Method for determining size of coal uncovering protection rock pillar of coal and gas outburst tunnel face

Abstract

The invention discloses a coal and gas outburst tunnel face coal uncovering protection rock pillar size determination method, and relates to the technical field of thickness measurement, and the method comprises the following steps: determining a deformation function of a protection rock pillar according to a displacement deformation function; based on the deformation function and boundary conditions of a plate theory, determining a stress component of stress of the protective rock pillar, and determining the maximum principal stress of the protective rock pillar according to the stress component; and when the maximum principal stress reaches the tensile strength of the protective rock pillar, determining the target safety thickness of the protective rock pillar according to the tensile strength. According to the method, the problem of reasonably reserving the protection rock pillar under the multi-field coupling condition of a surrounding rock stress field, a gas pressure field and the like is solved, and the calculation precision of the size of the coal uncovering protection rock pillar of the coal and gas outburst tunnel face is greatly improved by combining the plate theory and the elastic mechanics; and the problems of coal and rock pillar size optimization and construction safety under multi-field coupling of gas pressure and the like are effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of thickness measurement, and particularly relates to a method for determining the size of a protective rock pillar for uncovering coal at the tunnel face of a coal and gas outburst tunnel. Background Art

[0002] With the large-scale construction of underground projects in mountainous areas in western China, tunnel projects such as railways, highways, and hydropower projects are passing through coal-bearing or oil and gas strata more and more frequently. Gas has become one of the major threats to construction safety, and the disasters of tunnel projects passing through coal and gas outburst strata are becoming more and more serious. Before uncovering coal at the tunnel face, reasonably leaving a protective rock pillar is a safety barrier for outburst prevention during coal uncovering. Accurately reserving the protective rock pillar can ensure the safety and reliability of the tunnel outburst prevention measures, and a reasonable rock pillar thickness is conducive to the rapid discharge of gas; on the other hand, when the tunnel is excavated, the protective rock pillar needs to be blasted. If the blasting is not thorough, the residual rock pillar is difficult to resist the instantaneous release of the accumulated energy of coal and gas, threatening construction safety; if the amount of explosive is too large, it will cause the surrounding rock to be unstable, increase the support difficulty, and easily lead to the collapse accident of the tunnel face.

[0003] At present, Litovchenko determined the size of the protective coal seam above the high-voltage line tower in the coalfield; W. Haupt et al. studied the size of the safety coal pillar and the protected area using the Gaussian function; M. Zenke's research showed that the reserved parameters of the ore pillar are related to the movement and deformation of the ground surface and rock strata during mining; A.M. Zadorozhnyi et al. developed a practical calculation scheme for determining the stress state of the protective rock pillar; Joze et al. studied the relationship between the depth of shallow mines and the height of the ore pillar; Kortnik et al. studied the optimization of the size of the safety ore pillar. Xiong Chuanzhi et al. obtained the optimal size of the safety coal pillar by using the Newton tangent method, the damped least squares method, etc. with the coal volume pressed by the coal pillar as the objective function; Liu Tianxi et al. established a spatial relationship analysis function based on the parameters of the overpass roadway to determine the minimum size of the rock pillar between roadways; Wang Guohua determined the reasonable width of the coal pillar through theoretical analysis, numerical simulation, etc.; Jin Zhiyuan et al. used the UDEC software to analyze the stress, plastic zone and roof and floor deformation laws of the coal (rock) pillar between driving roadways, and accordingly determined the reasonable size of the rock (coal) pillar; Wang Zhiqiang et al. studied the reserved size of the water-proof (isolation) rock (coal) pillar according to the design method of the middle zone of the rock (coal) pillar in the yield zone of the rock (coal) pillar and the influence of the movement angle of the overlying rock; Yanlin Zhao et al. studied the stability of the water-resistant rock pillar by combining the water-hydro-mechanical coupling and the strength reduction method; Wang Youkai et al. obtained the relationship between the maximum single-section explosive charge and the size of the protective rock pillar by using regression analysis; Wu Liyun et al. established a gas flow equation to explain the theoretical basis of the protective rock pillar of 2m and 5m for uncovering coal at the tunnel face.

[0004] However, the above research on the protection size of rock pillars mainly focuses on the protection of production facilities, the safety of ground buildings, and disaster isolation, but ignores the optimization of the size of coal and rock pillars under multi-field coupling (such as gas pressure); at the same time, the technology of the protection rock pillar for tunnel coal uncovering mostly follows the old methods of coal mines and does not consider the differences between tunnels and coal mines. Therefore, it is crucial to study the size of the protection rock pillar for coal uncovering in coal and gas outburst tunnels for safe construction. Summary of the Invention

[0005] In view of the above deficiencies in the prior art, a method for determining the size of the protection rock pillar for coal uncovering at the heading face of a coal and gas outburst tunnel provided by the present invention solves the problem of safety construction caused by the inability to determine the size of the protection rock pillar for coal uncovering suitable for coal and gas outburst tunnels in the prior art.

[0006] In order to achieve the above invention purpose, the technical solution adopted by the present invention is as follows: A method for determining the size of the protection rock pillar for coal uncovering at the heading face of a coal and gas outburst tunnel, comprising: Determining the deformation function of the protection rock pillar according to the displacement deformation function, where the displacement deformation function is used to indicate the displacement deformation function in classical elasticity mechanics; Based on the deformation function and the boundary conditions of the plate theory, determining the stress components of the protection rock pillar under stress, and determining the maximum principal stress of the protection rock pillar according to the stress components; Obtaining the tensile strength of the protection rock pillar, and determining the target safety thickness of the protection rock pillar according to the tensile strength and the maximum principal stress.

[0007] Further, the determining the deformation function of the protection rock pillar according to the displacement deformation function includes: Calculating the deformation function by using the following formula:

[0008] where, w is the deformation function, m, n is a positive integer, π is the pi, represents positive infinity, is the constant coefficient of the expansion of the deformation function, is the width of the tunnel section corresponding to the protection rock pillar, is the height of the tunnel section corresponding to the protection rock pillar, is the horizontal distance of the protection rock pillar perpendicular to the tunnel driving direction, z is the distance of the protection rock pillar in the vertical direction.

[0009] Further, the plate theory is the classical elastic mechanics plate theory, and the boundary conditions are used to indicate the boundary conditions under which cracks first occur around the edge of the protective rock pillar. Determining the stress components of the protective rock pillar under stress based on the deformation function and the boundary conditions of the plate theory includes: Determining the position information of the boundary conditions and determining the stress component function corresponding to the deformation function by using the Kirchhoff-Love assumption. The position information of the boundary conditions is used to indicate the position information corresponding to the boundary conditions under which cracks first occur around the edge of the protective rock pillar. The position information corresponding to the boundary conditions under which cracks first occur around the edge of the protective rock pillar is (0 ，- / 2 ，h / 2), 、 ( ，- / 2 ，h / 2), where is the thickness of the protective rock pillar, and the thickness of the protective rock pillar is used to indicate the target safety thickness; Inputting the position information into the stress component function to obtain the stress components of the protective rock pillar under stress.

[0010] Further, the stress components are calculated by using the following formula:

[0011] where, is the horizontal stress component of the protective rock pillar perpendicular to the tunnel excavation direction, is the stress component of the protective rock pillar perpendicular to the horizontal direction, is the shear stress component of the protective rock pillar perpendicular to the first plane, and the first plane is used to indicate the plane formed by the horizontal direction and the direction perpendicular to the horizontal direction, P is the gas pressure generated by the action of coal seam gas on the protective rock pillar, is the Poisson's ratio of the protective rock pillar.

[0012] Further, determining the maximum principal stress of the protective rock pillar according to the stress components includes: Inputting the stress components into the maximum stress function to obtain the maximum principal stress, and the maximum stress function is the stress function in elasticity; The expression of the maximum principal stress is as follows:

[0013] where, is the solved maximum principal stress.

[0014] Further, determining the target safety thickness of the protective rock pillar according to the tensile strength and the maximum principal stress includes: When the maximum principal stress is not greater than the tensile strength, determining the target safety thickness according to the maximum principal stress.

[0015] Further, determining the target safety thickness according to the maximum principal stress includes: Calculating the target safety thickness by using the following formula:

[0016] where 1.22 is the geometric correction coefficient of the energy method, R t is the tensile strength.

[0017] Further, the tunnel section corresponding to the protective rock pillar is used to indicate the heading face of the coal and gas outburst tunnel, and the method further includes: When the width of the tunnel section corresponding to the protective rock pillar, the height of the tunnel section corresponding to the protective rock pillar, and the tensile strength are preset values, determining the target safety thickness according to the gas pressure generated by the action of coal seam gas on the protective rock pillar.

[0018] The beneficial effects of the present invention are as follows: The method first determines the deformation function of the protective rock pillar based on the displacement deformation function of classical elasticity mechanics, then calculates the stress components of the force on the rock pillar in combination with the boundary conditions of the plate theory, and determines the maximum principal stress therefrom. Finally, the target safety thickness that meets the safety conditions is determined through the tensile strength and the maximum principal stress of the protective rock pillar, solving the problem of reasonable setting of the protective rock pillar under the multi-field coupling conditions such as the surrounding rock stress field and the gas pressure field, being able to effectively solve the optimization problem of the size of the coal and rock pillar under the multi-field coupling of gas pressure, etc., and greatly improving the safety of construction under the multi-field coupling conditions. Description of the Drawings

[0019] Figure 1 is a schematic flow chart of the method; Figure 2 is a schematic diagram of the simplified processing of the tunnel section corresponding to the protective rock pillar of the method; Figure 3 is a schematic diagram of the calculation and processing model of the target safety thickness of the protective rock pillar of the method. Detailed Embodiments

[0020] The specific embodiments of the present invention will be described below to facilitate those skilled in the art of the present technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

[0021] As Figure 1 shown, the method for determining the size of the protective rock pillar for uncovering coal at the heading face of a coal and gas outburst tunnel includes the following steps: S1. Determine the deformation function of the protective rock pillar according to the displacement and deformation function, where the displacement and deformation function is used to indicate the displacement and deformation function in classical elasticity. Among them, before performing this step, for example, the protective rock pillar can also be pre-treated. Since the cross-section of the protective rock pillar corresponding to the tunnel is usually a rectangle plus an ellipse, for convenience, it can be simplified to a rectangle.

[0022] It can be understood that the above simplification process can more conveniently calculate the safety thickness of the protective rock pillar.

[0023] S2. Based on the deformation function and the boundary conditions of the plate theory, determine the stress components of the protective rock pillar under stress, and determine the maximum principal stress of the protective rock pillar according to the stress components. S3. Obtain the tensile strength of the protective rock pillar, and determine the target safety thickness of the protective rock pillar according to the tensile strength and the maximum principal stress.

[0024] The method for determining the size of the protective rock pillar for uncovering coal at the heading face of a coal and gas outburst tunnel provided in this embodiment first determines the deformation function of the protective rock pillar based on the displacement and deformation function of classical elasticity, then calculates the stress components of the rock pillar under stress in combination with the boundary conditions of the plate theory, and determines the maximum principal stress therefrom. Finally, the target safety thickness that meets the safety conditions is determined through the tensile strength and the maximum principal stress of the protective rock pillar, solving the problem of reasonable setting of the protective rock pillar under the multi-field coupling conditions such as the surrounding rock stress field and the gas pressure field, and obtaining a theoretical calculation formula, which can effectively solve the optimization problem of the size of the coal and rock pillar under the multi-field coupling such as gas pressure, greatly improving the safety of construction under the multi-field coupling conditions. Through this method, the reasonable setting problem of the protective rock pillar under the multi-field coupling conditions such as the surrounding rock stress field and the gas pressure field can be comprehensively studied, combining the plate theory and elasticity, greatly improving the calculation accuracy of the size of the protective rock pillar for uncovering coal at the heading face of a coal and gas outburst tunnel, having extremely high guiding significance for the setting of the actual safety rock pillar, and being able to effectively solve the optimization of the size of the coal and rock pillar under the multi-field coupling such as gas pressure and the construction safety problem.

[0025] Figure 2Schematic diagram of the simplified treatment of the tunnel section corresponding to the protective rock pillar provided by this method, as shown in Figure 2 shown, the rectangular plus elliptical tunnel is simplified to a rectangle. a is the length of the tunnel section corresponding to this protective rock pillar, and b is the height of the tunnel section corresponding to this protective rock pillar. Based on this figure, the calculation and treatment of the safety thickness of the protective rock pillar can be carried out more conveniently.

[0026] Figure 3 Schematic diagram of the calculation and treatment model of the target safety thickness of the protective rock pillar of this method, as shown in Figure 3 shown, the tunnel section corresponding to the protective rock pillar is affected by the gas pressure P accumulated in the coal seam. This gas pressure P forms a uniform load on the protective rock pillar in the reverse direction of tunnel advancement, and the protective rock pillar will deform. As the excavation progresses, when the thickness of the rock pillar is insufficient to resist the energy accumulated in the coal seam, a coal and gas outburst accident will occur. Among them, a is the width of the tunnel section, h is the height of the tunnel section, x is the horizontal distance of the protective rock pillar perpendicular to the tunnel excavation direction (transverse), y is the horizontal distance of the protective rock pillar along the tunnel excavation direction (longitudinal), z is the vertical distance of the protective rock pillar, and δ / 2 is half of the target safety thickness of the protective rock pillar. Based on this gas pressure P, the width a of the tunnel section, the height h of the tunnel section, the horizontal distance x of the protective rock pillar perpendicular to the tunnel excavation direction, the horizontal distance y of the protective rock pillar along the tunnel excavation direction (longitudinal), the vertical distance z of the protective rock pillar, and the target safety thickness δ of the protective rock pillar, the subsequent calculation and treatment of the target safety thickness of the protective rock pillar can be carried out more conveniently. In the figure, o is the coordinate origin, the horizontal distance of the protective rock pillar perpendicular to the tunnel excavation direction (transverse) is denoted as the x-axis, the horizontal distance of the protective rock pillar along the tunnel excavation direction (longitudinal) is denoted as the y-axis, and the vertical distance of the protective rock pillar is denoted as the z-axis. Then the positions where the edges of the protective rock pillar break first are the places with coordinates (0, -δ / 2, h / 2) and (a, -δ / 2, h / 2).

[0027] In a possible implementation manner, determining the deformation function of the protective rock pillar according to the displacement deformation function includes: The deformation function is calculated using the following formula:

[0028] Among them, w is the deformation function, m, n is a positive integer, π is the pi, represents positive infinity, is the constant coefficient of the expansion of the deformation function, is the width of the tunnel section corresponding to the protective rock pillar, is the height of the tunnel section corresponding to the protective rock pillar, is the horizontal distance of the protected rock pillar perpendicular to the tunnel driving direction, z is the distance of the protected rock pillar in the vertical direction.

[0029] It can be understood that this step uses the displacement deformation function as the deformation function of the protected rock pillar. According to the boundary conditions, the small deflection bending problem of the plate can be analyzed and solved, and the mathematical relationship between the thickness of the protected rock pillar and the tunnel excavation width, height, tensile strength of the rock pillar, and gas pressure can be deduced.

[0030] In a possible implementation, the plate theory is the classical elastic mechanics plate theory, and the boundary conditions are used to indicate the boundary conditions where cracks first occur around the edge of the protected rock pillar. Based on the deformation function and the boundary conditions of the plate theory, the stress components of the protected rock pillar are determined, including: Determine the position information of the boundary conditions and use the Kirchhoff-Love assumption to determine the stress component function corresponding to the deformation function. The position information of the boundary conditions is used to indicate the position information corresponding to the boundary conditions where cracks first occur around the edge of the protected rock pillar; therefore, in this embodiment, (0, -δ / 2, h / 2), ( , -δ / 2, h / 2) are used as the position information of the boundary conditions.

[0031] Among them, the formula of the Kirchhoff-Love assumption is expressed as:

[0032] Among them, is the elastic modulus of the protected rock pillar, and y is the horizontal distance of the protected rock pillar along the tunnel driving direction (longitudinal).

[0033] Input the position information into the stress component function to obtain the stress components of the protected rock pillar.

[0034] Among them, the plate theory can be, for example, that the protected rock pillar can be regarded as a "plate" with four sides fixed when it is restricted by the surrounding rock. The coal seam gas pressure acts on the protected rock pillar, which can be regarded as the "plate" being subjected to a uniformly distributed load. Based on the boundary conditions of this plate theory, the boundary conditions where cracks first occur around the edge of the protected rock pillar can be correspondingly determined. The position information can be, for example, the coordinate position information corresponding to the boundary conditions where cracks first occur around the edge of the protected rock pillar.

[0035] In a possible implementation, based on the position information of the boundary conditions obtained above, the stress components are calculated using the following formula:

[0036] Among them, is the horizontal stress component of the protected rock pillar perpendicular to the tunnel driving direction, is the stress component of the protected rock pillar perpendicular to the horizontal direction, To protect the shear stress component of the rock pillar in the direction perpendicular to the first plane, where the first plane is used to indicate the plane formed by the horizontal direction and the direction perpendicular to the horizontal direction, P To protect the gas pressure generated in the rock pillar under the action of coal seam gas, To protect the thickness of the rock pillar, and the thickness of the rock pillar is used to indicate the target safety thickness, To protect the Poisson's ratio of the rock pillar.

[0037] In a possible implementation, determining the maximum principal stress of the protective rock pillar according to the stress component includes: Inputting the stress component into the maximum stress function to obtain the maximum principal stress, where the maximum stress function is the stress function in elasticity mechanics; The solution expression of the maximum stress function is as follows:

[0038] Wherein, is the solved maximum principal stress, is the solved minimum principal stress, is the horizontal stress component of the protective rock pillar in the direction perpendicular to the tunnel driving direction, is the stress component of the protective rock pillar in the direction perpendicular to the horizontal direction, is the square of the shear stress component of the protective rock pillar in the direction perpendicular to the first plane, where the first plane is used to indicate the plane formed by the horizontal direction and the direction perpendicular to the horizontal direction.

[0039] Substituting the stress components in the above-mentioned protective rock pillar into the solution expression of the maximum stress function, the maximum principal stress of the protective rock pillar is obtained as follows:

[0040] Wherein, is the solved maximum principal stress, is the solved minimum principal stress.

[0041] Since in this embodiment has little influence on the target safety thickness of the protective rock pillar, in this embodiment, is used as the maximum principal stress of the protective rock pillar to calculate the target safety thickness.

[0042] For the face rock pillar of vulnerable materials, it can be considered that when the maximum tensile stress at any point in the rock pillar reaches the tensile strength R t the rock pillar generates tensile cracks and fails, that is:

[0043] Therefore, in a possible implementation, determining the target safety thickness of the protective rock pillar according to the tensile strength and the maximum principal stress includes: When the maximum principal stress is not greater than the tensile strength, determining the target safety thickness according to the maximum principal stress.

[0044] In a possible implementation, determining the target safety thickness according to the maximum principal stress includes: Calculating the target safety thickness using the following formula:

[0045] where 1.22 is the geometric correction coefficient of the energy method, R t is the tensile strength.

[0046] It can be understood that in the above formula for obtaining the target safety thickness, when the width of the tunnel section corresponding to the protective rock pillar, the height of the tunnel section corresponding to the protective rock pillar, and the tensile strength of the protective rock pillar are constant, the thickness of the protective rock pillar reserved for the coal seam uncovering at the heading face is proportional to the square root of the coal seam gas pressure.

[0047] In a possible implementation, the tunnel section corresponding to the protective rock pillar is used to indicate the heading face of the coal and gas outburst tunnel. The method further includes: If the width of the tunnel section corresponding to the protective rock pillar, the height of the tunnel section corresponding to the protective rock pillar, and the tensile strength are preset values, then determining the target safety thickness according to the gas pressure generated by the action of the coal seam gas on the protective rock pillar.

[0048] Specifically, different protective rock pillars in this step correspond to different tunnel section widths, tunnel section heights, and tensile strengths, which are not specifically limited here and are determined according to different scenarios in actual applications. After determining the specific situation of the tunnel section corresponding to the protective rock pillar, the width, height, and tensile strength of this tunnel section become fixed values. During the subsequent tunnel construction process, based on these determined values, the target safety thickness of the protective rock pillar can be specifically calculated according to the gas pressure generated by the action of the coal seam gas on the current protective rock pillar at different construction progress. While improving the calculation accuracy of the target safety thickness of the protective rock pillar, it also greatly simplifies the calculation process of the target safety thickness, having a certain practical application value.

[0049] It can be understood that by adopting the calculation formula of the target safety thickness, when the width of the tunnel section corresponding to the protective rock pillar, the height of the tunnel section corresponding to the protective rock pillar, and the tensile strength are preset fixed values, the target safety thickness can be directly determined according to the gas pressure generated by the action of coal seam gas on the protective rock pillar. Through the formula calculation method, the calculation accuracy of the target safety thickness is greatly improved, and the optimization problem of the size of the coal and rock pillar under the multi-field coupling such as gas pressure can be solved more accurately, which greatly improves the safety of construction under the multi-field coupling conditions.

[0050] In this method, the protective rock pillar in front of the tunnel face is simplified into a "plate" model with the characteristics of four-sided fixed support, and theoretical analysis is carried out based on the displacement and deformation functions of the "plate" model in elastic mechanics, and the theoretical calculation formula of the protective rock pillar is derived. It overcomes the drawbacks of the traditional tunnel coal uncovering protective rock pillar technology following the old coal mine method, and solves the problem of large errors in the safety thickness of the tunnel protective rock pillar caused by the differences between tunnels and coal mines.

[0051] To better support the accuracy of the calculation of the target safety thickness in this application, the following is an actual case verification process provided by this application, which is specifically as follows: A coal and gas outburst tunnel passes through the No. 44-middle, No. 45-upper, and No. 46-lower coal seams. The maximum original gas pressure measured in the coal seams in this tunnel area reaches 3.62 MPa (nearly 5 times exceeding the critical value of 0.74 MPa for coal seam outburst danger), and the maximum original gas content reaches 24.24 m 3 / t (about 3 times exceeding the critical value of 8 m 3 / t for the gas content in the coal seams in the outburst danger area). Coal and gas outbursts have occurred in the surrounding coal mines. Moreover, the outburst coal seams have a large dip angle and a small burial depth for outbursts, with the minimum being 192 m, while the maximum burial depth of the tunnel gas outburst work area section is about 647 m. From the above parameters, it can be seen that the harmfulness of outbursts in the tunnel coal uncovering area is very great. Taking the No. 46-lower coal seam with the largest accumulated gas pressure as an example, the thickness of the protective rock pillar is calculated. The No. 46-lower coal seam of this tunnel is a coal and gas outburst coal seam, the included angle between the coal seam and the tunnel is 20°, the roof and floor of the coal seam are mainly sandstone, conglomerate intercalated with mudstone, and the tunnel uncovers the coal from the coal seam floor. The average tensile strength R t = 4.04 MPa.

[0052] According to the formula for obtaining the target safety thickness above, when uncovering the No. 46-lower coal seam in the conventional section, the thickness δ c of the protective rock pillar is 3.44 m; when uncovering the No. 46-lower coal seam in the widened section, the thickness δ j of the protective rock pillar is 4.49 m.

[0053] During on-site construction, in the conventional section of the tunnel, the No. 46 - lower coal seam was exposed at a depth of approximately 5.7 m (converted to approximately 3.15 m at the weakest point) when drilling about 1 m from the bottom plate of the tunnel face. By comparing the theoretical calculation results with the measured values, the theoretical value was 9.2% higher than the actual value, and the error result was within the controllable range of safety accidents. Thus, it can be seen that the pillar setting deduced according to this theory conforms to the engineering practice, meets the requirements for the pillar setting size when uncovering coal at the tunnel face of a gas outburst tunnel, and has guiding significance for the setting of actual safety pillars.

Claims

1. A method for determining the size of a coal-and-gas outburst tunnel face coal-exposing protection rock pillar, characterized in that: include: Determining a deformation function of the protective rock column according to the displacement deformation function, wherein the displacement deformation function is used to indicate the displacement deformation function in classical elastic mechanics; Based on the deformation function and the boundary conditions of the plate theory, determine the stress components of the protective rock column, and determine the maximum principal stress of the protective rock column according to the stress components; The tensile strength of the protective rock column is obtained, and the target safe thickness of the protective rock column is determined according to the tensile strength and the maximum principal stress.

2. The method according to claim 1, characterized in that Determining the deformation function of the protective rock column according to the displacement deformation function includes: The deformation function is calculated using the following formula: in, w is the deformation function, m、n is a positive integer, π is the circumference of a circle, represents positive infinity, are constant coefficients of the deformation function expansion, is the width of the tunnel section corresponding to the protective rock column, is the height of the protective rock pillar corresponding to the tunnel section, is the horizontal distance of the protective rock pillar perpendicular to the tunnel excavation direction, z is the vertical distance of the protective rock column.

3. The method according to claim 2, characterized in that The plate theory is a classical elastic mechanics plate theory, the boundary conditions are used to indicate the boundary conditions for first generating cracks around the edge of the protective rock pillar, and the stress components of the protective rock pillar based on the deformation function and the boundary conditions of the plate theory are determined, including: Determine the position information of the boundary condition and determine the stress component function corresponding to the deformation function by using the Kirchhoff-Love assumption, wherein the position information of the boundary condition is used to indicate the position information corresponding to the boundary condition where cracks first occur around the edge of the protective rock column, and the position information corresponding to the boundary condition where cracks first occur around the edge of the protective rock column is (0 ，- / 2 ，h / 2) 、 ( ，- / 2 ，h / 2), is the thickness of the protective rock column, and the thickness of the protective rock column is used to indicate the target safety thickness; The position information is input into the stress component function to obtain the stress component of the protective rock column.

4. The method according to claim 3, characterized in that The stress component is calculated using the following formula: in, is the horizontal stress component of the protective rock pillar perpendicular to the tunneling direction, is the stress component of the protective rock column in the direction perpendicular to the horizontal direction, is the shear stress component of the protective rock column in a direction perpendicular to the first plane, the first plane is used to indicate the plane formed by the horizontal direction and the direction perpendicular to the horizontal direction, P The gas pressure generated by the coal seam gas in the protective rock pillar is is the Poisson's ratio of the protective rock column.

5. The method according to claim 4, characterized in that Determining the maximum principal stress of the protective rock column according to the stress components includes: Inputting the stress component into a maximum stress function to obtain the maximum principal stress, wherein the maximum stress function is a stress function in elastic mechanics; The expression of the maximum principal stress is as follows: in, is the maximum principal stress solved for.

6. The method according to claim 5, characterized in that The step of determining the target safe thickness of the protective rock column according to the tensile strength and the maximum principal stress comprises: When the maximum principal stress is not greater than the tensile strength, the target safety thickness is determined according to the maximum principal stress.

7. The method according to claim 6, characterized in that Determining the target safety thickness according to the maximum principal stress includes: The target safety thickness is calculated using the following formula: Among them, 1.22 is the energy method geometric correction coefficient, R t is the tensile strength.

8. The method according to claim 7, characterized in that The tunnel section corresponding to the protective rock pillar is used to indicate the tunnel face of coal and gas outburst, and the method further includes: If the width of the tunnel section corresponding to the protective rock pillar, the height of the tunnel section corresponding to the protective rock pillar and the tensile strength are preset values, the target safety thickness is determined based on the gas pressure generated by the coal seam gas on the protective rock pillar.

Images