Method and device for calculating influence of roof elastic performance on instability and failure of coal rock assembly

Abstract

The present application relates to the roof elastic performance influence calculation method and device of coal rock combination body instability damage, belongs to the coal mine safety technical field. The method first, through the borehole column chart obtains the roof and coal seam thickness ratio as the coal rock height ratio in the coal rock combination body;Obtain the coal seam gas pressure and take the core on the spot, process the sample pretreatment. Secondly, respectively to the coal rock combination body and pure coal test piece carries out the mechanics test to obtain the rock mass, coal body and coal rock combination body elastic modulus, according to the stress strain data collected in the test process, obtains the stress strain curve of rock mass, coal body, coal rock combination body in the coal rock combination body and pure coal test piece stress strain curve. Finally, the stress strain curve area is calculated to deduce the influence degree of roof elastic performance on combination body instability damage. The present application comprehensively considers the influence factor of roof elastic performance in coal rock gas dynamic disaster, provides the beneficial reference for the accurate prevention and control of mine coal rock gas dynamic disaster.

Description

Technical Field

[0001] This invention belongs to the field of coal mine safety technology and relates to a method and apparatus for calculating the impact of roof elasticity on the instability and damage of coal-rock composites. Background Technology

[0002] As coal mining in my country gradually extends to deeper levels, it faces complex environmental challenges such as high gas pressure, high gas content, high ground stress, and low permeability, making rock bursts and coal and gas outbursts particularly severe. Compared with traditional coal and rock dynamic disasters, the mechanisms of deep coal, rock, and gas combined dynamic disasters are more complex. Therefore, understanding the mechanisms of outburst-rock burst combined dynamic disasters is fundamental to their scientific prevention and control, and is one of the urgent problems to be solved to achieve safe and efficient mining in deep mines.

[0003] The instability and failure of coal-rock assemblages exhibit characteristics distinctly different from those of single coal or single rock formations. Their failure modes more closely resemble actual engineering conditions in coal mines. Since the strength and stiffness of rock mass are generally greater than those of coal, when coal fails, the rock mass remains in an elastic state, and the released elastic energy accelerates the coal's failure. Therefore, studying the evolution of the roof elastic energy's influence on the degree of failure in coal-rock assemblages and clarifying the specific role of roof elastic energy in disaster processes is crucial. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method and apparatus for calculating the impact of roof elasticity on the instability and failure of coal-rock composites, so as to clarify the influencing factors of roof elasticity in coal-rock gas dynamic disasters and provide a useful reference for the accurate prevention and control of coal-rock gas dynamic disasters in mines.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for calculating the impact of roof elasticity on the instability and failure of coal-rock composites, comprising the following steps: S1: Obtain the thickness of the top plate respectively h R With coal seam thickness h C , will the h R and h C The ratio of the height of the rock mass to the height of the coal mass in the coal-rock composite is used as the ratio of the rock mass height to the coal mass height. u ; S2: In gas-bearing coal seams, gas pressure is obtained using a gas pressure gauge. p Core samples were taken on-site and pre-treated to obtain standard specimens of coal-rock composites and pure coal specimens. S3: Under gas pressure p, the standard specimen of the coal-rock composite and the pure coal specimen obtained in S2 are subjected to mechanical tests using a mechanical device to obtain the elastic modulus of the roof. Elastic modulus of coal seam under gas pressure p and the elastic modulus of coal-rock composite ; S4: Based on the stress data collected during the entire test process of the standard sample mechanical test of the coal-rock composite and the strain data collected by the strain gauges attached to the outer surface of the entire coal-rock composite, the second stress-strain curve of the coal-rock composite is plotted. Then, the first and third stress-strain curves of the rock mass and the coal mass are obtained by the upper and lower axial extensometers, respectively. The fourth stress-strain curve is obtained based on the stress-strain data collected from the mechanical test of the pure coal specimen. S5: Plot the first, second, and third stress-strain curves in S4 in the same coordinate system, and plot the fourth stress-strain curve in another coordinate system. Calculate the residual elastic energy at the residual strength point after the coal body in the pure coal specimen and coal-rock composite reaches its peak value. S6: Based on the energy converted into residual elastic energy of the coal from the energy exerted by the rock mass on the coal in the coal-rock assembly, and the total energy exerted by the rock mass on the coal in the coal-rock assembly, calculate the energy dissipation ratio of the energy exerted by the rock mass on the coal in the coal-rock assembly. ; S7: Based on the total energy of the rock mass's interaction with the coal mass, the energy dissipated by the coal-rock assemblies from peak strength to post-peak residual strength, and the energy dissipation ratio of the rock mass's interaction with the coal mass within the coal-rock assemblies. Calculate the influence of the roof elastic energy on the instability and failure of the coal-rock composite. .

[0006] Furthermore, in step S2, the sample undergoes pretreatment, specifically as follows: One sample was processed into a pure coal specimen with a diameter of 50 mm and a height of 100 mm, and the other was processed into a coal-rock composite specimen with coal on the upper side and rock on the lower side. The composite specimen was processed into pure coal and pure rock specimens according to the coal-rock thickness ratio, and the surface of the specimens was polished. The processing accuracy of the specimens met the test specifications recommended by the International Society for Rock Mechanics. The coal-rock interface was bonded with strong adhesive.

[0007] Furthermore, in S4, the top plate thickness in the first, second, third, and fourth stress-strain curves... Coal seam thickness Elastic modulus of top plate Coal seam elastic modulus and the elastic modulus of coal-rock composite Satisfying equation (1): (1) Where u>0, v>0 and K>0, u is the height ratio of rock mass to coal mass in the coal-rock composite, v is the elastic modulus ratio of rock mass to coal mass in the coal-rock composite, and K is the correction coefficient.

[0008] Furthermore, in S5, the first, second, and third stress-strain curves from S4 are plotted in the same coordinate system, and the fourth stress-strain curve is plotted in another coordinate system. The residual elastic energy at the residual strength point after the coal body in the pure coal specimen and coal-rock assemblage reaches its peak value is calculated, specifically as follows: In the fourth stress-strain curve of the pure coal specimen, starting from the residual strength g point after the peak of the pure coal specimen, a straight line parallel to the elastic modulus of the pure coal is drawn, intersecting the horizontal axis at point o. The corresponding strain is... Points n and p are the projection points of the peak strength and residual strength of the specimen on the abscissa, respectively, and the corresponding strains are respectively , The area enclosed by points g, o, and p represents the residual elastic energy at the residual strength point after the pure coal specimen reaches its peak strength. Therefore, the residual elastic energy at the residual strength point after the pure coal specimen reaches its peak strength is expressed as: (2) in, , (3) in, The residual stress after the peak in the pure coal specimen. This represents residual strain; Substituting equation (3) into equation (2), the residual elastic energy after the peak of the standard pure coal specimen is obtained as follows: (4) Similarly, the residual elastic energy at the residual strength point after the coal body reaches its peak strength in the coal-rock composite is obtained, expressed as: (5) in, denoted as the residual stress of a standard specimen of a coal-rock composite, and u is the height ratio of the rock mass to the coal mass in the coal-rock composite.

[0009] Furthermore, in S6 Satisfying formula (6): (6) in, This refers to the energy that the rock mass exerts on the coal mass within the coal-rock composite, which is then converted into the residual elastic energy of the coal mass. This represents the total energy exerted by the rock mass on the coal mass within the coal-rock composite. Formula (4) represents the residual elastic energy after the peak of a standard pure coal specimen. Formula (4) is then converted into the residual elastic energy after the peak of the coal body in a coal-rock composite, expressed as: (7) In a coal-rock composite specimen, the energy exerted by the rock mass on the coal mass is converted into the residual elastic energy of the coal mass, which is expressed as: (8) The total energy exerted by the rock mass on the coal body in a coal-rock composite is expressed as: (9) in, , , (10) in, , These represent the peak strain and residual strain of the rock mass portion within the coal-rock composite, respectively. The peak stress of the coal-rock composite is... Residual stress in the coal-rock composite; Substituting formula (10) into formula (9) yields: (11) Substituting formulas (1), (8), and (11) into formula (6), we get... , is represented as: (12) in, The peak stress of the coal-rock composite is... This refers to the residual stress after the peak of the coal-rock composite. denoted as the residual stress after peak in the pure coal specimen; u represents the height ratio of the rock mass to the coal mass in the coal-rock assemblage, and v represents the elastic modulus ratio of the rock mass to the coal mass in the coal-rock assemblage.

[0010] Furthermore, in S7 Represented as: (13) in, This represents the total energy exerted by the rock mass on the coal seam. This represents the energy dissipated by the coal-rock composite from peak strength to post-peak residual strength. (14) in, Let S be the volume of the coal-rock composite, S be the area corresponding to the second stress-strain curve of the coal-rock composite, point b be the peak strength point of the coal-rock composite, point e be the residual strength point, and points m and f be the points exceeding the peak strength and residual strength, respectively. With the elastic modulus of the coal-rock composite as the slope, draw the intersection of the oblique line and the horizontal axis.

[0011] A mechanical testing device includes an upper pressure head 13, a base 14, an upper fixing ring 3, a lower fixing ring 5, a middle fixing ring 4, an upper axial extension measuring component 6, a lower axial extension measuring component 7, an upper radial extensometer 8, a lower radial extensometer 9, and a copper rod 10. The upper fixing ring 3 is installed in the middle of the upper pressure head 13, the lower fixing ring 5 is installed in the middle of the base 14, and the middle fixing ring 4 is installed in the middle of the test piece. The upper fixing ring 3, the lower fixing ring 5, and the middle fixing ring 4 are parallel to each other. The upper axial extension measuring component 6 is installed at one end of the upper fixed ring 3, and the lower axial extension measuring component 7 is installed at one end of the lower fixed ring 5 and is opposite to the end of the upper axial extension measuring component 6. The copper rods 10 are respectively installed at one side edge of the upper fixed ring 3 and the middle fixed ring 4 and at one side edge of the lower fixed ring 5 and the middle fixed ring 4. One end of the copper rod 10 installed at one side edge of the upper fixed ring 3 and the middle fixed ring 4 is connected to the upper axial extension measuring component 6 and the other end is connected to the middle fixed ring 4. One end of the copper rod 10 installed at one side edge of the lower fixed ring 5 and the middle fixed ring 4 is connected to the lower axial extension measuring component 7 and the other end is connected to the middle fixed ring 4. The upper radial extensometer 8 is installed above the middle fixing ring 4 and is located in the middle of the upper test piece; the lower radial extensometer 9 is installed below the middle fixing ring 4 and is located in the middle of the lower test piece. Strain gauges 15 are attached to the outer surface of the test piece and the strain gauges 15 are connected to the strain gauge via signal cables. The upper axial extension measurement component 6 and the lower axial extension measurement component 7 each include a data collection receiver 11 and a wireless communication module 12. The data collection receiver 11 collects the measured data and then transmits it to an external receiving terminal through the wireless communication module 12.

[0012] The beneficial effects of this invention are as follows: First, this invention comprehensively considers the influencing factors of roof elasticity in coal and rock gas dynamic disasters, providing a useful reference for the accurate prevention and control of coal and rock gas dynamic disasters in mines.

[0013] Secondly, the device for obtaining mechanical parameters of specimens provided by this invention has a simple structure, high stability, and can accurately obtain stress and strain data of coal and rock in coal-rock composite specimens, with good application effect.

[0014] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0015] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 A flowchart illustrating the calculation method for the influence of the elastic energy of the roof in a coal and rock mass on the instability and failure of the composite structure; Figure 2 Schematic diagrams of standard coal-rock composite specimens and pure coal specimens; Figure 2 (a) is a schematic diagram of a standard coal-rock composite specimen; Figure 2 (b) is a schematic diagram of a pure coal specimen; Figure 3 This is a schematic diagram of a mechanical testing apparatus; Figure 4 The axial stress-strain curves of rock, coal, and coal-rock assemblages are shown. Figure 5 This is the axial stress-strain curve of a pure coal specimen.

[0016] Reference numerals: 1-Rock mass, 2-Coal body, 3-Upper fixing ring, 4-Middle fixing ring, 5-Lower fixing ring, 6-Upper axial extensometer assembly, 7-Lower axial extensometer assembly, 8-Upper radial extensometer, 9-Lower radial extensometer, 10-Copper rod, 11-Data collection receiver, 12-Wireless communication module, 13-Upper pressure head, 14-Base, 15-Strain gauge. Detailed Implementation

[0017] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0018] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0019] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0020] Please see Figures 1-5 This invention relates to a calculation method and apparatus for the influence of roof elasticity on the instability and failure of coal-rock composites.

[0021] like Figure 1 , Figure 2 (a)- Figure 2 As shown in (b), the method for calculating the impact of the elastic energy of the roof on the instability and failure of the coal-rock composite is characterized by including the following steps: Step 1: Obtain the thickness h of the top plate. R With coal seam thickness h C The ratio is used as the height ratio of rock mass to coal mass in the coal-rock composite; Step 2: Select a suitable gas pressure gauge to obtain the gas pressure p of the gas-bearing coal seam, and take core samples on site. Process and pre-treat the samples. One type is processed into a pure coal specimen with a diameter of 50 mm and a height of 100 mm, and the other type is processed into a coal-rock composite specimen with upper rock and lower coal. Pure coal and pure rock specimens are processed according to the coal-rock thickness ratio. The surface of the specimens is polished. The processing accuracy of the specimens meets the test specifications recommended by the International Society for Rock Mechanics. The coal-rock interface is bonded with strong adhesive. Step 3: Prepare coal-rock composite samples based on the coal-rock height ratio. Conduct mechanical tests on the prepared coal-rock composite standard samples and pure coal specimens to obtain the roof elastic modulus. The elastic modulus of coal seam under gas pressure p and the elastic modulus of coal-rock composite ; Step four: Based on the stress data collected throughout the entire test process and the strain data collected by strain gauges attached to the entire outer surface of the coal-rock assembly, plot the second stress-strain curve of the coal-rock assembly. Since the rock mass and coal mass are connected in series in the coal-rock assembly, the stress of the rock mass, coal mass, and the overall coal-rock assembly is the same. Then, the first and third stress-strain curves of the rock mass and coal mass can be obtained from the upper and lower axial extensometers, respectively. Based on the stress-strain data collected from the mechanical test of the pure coal specimen, obtain the fourth stress-strain curve, where the roof thickness... Coal seam thickness Elastic modulus of top plate Coal seam elastic modulus and the elastic modulus of coal-rock composite Satisfy equation (1); (1) In the formula, u>0, v>0 and K>0, u is the height ratio of rock mass to coal mass in the coal-rock composite, v is the elastic modulus ratio of rock mass to coal mass, and K is the correction coefficient; Step 5: Plot the first, second, and third stress-strain curves in the same coordinate system, and plot the fourth stress-strain curve in another coordinate system. Calculate the residual elastic energy at the residual strength point after the coal body in the pure coal specimen and coal-rock assemblage reaches its peak strength. The detailed derivation process is as follows: Assume that the following conditions are met simultaneously: (1) When the coal-rock composite specimen fails under gas pressure p, the rock mass is simplified to an elastic body, that is, the rock mass remains relatively intact and there are no obvious cracks on the surface. Only the coal mass is considered to fail. From the perspective of dissipation, the dissipation energy of the rock mass is only the dissipation of itself before the peak, and the rest is converted into elastic energy. (2) Since the coal and rock mass in the coal-rock composite are in series, the peak stress and residual stress of the three are equal. (3) Of the energy of the upper rock mass acting on the lower coal mass of the coal-rock composite specimen, part is converted into dissipation energy to accelerate the failure of the coal mass, and the other part is converted into the residual elastic energy of the coal mass. (4) The elastic energy accumulated by the rock mass begins to act on the coal mass at the peak of the coal-rock composite. That is, the release rate of the roof elastic energy exceeds the crack propagation rate inside the coal mass at the beginning. From the peak, the coal mass loses its constraint, and the roof elastic energy is immediately released and acts on the coal mass, accelerating the failure of the coal mass. like Figure 4 It can be seen that the peak stress of the coal-rock composite is Peak strain is The residual stress is The residual strain is The peak strain and residual strain of the rock mass in the standard specimen of the coal-rock composite are respectively and The peak strain and residual strain of the coal portion in the standard specimen of the coal-rock composite are respectively and The elastic energy of the rock mass acts on the coal body starting from the peak strength. Taking the residual strength as the starting point, draw straight lines parallel to the elastic modulus of the composite body and the coal sample, intersecting the x-coordinate at points f and u, respectively. The corresponding strains are respectively... and , Figure 5 Similarly, the residual stress of the pure coal specimen can be obtained as follows: The residual strain is Starting from the residual strength, draw straight lines parallel to the elastic modulus of the pure coal specimen, intersecting the horizontal coordinate at point o. The corresponding strain is... ; The residual elastic energy at the residual strength point after the pure coal specimen reaches its peak strength can be obtained from equation (2): (2) in, , (3) Substituting equation (3) into equation (2), we can obtain the residual elastic energy after the peak of the standard pure coal specimen: (4) Similarly, the residual elastic energy at the residual strength point after the coal body reaches its peak strength in the coal-rock composite can be obtained: (5) Step 6: Calculate the energy dissipation ratio in the energy of the rock mass's interaction with the coal mass within the coal-rock composite. ,in Satisfy the following formula: (6) In the formula This refers to the energy that the rock mass exerts on the coal mass within the coal-rock composite, which is then converted into the residual elastic energy of the coal mass. This represents the total energy exerted by the rock mass on the coal mass within the coal-rock composite. Equation (4) represents the post-peak residual elastic energy of a standard pure coal specimen. Converting this to the post-peak residual elastic energy of the coal body in a coal-rock composite can be obtained from equation (7): (7) The energy of the rock mass acting on the coal mass in the coal-rock composite specimen is converted into the residual elastic energy of the coal mass, which can be obtained by equation (8): (8) Depend on Figure 4 It can be seen that the area enclosed by points a, d, h, and i is the total energy exerted by the rock mass on the coal body in the coal-rock composite: (9) in, , , (10) Substituting equation (10) into equation (9), we get: (11) Substituting equations (1), (8), and (11) into equation (6) yields... : (12) Step 7: Calculate the influence of the roof elastic energy on the instability and failure of the coal-rock composite. ; (13) in, This represents the total energy exerted by the rock mass on the coal seam. This represents the energy dissipated by the coal-rock composite from peak strength to post-peak residual strength. Specific (14) Let S be the volume of the coal-rock composite, S be the area corresponding to the second stress-strain curve of the coal-rock composite, point b be the peak strength point of the coal-rock composite, point e be the residual strength point, and points m and f be the points exceeding the peak strength and residual strength, respectively. With the elastic modulus of the coal-rock composite as the slope, draw the intersection of the oblique line and the horizontal axis.

[0022] To obtain the mechanical parameters of the above specimens, such as Figure 3 As shown, a mechanical testing device includes an upper pressure head 13 and a base 14. A coal-rock composite specimen or a pure coal specimen is placed between the upper pressure head and the base, where 1 represents the rock mass and 2 represents the coal mass. An upper fixing ring 3 is embedded in the middle of the upper pressure head, a lower fixing ring 5 is installed in the middle of the base, and a middle fixing ring 4 is placed at the interface between the rock mass and the coal mass in the coal-rock composite specimen. The upper fixing ring 3, the middle fixing ring 4, and the lower fixing ring 5 are installed in parallel. One end of an upper axial extensometer component 6 is connected to a copper rod 10, which is installed on one edge of the upper fixing ring 3 and the middle fixing ring 4, and is used to measure the axial strain of the rock mass. One end of a lower axial extensometer component 7 is connected to a copper rod 10, which is installed on one edge of the lower fixing ring 5 and the middle fixing ring 4, and is used to measure the axial strain of the coal mass. An upper radial extensometer 8 is installed in the middle of the rock mass, and a lower radial extensometer 9 is installed in the middle of the coal mass, and are used to measure the radial strain of the coal mass and the rock mass.

[0023] In the above scheme, strain gauges 15 are attached to the outer surface of the standard specimen of coal-rock composite, and the strain gauges 15 are connected to the strain gauge via signal cables.

[0024] In the above scheme, the upper axial extension measurement component 6 and the lower axial extension measurement component 7 are each equipped with a data collection receiver 11 and a wireless communication module 12. After the measured data is collected, it is transmitted to an external receiving terminal through the wireless communication module 12 for observation and recording.

[0025] Specifically, when using this device to test coal-rock composite specimens, firstly, strain gauges 15 are attached to the outer surface of the entire specimen to be tested, and upper radial extensometers 8 and lower radial extensometers 9 are installed in the middle of rock mass 1 and coal mass 2, respectively; then, the coal-rock composite specimen is placed between the upper pressure head 13 and the base 14; the upper fixing ring 3, middle fixing ring 4, and lower fixing ring 5 are installed on the upper pressure head 13, the coal-rock interface, and the base 14, respectively; then, one end of the upper axial extensometer measuring component 6 is connected to the copper rod 10, and the copper rod 10 is installed on one edge of the upper fixing ring 3 and middle fixing ring 4; one end of the lower axial extensometer measuring component 7 is connected to the copper rod 10, and the copper rod 10 is installed on one edge of the lower fixing ring 5 and middle fixing ring 4; then, the device is installed... The strain gauge 15 is placed in a high-pressure sealed cavity, and its signal cable is connected to the strain gauge through the lead port on the high-pressure sealed cavity. The gas pressure p and loading speed are set, and a mechanical test is conducted on the coal-rock combination using a rigid testing machine. During measurement, the deformation data is collected and summarized by the data collection receiver 11 in the upper axial extension measurement component 6 and the lower axial extension measurement component 7, and then transmitted to the external receiving terminal by the wireless communication module 12. The strain data of the rock mass and the coal body are recorded, and the strain data of the coal-rock combination is recorded by the strain gauge. Based on the stress data of the testing machine collected during the test, and the strain data of the rock mass, the coal-rock combination, and the coal body, the first, second, and third stress-strain curves are plotted.

[0026] Specifically, when using this device to test pure coal specimens, strain gauges 15 are first attached to the outer surface of the specimen to be tested. Then, the pure coal specimen is placed between the upper pressure head 13 and the base 14. After that, the device is placed in a high-pressure resistant sealed cavity, and the signal cable of the strain gauge 15 is connected to the strain gauge through the lead port on the high-pressure resistant sealed cavity. The gas pressure p and loading speed are set, and the pure coal specimen is subjected to mechanical testing using a rigid testing machine. During the measurement, the strain data of the coal-rock composite is recorded by the strain gauge, and the fourth stress-strain curve is plotted based on the stress data of the testing machine collected during the test.

[0027] The device for obtaining mechanical parameters of specimens provided in this embodiment of the invention has a simple structure, high stability, and can accurately obtain stress and strain data of coal and rock in coal-rock composite specimens, with good application effect.

[0028] In this embodiment: The coal and rock used in the experiment were all taken from the same working face. The gas pressure of the coal seam was measured to be 0.4 MPa using a gas pressure gauge. Based on the borehole columnar section, standard specimens of coal-rock composites were prepared using rock samples and coal samples at a 1:1 ratio. Mechanical tests were carried out on the coal-rock composite specimens and pure coal standard specimens under the conditions of gas pressure of 0.4 MPa and loading rate of 0.12 mm / min. The elastic modulus of the top plate was obtained from the experiment. The elastic modulus of the coal seam is 12.05 GPa. The elastic modulus of the coal-rock composite is 2.71 GPa. The peak stress of the coal-rock composite is 5.33 GPa. The residual stress is 17.89 MPa. The residual stress of the pure coal specimen is 4.53 MPa. The stress-strain curve shows that the energy dissipated by the coal-rock composite from peak strength to residual strength after peak strength is 3.15 MPa. It is 135.14 kJ / m 3 ; Substituting the data into equation (1), we get u=1, v=4.45, and K=1.2; The energy of the rock mass acting on the coal mass in the coal-rock composite specimen is converted into the residual elastic energy density of the coal mass, which can be obtained by equation (8). Substituting the data, we get: (15) Based on equation (11), which represents the total energy exerted by the rock mass on the coal mass in the coal-rock composite, and substituting the data, we obtain: (16) According to equation (6), the energy dissipation ratio of the energy of the rock mass acting on the coal mass in the coal-rock composite is obtained. ; The influence of the roof elastic energy on the instability and failure of the coal-rock composite is obtained by substituting the data into equation (13). .

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for calculating the influence of roof elasticity on the instability and failure of coal-rock composites, characterized in that, The method includes the following steps: S1: Obtain the thickness of the top plate respectively h R With coal seam thickness h C , will the h R and h C The ratio of the height of the rock mass to the height of the coal mass in the coal-rock composite is used as the ratio of the rock mass height to the coal mass height. u ; S2: In gas-bearing coal seams, gas pressure is obtained using a gas pressure gauge. p Core samples were taken on-site and pre-treated to obtain standard specimens of coal-rock composites and pure coal specimens. S3: Under gas pressure p, the standard specimen of the coal-rock composite and the pure coal specimen obtained in S2 are subjected to mechanical tests using a mechanical device to obtain the elastic modulus of the roof. Elastic modulus of coal seam under gas pressure p and the elastic modulus of coal-rock composite ; S4: Based on the stress data collected during the entire test process of the standard sample mechanical test of the coal-rock composite and the strain data collected by the strain gauges attached to the outer surface of the entire coal-rock composite, the second stress-strain curve of the coal-rock composite is plotted. Then, the first and third stress-strain curves of the rock mass and the coal mass are obtained by the upper and lower axial extensometers, respectively. The fourth stress-strain curve is obtained based on the stress-strain data collected from the mechanical test of the pure coal specimen. S5: Plot the first, second, and third stress-strain curves in S4 in the same coordinate system, and plot the fourth stress-strain curve in another coordinate system. Calculate the residual elastic energy at the residual strength point after the coal body in the pure coal specimen and coal-rock composite reaches its peak value. S6: Based on the energy converted into residual elastic energy of the coal from the energy exerted by the rock mass on the coal in the coal-rock assembly, and the total energy exerted by the rock mass on the coal in the coal-rock assembly, calculate the energy dissipation ratio of the energy exerted by the rock mass on the coal in the coal-rock assembly. ; S7: Based on the total energy of the rock mass's interaction with the coal mass, the energy dissipated by the coal-rock assemblies from peak strength to post-peak residual strength, and the energy dissipation ratio of the rock mass's interaction with the coal mass within the coal-rock assemblies. Calculate the influence of the roof elastic energy on the instability and failure of the coal-rock composite. .

2. The method for calculating the influence of roof elasticity on the instability and failure of coal-rock composites according to claim 1, characterized in that, In step S2, the sample undergoes pretreatment, specifically as follows: One sample was processed into a pure coal specimen with a diameter of 50 mm and a height of 100 mm, and the other was processed into a coal-rock composite specimen with coal on the upper side and rock on the lower side. The composite specimen was processed into pure coal and pure rock specimens according to the coal-rock thickness ratio, and the surface of the specimens was polished. The processing accuracy of the specimens met the test specifications recommended by the International Society for Rock Mechanics. The coal-rock interface was bonded with strong adhesive.

3. The method for calculating the influence of roof elasticity on the instability and failure of coal-rock composites according to claim 2, characterized in that, In S4, the top plate thickness in the first, second, third, and fourth stress-strain curves. Coal seam thickness Elastic modulus of top plate Coal seam elastic modulus and the elastic modulus of coal-rock composite Satisfying equation (1): （1） Where u>0, v>0 and K>0, u is the height ratio of rock mass to coal mass in the coal-rock composite, v is the elastic modulus ratio of rock mass to coal mass in the coal-rock composite, and K is the correction coefficient.

4. The method for calculating the influence of roof elasticity on the instability and failure of coal-rock composites according to claim 3, characterized in that, In step S5, the first, second, and third stress-strain curves from step S4 are plotted in the same coordinate system, and the fourth stress-strain curve is plotted in another coordinate system. The residual elastic energy at the residual strength point after the coal body in the pure coal specimen and coal-rock assemblage reaches its peak value is calculated, specifically as follows: In the fourth stress-strain curve of the pure coal specimen, starting from the residual strength g point after the peak of the pure coal specimen, a straight line parallel to the elastic modulus of the pure coal is drawn, intersecting the horizontal axis at point o. The corresponding strain is... Points n and p are the projection points of the peak strength and residual strength of the specimen on the abscissa, respectively, and the corresponding strains are respectively , The area enclosed by points g, o, and p represents the residual elastic energy at the residual strength point after the pure coal specimen reaches its peak strength. Therefore, the residual elastic energy at the residual strength point after the pure coal specimen reaches its peak strength is expressed as: （2） in, ， （3） in, The residual stress after the peak in the pure coal specimen. This represents residual strain; Substituting equation (3) into equation (2), the residual elastic energy after the peak of the standard pure coal specimen is obtained as follows: （4） Similarly, the residual elastic energy at the residual strength point after the coal body reaches its peak strength in the coal-rock composite is obtained, expressed as: （5） in, denoted as the residual stress of a standard specimen of a coal-rock composite, and u is the height ratio of the rock mass to the coal mass in the coal-rock composite.

5. The method for calculating the influence of roof elasticity on the instability and failure of coal-rock composites according to claim 4, characterized in that, In S6 Satisfying formula (6): （6） in, This refers to the energy that the rock mass exerts on the coal mass within the coal-rock composite, which is then converted into the residual elastic energy of the coal mass. This represents the total energy exerted by the rock mass on the coal mass within the coal-rock composite. Formula (4) represents the residual elastic energy after the peak of a standard pure coal specimen. Formula (4) is then converted into the residual elastic energy after the peak of the coal body in a coal-rock composite, expressed as: （7） In a coal-rock composite specimen, the energy exerted by the rock mass on the coal mass is converted into the residual elastic energy of the coal mass, which is expressed as: （8） The total energy exerted by the rock mass on the coal body in a coal-rock composite is expressed as: （9） in, ， ， （10） in, , These represent the peak strain and residual strain of the rock mass portion within the coal-rock composite, respectively. The peak stress of the coal-rock composite is... Residual stress in the coal-rock composite; Substituting formula (10) into formula (9) yields: （11） Substituting formulas (1), (8), and (11) into formula (6), we get... , is represented as: （12） in, The peak stress of the coal-rock composite is... This refers to the residual stress after the peak of the coal-rock composite. denoted as the residual stress after peak in the pure coal specimen; u represents the height ratio of the rock mass to the coal mass in the coal-rock assemblage, and v represents the elastic modulus ratio of the rock mass to the coal mass in the coal-rock assemblage.

6. The method for calculating the influence of roof elasticity on the instability and failure of coal-rock composites according to claim 5, characterized in that, In S7 Represented as: （13） in, This represents the total energy exerted by the rock mass on the coal seam. This represents the energy dissipated by the coal-rock composite from peak strength to post-peak residual strength. （14） in, Let S be the volume of the coal-rock composite, S be the area corresponding to the second stress-strain curve of the coal-rock composite, point b be the peak strength point of the coal-rock composite, point e be the residual strength point, and points m and f be the points exceeding the peak strength and residual strength, respectively. With the elastic modulus of the coal-rock composite as the slope, draw the intersection of the oblique line and the horizontal axis.

7. A mechanical testing apparatus, characterized in that, It includes an upper pressure head (13), a base (14), an upper fixing ring (3), a lower fixing ring (5), a middle fixing ring (4), an upper axial extension measuring assembly (6), a lower axial extension measuring assembly (7), an upper radial extensometer (8), a lower radial extensometer (9), and a copper rod (10). The upper fixing ring (3) is installed in the middle of the upper pressure head (13), the lower fixing ring (5) is installed in the middle of the base (14), and the middle fixing ring (4) is installed at the interface between the rock mass and the coal mass in the coal-rock composite specimen. The upper fixing ring (3), the lower fixing ring (5), and the middle fixing ring (4) are parallel. The upper axial extension measuring component (6) is installed at one end of the upper fixed ring (3), and the lower axial extension measuring component (7) is installed at one end of the lower fixed ring (5) and is opposite to the end of the upper axial extension measuring component (6). The upper axial extension measuring component (6) is used to measure the axial strain of the rock mass, and the lower axial extension measuring component (7) is used to measure the axial strain of the coal mass. The copper rod (10) is installed at one side edge of the upper fixed ring (3) and the middle fixed ring (4) and at one side edge of the lower fixed ring (5) and the middle fixed ring (4), respectively. One end of the copper rod (10) installed at one side edge of the upper fixed ring (3) and the middle fixed ring (4) is connected to the upper axial extension measuring component (6), and the other end is connected to the middle fixed ring (4). One end of the copper rod (10) installed at one side edge of the lower fixed ring (5) and the middle fixed ring (4) is connected to the lower axial extension measuring component (7), and the other end is connected to the middle fixed ring (4). The upper radial extensometer (8) is installed above the middle fixing ring (4) and is located in the middle of the rock mass in the coal-rock composite specimen; the lower radial extensometer (9) is installed below the middle fixing ring (4) and is located in the middle of the coal mass in the coal-rock composite specimen. Strain gauges (15) are attached to the outer surface of the test piece and the strain gauges (15) are connected to the strain gauge via signal cables. The upper axial elongation measurement component (6) and the lower axial elongation measurement component (7) include: a data collection receiver (11) and a wireless communication module (12). The data collection receiver (11) collects the measured data and transmits it to an external receiving terminal through the wireless communication module (12). The device is used to implement step S4 of the method of claim 1, wherein the first and third stress-strain curves of the rock mass and the coal mass are obtained by the upper axial extensometer (6) and the lower axial extensometer (7), respectively.

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