CN111720165A - A flexible roadway protection method for gob-side entry retention in large dip angle coal seams - Google Patents

Abstract

The invention discloses a gob-side entry retaining flexible entry retaining method for a large-dip-angle coal seam, which is characterized in that an advance groove with the length of 5-10 m and the width of 3-5 m is constructed at the lower end of a working face in the moving direction of the working face in a blasting excavation mode, a specially-made steel bar net is arranged in the advance groove through fixing an anchor rod on a top bottom plate to form a flexible structure, gangue falling down from a goaf is intercepted and wrapped to form a roadside support body taking the gangue as an aggregate, and the roadside support body and an in-lane anchor net cable jointly support the retaining surrounding rock to maintain the stability. The gob-side entry retaining flexible entry retaining method for the coal seam with the large inclination angle has the characteristics of small influence on the production of a working face, low entry retaining cost, simple process and high entry retaining speed.

Description

A flexible roadway protection method for gob-side entry retention in large dip angle coal seams

technical field

The invention belongs to the technical field of gobside entry retaining and roadside support, and in particular relates to a flexible roadway protection method for gob-side entry retaining in a coal seam with a large dip angle.

technical background

Gob-side entry retention is a technology for maintaining the original mining roadway along the edge of the gob after the working face is mined. The use of gob-side entry retaining technology can prevent mine disasters caused by coal pillar retention, and at the same time improve the coal recovery rate, reduce the roadway excavation rate, reduce the cost per ton of coal, and alleviate the contradiction between mining and replacement tension.

The mining conditions of coal resources in my country are complex, and the coal production of large dip angle (35°～55°) coal seams accounts for about 10% of the country's total coal production. In recent years, as the application of gob-side entry retention technology in near-horizontal and gently inclined coal seam mining continues to mature, some domestic mines have gradually applied gob-side entry retention technology to high-dip coal seam mining. At present, the domestic gob-side entry retaining and roadside support technologies usually include: gangue filling, concrete blocks, dense pillars, paste filling, high water filling and forced roof cutting. For example, the invention patent CN111173511A discloses a gob-side entry retaining roof cutting method. The technology uses a directional drilling machine to arrange a saw wire above the basic roof, and uses the wire saw machine to drive the saw wire to cut the direct roof and the basic roof. After the transparent roof and the basic roof, the gob-side entry retaining and roof cutting process is completed. However, this method is only effective for the hard roof of the near-horizontal or gently inclined coal seam, and it is not applicable when the roof and floor conditions are poor or the inclination of the coal seam is large. Invention patent CN108222938B discloses a combined grouting and filling mining method in goaf of high-dip angle coal seam. This technology installs gob-side entry retaining filling template in the return airway of high-dip angle coal seam working face, and implements grouting filling through grouting pipe. However, this technology has a high cost of retaining entry, and the construction process is more complicated, and the entry speed is slow, which seriously affects the normal mining of the working face. Invention patent CN103397905A discloses a system and method for natural caving and filling of coal seams, flexible roadway protection, and complete gob-side entry retention, and firstly proposes a gob-side entry-retention flexible roadway protection technology for large dip angle coal seams. The disadvantage is that this patent only provides a general concept of gob-side entry retaining and flexible road protection for high-dip coal seams, and there is still no practical construction technology, and this method can only be used under the conditions of medium-thick and thick coal seams with hard roofs.

A comprehensive analysis of the existing technology shows that the currently widely used gob-side entry retaining and roadside support methods are mostly suitable for near-horizontal or gently inclined coal seam mining, and the construction process is relatively complex. Improve processes and equipment. At the same time, the sliding impact force of the collapsed gangue in the goaf of the high-dip coal seam will greatly test the rigid roadside support technology, and the impact of the gangue will cause the rigid support body to become unstable or even cause disasters. Therefore, how to deal with the sloping gangue in the goaf has become the key to the success of the gob-side entry retention in the high-dip coal seam. According to the large dip angle coal seam stope and its special mine pressure distribution and surrounding rock migration law. In the process of roadway retention, it is required that the roadside support body can withstand the huge impact force generated by the rolling of gangue, and at the same time can provide sufficient support resistance for the key fracture blocks of the roof to limit their rotation and sinking.

SUMMARY OF THE INVENTION

Aiming at the technical difficulties of the existing gob-side entry retaining technology, such as complex technology, high road protection cost, and affecting the normal production of the working face, the present invention provides a gob-side entry retaining flexible entry retaining method in a coal seam with a large dip angle. The method works in the roadway. A certain size of advance trough is constructed in front of the front. In the advance trough, steel mesh is arranged through the fixed anchor rods on the roof and bottom plate to form a flexible structure, which intercepts the gangue that wraps the goaf and slumps, and forms the roadside support body with the caving gangue as the aggregate. The stability of the surrounding rock of the roadway retention is maintained by the joint action of the roadside support and the combined support of the anchor, mesh and cable in the roadway.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical solutions:

A flexible roadway protection method for gob-side entry retaining in a coal seam with a large inclination angle. Specifically, an advance groove with a length of 5 to 10 m and a width of 3 to 5 m is constructed along the direction of the working face by blasting at the lower end of the working face. A flexible structure is formed by arranging steel mesh through the fixed anchor rods on the top and bottom plates, intercepting and wrapping the gangue falling down in the goaf, forming a roadside support body with gangue as aggregate, and the roadside support body is combined with the anchor mesh cable in the roadway. The joint action of the support maintains the stability of the surrounding rock of the entry retaining. Figure 1 shows the process flow of the gob-retaining flexible roadway protection method, Figure 2 is a schematic diagram of the working face of the gob-side entry retaining flexible roadway protection, and Figure 3 is a schematic cross-sectional view of the gob A-A in Figure 2. The specific technical scheme is as follows:

A flexible roadway protection method for gob-side entry retention in a coal seam with a large dip angle, the method comprises the following steps:

1) Production of steel mesh for road protection

The reinforcement mesh for road protection includes main reinforcement and auxiliary reinforcement. The main bars are located around, and the auxiliary bars are located inside the main bars. The auxiliary bars include longitudinally distributed auxiliary bars and laterally distributed auxiliary bars. The intersections between the longitudinally distributed auxiliary bars and the laterally distributed auxiliary bars are connected by welding. An intersecting network structure is formed between the quasi-auxiliary bars; the longitudinally and laterally distributed auxiliary bars and the main bars are all connected by means of outstretching, bending and welding of the auxiliary bars. The four corners of the main rib extend out of the steel mesh, and the overhanging section is formed by bending and welding to form a fixed steel ring. The reinforcement meshes for different roadway protections are connected by stirrups. In this embodiment, the connection of adjacent roadway protection reinforcement meshes is hinged through stirrups with a diameter of 3.0 mm. The reinforcement mesh structure is shown in Figure 4. In order to prevent the main reinforcement and the auxiliary reinforcement from staggering each other, each reinforcement joint is welded and fixed, and the enlarged views of the welded area of the reinforcement mesh are shown in Figure 5(A), Figure 5(B), Figure 5(C) and Figure 5(D) Fig. 5(A) is an enlarged view at A in Fig. 4, Fig. 5(B) is an enlarged view at B in Fig. 4, Fig. 5(C) is an enlarged view at C in Fig. 4, and Fig. 5(D) is an enlarged view of D in FIG. 4 . The mesh size of the steel mesh is determined according to the size of the caving gangue block, usually 200mm×200mm. At the same time, in order to solve the problem that the gangue smaller than the mesh hole diameter passes through the steel mesh before the formation of the gangue wall bearing body, a layer of wire mesh with small diameter can be laid in the steel mesh.

According to the mining height and roof and floor conditions of different mine working faces, four different types of reinforcement meshes are selected. The structures of different types of reinforcement meshes are shown in Figure 6(A), Figure 6(B), Figure 6(C) and Figure 6( D), respectively:

For the working face where the mining height is less than 3.5m and the roof and floor are hard, the 1-shaped steel mesh is used. The roadway protection reinforcement mesh is a plane reinforcement mesh. (A).

For the working face with mining height > 3.5m and hard roof and bottom plate, wave-type steel mesh is used, and the roadway protection reinforcement mesh is wave-shaped. 6(B).

For the working face where the mining height is less than 3.5m and the roof and floor are weak and broken, L-shaped steel mesh is selected. The roadway protection steel mesh is L-shaped composed of vertical plane steel mesh and horizontal plane steel mesh. The outriggers of the four corners of the main reinforcement are vertical. Reinforced mesh on a vertical plane, as shown in Figure 6(C).

For the mining height > 3.5m, the roof and floor are weak and broken, L-wave type steel mesh is selected. The overhangs are perpendicular to the straight lines at both ends of the L-wave-shaped steel mesh, as shown in Figure 6(D).

2) Determine the diameter of the main reinforcement of the steel mesh

According to the structural characteristics of the reinforcement mesh, the tensile strength of a single reinforcement mesh is mainly controlled by the upper and lower main bars; the diameter of the main reinforcement of the reinforcement mesh is determined according to the following steps:

2.1) Calculate the impact velocity v ₃ of the caving gangue

As shown in Figure 7, the movement of the gangue after the collapse is divided into three stages, namely: the free fall stage, the sliding stage and the rolling stage. The gangue block finally acts on the roadside support body in the form of rolling impact;

(1) Free fall stage

The length h ₁ of the free fall stage after the collapse of the gangue is calculated as follows:

h ₁ =h _m /cosα;

Among them, α is the dip angle of the coal seam, and h _m is the thickness of the coal seam;

According to the dynamic principle, the velocity of an object in free fall at any height is:

where g is the acceleration of gravity;

After the gangue caving through the free fall stage, it comes into contact with the floor of the working face at a certain angle and collides with it; after the collision, the velocities along the normal and tangential directions of the floor of the working face change to varying degrees. The components in the direction are:

where e _n and e _τ are the restitution coefficients (dimensionless) of the velocity component after the gangue is in contact with the bottom plate, v _1n and v _1τ are the components of the velocity in the normal and tangential directions before the gangue collides, v _2n , v _2t are the components of the velocity in the normal and tangential directions after the gangue collides, respectively.

The gangue is constrained by the bottom plate, and the speed of the gangue in the normal direction of the bottom plate is zero. Therefore, after the gangue collides with the bottom plate, the initial velocity v _2τ when entering the sliding stage is:

v _2τ =e _τ v ₁ sin α

(2) Sliding stage

The inclination angle of the rock formation in the coal seam working face with a large dip angle is greater than the natural angle of repose of the gangue, and at the same time affected by the initial velocity of the gangue, the gangue moves in the form of accelerated sliding, and the final velocity v ₂ formula is:

In the formula, μ is the sliding friction factor between the gangue and the bottom plate; x ₁ is the sliding distance of the gangue;

(3) Rolling stage

Under the combined action of self-weight stress and frictional force, the movement mode of gangue changes from sliding to rolling. At this time, the gangue will have translational speed and rolling speed:

In the formula, m is the mass of the gangue block, x ₂ is the rolling distance of the gangue; v ₃ is the translational velocity of the gangue; w ₃ is the rolling speed of the gangue; f is the rolling friction between the gangue and the bottom plate; r is the radius of the gangue, J _z is the moment of inertia of the gangue;

Assuming that the gangue is in pure rolling motion, there are:

Therefore, the final velocity _v3 of the gangue in the rolling phase is calculated as follows:

2.2) Calculate the maximum impact force p _max of caving gangue

The impact of the rolling down gangue block on the gangue cushion is shown in Figure 8. When the gangue block hits the gangue cushion, the impact force p _c is calculated as follows:

where σ _z is the impact stress on the gangue cushion; s is the contact area between the rolling gangue and the gangue cushion;

Simplifying the rolling gangue into a cylinder, the impact force per unit length of the contact segment is:

In the formula, S _l is the arc length of the contact section between the rolling gangue and the gangue cushion, u is the maximum displacement of the contact section; r is the collapse radius;

After the rolling gangue is in contact with the gangue cushion, the strain ε ₀ at the contact point is:

ε ₀ =u ₀ /h _l

In the formula, u ₀ is the average displacement of the contact section; h _l is the thickness of the cushion;

From the geometric relationship, we can get:

u ₀ =ur(1-cos α)

In the formula, α is the central angle corresponding to the arc;

It can be approximated that the arc length is equal to the chord length, and the above formula can be changed to:

The comprehensively available impact force on the gangue cushion is:

In the formula, E ₀ is the instantaneous elastic modulus of the gangue cushion, and y is the compression amount of the gangue cushion impacted by the gangue;

According to the functional relationship, under the condition of ignoring the influence of gravity, the instantaneous velocity of rolling gangue hitting the gangue cushion satisfies the following formula:

The roadside support composed of steel mesh and gangue cushion can be regarded as a flexible gangue retaining structure, and there is no rebound phenomenon of rolling gangue. Therefore, v ₄ =0, the displacement value of rolling gangue is:

From this, the formula for calculating the average impact force of rolling gangue is:

The formula for calculating the maximum impact force is:

p _max =np _c

In the formula, n is the impact force amplification coefficient, and its value is related to the normal recovery coefficient e _n :

The coefficient of restitution e _n is related to the properties of the material itself, the harder the bottom plate, the stronger the resilience, and the greater the coefficient of restitution;

It can be seen from the above that the impact velocity and the maximum impact force at the moment of contact between the rolling gangue and the gangue cushion are:

2.3) Calculate the diameter φ of the main reinforcement of the steel mesh

When the rolling gangue hits the gangue cushion, multiple steel meshes are jointly stressed, and the strength of the two main bars below and below the single steel mesh should meet the following formula:

In the formula, [σ] is the material strength; φ is the diameter of the main reinforcement, and n is the number of reinforcement meshes that can be loaded at the same time;

The strength of the material is determined by the model of the main bar, from which the diameter of the main bar of the steel mesh can be determined:

3) Excavate advance groove and support

As shown in Fig. 9, during the mining process of the working face, an advanced groove with a length of 5 to 10 m is constructed at the lower end of the working face along the direction of the working face by means of blasting, and the width of the advanced groove is 3 to 5 m. The pillars and hinged top beams are used to support the exposed roof of the advanced trough, and the row spacing between the single pillars is 1.0m × 0.75m; the upper coal wall side of the advanced trough is protected by a row of single pillars and bamboo fences, and the row spacing of the single pillars is 1.0m; the section of the lead slot is shown in Figure 10.

4) Reinforcement mesh laying

After the support of the advance groove is completed, first clean up the broken roof and floor floating coal floating gangue in the advance groove, at the same time mark the installation position of the fixed anchor rods of the roof and bottom plates according to the size of the reinforcement mesh, and install the fixed anchor rods of the top and bottom plates according to the construction sequence of the anchor rods; then Lay the steel mesh, and use the anchor rod fastening device to connect the four-angle steel ring of the steel mesh with the anchor rod; finally, set up a row of single dense pillars in the machine lane near the steel mesh side, with a spacing of 1.0m; after the above steps are completed, The reinforcement mesh is successfully laid, and the structure after the reinforcement mesh is laid is shown in Figure 11. The laying of steel mesh, the installation of fixed anchors on the roof and floor, the retraction of the single pillars in the advance groove and the installation of the single dense pillars in the roadway are all carried out simultaneously with the advancement of the working face.

5) The working face is mined and the gangue is released to form a flexible road protection structure

The steel mesh and the gangue cushion are combined to form a flexible road protection structure, and a large amount of gangue in the goaf will easily lead to the failure of the steel mesh when a large amount of gangue hits the steel mesh. That is, a small amount of gangue with a small diameter is first placed, and a gangue cushion of 0.3 to 1.0 m is formed in the steel mesh, so that the flexible road protection structure composed of the steel mesh and the gangue cushion can effectively alleviate the impact of large diameter gangue; then The hydraulic support moves forward, and the rest of the gangue is lowered.

6) Dense pillars in the retraction machine lane

The single dense pillars in the gob-side entry retention can only be withdrawn after the deformation of the surrounding rock of the roadway is stable (that is, the stress deformation of the steel mesh tends to be stable). It depends on the situation, generally not less than 60m. After the dense pillars in the roadway are withdrawn, if the deformation of the surrounding rock of the roadway is within the controllable range, it means that the roadway retention is successful. The structure of the roadway retention is shown in Figure 12.

Compared with the prior art, the present invention has the following technical effects:

1. Compared with the entry retention techniques such as gangue filling, concrete block, paste filling and high-water filling, a kind of flexible roadway protection method for gob-side entry retention in a high-dip coal seam provided by the present invention has the advantages of less influence on the production of working face, and less retention. The lane cost is low, the process is simple, and the lane retention speed is fast.

2. The flexible road protection structure formed by steel mesh, fixed anchor rods and dense pillars on the side of the gob-side entry retaining gob can effectively control the deformation of the surrounding rock of the roadway; The roadside support body with the caving gangue as aggregate can prevent the sliding impact force generated by the gangue sliding in the goaf from causing casualties and equipment damage in the roadway or working face, and at the same time, it can achieve fast and effective support for the gob-side entry retention in the coal seam with large dip angle. .

3. The flexible roadway protection technology of gob-side entry retaining in large dip angle coal seams can improve the coal recovery rate, reduce the roadway excavation rate, reduce the cost per ton of coal, and relieve the tension of mining replacement.

Description of drawings

Fig. 1 is the flow chart of the flexible support method of gob-side entry retaining;

Fig. 2 is the schematic diagram of the working face of gob-side entry retaining flexible road protection;

Fig. 3 is the cross-sectional schematic diagram of gob A-A in Fig. 2;

Fig. 4 is the structural representation of combined L-shaped steel mesh;

Fig. 5 (A) is the enlarged view of A place in Fig. 4;

Figure 5 (B) is an enlarged view at B in Figure 4;

Fig. 5 (C) is the enlarged view at C place in Fig. 4;

Figure 5 (D) is an enlarged view at D in Figure 4;

Fig. 6 (A) is the structural representation of 1-shaped steel mesh;

Fig. 6 (B) is the structural representation of wave-shaped steel mesh;

Fig. 6 (C) is the structural representation of L-shaped steel mesh;

Figure 6 (D) is a schematic structural diagram of an L-wave-shaped steel mesh;

Fig. 7 is the gangue movement state diagram of gob in Fig. 2;

Figure 8 is a schematic diagram of the force of the gangue cushion;

Fig. 9 is the operation plan view of gob-side entry retaining flexible road protection;

Figure 10 is a schematic cross-sectional view of the lead groove in the direction B-B in Figure 9;

Figure 11 is a schematic cross-sectional view in the direction C-C of the gob-side entry retaining support section in Figure 9;

FIG. 12 is a schematic cross-sectional view in the direction of D-D of the lag section of gob-side entry retention in FIG. 9 .

In the figure: 1. Steel mesh; 11. Main reinforcement; 111. Main transverse reinforcement; 112. Main longitudinal reinforcement; 12. Secondary reinforcement; 121. Horizontal reinforcement; 122. Longitudinal reinforcement; 13. Fixed steel ring; 14. Stirrup; Roof fixed anchor; 16. Bottom fixed anchor; 2. Advance slot; 21. Single pillar; 22. Dense pillar; 23. Hinged roof beam; 24. Bamboo fence; 3. Falling gangue block; 31. Pressed Solid gangue body; 32, gangue cushion; 4, working face; 41, machine road; 42, wind road; 43, hydraulic support; 44, compaction area; 45, transition area; 46, free fall accumulation area; 47 , goaf; 48, roof rock formation; 49, floor rock formation.

Detailed ways

The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

A flexible roadway protection method for gob-side entry retention in a coal seam with a large dip angle, the method comprises the following steps:

1) Production of steel mesh for road protection

The test site was selected as the 3153 working face 4 of a mine in Sichuan Province. The coal mining method of the working face is the comprehensive mechanized coal mining method of the long-wall with the pseudo-oblique strike, and the pseudo-inclined angle is 35°. In the test section, working face 4 has a buried depth of 552-582 m, working face 4 inclination length is 110 m, strike length is 900 m, average mining height is 2.6 m, and the average inclination angle of coal seam is 46°. The top rock layer 48 and the bottom rock layer 49 of the working face 4 are both carbonaceous mudstone with soft lithology. Therefore, according to the selection principle of reinforcement mesh 1 for roadway protection, L-shaped reinforcement mesh is selected. The length parameters a×b×c of reinforcement mesh 1 are: 1m×2.6m×0.8m, and the structure of reinforcement mesh 1 is shown in Figure 4.

2) Calculate the diameter of the main reinforcement of the steel mesh

The material of steel mesh 1 is ordinary carbon steel, the tensile strength is 450MPa, and the thickness of the gangue cushion layer 32 is taken as the minimum value of 0.3m, which can be obtained from the calculation formula of the diameter of the main reinforcement 11 of the reinforcement mesh 1. When the diameter of the main reinforcement 11 of the reinforcement mesh 1 is greater than or equal to 9.53mm When the strength of the steel mesh 1 meets the requirements. In fact, with the mining of the working face 4, a large number of gangue blocks 3 collapse and accumulate inside the steel mesh 1, and the thickness of the formed gangue cushion layer 31 is much greater than 0.3 m. Therefore, selecting the steel mesh 1 with the diameter Φ of the main reinforcement 11 of 10 mm can meet the requirements of road protection on site. At the same time, considering the specifications of ordinary carbon steel bars, the diameter of the main bar 11 of the steel mesh 1 is finally determined to be 10mm, the diameter of the secondary bar 12 is determined to be 8mm, and the mesh size is 200mm×200mm.

3) Excavate advance groove and support

During the mining process of the 3153 working face 4, a forward groove 2 with a length of 8m and a width of 3m was constructed at the lower end of the working face along the direction of the working face 4 by means of blasting. During the construction process of the advance slot 2, the single pillar 21 and the hinged roof beam 23 are used to support the exposed roof, and the row spacing between the single pillars is 1.2m×0.75m. A row of single pillars and bamboo fences are used for wall protection on the upper coal wall side of the advance trough, with a row spacing of 1.2m, as shown in Figure 9.

4) Laying of steel mesh

After the excavation and support of advance slot 2 is completed, first clean the broken top and bottom floating coal gangue in advance slot 2, and mark the installation positions of the top plate fixing anchor rod 15 and the plate fixing anchor rod bottom 16 according to the size of the reinforcement mesh 1. The construction sequence (drilling → installing resin anchoring agent → stirring anchoring agent → tightening the anchor rod), install the top plate fixing anchor rod 15 and the bottom plate fixing anchor rod 16; then lay the reinforcement mesh 1, and use the anchor rod fastening device to fasten the reinforcement mesh The fixed steel ring 13 is connected with the anchor rod; finally, a row of single dense pillars 22 is erected in the machine lane 41 near the side of the steel mesh 1 . After the above steps are completed, the reinforcement mesh 1 is successfully laid.

5) The working face is mined and the gangue is released to form a flexible road protection structure

Use the gangue blocking device behind the hydraulic support 43 to lower the gangue 3 in the goaf 47 step by step. First, a small amount of gangue 3 with a small diameter is lowered, and a 0.5m thick gangue cushion 32 is formed in the steel mesh 1 to make the steel mesh 1 and the gangue cushion 32 to form a flexible road protection structure; then the hydraulic support moves forward, and the rest of the gangue is lowered.

6) Dense pillars in the retraction machine lane

The force and deformation of the steel mesh 1 lagging behind the working face 4 by 25 m gradually tend to be stable, so the distance of the retreating lagging working face of the single dense pillar 22 in the roadway is determined to be 30 m. Regular monitoring of the reinforcement mesh 1 shows that the maximum deformation rate of the reinforcement mesh 1 occurs in the early stage of the reinforcement mesh 1, and the reinforcement mesh 1 is deformed in a "C" shape. The upper and lower deformations are relatively small, 200mm and 180mm, respectively. Reinforced mesh 1 is filled with gangue densely, which provides sufficient support for the roof. In addition, the dense monolithic struts effectively limit the deformation of the steel mesh.

It can be seen from the above analysis that the on-site implementation of gob-side entry retaining in 3153 working face 4 by the flexible roadway protection method is very effective.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be Modifications or equivalent substitutions without departing from the spirit and scope of the technical solutions of the present invention should be included in the scope of the claims of the present invention.

Claims (3)

1. a large dip angle coal seam gob-side entry retaining flexible roadway protection method, is characterized in that, the method comprises the steps: 1) Production of steel mesh for road protection The reinforcement mesh for road protection includes main reinforcement and auxiliary reinforcement; the main reinforcement is located around, and the auxiliary reinforcement is located inside the main reinforcement. The auxiliary reinforcement includes longitudinally distributed auxiliary reinforcement and laterally distributed auxiliary reinforcement. The longitudinally distributed auxiliary reinforcement and lateral distribution The intersections between the auxiliary ribs are connected by welding, and an intersecting network structure is formed between the two types of auxiliary ribs. Connecting; the four corners of the main rib extend out of the steel mesh, and the overhanging section is formed by bending and welding to form a fixed steel ring; the reinforcement meshes of different road protection are connected by stirrups; 2) Determine the diameter of the main reinforcement of the steel mesh According to the structural characteristics of the reinforcement mesh, the tensile strength of a single reinforcement mesh is mainly controlled by the upper and lower main bars; the diameter of the main reinforcement of the reinforcement mesh is determined according to the following steps: 2.1) Calculate the impact velocity v ₃ of the caving gangue The movement of gangue after collapse is divided into three stages: free fall stage, sliding stage and rolling stage. The gangue block finally acts on the roadside support body in the form of rolling impact; (1) Free fall stage The length h ₁ of the free fall stage after the collapse of the gangue is calculated as follows: h ₁ =h _m /cosα; Among them, α is the dip angle of the coal seam, and h _m is the thickness of the coal seam; According to the dynamic principle, the velocity of an object in free fall at any height is:

where g is the acceleration of gravity; After the gangue caving goes through the free fall stage, it comes into contact with the floor of the working face at a certain angle and collides with it; after the collision, the velocities along the normal and tangential directions of the floor of the working face change to varying degrees. The components in the tangential direction are:

In the formula, e _n and e _τ are the restitution coefficients of the velocity components after the gangue is in contact with the bottom plate, v _1n and v _1τ are the components of the velocity in the normal and tangential directions before the gangue collides, and v _2n and v _2t are respectively It is the component of its velocity in the normal and tangential directions after the gangue collides. The gangue is constrained by the bottom plate, and the speed of the gangue in the normal direction of the bottom plate is zero. Therefore, after the gangue collides with the bottom plate, the initial velocity v _2τ when entering the sliding stage is: v _2τ =e _τ v ₁ sinα (2) Sliding stage The inclination angle of the rock formation in the coal seam working face with a large dip angle is greater than the natural angle of repose of the gangue, and at the same time affected by the initial velocity of the gangue, the gangue moves in the form of accelerated sliding, and the final velocity v ₂ formula is:

In the formula, μ is the sliding friction factor between the gangue and the bottom plate; x ₁ is the sliding distance of the gangue; (3) Rolling stage Under the combined action of self-weight stress and frictional force, the movement mode of gangue changes from sliding to rolling. At this time, the gangue will have translational speed and rolling speed:

In the formula, m is the mass of the gangue block, x ₂ is the rolling distance of the gangue; v ₃ is the translational velocity of the gangue; w ₃ is the rolling speed of the gangue; f is the rolling friction between the gangue and the bottom plate; r is the radius of the gangue, J _z is the moment of inertia of the gangue; Assuming that the gangue is in pure rolling motion, there are:

Therefore, the final velocity _v3 of the gangue in the rolling phase is calculated as follows:

2.2) Calculate the maximum impact force p _max of caving gangue When the gangue block hits the gangue cushion, the impact force p _c is calculated as follows:

where σ _z is the impact stress on the gangue cushion; s is the contact area between the rolling gangue and the gangue cushion; Simplifying the rolling gangue into a cylinder, the impact force per unit length of the contact segment is:

In the formula, s _l is the arc length of the contact section between the rolling gangue and the gangue cushion, u is the maximum displacement of the contact section; r is the radius of collapse; After the rolling gangue is in contact with the gangue cushion, the strain ε ₀ at the contact point is: ε ₀ =u ₀ /h _l In the formula, u ₀ is the average displacement of the contact section; h ₁ is the thickness of the cushion; From the geometric relationship, we can get: u ₀ =ur(1-cosα) In the formula, α is the central angle corresponding to the arc; It can be approximated that the arc length is equal to the chord length, and the above formula can be changed to:

The comprehensively available impact force on the gangue cushion is:

In the formula, E ₀ is the instantaneous elastic modulus of the gangue cushion, and y is the compression amount of the gangue cushion impacted by the gangue; According to the functional relationship, under the condition of ignoring the influence of gravity, the instantaneous velocity of rolling gangue hitting the gangue cushion satisfies the following formula:

The roadside support composed of steel mesh and gangue cushion can be regarded as a flexible gangue retaining structure, and there is no rebound phenomenon of rolling gangue. Therefore, v ₄ =0, the displacement value of rolling gangue is:

From this, the formula for calculating the average impact force of rolling gangue is:

The formula for calculating the maximum impact force is: p _max =np _c In the formula, n is the impact force amplification coefficient, and its value is related to the normal recovery coefficient e _n :

The coefficient of restitution e _n is related to the properties of the material itself, the harder the bottom plate, the stronger the resilience, and the greater the coefficient of restitution; It can be seen from the above that the impact velocity and the maximum impact force at the moment of contact between the rolling gangue and the gangue cushion are:

2.3) Calculate the diameter φ of the main reinforcement of the steel mesh When the rolling gangue hits the gangue cushion, multiple steel meshes are jointly stressed, and the strength of the two main bars below and below the single steel mesh should meet the following formula:

In the formula, [σ] is the material strength; φ is the diameter of the main reinforcement, and n is the number of reinforcement meshes that can be loaded at the same time; The strength of the material is determined by the model of the main bar, from which the diameter of the main bar of the steel mesh can be determined:

3) Excavate advance groove and support During the mining process of the working face, a 5-10m long and 3-5m wide advance trough is constructed at the lower end of the working face along the direction of the working face by means of blasting. The roof is exposed for support, and the row spacing between the single pillars is 1.0m × 0.75m; a row of single pillars and bamboo fences or wooden boards are used to protect the wall on the upper coal wall side of the advance trough, and the spacing between the single pillars is 1.0m; 4) Reinforcement mesh laying After the support of the advance groove is completed, first clean up the broken roof and floor floating coal floating gangue in the advance groove, at the same time mark the installation position of the fixed anchor rods of the roof and bottom plates according to the size of the reinforcement mesh, and install the fixed anchor rods of the top and bottom plates according to the construction sequence of the anchor rods; then Lay a special steel mesh, and use the anchor bolt fastening device to connect and fix the four-angle steel ring of the steel mesh with the anchor rod; finally, a row of single dense pillars is erected in the machine lane near the steel mesh to effectively limit the initial stage of the steel mesh. Large deformation; after the above process is completed, the reinforcement mesh is successfully laid; 5) The working face is mined and the gangue is released to form a flexible road protection structure The steel mesh and the gangue cushion are combined to form a flexible road protection structure, and a large amount of gangue in the goaf will easily lead to the failure of the steel mesh when a large amount of gangue hits the steel mesh. That is to say, a small amount of gangue with a small diameter is first put down, and a gangue cushion of 0.3 to 1.0 m is formed in the steel mesh, so that the flexible road protection structure composed of the steel mesh and the gangue cushion can effectively alleviate the impact of large diameter gangue; then The hydraulic support is moved forward, and the remaining gangue is lowered, and finally, the roadside support body with the compacted gangue body as the main bearing structure is formed; 6) Dense pillars in the retraction machine lane The single dense pillars in the gob-side entry retention can only be withdrawn after the surrounding rock deformation of the roadway is stable. The retreat lag distance of the single dense pillars should be determined according to the gob-side entry retention at the site, generally not less than 60m. If the deformation of the surrounding rock of the roadway is within the controllable range after the retraction of the dense pillars, it means that the roadway retention is successful. 2. a kind of high dip angle coal seam gob-side entry retaining flexible roadway protection method according to claim 1, is characterized in that, according to the mining height and roof and floor conditions of different mine working faces, select four different types of steel mesh, respectively for: For the working face where the mining height is less than 3.5m and the roof and floor are hard, the 1-shaped steel mesh is used. For the working face with mining height > 3.5m and hard roof and floor, use wave-type steel mesh, the roadway protection reinforcement mesh is a wave-type reinforcement mesh, and the outriggers of the four corners of the main reinforcement are perpendicular to the straight lines at both ends of the roadway protection reinforcement mesh; For the working face where the mining height is less than 3.5m and the roof and floor are weak and broken, L-shaped steel mesh is used. Reinforcement mesh in vertical plane; For the mining height > 3.5m, the roof and floor are weak and broken, L-wave type steel mesh is selected. The overhangs are perpendicular to the straight edges at both ends of the L-wave-shaped steel mesh. 3. A kind of flexible roadway protection method for gob-side entry retaining in a large dip angle coal seam according to claim 1, characterized in that, the excavation and support of the advance groove, the arrangement of the fixed anchor rods of the roof and the floor, the laying of the steel mesh, the advance The retraction of the single pillars in the tank and the installation and retraction of the single dense pillars in the machine lane are carried out in a synchronous cycle with the advancement of the working face.

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