Method for calculating roof cutting height of thick and hard roof of coal mine roadside filling gob-side entry retaining

Abstract

The invention discloses a method for calculating the roof cutting height of a thick and hard roof of coal mine roadside filling gob-side entry retaining. The method comprises the steps that gob-side entry retaining engineering geological condition parameters are obtained; based on the geological condition parameters of the gob-side entry retaining engineering, establishing a presplitting basic roof fracture discrimination equation; and based on the presplitting basic roof fracture discriminant equation, the height of the cut roof is obtained. According to the method, the presplitting basic roof fracture judgment is established based on the roof structure relation to solve the roof cutting height, the obtained roof cutting height is more scientific and reasonable, and the problem that the roof cannot be cut off in time or the production cost is increased due to the fact that the height is insufficient or the roof cutting height is too large due to the roof cutting design reason can be solved.

Description

Technical Field

[0001] The invention belongs to the field of coal mining, and in particular relates to a method for calculating the top cutting height of a thick hard roof slab in a gob-side filling lane retaining in a coal mine. Background Art

[0002] The hard roof of a coal mine refers to the roof that exists directly above the coal seam or above the thin direct roof. It has the characteristics of high hardness, good integrity, and large layer thickness. About one-third of coal mines in my country are troubled by hard roof during mining. After the mining of the working face is completed, the hard roof often appears to be suspended. The large area of ​​suspended roof will cause stress and energy concentration, resulting in strong dynamic pressure phenomena such as impact ground pressure, coal and gas outburst, or large deformation of the tunnel in the mining space. At the same time, it also provides space for gas accumulation, resulting in excessive gas in the end area of ​​the working face, affecting the normal advancement and safety of the working face. For the goaf-retained tunnel, the long overhang of the hard roof in the goaf area will also increase the pressure of the tunnel support and the surrounding rock of the tunnel, which will cause great trouble to the maintenance and safety of the tunnel. In order to allow the thick hard roof to collapse in time and ensure the safety of the working face mining, the advanced pre-splitting roof method is often used on site to control the collapse of the roof, such as hydraulic fracturing and blasting pre-splitting technology.

[0003] When using pre-splitting to solve the problem of hard roof, the top cutting height is a very important parameter. There are two main design ideas at present. One is the design method that considers the crushing and swelling characteristics of the roof rock layer and the mining height, and the other is the design method that considers the residual shear strength of the pre-splitting rock layer. The former method fills the goaf by cutting off a certain thickness of the roof, thereby achieving effective support for the roof. This method is feasible in theory, but because the rock mass has a small crushing and swelling property, and the crushing and swelling property of the collapsed rock mass will be further reduced during the compaction process, the calculated top cutting height may not be reasonable. If the crushing and swelling property is estimated too large, the calculated top cutting height is too low, and the hanging roof problem still exists; if the crushing and swelling property is estimated too low, the calculated top cutting height is too high, and the construction cost and construction time will be greatly increased. The latter method starts from the shear strength of the roof and calculates a reasonable top cutting height based on the relationship between the shear strength of the rock layer and the force. However, the tensile strength of the rock mass is much smaller than the shear strength, and the maximum tensile stress on the roof is generally more than 4 times the shear stress. Therefore, before the shear failure occurs, the rock mass will first undergo tensile failure. If the design is based on shear strength, the top cutting height will be too high, which will increase the construction cost and prolong the construction time. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a method for calculating the cutting height of the thick hard roof of the coal mine side filling and goaf retaining lane, which can avoid the problem of insufficient height (or too large cutting height) due to the cutting design, thereby causing the roof to fail to be cut off in time (or increase production costs).

[0005] To achieve the above object, the present invention provides a method for calculating the top cutting height of thick hard roof slab in gob-side filling lane retaining in coal mines, comprising:

[0006] Obtain the engineering geological condition parameters of gob-side entry retention;

[0007] Based on the engineering geological condition parameters of gob-side entry retention, a pre-splitting basic top fracture discrimination equation is established;

[0008] Based on the pre-splitting basic top fracture discriminant equation, the height of the top cutting is obtained.

[0009] Optionally, the engineering geological condition parameters of the goaf-side tunnel retaining include: basic top thickness, horizontal distance from the borehole to the tunnel wall, lateral cantilever length of the basic top, distance from the tunnel roof to the bottom of the basic top, angle between the pre-crack hole and the horizontal direction, additional load caused by overlying rock stress and self-weight load, and uniaxial tensile strength of the basic top rock layer.

[0010] Optionally, the pre-splitting basic top fracture discrimination equation is:

[0011]

[0012] Among them, W z is the bending section coefficient of the beam, M is the bending moment of the basic top residual section beam, σ t It is the uniaxial tensile strength of pre-cracked rock formation.

[0013] Optionally, the bending section coefficient of the beam is:

[0014]

[0015] The bending moment of the cross-section beam at the end position of the pre-cracked basic top is:

[0016]

[0017] Among them, L 2 L is the horizontal distance between the end of the top crack and the side of the tunnel, 1 h is the horizontal distance between the borehole and the tunnel wall, i h is the distance between the tunnel roof and the basic top and bottom, n is the thickness of the un-pre-cracked basic top, L 0 is the basic top lateral cantilever length, and q is the additional load caused by the overlying rock stress and deadweight load.

[0018] Optionally, based on the pre-splitting basic top fracture discrimination equation, before obtaining the top cutting height, the method further includes:

[0019] Based on the pre-splitting basic top fracture discriminant equation, the thickness of the non-pre-splitting section is obtained;

[0020] The height of the top cut is obtained by combining the thickness of the non-pre-splitting section.

[0021] Optionally, the thickness of the non-pre-splitting section is:

[0022]

[0023] Among them, α is the angle between the pre-crack hole and the horizontal direction.

[0024] Optionally, the height of the top cut is:

[0025] L b =h m +h i -h n

[0026] Among them, L b is the cutting height, h m It is the basic top thickness.

[0027] Optionally, the top cutting method includes: concentrated energy blasting and hydraulic fracturing.

[0028] Compared with the prior art, the present invention has the following advantages and technical effects:

[0029] The present invention establishes a pre-crack basic top fracture judgment based on the roof structure relationship to solve the top cutting height. The obtained top cutting height is more scientific and reasonable, which can avoid the problem of insufficient height (or too large top cutting height) caused by top cutting design, thereby causing the top plate to be unable to be cut off in time (or increasing production costs). BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0031] Figure 1 It is a flow chart of a method for calculating the top cutting height of a thick hard roof slab in a gob-side lane retaining for lane filling in a coal mine according to an embodiment of the present invention;

[0032] Figure 2 Schematic diagram of top cutting drilling of gob-side entry retaining according to an embodiment of the present invention;

[0033] Figure 3 It is a schematic plan view of the arrangement of the top cutting drilling holes according to an embodiment of the present invention;

[0034] Figure 4 This is a schematic diagram of the top cutting implementation effect of an embodiment of the present invention;

[0035] Figure 5 It is a stress model diagram of the roof structure of the gob-side tunnel retaining according to an embodiment of the present invention. DETAILED DESCRIPTION

[0036] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0037] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0038] The present invention proposes a method for calculating the top cutting height of thick hard roof slab in gob-side filling lane retaining in coal mines. Figure 1 As shown, the specific steps include:

[0039] Obtain the engineering geological condition parameters of gob-side entry retention;

[0040] Based on the parameters of engineering geological conditions of gob-side entry retention, the pre-splitting basic top fracture discrimination equation is established;

[0041] Based on the pre-splitting basic top fracture discriminant equation, the height of the top cut is obtained.

[0042] Furthermore, the parameters of engineering geological conditions for retaining tunnels along the goaf include: basic roof thickness, horizontal distance from the borehole to the tunnel wall, lateral cantilever length of the basic roof, distance from the tunnel roof to the bottom of the basic roof, angle between the pre-crack hole and the horizontal direction, additional load caused by overlying rock stress and deadweight load, and uniaxial tensile strength of the basic roof rock layer.

[0043] Specifically, obtain the horizontal distance between the borehole and the tunnel wall, the lateral cantilever length of the basic top, the distance between the tunnel roof and the bottom of the basic top, the angle between the pre-cracked hole and the horizontal direction, the additional load caused by the stress of the overlying rock formation and the deadweight load, and the uniaxial tensile strength of the pre-cracked rock formation.

[0044] Further, according to the above data, the pre-crack basic top fracture discrimination equation is established and the top cutting height is solved. Based on the fact that the un-pre-cracked part of the top plate still has a certain thickness and strength, the thick hard top plate needs to overcome the strength of this part of the rock mass under the action of its own weight and the load of the overlying rock layer before it can collapse. The left side of the model is the location of the basic top fracture line, and the upper boundary is subjected to the uniform load of the overlying rock layer. The fracture condition of the pre-cracked rock layer is:

[0045]

[0046] Among them, W z is the bending section coefficient of the beam, M is the bending moment of the section beam at the end position of the pre-cracked basic top, σ t It is the uniaxial tensile strength of pre-cracked rock formation.

[0047] Furthermore, the bending section coefficient of the beam is:

[0048]

[0049] The bending moment of the section beam at the end position of the pre-cracked basic top is:

[0050]

[0051] Among them, L 2 L is the horizontal distance between the end of the top crack and the side of the tunnel, 1 h is the horizontal distance between the borehole and the tunnel wall, i h is the distance between the tunnel roof and the basic top and bottom, n is the thickness of the un-pre-cracked basic top, L 0 is the basic top lateral cantilever length, and q is the additional load caused by the overlying rock stress and deadweight load.

[0052] Furthermore, based on the pre-splitting basic top fracture discrimination equation, before obtaining the top cutting height, the following steps are also included:

[0053] Based on the pre-splitting basic top fracture discriminant equation, the thickness of the non-pre-splitting section is obtained;

[0054] Combined with the thickness of the non-pre-splitting section, the height of the top cut is obtained.

[0055] Furthermore, the thickness of the non-pre-splitting section is:

[0056]

[0057] Among them, α is the angle between the pre-crack hole and the horizontal direction.

[0058] Furthermore, the height of the top cut is:

[0059] L b =h m +h i -h n

[0060] Among them, L b is the cutting height, h m It is the basic top thickness.

[0061] Specifically, the horizontal distance L between the borehole and the tunnel wall 1 The value is generally not more than 0.1 to 0.4 m;

[0062] L 0 is the basic top lateral cantilever length, determined based on the mine pressure observation data;

[0063] h i It is the distance between the tunnel roof and the bottom of the basic roof, generally the thickness of the immediate roof;

[0064] α is the angle between the pre-crack hole and the horizontal direction, generally 75°~85°;

[0065] q is the additional load caused by the overlying rock stress and self-weight load, calculated according to the key layer theory.

[0066] Specifically, according to the thickness formula of the non-pre-splitting section, two thickness values ​​of the non-pre-splitting section can be obtained, and then two top cutting heights can be obtained. It is necessary to select a reasonable top cutting height according to the actual thickness of the top rock layer of the working face. n The formula results in two h n value, which will result in two top cutting heights. If the calculated top cutting heights are both less than h i +h m , select the minimum value of the top cutting height; if the calculated top cutting height is greater than h i +h m A smaller than h i +h m , choose less than h i +h m The top cutting height; if the calculated top cutting height is greater than h i +h m , select hi+h for top cutting height m .

[0067] In this embodiment, the arrangement of gob-side entry retention is as follows: Figure 2 and Figure 3 As shown. After the previous working face is mined, the side filling body is constructed along the edge of the goaf to preserve the roadway for use by this working face. In order to reduce the roof pressure and maintenance difficulty of the goaf-retained roadway, pre-splitting drill holes are arranged along the edge of the previous working face during the mining process of the previous working face. The pre-splitting drill holes are along the extension direction of the roadway. After the drilling construction, hydraulic fracturing or blasting techniques can be used to weaken the roof. Under the action of the roof's own weight and the load of the overlying rock formation, the roof collapses along the edge of the side filling body, and the effect is as shown. Figure 4 After pre-splitting and cutting, the stress model of the roof structure of the gob-side entry is as follows: Figure 5 As shown in the figure, it is a cantilever beam structure with one end fixed. Under the action of load, tensile failure occurs, causing the top plate to crack along the weakened crack. Figure 4 As shown in the figure, after pre-splitting and top cutting, the vertical stress on the tunnel side and the filling body beside the tunnel is greatly reduced compared with that before top cutting, which is beneficial to tunnel maintenance.

[0068] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for calculating the cutting height of thick hard roof in gob-side filling in coal mines. It is characterized in that include: Obtain the engineering geological condition parameters of gob-side entry retention; Based on the engineering geological condition parameters of gob-side entry retention, a pre-splitting basic top fracture discrimination equation is established; Based on the pre-splitting basic top fracture discriminant equation, the height of the top cutting is obtained.

2. A method for calculating the top cutting height of thick hard roof slab in gob-side filling in coal mines according to claim 1, It is characterized in that The engineering geological condition parameters of the goaf-side tunnel retaining project include: basic roof thickness, horizontal distance between the borehole and the tunnel wall, lateral cantilever length of the basic roof, distance between the tunnel roof and the bottom of the basic roof, angle between the pre-crack hole and the horizontal direction, additional load caused by overlying rock stress and deadweight load, and uniaxial tensile strength of the basic roof rock layer.

3. A method for calculating the top cutting height of thick hard roof slabs in gob-side lane retaining for side filling in coal mines according to claim 2, It is characterized in that The pre-splitting basic top fracture discrimination equation is: Among them, W z is the bending section coefficient of the beam, M is the bending moment of the basic top residual section beam, σ t It is the uniaxial tensile strength of pre-cracked rock formation.

4. A method for calculating the top cutting height of thick hard roof slab in gob-side lane retaining for side filling in coal mines according to claim 3, It is characterized in that The bending section coefficient of the beam is: The bending moment of the cross-section beam at the end position of the pre-cracked basic top is: Among them, L 2 L is the horizontal distance between the end of the top crack and the side of the tunnel, 1 h is the horizontal distance between the borehole and the tunnel wall, i h is the distance between the tunnel roof and the basic top and bottom, n is the thickness of the un-pre-cracked basic top, L 0 is the basic top lateral cantilever length, and q is the additional load caused by the overlying rock stress and deadweight load.

5. A method for calculating the top cutting height of thick hard roof slab in gob-side lane retaining for side filling in coal mines according to claim 4, It is characterized in that Based on the pre-splitting basic top fracture discrimination equation, before obtaining the top cutting height, the following steps are also included: Based on the pre-splitting basic top fracture discriminant equation, the thickness of the non-pre-splitting section is obtained; The height of the top cut is obtained by combining the thickness of the non-pre-splitting section.

6. A method for calculating the top cutting height of thick hard roof slab in gob-side lane retaining for side filling in coal mines according to claim 5, It is characterized in that The thickness of the non-pre-splitting section is: Among them, α is the angle between the pre-crack hole and the horizontal direction.

7. A method for calculating the top cutting height of thick hard roof slabs in gob-side filling in coal mines according to claim 6, It is characterized in that The height of the cut top is: L b h m +h i -h n Among them, L b is the cutting height, h m It is the basic top thickness.

8. A method for calculating the top cutting height of thick hard roof slab in gob-side lane retaining for lane filling in coal mines according to claim 1, It is characterized in that The methods of cutting the top include: concentrated energy blasting and hydraulic fracturing.

Images