Tunnel gas disaster prediction method based on numerical simulation
By using numerical simulation and a damage-seepage coupling model, the problem of accurate and early warning of gas disasters in tunnel construction was solved, and accurate prediction and early warning of gas outbursts were achieved, thus improving the safety of tunnel construction.
Patent Information
- Application Number
- CN202510920058.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-04
- Publication Date
- 2025-10-21
AI Technical Summary
Existing technologies are unable to accurately and early warn of gas disasters during tunnel construction, especially under complex geological conditions. Dynamic prediction methods rely on weak data and lack consideration of the impact of excavation disturbance damage.
A numerical simulation method was used in combination with the damage-seepage coupling model. A coal tunnel model was established using COMSOL software to simulate the gas emission during tunnel excavation. The damage-seepage coupling model was used to output the gas emission at the tunnel face and compared it with the warning threshold to achieve gas disaster early warning.
It has achieved accurate and early warning of gas disasters during tunnel excavation, can judge the danger level according to the amount of gas outburst, and improves the accuracy and timeliness of the warning.
Smart Images
Figure CN120823697A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of tunnel excavation gas disaster early warning, and in particular to a tunnel excavation gas disaster early warning method. Background Art
[0002] In recent years, scholars have proposed various tunnel gas hazard prediction methods, encompassing both qualitative and quantitative prediction. Both approaches have been widely used. However, static predictions lack the ability to predict hazard risks in a timely manner as tunnel construction disturbances occur, and thus have certain limitations. Dynamic predictions rely heavily on data and lack a solid foundation in laws. Given these limitations, more accurate prediction indicators and methods are needed for more reliable predictions.
[0003] Numerical simulations of gas migration under the influence of mining indicate that, under mining conditions, gas migrates through fissure channels into the goaf. Gas permeability increases significantly in areas of the rock strata rich in vertical fractures within the deformation and failure zone. Research on the mechanism of tunnel gas emission indicates that the amount of tunnel gas emission is controlled by gas pressure, geostress, surrounding rock integrity, and the intensity of excavation disturbance. Essentially, it represents a dynamic rebalancing process after excavation disrupts the original gas balance in the rock mass. Theoretical analysis of the surrounding rock mechanics and gas migration patterns under tunnel excavation disturbance, along with the development of numerical models and simulation experiments, reveals the mechanism of surrounding rock gas migration under tunnel excavation disturbance. By combining theoretical analysis with actual construction, the diffusion and migration patterns of gas within the surrounding rock can be studied, clarifying the key factors influencing gas hazards during gas tunnel construction in coal-bearing strata. Analyzing the factors influencing tunnel gas emission can identify the emission source and construct a source-based prediction model for gas emission in tunnels with complex geological structures such as multiple coal seams or high gas content. By establishing a mathematical model, it was found that gas flow in coal seam fractures and pores follows Darcy's permeation law and Fick's diffusion law. Based on the diffusion and seepage laws, the governing equations for gas migration were derived. Taking into account the effects of high gas compressibility, desorption, and the Klinkenberg effect on permeability, as well as gas adsorption and desorption related to gas pressure and coal seam porosity, a governing equation for coupled gas flow and solid deformation in saturated porous media was proposed. However, the impact of excavation damage on coal seam gas emission in tunnels was not considered.
[0004] Most of these methods and theories combine excavation disturbance and seepage mechanism, but do not combine excavation disturbance, static adverse geological damage and dynamic gas seepage, and cannot provide accurate and early warning of disasters in gas tunnels. Summary of the Invention
[0005] In view of this, the purpose of the present invention is to provide a tunnel gas disaster prediction method based on numerical simulation, which aims to obtain accurate and early disaster warnings based on the complex geological conditions of the tunnel and cooperates with the coupling model simulation to solve the technical problem of accurate early warning of gas disasters during tunnel excavation.
[0006] The tunnel gas disaster prediction method based on numerical simulation of the present invention comprises the following steps:
[0007] 1) Collect rock and coal samples from the tunnel construction section and measure their mechanical and seepage parameters;
[0008] 2) establishing a coal tunnel model using COMSOL software, setting the mechanical parameters and seepage parameters of the rock and coal seams of the coal tunnel model based on the mechanical parameters and seepage parameters measured in step 1); setting the periphery of the coal tunnel model as a stagnant boundary and the interior as a free boundary; applying a uniformly distributed load to the upper boundary to simulate the original ground stress, the load magnitude being calculated based on the tunnel burial depth; and embedding a damage-seepage coupling model into the coal tunnel model, the damage-seepage coupling model comprising a coal seam deformation governing equation, a rock seam deformation governing equation, a total gas content equation of the coal body, a coal seam matrix porosity equation, a coal seam fissure porosity equation, a coal seam permeability equation, a coal seam diffusion equation, a coal seam seepage equation, a rock seam porosity equation, a rock seam permeability equation, a rock seam seepage equation, and a damage model;
[0009] 3) Setting pressure and flow boundary conditions for gas flow in rock and coal seams, numerically simulating the coal tunnel excavation process, and outputting the gas outburst rate at the tunnel face using the damage-seepage coupling model;
[0010] 4) Compare the gas emission volume at the tunnel face outputted in step 3) with the set gas warning threshold value to determine the danger level of the gas emission volume.
[0011] Furthermore, the coal seam deformation control equation and rock formation deformation control equation are as follows:
[0012]
[0013] Where u i,kk Indicates the derivative operation of the displacement in the positive direction, u k,ki represents the derivative of the positive displacement in the i direction, α is the Biot effective stress coefficient of the porous medium, and ε s is the adsorption strain of the gas; p ,i is the gas pressure component in the i direction, f ,i is the body force component in the i direction;
[0014]
[0015] Where G is the shear modulus of the porous medium, D is the effective elastic modulus of the porous medium, v is the Poisson's ratio, E is the elastic modulus of the coal seam, and a m is the crack width of coal, K is the bulk modulus of porous media, K s is the bulk modulus of the coal skeleton, K n is the fracture stiffness of the coal body, E s is the elastic modulus of the coal skeleton, α m is the Biot effective stress coefficient of the coal matrix, α f is the Biot effective stress coefficient of coal fracture;
[0016] The total gas content equation of coal is as follows:
[0017]
[0018] Where m is the total amount of gas stored in the coal body, V L is the Langmuir volume constant, p m is the gas pressure of coal matrix, P L is the Langmuir pressure constant, ρ a is the apparent density of coal, ρ s M is the gas density at 101kPa standard atmospheric pressure; c is the molar mass of gas molecules, R is the ideal gas constant, T is 273.5K, is the coal seam matrix porosity, is the coal seam fracture porosity, p f is the coal body fissure gas pressure;
[0019] The coal seam matrix porosity equation is as follows:
[0020]
[0021] Where, is the initial porosity of the coal body, ε e is the volume strain of coal body, Δp m is the change in coal matrix gas pressure;
[0022] The coal seam fracture porosity equation is as follows:
[0023]
[0024] Where, is the initial porosity of the fracture system, α m is the effective stress coefficient of coal matrix, α f is the effective stress coefficient of coal body fracture, p0 is the standard atmospheric pressure, ε Lis the volume strain constant; M is the axial modulus, M = (E(1-v)) / ((1+v)(1-2v));
[0025] The coal seam permeability equation is as follows:
[0026]
[0027] Where k0 is the initial permeability of the coal seam;
[0028] The coal seam diffusion equation is as follows:
[0029]
[0030] Where t is time, τ is adsorption time, V c is the volume of gas under standard conditions;
[0031] The coal seam seepage equation is as follows:
[0032]
[0033] Where μ is the gas dynamic viscosity coefficient, b is the slip effect factor, is the gas pressure gradient in coal fissures;
[0034] The porosity equation of rock formation is as follows:
[0035]
[0036] Where, is the rock porosity after the change; is the initial rock porosity; ε v is the volume strain of rock;
[0037] The rock permeability equation is as follows:
[0038]
[0039] Where k0′ is the initial permeability of the rock formation;
[0040] The rock formation seepage equation is as follows:
[0041]
[0042] Where p is the gas pressure in the rock formation, represents the Laplace operator, k is the rock formation permeability, and μ is the gas dynamic viscosity coefficient;
[0043] The damage model is as follows:
[0044]
[0045] Where k ais the instantaneous permeability during the elastic deformation stage, k b is the instantaneous permeability during the plastic stress stage, k c is the instantaneous permeability in the residual stress stage, k no is the permeability without considering plastic failure, ξ is the permeability sudden increase coefficient, r p is the softening parameter, is the equivalent plastic strain when the residual stress is .
[0046] Furthermore, the gas pressure conditions set in step 3) are as follows:
[0047] p=p1
[0048] Where: p1 represents the pressure around the tunnel excavation and on one side of the tunnel face, which is the main boundary condition causing gas flow;
[0049] The gas flow boundary conditions are set as follows:
[0050] n·p=q
[0051] Where: n represents the direction of the outer normal on the boundary, q represents the flow rate per unit area on the boundary, and the value is positive for inflow and negative for outflow according to the flow direction;
[0052] The initial values of the variables p for coal seams and rock strata are set with reference to the measured values of the on-site geological conditions.
[0053] Beneficial effects of the present invention:
[0054] The present invention is a tunnel gas disaster prediction method based on numerical simulation. It combines the coal tunnel model and the damage-seepage coupling model. By simulating the tunnel excavation process, it can accurately predict the gas emission volume from the tunnel face, and then realize early warning of gas disasters based on the gas emission volume. BRIEF DESCRIPTION OF THE DRAWINGS
[0055] Figure 1 This is a schematic diagram of continuous dynamic tunnel excavation achieved through COMSOL software. DETAILED DESCRIPTION
[0056] The present invention will be further described below with reference to the accompanying drawings and examples.
[0057] The tunnel gas disaster prediction method based on numerical simulation in this embodiment includes the following steps:
[0058] 1) Collect rock and coal samples from the tunnel construction section, and measure the mechanical parameters and seepage parameters of the rock and coal samples. The mechanical parameters and seepage parameters of the rock and coal samples measured experimentally in this embodiment are shown in the following table:
[0059] Mechanical parameters of coal seams and rock formations
[0060]
[0061] Seepage parameters of coal seams and rock formations
[0062]
[0063] 2) Use COMSOL software to create a coal tunnel model. In this example, coal rock simulates thin coal seams, and sandstone simulates surrounding rock. Coal seam inclination and gas pressure parameters can be referenced from actual exploration data. The simulated rock layer is a rectangular parallelepiped measuring 50m (height) x 50m (depth) x 50m (width), with a 3m wide, 45° inclination through the coal seam. The tunnel cross-section is simplified to a circle and placed at the center of the left boundary of the model.
[0064] According to the mechanical parameters and seepage parameters measured in step 1), the mechanical parameters and seepage parameters of the rock layer and coal layer of the coal tunnel model are set; the four sides of the coal tunnel model are set as non-flow boundaries, and the interior is set as a free boundary; a uniformly distributed load is applied to the upper boundary to simulate the original ground stress, and the load size is calculated based on the tunnel burial depth; and a damage-seepage coupling model is embedded in the coal tunnel model. The damage-seepage coupling model is composed of the coal seam deformation control equation, the rock layer deformation control equation, the total gas content equation of the coal body, the coal seam matrix porosity equation, the coal seam fracture porosity equation, the coal seam permeability equation, the coal seam diffusion equation, the coal seam seepage equation, the rock layer porosity equation, the rock layer permeability equation, the rock layer seepage equation and the damage model. The equations included in the damage-seepage coupling model are as follows:
[0065] The coal seam deformation control equation and rock stratum deformation control equation are as follows:
[0066]
[0067] Where u i,kk Indicates the derivative operation of the displacement in the positive direction, u k,ki represents the derivative of the positive displacement in the i direction, α is the Biot effective stress coefficient of the porous medium, and ε s is the adsorption strain of the gas; p,i is the gas pressure component in the i direction, f ,i is the body force component in the i direction;
[0068]
[0069] Where G is the shear modulus of the porous medium, D is the effective elastic modulus of the porous medium, v is the Poisson's ratio, E is the elastic modulus of the coal seam, and a m is the crack width of coal, K is the bulk modulus of porous media, K s is the bulk modulus of the coal skeleton, K n is the fracture stiffness of the coal body, Es is the elastic modulus of the coal skeleton, α m is the Biot effective stress coefficient of the coal matrix, α f is the Biot effective stress coefficient of coal fracture.
[0070] The total gas content equation of coal is as follows:
[0071]
[0072] Where m is the total amount of gas stored in the coal body, V L is the Langmuir volume constant, p m is the gas pressure of coal matrix, P L is the Langmuir pressure constant, ρ a is the apparent density of coal, ρ s M is the gas density at 101kPa standard atmospheric pressure; c is the molar mass of gas molecules, R is the ideal gas constant, T is 273.5K, is the coal seam matrix porosity, is the coal seam fracture porosity, p f It is the gas pressure in coal fissures.
[0073] The coal seam matrix porosity equation is as follows:
[0074]
[0075] Where, is the initial porosity of the coal body, ε e is the volume strain of coal body, Δp m is the change in coal matrix gas pressure.
[0076] The coal seam fracture porosity equation is as follows:
[0077]
[0078] Where, is the initial porosity of the fracture system, α m is the effective stress coefficient of coal matrix, α f is the effective stress coefficient of coal body fracture, p0 is the standard atmospheric pressure, ε L is the volume strain constant; M is the axial modulus, M = (E(1-v)) / ((1+v)(1-2v)).
[0079] The coal seam permeability equation is as follows:
[0080]
[0081] Where k0′ is the initial permeability of the rock formation.
[0082] The coal seam diffusion equation is as follows:
[0083]
[0084] Where t is time, τ is adsorption time, V c It is the volume of methane gas under standard conditions.
[0085] The coal seam seepage equation is as follows:
[0086]
[0087] Where μ is the gas dynamic viscosity coefficient, b is the slip effect factor, It is the gas pressure gradient in coal body fissures.
[0088] The porosity equation of rock formation is as follows:
[0089]
[0090] Where, is the rock porosity after the change; is the initial rock porosity; ε v is the volume strain of rock.
[0091] The rock permeability equation is as follows:
[0092]
[0093] Where k0′ is the initial permeability of the rock formation.
[0094] The rock formation seepage equation is as follows:
[0095]
[0096] Where p is the gas pressure in the rock formation, represents the Laplace operator, k is the rock formation permeability, and μ is the gas dynamic viscosity coefficient;
[0097] The damage model is as follows:
[0098]
[0099] Where k a is the instantaneous permeability during the elastic deformation stage, k b is the instantaneous permeability during the plastic stress stage, k c is the instantaneous permeability in the residual stress stage, k no is the permeability without considering plastic failure, ξ is the permeability sudden increase coefficient, r p is the softening parameter, is the equivalent plastic strain when the residual stress is .
[0100] 3) Set the pressure boundary conditions and flow boundary conditions for gas flow in rock and coal seams as follows:
[0101] Gas pressure conditions are as follows:
[0102] p=p1
[0103] Where: p1 represents the pressure around the tunnel excavation and on one side of the tunnel face, which is the main boundary condition causing gas flow;
[0104] The gas flow boundary conditions are set as follows:
[0105] n·p=q
[0106] Where: n represents the direction of the outer normal on the boundary, q represents the flow rate per unit area on the boundary, and the value is positive for inflow and negative for outflow according to the flow direction;
[0107] The initial values of the variables p for coal seams and rock strata are set with reference to the measured values of the on-site geological conditions.
[0108] Numerical simulation of coal tunnel excavation process. Figure 1 To implement a schematic diagram of continuous dynamic tunnel excavation using COMSOL software, the conditions for tunnel excavation through coal are simulated as follows: After an initial 5m of tunnel excavation is completed, the tunnel is excavated in stages, continuing from the 5m point, with each step excavating a distance of L, over a period of 16 hours. Each step is followed immediately by the next excavation step until the tunnel face gradually approaches and eventually completely penetrates the coal seam, simulating the entire dynamic continuous excavation process. The figure shows that the established geometric model simulates the conditions of a tunnel passing through a coal seam (representing a poor geological body). The light gray rectangle represents the surrounding rock, the dark gray rectangle obliquely penetrating the middle of the surrounding rock represents the coal seam, and the tunnel profile is located at the center of the geometric model.
[0109] Dynamic tunnel excavation is achieved by performing a parametric sweep using the built-in stretch command in COMSOL software. The stretch length of the cylinder on the tunnel profile is set to nL (n = 1 to 10). The cylinder is then removed from the surrounding rock and coal seam using a Boolean difference operation, thereby achieving continuous dynamic tunnel excavation. The results of the previous excavation step serve as the initial conditions for the next excavation step. By selecting "Reuse previous solution" in the parametric sweep, the results of the previous excavation step, such as von Mises stress (σ), equivalent plastic strain (ε), and gas pressure (p), are inherited as the initial conditions for the next excavation step, thus achieving continuity in the dynamic tunnel excavation simulation results.
[0110] During the excavation process, the gas emission rate at the tunnel face is output by formula (3) of the damage-seepage coupling model.
[0111] 4) Compare the gas emission volume at the tunnel face outputted in step 3) with the set gas warning threshold value to determine the danger level of the gas emission volume.
[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.
Claims
1. A tunnel gas disaster prediction method based on numerical simulation, characterized in that: The following steps are involved: 1) Collect rock and coal samples from the tunnel construction section and measure their mechanical and seepage parameters; 2) establishing a coal tunnel model using COMSOL software, setting the mechanical parameters and seepage parameters of the rock and coal seams of the coal tunnel model based on the mechanical parameters and seepage parameters measured in step 1); setting the periphery of the coal tunnel model as a stagnant boundary and the interior as a free boundary; applying a uniformly distributed load to the upper boundary to simulate the original ground stress, the load magnitude being calculated based on the tunnel burial depth; and embedding a damage-seepage coupling model into the coal tunnel model, the damage-seepage coupling model comprising a coal seam deformation governing equation, a rock seam deformation governing equation, a total gas content equation of the coal body, a coal seam matrix porosity equation, a coal seam fissure porosity equation, a coal seam permeability equation, a coal seam diffusion equation, a coal seam seepage equation, a rock seam porosity equation, a rock seam permeability equation, a rock seam seepage equation, and a damage model; 3) Setting pressure and flow boundary conditions for gas flow in rock and coal seams, numerically simulating the coal tunnel excavation process, and outputting the gas outburst rate at the tunnel face using the damage-seepage coupling model; 4) Compare the gas emission volume at the tunnel face outputted in step 3) with the set gas warning threshold value to determine the danger level of the gas emission volume.
2. The method for predicting tunnel gas disasters based on numerical simulation according to claim 1, characterized in that: The coal seam deformation control equation and rock stratum deformation control equation are as follows: Where u i,kk Indicates the derivative operation of the displacement in the positive direction, u k,ki represents the derivative of the positive displacement in the i direction, α is the Biot effective stress coefficient of the porous medium, and ε s is the adsorption strain of the gas; p,i is the gas pressure component in the i direction, and f,i is the volume force component in the i direction; Where G is the shear modulus of the porous medium, D is the effective elastic modulus of the porous medium, v is the Poisson's ratio, E is the elastic modulus of the coal seam, and a m is the crack width of coal, K is the bulk modulus of porous media, K s is the bulk modulus of the coal skeleton, K n is the fracture stiffness of the coal body, E s is the elastic modulus of the coal skeleton, α m is the Biot effective stress coefficient of the coal matrix, α f is the Biot effective stress coefficient of coal fracture; The total gas content equation of coal is as follows: Where m is the total amount of gas stored in the coal body, V L is the Langmuir volume constant, p m is the gas pressure of coal matrix, P L is the Langmuir pressure constant, ρ a is the apparent density of coal, ρ s M is the gas density at 101kPa standard atmospheric pressure; c is the molar mass of gas molecules, R is the ideal gas constant, T is 273.5K, is the coal seam matrix porosity, is the coal seam fracture porosity, p f is the coal body fissure gas pressure; The coal seam matrix porosity equation is as follows: Where, is the initial porosity of the coal body, ε e is the volume strain of coal body, Δp m is the change in coal matrix gas pressure; The coal seam fracture porosity equation is as follows: Where, is the initial porosity of the fracture system, α m is the effective stress coefficient of coal matrix, α f is the effective stress coefficient of coal body fracture, p0 is the standard atmospheric pressure, ε L is the volume strain constant; M is the axial modulus, M = (E(1-v)) / ((1+v)(1-2v)); The coal seam permeability equation is as follows: Where k0 is the initial permeability of the coal seam; The coal seam diffusion equation is as follows: Where t is time, τ is adsorption time, V c is the volume of gas under standard conditions; The coal seam seepage equation is as follows: Where μ is the gas dynamic viscosity coefficient, b is the slip effect factor, and ▽p f is the gas pressure gradient in coal fissures; The porosity equation of rock formation is as follows: Where, is the rock porosity after the change; is the initial rock porosity; ε v is the volume strain of rock; The rock permeability equation is as follows: Where k0′ is the initial permeability of the rock formation; The rock formation seepage equation is as follows: Where p is the gas pressure in the rock formation, ▽ represents the Laplace operator, k is the rock formation permeability, and μ is the gas dynamic viscosity coefficient; The damage model is as follows: Where k a is the instantaneous permeability during the elastic deformation stage, k b is the instantaneous permeability during the plastic stress stage, k c is the instantaneous permeability in the residual stress stage, k no is the permeability without considering plastic failure, ξ is the permeability sudden increase coefficient, r p is the softening parameter, is the equivalent plastic strain when the residual stress is .
3. The method for predicting tunnel gas disasters based on numerical simulation according to claim 1, characterized in that: The gas pressure conditions set in step 3) are as follows: p=p1 Where: p1 represents the pressure around the tunnel excavation and on one side of the tunnel face, which is the main boundary condition causing gas flow; The gas flow boundary conditions are set as follows: n·p=q Where: n represents the direction of the outer normal on the boundary, q represents the flow rate per unit area on the boundary, and the value is positive for inflow and negative for outflow according to the flow direction; The initial values of the variables p for coal seams and rock strata are set with reference to the measured values of the on-site geological conditions.