A method for processing safe thickness of rock outburst in non-coal stratum tunnels based on energy method

Abstract

The present invention relates to the technical field of tunnel engineering, and in particular to a method for processing the safe thickness of rock outbursts in non-coal strata tunnels based on an energy method. The system comprises S1, making basic assumptions and limitations on the tunnel being excavated; S2, establishing a relationship between gas pressure and the minimum anti-outburst thickness of the rock mass according to the principle of energy conservation; S3, calculating the gas pressure before outburst in actual cases according to the energy method; and S4, verifying the correctness of the calculation results by using FLAC3D software. The present invention solves the problem that the prior art cannot effectively realize the calculation of gas and rock outbursts in non-coal strata.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel engineering, and in particular to a method for processing the safe thickness of rock outbursts in non-coal stratum tunnels based on an energy method. Background Art

[0002] Gas and rock bursts during tunnel construction can lead to face collapse, intrusion of protrusions into the tunnel space, damage to the tunnel support structure, and damage to construction machinery. Large amounts of protruding gas may cause suffocation or even explosion. Coal and gas bursts are the most common type of outburst accidents during tunnel construction. There are a lot of studies on gas outbursts in coal seam tunnels and some special technologies have been used to prevent coal and gas outbursts in tunnel construction based on coal mining experience. In order to predict the cost of rock and gas outbursts in the hard coal deposit "Nowa RudaPole Piast Wacaw-Lech", a prediction model for the degree of gas and rock outbursts was established using the random forest algorithm with the "XGBoost" machine learning method. The model can predict the range of rock and gas outbursts. The prediction of the range of outbursts is related to the mass of the outburst rock, the volume of gas, and the length of the outburst cavity.

[0003] It is currently believed that the combined factors of ground stress, rock mechanical parameters and gas pressure lead to the occurrence of outbursts. The mechanism of rock and CO2 outburst was discussed, the physical model of rock and CO2 outburst was established, the process and mechanical environment of rock and CO2 outburst were analyzed, and it was pointed out that the key structure theory based on coal and gas outburst is applicable to rock and gas outburst in non-coal strata. At the same time, the rock and CO2 outburst criterion was established using the energy method. The study deeply studied the mechanism of gas and rock outburst, and pointed out that the energy of outburst comes from the elastic deformation energy of rock, gas expansion energy and rock gravity potential energy. The ground stress, rock mechanical parameter test and CO2 gas pressure were measured, and the tunnel stress field analysis was calculated using numerical software, and the outburst mechanism was discussed from a mechanical perspective. Skoczylas, N obtained relevant knowledge and experience by consulting experts engaged in the assessment and prediction of gas and rock outbursts, and then established an expert system for estimating the risk of gas and rock outbursts based on fuzzy logic. Then, in order to predict the cost caused by rock and gas outbursts in the hard coal deposit "Nowa RudaPole Piast Wacaw-Lech", a prediction model for the degree of gas and rock outbursts was established using the random forest algorithm with the "XGBoost" machine learning method. The obtained model can predict the range of rock and gas outbursts. The prediction of the outburst range is related to the outburst rock mass, gas volume and outburst cavity length.

[0004] In recent years, due to the development of deep space, the losses and hazards caused by gas and rock outbursts can no longer be ignored, or in other words, gas and rock outbursts have become one of the main disasters in deep space, and have attracted people's attention. Mathematical methods have begun to be introduced into the application technology of gas and rock outburst prediction. However, the existing research results mainly study the geological environment where outbursts occur and outburst prediction and prevention, while there are few studies on high-pressure gas and rock outbursts in non-coal strata tunnels and related prevention. Summary of the invention

[0005] The purpose of the present invention is to provide a method for processing the safe thickness of rock outbursts in non-coal strata tunnels based on an energy method, so as to solve the problem that the prior art cannot effectively calculate the gas and rock outbursts in non-coal strata.

[0006] The purpose of the present invention is achieved by the following technical scheme: a method for processing rock outburst safety thickness in a non-coal stratum tunnel based on an energy method, comprising the following steps:

[0007] S1. Make basic assumptions about the tunnel being excavated;

[0008] S2. Establish the relationship between gas pressure and minimum rock outburst prevention thickness based on the principle of energy conservation;

[0009] S3. Calculate the gas pressure before outburst in actual cases according to the energy method;

[0010] S4. Verify the correctness of the calculation results using FLAC3D software.

[0011] It should be noted that the energy method, a comprehensive method used to study the mechanism of non-coal formation gas and rock outburst, is introduced into the study of the mechanism of non-coal formation gas and rock outburst in tunnel engineering. The non-coal formation gas and rock outburst is studied to obtain the mechanism of non-coal formation gas and rock outburst, and to implement corresponding prevention and remedial measures for non-coal formation gas and rock outburst.

[0012] Furthermore, the basic assumptions in S1 include the following:

[0013] S101. Assume that the tunnel excavation section is circular;

[0014] S102. Assume that the main energy of the outburst comes from the gas expansion energy and the elastic potential of the outburst rock mass;

[0015] S103. Assume that the failure of the rock mass complies with the Mohr–Coulomb criterion;

[0016] S104. Assume that the rock mass conforms to the relevant assumptions of elasticity mechanics;

[0017] S105. Assume that the outburst pushes out all the rock mass in front of the outburst termination line.

[0018] It should be noted that since the energy method needs to consider the impact of comprehensive factors such as rock physical and mechanical properties, gas rock mass and ground stress on the outburst, corresponding assumptions are made to achieve advanced research.

[0019] Furthermore, the S2 mainly considers the surface energy required for the generation of the new surface and the kinetic energy required for throwing the rock mass, specifically including:

[0020] S201. According to the principle of conservation of energy, the calculation expression (1) is obtained;

[0021] E2+W=E1+A i (1)

[0022] Among them, E2 is the work done by gas expansion, W is the elastic potential of the protruding rock mass, E1 is the surface energy required for the generation of the new surface, and A i (i=1, 2) is the kinetic energy required to throw the rock

[0023] The mass conservation expression (2) of gas and rock mass during the outburst process is:

[0024] M=ρ1V1=ρ2V2 (2);

[0025] Where M is the mass of the protruding rock mass, ρ1 is the average density of the rock mass before it is ejected, V1 is the volume of the rock mass before it is ejected, ρ2 is the average density of the rock mass after it is ejected, and V2 is the accumulated volume of the rock mass after it is ejected.

[0026] Wherein, S2 also includes S202. The surface energy E1 required for the generation of the new surface is that a certain amount of energy must be consumed to break the rock mass into a certain size. Assuming that the particles after the rock mass is broken are spherical, the surface energy expression (3) required for the generation of the new surface is:

[0027] E1=eV1=6W∑(γ i 1 / d i )V1 (3)

[0028] Among them, e is the crushing specific work, i is the crushing ratio, V1 is the volume of the rock mass before the outburst, γ i is the content percentage, d i is the particle size, and W represents the energy including losses required to create a new unit surface area.

[0029] It is necessary to explain that the above is a method for calculating the crushing work.

[0030] Wherein, S2 also includes S203. The surface energy 1 required for the generation of new surface is that the rock mass must consume a certain amount of energy to be broken into a certain size. For dense rock, the effect of gas desorption on expansion energy does not need to be considered. The expression (4) of the work done by high-pressure gas expansion 2 is:

[0031] E2=w=P2V2 / (n-1)[((p1 / p2) n-1 / n)-1] (4)

[0032] Among them, P1 is the high-pressure gas pressure of the rock formation, V1 is the volume of high-pressure gas in the rock formation, P2 is the high-pressure gas pressure of the mining face after the outburst occurs, V2 is the high-pressure gas volume of the mining face after the outburst occurs, and n is the process index.

[0033] It should be noted that the above is a method for calculating the internal energy of a gas.

[0034] Wherein, the S2 also includes S204, the main energy source of the protrusion is the elastic strain energy in the protruding rock mass,

[0035] The expression (5) for the energy of the rock mass in a certain area is:

[0036] W = ∫ Vs U e dV (5)

[0037] Among them, Vs is the volume of the rock mass before the outburst, and E is the elastic modulus of the rock mass before the outburst.

[0038] It is necessary to explain that the above is a method for calculating the elastic potential of rock mass.

[0039] Wherein, the S2 also includes S205. Without considering the influence of the construction on the disturbance of the rock mass in front of the working face, the expression (6) of the rock mass thickness is:

[0040] L={6W∑(γ i 1 / d i )V1-P2V2 / (n-1)[((p1 / p2) n-1 / n)-1]} / (s×U e ) (6)

[0041] Among them, s is the cross-sectional area of ​​the protruding part of the rock mass.

[0042] It should be noted that the above is a method for calculating the ejection work.

[0043] Compared with the prior art, the present invention has the following advantages and beneficial effects: the energy sources of the outburst process are the elastic potential of the rock mass and the expansion work of the gas, the energy consumption part is mainly the rock mass crushing work and the ejection work, and the critical condition for the outburst is that only the rock mass crushing consumes energy, so as to obtain the formula for the safe thickness of the high-pressure gas outburst prevention, and the high-pressure gas pressure has a great influence on the minimum safe thickness of the rock mass; the energy method takes into account the influence of ground stress, gas pressure and the physical and mechanical properties of the surrounding rock on the outburst, and considers the factors affecting the outburst more comprehensively. The gas pressure of the high-pressure gas outburst in the Hongdoushan inclined shaft was inverted using FLAC3D software to be 7.5MPa, which is consistent with the actual situation, verifying the applicability of the formula. The method described in the research application can provide ideas for high-pressure gas outburst prevention in non-coal stratum tunnels and effectively reduce the occurrence of outburst accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] none DETAILED DESCRIPTION

[0045] Embodiment 1:

[0046] This embodiment provides a method for processing the safe thickness of rock outbursts in tunnels in non-coal formations based on the energy method. The method for processing the safe thickness of rock outbursts in tunnels in non-coal formations based on the energy method is mainly used to solve the problem that the existing technology cannot effectively calculate the gas and rock outbursts in non-coal formations. The method for processing the safe thickness of rock outbursts in tunnels in non-coal formations based on the energy method is already in the actual use stage.

[0047] The present application is carried out through the following embodiments, and a method for processing rock outburst safety thickness in a non-coal stratum tunnel based on an energy method comprises the following steps:

[0048] S1. Make basic assumptions about the tunnel being excavated;

[0049] S2. Establish the relationship between gas pressure and minimum rock outburst prevention thickness based on the principle of energy conservation;

[0050] S3. Calculate the gas pressure before outburst in actual cases according to the energy method;

[0051] S4. Verify the correctness of the calculation results using FLAC3D software.

[0052] It should be noted that regarding the minimum thickness of the rock mass before the gas and rock outburst, the energy method, a comprehensive method used for the study of the outburst mechanism, is introduced into the study of the outburst mechanism of gas and rock in non-coal strata in tunnel engineering. The energy method takes into account the influence of comprehensive factors such as rock physical and mechanical properties, gas rock mass and ground stress on the outburst. When the tunnel is excavated, the force balance of the rock mass in the original stress state in front of the face is broken, and stress reduction zone, stress concentration zone and original stress zone appear in sequence. The sudden change of stress in the rock mass causes high-speed destruction of the rock mass, and the rock mass undergoes body displacement under the action of rock mass elastic potential and gas expansion energy. Ground stress mainly plays the role of crushing the rock mass, and gas expansion energy plays the role of crushing the rock mass and transporting the outburst. In terms of the order of magnitude of energy, gas expansion energy accounts for the main part.

[0053] The basic assumptions in S1 include the following:

[0054] S101. Assume that the tunnel excavation section is circular;

[0055] S102. Assume that the main energy of the outburst comes from the gas expansion energy and the elastic potential of the outburst rock mass;

[0056] S103. Assume that the failure of the rock mass complies with the Mohr–Coulomb criterion;

[0057] S104. Assume that the rock mass conforms to the relevant assumptions of elasticity mechanics;

[0058] S105. Assume that the outburst pushes out all the rock mass in front of the outburst termination line.

[0059] It should be noted that the crushing work, internal energy of the gas, elastic potential of the rock mass, and ejection work need to be determined.

[0060] The calculation method of crushing work is as follows: S2 mainly considers the surface energy required for the generation of new surface and the kinetic energy required for throwing rock mass, specifically including: S201, according to the principle of conservation of energy, the calculation expression (1) is obtained;

[0061] E2+W=E1+A i (1)

[0062] Among them, E2 is the work done by gas expansion, W is the elastic potential of the protruding rock mass, E1 is the surface energy required for the generation of the new surface, and A i (i=1, 2) is the kinetic energy required to throw the rock

[0063] The mass conservation expression (2) of gas and rock mass during the outburst process is:

[0064] M=ρ1V1=ρ2V2 (2);

[0065] Where M is the mass of the protruding rock mass, ρ1 is the average density of the rock mass before it is ejected, V1 is the volume of the rock mass before it is ejected, ρ2 is the average density of the rock mass after it is ejected, and V2 is the accumulated volume of the rock mass after it is ejected.

[0066] It should be noted that the main energy provided by the outburst of gas and rock in the tunnel is the work done by gas expansion and the elastic potential of the outburst rock. The energy consumed in the outburst process mainly includes: acoustic energy, heat generated by internal surface slip, surface energy required for new surface generation, local resistance energy consumption in the outburst path, friction resistance energy consumption, kinetic energy required for tearing and throwing rock in the outburst path, and residual kinetic energy corresponding to the minimum speed required for high-pressure gas to enter the air.

[0067] In this embodiment, S2 also includes S202. The surface energy E1 required for the generation of the new surface is that a certain amount of energy must be consumed to break the rock mass into a certain size. Assuming that the particles after the rock mass is broken are spherical, the surface energy expression (3) required for the generation of the new surface is:

[0068] E1=eV1=6W∑(γ i 1 / d i )V1 (3)

[0069] Among them, e is the crushing specific work, i is the crushing ratio, V1 is the volume of the rock mass before the outburst, γ i is the content percentage, d i is the particle size, and W represents the energy including losses required to create a new unit surface area.

[0070] Specifically, a certain amount of energy must be consumed to break the rock mass into a certain size. The rock mass is broken from size D to size d, and its crushing ratio is represented by i, that is, expression (301):

[0071] i=D / d (301)

[0072] The larger the crushing ratio, the more work is required to crush a unit volume of rock, that is, the greater the crushing specific work e. The new surface theory is used to solve the crushing work of the protruding rock mass. The new surface theory believes that the only difference before and after the object is crushed is the addition of a new surface, and the energy required to obtain the new surface is proportional to the crushing work. When the size is crushed from D to d, the change in the surface area of ​​the unit volume of the object is proportional to (1 / d-1 / D). Therefore, the crushing specific work is shown in formula (302):

[0073] e=K R (1 / d-1 / D) (302)

[0074] Among them, K Ris a constant that depends on the material properties and crushing method. It should be noted that the harder the rock mass, the more work is consumed in crushing. It is expressed by the crushing ratio i, and then as shown in formula (303):

[0075] e=K R / D(i-1) (303)

[0076] Furthermore, when calculating the crushing ratio work, the average size should be calculated by using the weighted average method of the inverse of the content of each size (particle size). When the crushing ratio is large, that is, (1 / D) is very small compared to (1 / d), (1 / D) can be ignored, and equation (303) can be written as shown in equation (304):

[0077] e=K R / d (304)

[0078] Furthermore, assuming that the particle is regarded as a sphere, the surface area per unit volume is 6 / d, and W represents the energy spent on establishing a new unit surface area, including the energy lost, then equation (304) can be written as shown in equation (305):

[0079] e=6W∑(γ i 1 / d i ) (305)

[0080] Therefore, based on the mass conservation, crushing ratio and laboratory SHPB test, the energy consumption expression of the crushed rock crushing surface can be obtained (3):

[0081] E1=eV1=6W∑(γ i 1 / d i )V1 (3)

[0082] In this embodiment, the calculation method of gas internal energy: S2 also includes S203. The surface energy required for the generation of a new surface is that a certain amount of energy must be consumed to break the rock mass into a certain size. For dense rocks, the effect of gas desorption on expansion energy does not need to be considered. The expression (4) for the work done by high-pressure gas expansion is:

[0083] E2=w=P2V2 / (n-1)[((p1 / p2) n-1 / n)-1] (4)

[0084] Among them, P1 is the high-pressure gas pressure of the rock formation, V1 is the volume of high-pressure gas in the rock formation, P2 is the high-pressure gas pressure of the mining face after the outburst occurs, V2 is the high-pressure gas volume of the mining face after the outburst occurs, and n is the process index.

[0085] Furthermore, at the moment of outburst, gas is stored in the rock mass. The heat energy required for gas expansion comes from the rock mass, because the heat capacity and thermal conductivity of the rock mass are relatively large. At the same time, when the ground stress breaks the rock mass, part of the elastic energy is converted into heat energy, which can be supplied to the gas for expansion. At this time, the internal energy of the expanding gas can be calculated according to the isothermal process; when the broken rock mass separates from the parent body, the internal energy of the expanding gas belongs to a variable process, and finally approaches an adiabatic process. This is because the gas in the rock layer is in a state of thermal expansion at this time, and the expanding gas does not have time to exchange heat with the outside world. According to the first law of thermodynamics, formula (401):

[0086] dQ=dE2+PdV (401)

[0087] Furthermore, in the adiabatic process, the energy exchange between the system and the outside world is 0, so equation (401) can be expressed as (402):

[0088] dE2+PdV=0 or dw=PdV=-dE2 (402)

[0089] Furthermore, in the adiabatic process, only through the change of the internal energy of the gas in the rock formation can work w be done to the outside world. From thermodynamics, it is known that when the temperature changes, the change relationship of the internal energy of the rock formation gas is as shown in (403):

[0090] dE2=MCγdT / U (403)

[0091] Where M is the mass of the gas, U is the molecular weight, and C γ is the molecular heat capacity of the gas at constant volume, and T is the absolute temperature.

[0092] Furthermore, the work done by the gas outward, that is, the expansion energy of the gas, is expressed as shown in (404):

[0093] W=∫dw=-∫ T1 T2 MCγ / UdT=M / U·Cγ(T1-T2) (404)

[0094] It should be noted that in the art, it is relatively easy to measure the gas pressure of rock formations during tunnel excavation. Therefore, the expression of the gas pressure P can be obtained based on the relationship between the gas pressure P, the gas volume V and the gas temperature T during the adiabatic equilibrium process. That is, the expressions between P, V and T are shown in (405), (406), (407) and (408):

[0095] P1V1 n =P2V2 n (405)

[0096] V1 n-1 T1=V2 n-1T2 (406)

[0097] P1 n-1 T1 -n =P2 n-1 T2 -n (407)

[0098] n=C P / C γ (408)

[0099] Among them, P1 is the high-pressure gas pressure of the rock formation, V1 is the volume of high-pressure gas in the rock formation, and T1 is the temperature of high-pressure gas in the rock formation; P2 is the high-pressure gas pressure of the mining face after the outburst occurs, V2 is the volume of high-pressure gas in the mining face after the outburst occurs, and T2 is the gas temperature of the mining face after the outburst occurs; n is the process index, C P is the molecular heat capacity of the gas at constant pressure.

[0100] Therefore, the expression (4) for the work done by the expansion of high-pressure gas is:

[0101] E2=w=P2V2 / (n-1)[((p1 / p2) n-1 / n)-1] (4)

[0102] In this embodiment, the calculation method of rock mass elastic potential: S2 further includes S204, the main energy source of the protruding rock mass is the elastic strain energy,

[0103] The expression (5) for the energy of the rock mass in a certain area is:

[0104] W = ∫ Vs U e dV (5)

[0105] Among them, Vs is the volume of the rock mass before the outburst, and E is the elastic modulus of the rock mass before the outburst.

[0106] It should be noted that tunnel excavation will cause stress redistribution in the front, forming stress reduction zone, stress concentration zone and original stress zone in sequence. As excavation gradually advances, the stress in front of the face changes, and the accurate solution of stress redistribution caused by mining is difficult to obtain. In addition, the rock mass in the tunnel is complex and anisotropic, and the tectonic stress leads to uneven stress distribution in the rock mass. There are many interference factors in the energy release area, which are related to ground stress, physical and mechanical properties of rock mass, etc. It is impractical to fully conform to the energy derivation on site, and it is not generally representative. The rock mass around the protruding rock mass provides little energy for the protrusion, and the main energy source of the protrusion is the elastic strain energy in the protruding rock mass. Therefore, it is reasonable to calculate the elastic potential of the rock mass under the S1 assumption. The energy stored in the rock mass exists in the form of elastic deformation energy and plastic deformation energy. Only the elastic deformation energy in the rock mass has the ability to do work externally. The formula for the elastic deformation energy density of the rock mass in the rock mass is shown as (501):

[0107] U e =1 / 2E[(σ1 2 +σ2 2 +σ3 2 )-2μ(σ1·σ2+σ1·σ3+σ2·σ3)] (501)

[0108] Therefore, the expression (5) for the energy of the rock mass in a certain area is:

[0109] W = ∫ Vs U e dV (5)

[0110] Wherein, Vs is the volume of the rock mass before the outburst, σ1 is the first principal stress in the rock mass before the outburst, σ2 is the second principal stress in the rock mass before the outburst, σ3 is the third principal stress in the rock mass before the outburst, E is the elastic modulus of the rock mass before the outburst, and μ is the Poisson's ratio of the rock mass before the outburst.

[0111] It should be noted that when the stress distribution of the protruding rock mass is difficult to obtain, the elastic potential of the rock mass can be calculated by approximately using the stresses in the maximum stress area of ​​the rock mass. At this time, the calculated elastic potential is large, which will cause the safety thickness calculated later to be larger than the accurate value. The elastic potential calculated under the assumption of uniformly distributed stress may be larger than the actual value.

[0112] In this embodiment, the calculation method of ejection work is as follows: S2 also includes S205, ignoring the influence of construction on the disturbance of the rock mass in front of the working face, the expression (6) of the rock mass thickness is:

[0113] L={6W∑(γ i 1 / d i )V1-·P2V2 / (n-1)[((p1 / p2) n-1 / n)-1]} / (s×U e )

[0114] Among them, s is the cross-sectional area of ​​the protruding part of the rock mass.

[0115] It should be noted that the broken rock mass is converted into the energy of the movement of the rock mass in the tunnel, the friction heat of the airflow and the rock mass hitting the tunnel wall, brackets and other obstacles, sound energy, vibration and other energies during the outburst process. The straighter the tunnel, the fewer obstacles there are in the tunnel, and the farther the rock mass is thrown in the tunnel, among which the energy consumption is mainly the movement of the rock mass. When the outburst intensity is large, the outbursts fill the entire tunnel, and the calculation formula for the accumulation surface position is shown in (601):

[0116]

[0117] Where r is the tunnel height,

[0118] Furthermore, when the protrusion intensity is small and the protrusion cannot fill the entire tunnel, the relationship between the ejected rock mass and the ejection position is as shown in formula (602):

[0119] f(x)=-tanα2·x+|OF|·tanα2·x (602)

[0120] According to BB Hodott's calculation and the assumptions in this paper, the expression of the unit's ejection work is shown in (603):

[0121] dA=xgf1dm (603)

[0122] The rough calculation expression of the coal mass in the slope part of the above two outburst situations is shown as (604):

[0123] dm=2rρf(x)dx (604)

[0124] Furthermore, the expression for calculating prominence is obtained by combining the calculation expression (18);

[0125] When the protrusion strength is large, the calculation formula is as shown in (605):

[0126] A1=∫0 |OD| dA=∫0 |OE| xgf1ρ1 / 2Πr 2 dx+∫ |OE| |OD| xgf12rρf(x)dx

[0127] =1 / 4Πgρf1r 2 |OE| 2 +2rρgf1tan·α1[1 / 3|OE| 3 +1 / 6|OD| 3-1 / 2|OD||OE| 2 ] (605)

[0128] When the protrusion strength is small, the ejection work is shown as (606);

[0129] A2=∫0 OF dA=∫0 OF xgf12rρf(x)dx

[0130] =1 / 3rρgf1·|OF| 3 tanα2 (606)

[0131] Among them, f1 is the friction factor, ρ is the density of the rock mass after the outburst, α1 and α2 are the angles between the outburst accumulation and the horizontal plane, |OF| is the length of the accumulation, r is the height of the tunnel, and g is the acceleration of gravity.

[0132] Furthermore, when the energy provided is only used to break the rock mass to form a new surface, this is a critical state of protrusion. According to the principle of conservation of energy, the energy conservation equation is established, expression (607). The rock mass thickness calculated by equation (607) plus the excavation disturbance thickness is the minimum safe thickness.

[0133] P2V2 / (n-1)[((p1 / p2) n-1 / n)-1]+∫ Vs U e dV=6W∑(γ i 1 / d i )V1 (607)

[0134] Therefore, assuming that the in-situ stress in the protruding rock mass is uniformly distributed, equation (607) can be expressed as equation (6):

[0135] L={6W∑(γ i 1 / d i )V1-·P2V2 / (n-1)[((p1 / p2) n-1 / n)-1]} / (s×U e ) (6)

[0136] Among them, s represents the cross-sectional area of ​​the rock mass of the protruding part.

[0137] Furthermore, this formula does not consider the impact of construction on the rock mass disturbance in front of the working face. The formula that considers the impact of construction on the disturbance depth of the working face is (608) as follows:

[0138] L=l+l1 (608)

[0139] Where, l is the calculated rock mass thickness;

[0140] l1 is the impact depth of construction on the working surface, which can be obtained through detection or calculation with numerical software.

[0141] Embodiment 2:

[0142] After the Hongdoushan No. 1 inclined well gas and rock protruded, the gas flowed out of the cave in a reverse direction. After the protrusion, the residual CO2 gas pressure in the formation water was 0.2-0.3MPa. The protruding gas was mainly CO2, followed by N2 and O2, and the associated gases were H2S, NH3, SO2, CO and other harmful gases. After sampling and indoor analysis, it was determined that the gas was a mixed source gas of mantle origin and metamorphic origin.

[0143] The maximum length of the protruding rock mass in front of the face is 15m, with a total volume of 150m 3 The protruding rock mass is granite mylonite, which is loose, fine sand and powdery, mixed with gravel, with a particle size of 10 to 20 cm and a dark gray color. There is water accumulation in the protrusions. The surrounding rock is strongly weathered granite mylonite, with slightly lower rock strength, well-developed joints and fissures, developed closed joints, poor rock integrity, many weak interlayers, and water seepage.

[0144] Further, the relevant data of the on-site investigation: the physical and mechanical indicators of the rock mass in the area are shown in Table 1. According to the on-site cleaning of the protrusions, it was found that the rock mass deposits were loose, with a large percentage of powder and dust. The density of the protrusions was determined to be 1.6t / m 3 The tunnel site has experienced multiple tectonic activities, and faults are developed in the area. Gas in the deep strata migrates to the shallow rock fragmentation zone through faults and other means for storage. Due to the strong tectonic activities, ground stress measurements were conducted to prevent rock bursts, as shown in Table 2. The study found that the energy required to create a new surface area per unit of medium-strength rock is 0.1-0.12 MJ / m 2 The distribution of the specific work of crushing granite by diamond drill bits in granite formations is shown in Table 3.

[0145] Table 1 Mechanical indexes of rock mass in Hongdoushan outburst section (exploration data)

[0146]

[0147] Table 2 In-situ stress measurement results of Hongdoushan No. 1 inclined well hydraulic fracturing

[0148]

[0149] Further, the energy method model of this application is applied, and the FLAC3D model and related conditions are used to eliminate the boundary effect. According to the elastic mechanics theory, the surrounding rock at a radius of 6 times the tunnel is basically in the original rock stress state. When modeling in the FLAC3D software, the surrounding rock thickness around the tunnel is 6 times the tunnel radius. In the physical model, the cylindrical tunnel periphery gradient radial grid units and hexahedral block grid units are used. The tunnel radius is set to 3m. The blocking rock mass should be set to a fluid-solid coupling model. Because the local rock mass is set to fluid-solid coupling and cannot run in FLAC3D, the gas pressure is set to uniform stress acting on the rock mass surface. The gas pressure is set to 3MPa, 4MPa, 5MPa, 6MPa, 7.5MPa, 9MPa in turn, and the rock mass blocking thickness is 2.6m. The upper surface of the Z axis is free, and the other surfaces are set to fixed constraints. The physical and mechanical parameters of the rock mass are the physical and mechanical parameters of granite as shown in Table 3. The ground stress is applied according to the measured value, and the ground stress is generated by the elastic solution method. Then the tunnel is excavated to calculate the deformation of the blocking section rock mass at different stress levels.

[0150] Table 3 Physical and mechanical parameters of granite

[0151]

[0152]

[0153] Furthermore, the energy calculation of the protrusion example and the protrusion related parameters are shown in Table 4. According to the data in the table, the rock mass thickness is calculated to be about 2.6m. When using the energy method to calculate the rock mass potential, it is difficult to obtain the stress distribution in the rock mass. It is assumed that the above stress is evenly distributed in the protruding rock mass, and the elastic potential of the protruding rock mass is calculated to be 0.55MJ. The calculation of crushing work and moving work are listed in Tables 5 and 6 respectively.

[0154] Table 4 Rock mass outburst parameters

[0155]

[0156] Table 5 Crushing work calculation parameters

[0157]

[0158] Table 6 Parameters for calculation of mobile work

[0159]

[0160] Since the gas pressure before the outburst and the gas volume after the outburst were not obtained, by collecting CO2 and rock outburst cases, it was found that the gas volume had no correlation with the amount of outburst rock mass, so the trial calculation method was used to calculate the gas pressure and gas volume. The gas process index was 1.25, and the residual gas pressure was 0.25MPa; after the trial calculation, the final gas pressure was 7.5MPa and the gas volume was 814.469m3.

[0161] Therefore, according to the inversion of the relevant parameters of the outburst, the granite plugging thickness is 2.6m, the gas pressure is 7.5MPa, and the gas volume is 814.469m3. The calculation results of FLAC3D show that the deformation of the tunnel face is 4.7cm when the gas pressure is 3MPa, the deformation of the tunnel face is 4.7cm when the pressure is 4MPa, and the maximum deformation of the tunnel face is 47cm under the gas pressure of 5MPa. When the applied pressure is 6MPa, the maximum deformation of the tunnel face is 4.7m. When the pressure exceeds 6MPa, the maximum deformation of the tunnel face remains unchanged at 4.7m. The first change in the slope of the straight line is the rock breaking (blocks falling in the tunnel, tunnel face bulging, etc.), and the second change in the slope of the straight line is the crushing and ejection of the relatively broken rock.

[0162] The energy sources of the outburst process are the elastic potential of the rock mass and the expansion work of the gas. The energy consumption part is mainly the rock mass crushing work and the ejection work. The critical condition of the outburst is that only the rock mass crushing consumes energy. Based on this, the formula for the safe thickness of high-pressure gas outburst prevention is derived. The high-pressure gas pressure has a great influence on the minimum safe thickness of the rock mass. The energy method takes into account the influence of ground stress, gas pressure and the physical and mechanical properties of the surrounding rock on the outburst, and considers the factors affecting the outburst more comprehensively. The gas pressure of the high-pressure gas outburst in the Hongdoushan inclined shaft was inverted using FLAC3D software to be 7.5MPa, which is consistent with the actual situation, verifying the applicability of the formula. The method described in the research application can provide ideas for high-pressure gas outburst prevention in non-coal formation tunnels and effectively reduce the occurrence of outburst accidents.

[0163] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for processing the safe thickness of rock outburst in non-coal stratum tunnels based on energy method, characterized in that: The following steps are involved: S1. Make basic assumptions about the tunnel being excavated; S2. Establish the relationship between gas pressure and minimum rock outburst prevention thickness based on the principle of energy conservation; S3. Calculate the gas pressure before outburst in actual cases according to the energy method; S4. Verify the correctness of the calculation results by FLAC3D software; The S2 mainly considers the surface energy required for the generation of new surface and the kinetic energy required for throwing the rock mass, including: S201. According to the principle of energy conservation, the calculation expression (1) is obtained; <h2 style=";text-align:left;direction:ltr">E2+W=E1+A<h2 style=";text-align:left;direction:ltr"> i <h2 style=";text-align:left;direction:ltr"> (1) Among them, E2 is the work done by gas expansion, W is the elastic potential of the protruding rock mass, E1 is the surface energy required for the generation of the new surface, and A i Kinetic energy required to throw the rock The mass conservation expression (2) of gas and rock mass during the outburst process is: M=ρ1V1=ρ2V2 (2); Where M is the mass of the protruding rock mass, ρ1 is the average density of the rock mass before it is ejected, V1 is the volume of the rock mass before it is ejected, ρ2 is the average density of the rock mass after it is ejected, and V2 is the accumulated volume of the rock mass after it is ejected; The S2 further includes: S202, the surface energy E1 required for the generation of a new surface is the energy required to break the rock mass into a certain size. Assuming that the particles after the rock mass is broken are spherical, the surface energy expression (3) required for the generation of a new surface is: E1=eV1=6W∑(γ i* 1 / d i )V1 (3) Among them, e is the crushing specific work, i is the crushing ratio, V1 is the volume of the rock mass before the outburst, γ i is the content percentage, d i is the particle size, W represents the energy including losses spent to create a unit new surface area; The S2 further includes: S203. The surface energy required for the generation of new surfaces is the energy required to break the rock mass into certain pieces. For dense rocks, the effect of gas desorption on expansion energy does not need to be considered. The expression (4) for the work done by high-pressure gas expansion is: Among them, p1 is the high-pressure gas pressure of the rock formation, V1 is the high-pressure gas volume of the rock formation, p2 is the high-pressure gas pressure of the mining face after the outburst occurs, V2 is the high-pressure gas volume of the mining face after the outburst occurs, and n is the process index; The S2 further includes: S204. The main energy source of the outburst is the elastic strain energy in the outburst rock mass. The expression (5) for the energy of the rock mass in a certain area is: W=∫ Vs U e dV (5) Among them, Vs is the volume of the protruding rock mass before the protrusion, U e is the energy density of elastic deformation of rock mass.

2. The method for processing rock outburst safety thickness in non-coal stratum tunnels based on energy method according to claim 1 is characterized in that: The basic assumptions in S1 include the following: S101. Assume that the tunnel excavation section is circular; S102. Assume that the main energy of the outburst comes from the gas expansion energy and the elastic potential of the outburst rock mass; S103. Assume that the failure of the rock mass complies with the Mohr–Coulomb criterion; S104. Assume that the rock mass conforms to the relevant assumptions of elasticity mechanics; S105. Assume that the outburst pushes out all the rock mass in front of the outburst termination line.

3. The method for processing rock outburst safety thickness in non-coal stratum tunnels based on energy method according to any one of claims 1-2, characterized in that: The S2 further includes: S205. Without considering the impact of construction on the rock mass disturbance in front of the working face, the expression (6) for rock mass thickness is: Where s is the cross-sectional area of ​​the protruding rock mass; U e is the energy density of rock mass elastic deformation; e is the crushing work, i represents the crushing ratio, V1 is the volume of rock mass before outburst, γ i is the content percentage, d i is the particle size, W represents the energy including loss spent to establish unit new surface area; p1 is the high-pressure gas pressure of the rock formation, V1 is the volume of high-pressure gas in the rock formation, p2 is the high-pressure gas pressure of the mining face after the outburst occurs, V2 is the volume of high-pressure gas in the mining face after the outburst occurs, and n is the process index.

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