this construction method is the rock layer formed as a whole after blasting and settlement and the broken and expanded rock in the goaf 4 below it. Compared with the traditional overall grouting reinforcement within the boundary angle or moving angle, this construction method can not only ensure the stability and safety of the rock layer structure, but also reduce the amount of grouting, shorten the construction period and reduce the construction cost.

[0109] An exemplary implementation of a construction method based on directional blasting to cut off a key layer proposed in the present invention is described in detail above with reference to a preferred embodiment. However, those skilled in the art will appreciate that, without departing from the concept of the present invention, various modifications and variations can be made to the above-mentioned specific embodiments, and various technical features and structures proposed in the present invention can be combined in various ways without exceeding the protection scope of the present invention, which is determined by the attached claims.

Claims

1. A construction method for cutting off key layers based on directional blasting, characterized in that: The specific steps include: S1, sampling and lithology analysis of rock layers to obtain the physical and mechanical parameters of each rock layer; S2, determining the position of the key layer in the rock formation according to the physical and mechanical parameters of the rock formation in step S1; S3, predicting the movement and deformation of the rock formation after mining, and establishing a rock formation movement and deformation map; S4, based on the position of the key layer in the rock formation in step S2 and the rock formation movement deformation diagram in step S3, determine the position of the key layer after the rock formation movement and deformation and perform directional blasting, the overlying rock formation settles under the influence of blasting to form a compacted delamination, and verify whether the settlement value meets the standard; S5, fill and reinforce the rock layer and mined-out area, and then carry out road or railway construction after completion.

2. A construction method based on directional blasting to cut off key layers according to claim 1, characterized in that: In step S2, the rock layers are defined from 1 to n layers from bottom to top based on the goaf where the coal seam is located. The rock layers are subjected to a uniformly distributed load q, and the load q(n) formed by the influence of the nth layer on the ith layer (1≤i≤n) is calculated. i , and its calculation formula is: Among them, E i 、E i+1 …E n is the elastic modulus of each rock layer from the i-th layer upwards, in Pa; h i 、h i+1 …h n is the thickness of each rock layer from the i-th layer upwards, in meters; r i 、r i+1 …r n is the bulk density of each rock layer starting from the i-th layer, in N / m 3 ; Determine the position of the key layer, based on the load q(n) formed by the influence of the nth layer on the ith layer i The calculation formula is used to compare the loads of the upper and lower adjacent rock layers. When the load q(n) of the i-th layer is i Greater than the load q(n) of the i+1th layer i+1 When , the i-th layer is determined to be the key layer.

3. A construction method based on directional blasting to cut off key layers according to claim 1, characterized in that: In step S3, multiple prediction points are set at each rock layer after mining, and the deformation at the prediction point is obtained by calculating the vertical displacement and horizontal displacement at the prediction point; Multiple prediction points in the same layer are fitted to predict the movement and deformation of the i-th rock layer, thereby establishing a rock layer movement and deformation map.

4. A construction method based on directional blasting to cut off key layers according to claim 3, characterized in that: The vertical displacement S(x,z i ) is calculated as: The horizontal displacement U(x,z i ) is calculated as: Where m is the mining thickness of the coal seam (1), a i is the ground subsidence coefficient of the i-th layer, R i is the main influence radius of the i-th layer; L is the advancement distance of the coal seam (1), d1 is the offset of the turning point on the left side of the goaf, and d2 is the offset of the turning point on the right side of the goaf; x' is the horizontal coordinate of the prediction point in the local coordinate system, z i is the ordinate of the predicted point in the i-th layer in the global coordinate system.

5. The construction method based on directional blasting to cut off the key layer according to claim 1 is characterized in that: In step S4, When C s When <C1, it means that the settlement has not reached the standard; When C s When ≥C1, it means that the settlement meets the standard; Among them, C s To measure the height of ground subsidence; C1 is the theoretical value of settlement height, and the calculation formula is: C1=0.83K Z Among them, K Z =K0+K1+K2+...+K m K0 is the thickness of goaf 4, K1, K2, ..., K m is the thickness of each delamination layer.

6. A construction method based on directional blasting to cut off key layers according to any one of claims 1 to 5, characterized in that: In step S5, a grouting station is used to fill and reinforce the rock layer and the goaf; The number of grouting stations is the integer of W / 50, where W is the width of the road / railway and its protection zone.

7. A construction method based on directional blasting to cut off key layers according to claim 6, characterized in that: In step S5, the calculation formula of the grouting amount V of the grouting station is: V=P2(D3-d)·WN Among them, P2 is the porosity of the rock in the goaf after the directional blasting settlement of the rock layer; D3 is the thickness of goaf 4; d is the settlement thickness of goaf 4; W is the width of the road / railway and its protection zone; N is the length of the road / railway.

8. The construction method based on directional blasting to cut off the key layer according to claim 6 is characterized in that: In step S5, a plurality of grouting stations are arranged at a distance of 25 m from the center of the highway / railway, and the plurality of grouting stations are arranged at intervals of 50 m along the length direction of the highway / railway.

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