A method for predicting the characteristics of a mud film closed gas and stratum deformation of a shield with a pressurized opening

Abstract

The application discloses a method for predicting the characteristics of a slurry membrane closed gas and stratum deformation of a shield with pressure opening, and belongs to the technical field of tunnel engineering. Based on the Biot poroelasticity mechanics framework, a fluid-solid coupling simulation model of a slurry membrane-soil composite system is established, the dispersing effect of high-pressure gas on interstitial water is characterized by a water holding capacity function, and the whole process of gas breaking through the slurry membrane and seeping to the ground surface and the stratum deformation response are reproduced. By preparing slurry and collecting stratum samples, the porosity, density, permeability coefficient, elastic modulus, Poisson's ratio and soil water characteristic curve parameters are obtained through permeation, triaxial, water holding capacity and other tests, and the test parameters are assigned to a geometric model established according to the engineering burial depth, shield diameter and underground water level; under the boundary conditions of setting the initial displacement of self-weight, the pore water pressure distribution of the underground water level and the transition of the excavation face from slurry support to gas pressure support, numerical calculation is carried out under different gas pressures, slurry membrane thicknesses, burial depths and underground water levels, and the high-pressure gas seepage path and stratum deformation are predicted. The technology can reveal the failure mechanism of the slurry membrane closed gas performance and the development law of the stratum deformation, and provides a theoretical basis and technical support for the support gas pressure design of the shield with pressure opening.

Description

Technical Field

[0001] This application relates to the field of tunnel engineering technology, and in particular to a method for predicting mud film air-tightness and stratum deformation during pressurized tunnel boring machine (TBM) opening. Background Technology

[0002] With the continuous advancement of urbanization, the development of underground space plays an increasingly important role in modern urban construction. Especially in the field of tunnel engineering, shield tunneling technology has become a key method for underground space development due to its high efficiency, safety, and minimal impact on the surrounding environment.

[0003] However, wear and tear on equipment is inevitable during tunnel boring machine (TBM) excavation, especially the high-intensity work on the cutterhead and cutting tools. Therefore, regular chamber opening for inspection and maintenance is required. While traditional atmospheric pressure chamber opening technology can ensure normal equipment operation in certain situations, it relies on ground reinforcement and is difficult to implement effectively in highly permeable strata. Furthermore, atmospheric pressure chamber opening involves a large amount of auxiliary engineering and a long construction period. In addition, ground reinforcement is often unavailable in densely built-up urban areas and during TBM excavation beneath rivers, lakes, and seas. Therefore, pressurized chamber opening technology has emerged. This technology balances ground water and soil pressure by applying gas pressure to the surface mud film at the tunnel face, thus providing a safe and stable working environment for workers entering the pressurized chamber. The core of this technology is the balance between gas pressure and ground pressure; however, applying too much or too little gas pressure during pressurized chamber opening can pose risks. For example, when the mud film has good air-tightness, excessive air pressure loading may cause surface heave, leading to building cracking and deformation. However, if the air pressure increases further, the mud film may rupture and leak gas, causing its support function to fail, resulting in excavation face instability, surface subsidence, and building cracking. Sudden gas leakage may also induce decompression sickness and other health problems for workers. Conversely, excessively low air pressure may lead to insufficient pressure at the excavation face, causing ground collapse or water backflow, thus threatening construction safety. Therefore, accurately balancing air pressure and ground pressure is key to pressurized tunneling technology. However, although domestic and foreign professionals have completed numerous pressurized tunneling operations through practical experience, existing support air pressure loading still suffers from limitations such as inconsistent design standards and significant reliance on engineering experience. Currently, there is no calculation tool that can capture the mud film air-tightness characteristics and ground deformation patterns during the pressurized tunneling process of a shield tunnel. Summary of the Invention

[0004] This invention addresses the technical problems existing in the background art by proposing a method for predicting the air-tightness characteristics of mud film and the deformation of the stratum during pressurized tunnel boring machine (TBM) opening. It utilizes the Biot pore elasticity framework to establish a fluid-structure interaction simulation model of the mud film-soil composite system under air chamber pressure. Based on the water-holding capacity function, it characterizes the dispersal effect of high-pressure gas on interstitial water, thereby reproducing the gas migration process and stratum deformation response throughout the entire stage of mud film rupture and surface leakage. The technical results can provide important theoretical guidance and technical support for revealing the failure mechanism of mud film air-tightness and the development law of stratum deformation during pressurized TBM opening, and thus guiding the design of support air pressure.

[0005] To solve the technical problem, the technical solution of the present invention is as follows:

[0006] A method for predicting mud film air-tightness characteristics and formation deformation during pressurized tunnel boring machine (TBM) opening, the method comprising the following steps:

[0007] S1: Based on the theory of pore elasticity, a fluid-structure interaction simulation model is constructed to simultaneously describe the coupling of the solid mechanical field, pore water seepage field and pore gas seepage field in the composite medium composed of mud film and formation.

[0008] S2: Prepare mud material for the shield excavation face and collect soil samples corresponding to the shield tunnel construction area;

[0009] S3: Conduct experiments on the mud material and formation soil samples to obtain the parameter information required for the fluid-structure interaction simulation model to characterize the pore structure, permeability, mechanical elasticity and water holding capacity of the materials.

[0010] S4: Based on the engineering design conditions of the shield tunnel, establish a geometric model including the mud film layer and the surrounding strata, and assign all the parameter information obtained in step S3 to the material region corresponding to the geometric model to complete the parametric modeling of the fluid-structure interaction simulation model.

[0011] S5: Based on the model framework constructed in step S1 and the parameterized model established in step S4, according to the shield tunneling pressurized opening condition, initial and boundary conditions are set for the solid mechanics field, pore water seepage field and pore gas seepage field respectively. Among them, the support loading condition for transitioning from the slurry support state in the tunneling stage to the gas support state in the pressurized opening stage is set at the shield tunneling face, and the fluid-structure interaction simulation model with initial and boundary conditions is obtained.

[0012] S6: Using the fluid-structure interaction simulation model with the initial boundary conditions set, numerical calculation and analysis are performed under different gas support pressure, mud film thickness, shield tunneling depth and groundwater level conditions to obtain the leakage path of high-pressure gas breaking through the mud film and migrating to the surface and the corresponding stratum deformation response results.

[0013] Furthermore, the fluid-structure interaction simulation model achieves the coupling and synchronous evolution of pore fluid pressure changes, fluid migration processes, and soil volume deformation processes by uniformly solving the pore water seepage field, pore air seepage field, and solid mechanical field.

[0014] The pore water seepage field and pore gas seepage field are used to describe the seepage process in a porous medium under unsaturated conditions where the water phase and gas phase coexist and compete with each other. The saturation state of the water phase is dynamically adjusted with the change of gas pressure.

[0015] Furthermore, the fluid-structure interaction simulation model introduces a function to characterize the water-holding capacity of the material. By varying the difference between gas pressure and pore water pressure, the dispersing effect of high-pressure gas on pore water after entering the pores is described.

[0016] Furthermore, the water-holding capacity function is used to determine the correspondence between the water phase saturation and the pore pressure state in the porous medium, and the water phase saturation is used as an intermediate state variable in the calculation of the seepage capacity of pore water and pore gas.

[0017] In the fluid-structure interaction simulation model, the seepage capacity of pore water and pore gas is adjusted according to the saturation state of their respective phases, thereby reflecting the difference in seepage capacity between the water phase and the gas phase under different saturation conditions.

[0018] Furthermore, the results of the changes in pore water pressure and pore air pressure are incorporated into the soil mechanics calculation process to determine the influence of pore fluid pressure on the soil stress state and volume deformation.

[0019] Furthermore, the parameter information obtained in step S3 includes: parameters describing the pore structure state, parameters describing the fluid seepage capacity in the pores, parameters describing the elastic deformation characteristics of the soil, and parameters describing the water holding capacity and saturation state change characteristics of the material. These parameters are used to calculate the corresponding physical processes.

[0020] Furthermore, the initial conditions set in step S5 include: setting the initial pressure distribution of the pore water seepage field based on the groundwater level, and setting the initial stress and displacement state of the solid mechanical field based on the self-weight of the stratum.

[0021] The numerical calculation analysis is a time history analysis, which involves applying gas support pressure under the initial conditions and solving the fluid-structure interaction simulation model over time to obtain the time evolution results of gas migration and formation deformation.

[0022] Furthermore, by analyzing the continuous migration process of pore gas in the mud film and formation, we can determine the moment when high-pressure gas breaks through the mud film and enters the formation, as well as the path characteristics of its subsequent migration to the surface.

[0023] Furthermore, the fluid-structure interaction simulation model is based on Biot's theory of pore elasticity. By introducing a two-way coupling relationship between pore fluid pressure and soil skeleton deformation, it uniformly describes the migration process of pore water and pore gas and the mechanical response process of the soil.

[0024] Furthermore, the parameters used to describe the water-holding capacity and saturation state change characteristics of the material are soil-water characteristic curve model parameters determined by water-holding capacity test; the soil-water characteristic curve model parameters are used to determine the water-holding capacity function to quantitatively characterize the dynamic evolution of pore water retention capacity and saturation under gas pressure change conditions.

[0025] In the calculation process of the fluid-structure interaction simulation model, the soil-water characteristic curve model parameters are used to dynamically calculate the water phase saturation under the current pore pressure state. The seepage capacity of pore water and pore gas is adjusted by the relative permeability model to simulate the migration path of high-pressure gas in mud film and formation and the formation deformation response induced by it.

[0026] This application has the following advantages:

[0027] This application establishes a fluid-structure interaction simulation model of the mud film-soil composite system based on the Biot porous elasticity framework. This technical achievement can reasonably reproduce the complete process of high-pressure gas breaking through the mud film and seeping to the surface during shield tunneling pressurized entry operations, as well as the induced stratum deformation response. Furthermore, it can reveal the failure mechanism of the mud film's airtightness and the development law of stratum deformation during the shield tunneling pressurized opening process, ultimately providing important theoretical guidance and technical support for the support air pressure design of shield tunneling pressurized entry operations in complex urban environments. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 The graph shows the evolution of horizontal displacement at the measuring point in the middle of the excavation face under different gas chamber pressure conditions (negative values ​​are shown towards the outside of the excavation face).

[0030] Figure 2 The graph shows the evolution curves of pore water saturation at the measuring point in the middle of the excavation face under different gas chamber pressure conditions.

[0031] Figure 3 shows the formation pore water saturation distribution after 7 days of loading at different gas pressures (a pressure = 50 kPa, b pressure = 250 kPa, c pressure = 450 kPa, d pressure = 750 kPa).

[0032] Figure 4 The graph shows the vertical displacement evolution curves of surface measuring points under different gas chamber pressure conditions (upward is positive).

[0033] Figure 5 shows the distribution of excess pore pressure in the formation after 10 days of loading at different gas pressures (a = 50 kPa, b = 250 kPa, c = 450 kPa, d = 750 kPa).

[0034] Figure 6 This is a map showing the horizontal displacement distribution of the formation after 30 days of loading at a gas chamber pressure of 50 kPa.

[0035] Figure 7 This is a diagram showing the vertical displacement distribution of the formation after 30 days of loading at a gas chamber pressure of 50 kPa.

[0036] Figure 8 The distribution of horizontal displacement of the formation after loading for 30 days at a gas chamber pressure of 650 kPa.

[0037] Figure 9 Vertical displacement distribution of the formation after 30 days of loading at a gas chamber pressure of 650 kPa. Detailed Implementation

[0038] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0039] Example 1:

[0040] This application proposes a method for predicting the mud film air-tightness characteristics and formation deformation during pressurized tunnel boring machine (TBM) opening, including the following steps:

[0041] The governing equations for the movement of pore water and pore gas, as well as the mechanical equilibrium equations for the soil, are established. The van Genuchten model and the generalized Hooke's law required for solving these equations are then embedded. Furthermore, a fluid-structure interaction simulation model of the mud-film-soil composite system under the pressure of the air chamber is established for the actual tunnel burial depth, shield diameter, and groundwater level conditions during pressurized tunneling operations.

[0042] Prepare mud as needed and collect soil samples from the site.

[0043] The porosity (saturated water content), density, and residual water content of mud and formation were determined by conventional physical property tests. The hydraulic conductivity of mud and formation was determined by permeability tests. The elastic modulus and Poisson's ratio of mud and formation were determined by triaxial tests. The soil-water characteristic curves of mud and formation (parameters of the van Genuchten model characterizing the water-holding capacity of soil) were determined by water-holding capacity tests.

[0044] A geometric model is established based on the engineering design, and the material parameters obtained in the above steps are then incorporated into the fluid-structure interaction simulation model of the mud-film-soil composite system.

[0045] The initial and boundary conditions for the solid mechanics field and the water vapor seepage field are set according to the pressurized excavation design. Specifically, regarding the initial conditions, the initial condition for the solid mechanics field is the stratum displacement caused by its own weight; the initial condition for the water vapor seepage field is the pore water pressure distribution determined by the groundwater level; and the initial condition for the gas seepage field is the location-dependent gas pressure distribution. Regarding the boundary conditions, the solid mechanics field at the excavation face is set as a gradual function transitioning from the slurry pressure during the tunneling stage to the pneumatic support force (obtained from the gas pressure * pore water saturation specified in the pressurized excavation design), with the ground surface as a free boundary and the remaining areas as roller supports. The water vapor seepage field at the excavation face is set as an impermeable boundary, with the remaining areas as the pore water pressure distribution determined by the groundwater level. The gas seepage field at the excavation face is set as the gas pressure specified in the pressurized excavation design, with the remaining areas as the location-dependent gas pressure distribution.

[0046] Based on this, simulation calculations and analyses can be carried out under different loading air pressures, mud film thicknesses, shield tunneling depths, groundwater levels, etc., ultimately enabling the prediction of gas leakage paths and ground deformation responses during the pressurized tunneling process.

[0047] Specifically, the implementation steps of this application are as follows:

[0048] (1) The governing equations for the movement of pore water and pore gas during the pressurized opening of the shield tunnel are:

[0049]

[0050]

[0051] In the formula, n represents porosity, and α = 1 − K d / K s K represents the Biot coefficient. d K represents the bulk modulus of the infill skeleton. s ε represents the stiffness of the solid particles. v p represents the volumetric deformation of the filling material. w and p gLet T and S represent pore water pressure and air pressure, respectively, T represent temperature, and S represent water saturation. K represents the pressure at which water is saturated. w p represents the stiffness of water. c =p g -p w Indicates capillary pressure, v rw and v rg M represents the apparent flow velocities of water and gas relative to the solid phase in the pores, respectively. g R represents the molecular mass of the gas phase, and R represents the universal gas constant.

[0052] The mechanical equilibrium equation of the soil during the pressurized opening of the tunnel boring machine can be written as:

[0053]

[0054] In the formula, σ represents the total stress tensor, ρ is the total density of the soil, and ρ s ρ w and ρ g Let represent the densities of each phase, and g represent the gravitational acceleration.

[0055] (2) To solve the above partial differential equations, the following constitutive relations are required.

[0056] The generalized Darcy's law describing water vapor transport under unsaturated conditions can be written as:

[0057]

[0058]

[0059] In the formula, k rw and k rg Each represents the relative permeability of the phase, μ w and μ g represents the dynamic viscosity of each phase, and k represents the inherent permeability of the soil.

[0060] The relative permeability of each phase is related to the water content or saturation of the soil and can be calculated by the following formula:

[0061]

[0062]

[0063] In the formula, m s The saturation degree S of pore water, a parameter representing the soil's water-holding capacity, can be calculated using the following formula:

[0064]

[0065] In the formula, θ, θ r θ s These are the volumetric moisture content, residual moisture content, and saturated moisture content, respectively. The volumetric moisture content θ can be calculated using the following formula:

[0066]

[0067] In the formula, α s For another soil water-holding capacity parameter, the capillary head H p and material parameter n s It can be calculated using the following formula:

[0068]

[0069]

[0070] The total stress of the soil can be calculated using the following formula:

[0071]

[0072] In the formula, D is the stiffness matrix composed of the elastic modulus and Poisson's ratio, and ε is the strain tensor. Kroneckerdelta is used to represent the contribution of isotropic pore pressure to the normal stress component. It represents the equivalent pore pressure, which can be obtained by weighting the pore water pressure and gas pressure according to the degree of saturation.

[0073] Example 2:

[0074] This embodiment applies to Embodiment 1 and proposes a specific application scenario for a method to predict the mud film airtightness characteristics and stratum deformation during pressurized tunnel boring machine (TBM) chamber opening. Taking a subway pressurized chamber entry operation as an example, the method includes the following steps:

[0075] (1) Prepare mud as required and collect soil samples from the site.

[0076] (2) The porosity, density and residual water content of mud and strata were determined by conventional physical property tests, the hydraulic conductivity of mud and strata was determined by permeability tests, the elastic modulus and Poisson's ratio of mud and strata were determined by triaxial tests, and the soil-water characteristic curves of mud and strata (van Genuchten model parameters characterizing soil water-holding capacity) were determined by water-holding capacity tests.

[0077] (3) The subway shield has a diameter of 4m, a shield length of 15m, a shield burial depth of 15m, and a groundwater burial depth of 0m. By filling the soil chamber with mud and applying pressure, a mud film of about 14cm is finally formed.

[0078] (4) Excess mud is discharged by air pressure loading. Finally, combined with engineering experience and shield burial depth, air chamber pressure is applied to balance the soil and water pressure at the excavation face, thereby providing a safe working environment for pressurized entry into the chamber to carry out tool maintenance and repair replacement.

[0079] (5) In order to predict the air-tight characteristics of the mud film and the formation deformation response during the pressurized opening process, a geometric model is established based on the engineering design in step (3), and the material parameters obtained in step (2) are brought into the fluid-solid coupling simulation model of the mud film-soil composite system.

[0080] (6) Set the initial and boundary conditions for the corresponding solid mechanical field and water vapor seepage field according to the pressurized opening design. Specifically, in terms of initial conditions, the initial condition of the solid mechanical field is the stratum displacement caused by its own weight, the initial condition of the water seepage field is the pore water pressure distribution determined by the groundwater level, and the initial condition of the gas seepage field is the gas pressure distribution related to the location. In terms of boundary conditions, the solid mechanical field at the excavation face is set as a gradual function transitioning from the slurry pressure during the tunneling stage to the pneumatic support force (obtained from the gas pressure * pore water saturation determined by the pressurized opening design), the ground surface is a free boundary, and the rest of the area is supported by rollers. The water seepage field at the excavation face is set as an impermeable boundary, and the rest of the area is the pore water pressure distribution determined by the groundwater level. The gas seepage field at the excavation face is set as the gas pressure determined by the pressurized opening design, and the rest of the area is the gas pressure distribution related to the location.

[0081] (7) Based on this, the simulation calculation of gas leakage process and stratum stress-strain response of mud film-soil composite system can be realized, and parametric prediction analysis can be carried out under different loading air pressure, mud film thickness, shield tunneling depth, groundwater level and other conditions. In this way, the failure mechanism of mud film air tightness and stratum deformation development law during the shield tunneling pressurized opening process can be revealed, and finally the support air pressure design of shield tunneling pressurized entry operation in complex urban environments can be guided.

[0082] (8) Taking different gas chamber pressures as examples (50[kPa], 250[kPa], 450[kPa], 650[kPa]), the evolution curves of horizontal displacement and pore water saturation at the measuring points in the middle of the excavation face can be obtained through calculation and monitoring, as shown in the figure. Figure 1 and Figure 2 As shown.

[0083] The calculation results show that when the applied gas chamber pressure is low, the support force at the excavation face decreases rapidly, leading to significant outward extrusion deformation. When the gas chamber pressure exceeds the initial earth pressure, the excavation face will first undergo inward compression deformation under the greater support force. After the gas pressure loading ends, the pore water saturation evolution curves at the measuring points show that the high-pressure gas gradually breaks through the mud film, causing the gas pressure support to gradually fail. Ultimately, the excavation face rapidly undergoes outward extrusion deformation, which converges as the study area and flow field boundary gradually reach equilibrium. It is noteworthy that although higher gas chamber pressure will cause greater inward compression deformation at the excavation face during the initial loading stage, the formation saturation distribution after 7 days of gas pressure loading (Figure 3) shows that a larger pressure gradient will also induce more significant gas leakage, further exacerbating support failure. Ultimately, the excavation face will undergo greater outward extrusion deformation during the pressure stabilization stage.

[0084] The calculation results of vertical displacement of surface measuring points under different gas chamber pressures are as follows: Figure 4 As shown, from Figure 4 As can be seen from the data, during the pneumatic loading process, when the support pressure is insufficient, the surface of the study area will undergo settlement deformation due to the outward extrusion of the excavation face. As the pressure of the gas chamber increases, the surface measuring points will undergo uplift deformation due to the combined effect of pore elasticity and inward compression of the excavation face. After the pneumatic loading ends, the pore pressure at the measuring points will gradually dissipate under the action of boundary drainage, and the surface will gradually undergo consolidation settlement when the gas chamber pressure is relatively low. However, as shown in Figure 3 above, a higher gas chamber pressure will cause significant gas leakage. Therefore, the high-pressure gas after breaking through the mud film will continuously diffuse to the far end under the action of the pressure gradient, and then generate considerable superpore pressure as shown in Figure 5 through seepage. Finally, the surface will undergo uplift deformation again due to the reduction of effective stress, until the formation pressure generated by the pneumatic loading gradually dissipates under the action of drainage and then slowly converges.

[0085] In summary, insufficient gas chamber pressure during the pressurized opening process may cause the working face to collapse. Figure 6 ) and surface subsidence ( Figure 7 Simultaneously, excessive air pressure load will induce instantaneous surface uplift through the combined effect of pore elasticity and face compression, and will maintain upward displacement for a long time under the action of excess pore pressure caused by gas diffusion. Figure 8 and Figure 9 In contrast, although high-pressure gas will cause instantaneous inward compression of the excavation face during the initial loading stage, it will eventually cause significant outward extrusion deformation due to mud film rupture failure. Figure 8 ).

[0086] The simulation results above demonstrate that the fluid-structure interaction simulation model of the mud film-soil composite system established in this application can reasonably reproduce the complete process of high-pressure gas puncturing the mud film and leaking to the surface during pressurized shield tunneling operations, as well as the resulting stratum deformation response. Therefore, this application can be used to reveal the failure mechanism of the mud film's airtightness and the development law of stratum deformation during pressurized shield tunneling operations, ultimately providing important theoretical guidance and technical support for the design of support air pressure during pressurized shield tunneling operations in complex urban environments.

[0087] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0088] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for predicting mud film airtightness and formation deformation during pressurized tunnel boring machine (TBM) opening, characterized in that, The method includes the following steps: S1: Based on the theory of pore elasticity, a fluid-structure interaction simulation model is constructed to simultaneously describe the coupling of the solid mechanical field, pore water seepage field and pore gas seepage field in the composite medium composed of mud film and formation. S2: Prepare mud material for the shield excavation face and collect soil samples corresponding to the shield tunnel construction area; S3: Conduct experiments on the mud material and formation soil samples to obtain the parameter information required for the fluid-structure interaction simulation model to characterize the pore structure, permeability, mechanical elasticity and water holding capacity of the materials. S4: Based on the engineering design conditions of the shield tunnel, establish a geometric model including the mud film layer and the surrounding strata, and assign all the parameter information obtained in step S3 to the material region corresponding to the geometric model to complete the parametric modeling of the fluid-structure interaction simulation model. S5: Based on the model framework constructed in step S1 and the parameterized model established in step S4, according to the shield tunneling pressurized opening condition, initial and boundary conditions are set for the solid mechanics field, pore water seepage field and pore gas seepage field respectively. Among them, the support loading condition for transitioning from the slurry support state in the tunneling stage to the gas support state in the pressurized opening stage is set at the shield tunneling face, and the fluid-structure interaction simulation model with initial and boundary conditions is obtained. S6: Using the fluid-structure interaction simulation model with the initial boundary conditions set, numerical calculation and analysis are performed under different gas support pressure, mud film thickness, shield tunneling depth and groundwater level conditions to obtain the leakage path of high-pressure gas breaking through the mud film and migrating to the surface and the corresponding stratum deformation response results.

2. The method for predicting mud film airtightness and formation deformation during pressurized tunnel boring machine (TBM) opening according to claim 1, characterized in that, The fluid-structure interaction simulation model achieves the coupling and synchronous evolution of pore fluid pressure changes, fluid migration processes, and soil volume deformation processes by uniformly solving the pore water seepage field, pore air seepage field, and solid mechanical field. The pore water seepage field and pore gas seepage field are used to describe the seepage process in a porous medium under unsaturated conditions where the water phase and gas phase coexist and compete with each other. The saturation state of the water phase is dynamically adjusted with the change of gas pressure.

3. The method for predicting mud film airtightness and formation deformation during pressurized tunnel boring machine (TBM) opening according to claim 2, characterized in that, The fluid-structure interaction simulation model introduces a function to characterize the water-holding capacity of the material. By varying the difference between gas pressure and pore water pressure, it describes the dispersing effect of high-pressure gas on pore water after entering the pores.

4. The method for predicting mud film airtightness and formation deformation during pressurized tunnel boring machine (TBM) opening according to claim 3, characterized in that, The water-holding capacity function is used to determine the correspondence between the water phase saturation and the pore pressure state in the porous medium. The water phase saturation is used as an intermediate state variable in the calculation of the seepage capacity of pore water and pore gas. In the fluid-structure interaction simulation model, the seepage capacity of pore water and pore gas is adjusted according to the saturation state of their respective phases, thereby reflecting the difference in seepage capacity between the water phase and the gas phase under different saturation conditions.

5. The method for predicting mud film airtightness and formation deformation during pressurized tunnel boring machine (TBM) opening according to claim 3, characterized in that, The results of the changes in pore water pressure and pore air pressure are incorporated into the soil mechanics calculation process to determine the influence of pore fluid pressure on the soil stress state and volume deformation.

6. The method for predicting mud film airtightness and formation deformation during pressurized tunnel boring machine (TBM) opening according to claim 1, characterized in that, The parameter information obtained in step S3 includes: parameters describing the pore structure state, parameters describing the fluid seepage capacity in the pores, parameters describing the elastic deformation characteristics of the soil, and parameters describing the water holding capacity and saturation state change characteristics of the material. These parameters are used to calculate the corresponding physical processes.

7. The method for predicting mud film airtightness and formation deformation during pressurized tunnel boring machine (TBM) opening according to claim 1, characterized in that, The initial conditions set in step S5 include: setting the initial pressure distribution of the pore water seepage field based on the groundwater level, and setting the initial stress and displacement state of the solid mechanical field based on the self-weight of the stratum. The numerical calculation analysis is a time history analysis, which involves applying gas support pressure under the initial conditions and solving the fluid-structure interaction simulation model over time to obtain the time evolution results of gas migration and formation deformation.

8. The method for predicting mud film airtightness and formation deformation during pressurized tunnel boring machine (TBM) opening according to claim 1, characterized in that, By analyzing the continuous migration process of pore gas in mud film and formation, the timing of high-pressure gas breaking through mud film and entering formation and the subsequent path characteristics of its migration to the surface can be determined.

9. The method for predicting mud film airtightness and formation deformation during pressurized tunnel boring machine (TBM) opening according to claim 1, characterized in that, The fluid-structure interaction simulation model is based on Biot's theory of pore elasticity. By introducing a two-way coupling relationship between pore fluid pressure and soil skeleton deformation, it uniformly describes the migration process of pore water and pore gas and the mechanical response process of soil.

10. The method for predicting mud film airtightness and formation deformation during pressurized tunnel boring machine (TBM) opening according to claim 6, characterized in that, The parameters used to describe the water-holding capacity and saturation state change characteristics of the material are soil-water characteristic curve model parameters determined by water-holding capacity test; the soil-water characteristic curve model parameters are used to determine the water-holding capacity function to quantitatively characterize the dynamic evolution of pore water retention capacity and saturation under gas pressure change conditions. In the calculation process of the fluid-structure interaction simulation model, the soil-water characteristic curve model parameters are used to dynamically calculate the water phase saturation under the current pore pressure state. The seepage capacity of pore water and pore gas is adjusted by the relative permeability model to simulate the migration path of high-pressure gas in mud film and formation and the formation deformation response induced by it.

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