Tunnel poor alteration zone instability criterion method and stability control method

Abstract

The application belongs to the technical field of surrounding rock stability evaluation in tunnel engineering, and specifically discloses a tunnel poor alteration zone instability criterion method and a stability control method, which comprises the following steps: obtaining core parameters of the poor alteration zone and the surrounding rock mass; based on the core parameters, calculating the uniform action force of the alteration zone and water on the tunnel vault rock slab after tunnel excavation; based on the uniform action force, calculating the displacement of the alteration zone in the natural state and the tunnel excavation unloading state respectively, and based on the displacement and the core parameters, calculating the gravity potential energy difference, the elastic potential energy difference, the seepage kinetic energy difference and the friction energy consumption between the two states; based on the gravity potential energy difference, the elastic potential energy difference, the seepage kinetic energy difference and the friction energy consumption, calculating the kinetic energy of the alteration zone through an energy equation, and combining with the geological attribute parameters, determining whether the poor alteration zone is in a stable state, a large deformation instability state or a slurry flow gushing instability state. The application can effectively improve the accuracy of the instability discrimination of the tunnel poor alteration zone.

Description

Technical Field

[0001] This application belongs to the technical field of surrounding rock stability evaluation in tunnel engineering, and more specifically, relates to a method for determining instability in tunnel adverse alteration zones and a method for stability control. Background Technology

[0002] In the field of tunnel engineering, adverse alteration zones differ from traditional unfavorable geological bodies such as faults and solution structures. They are a special type of high-risk geological body, formed from primary rocks through subsequent hydrothermal alteration. Adverse alteration zones often develop large-scale sericitization, chloritization, kaolinization, montmorillonization, illiterization, and other alteration minerals. These mineral aggregates are characterized by low cohesion, small internal friction angles, and easy softening upon contact with water, and are often associated with aquifer structures. Tunnel excavation disrupts the original stress and seepage balance of the adverse alteration zone: on the one hand, excavation unloading releases the gravitational potential energy of the alteration zone, potentially triggering large deformations; on the other hand, excavation may expose aquifer structures or damage impermeable layers, allowing groundwater to seep into the alteration zone and generate seepage kinetic energy, easily inducing severe geological disasters such as mudflow surges and large deformations.

[0003] Existing instability criteria for such adverse alteration zones typically focus only on a single driving factor such as gravity or seepage, failing to comprehensively consider the competition and transformation relationships among gravitational potential energy, elastic potential energy, seepage kinetic energy, and frictional energy dissipation. This single-factor-based analytical method cannot fully reflect the complex energy dynamics of the surrounding rock system under tunnel excavation disturbance, resulting in insufficient accuracy in judging the critical state and type of instability.

[0004] Therefore, improving the accuracy of instability assessment of adverse alteration zones in tunnels is an urgent problem that needs to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this application is to provide a method for determining instability in tunnels with adverse alteration zones and a method for controlling stability, which can effectively improve the accuracy of instability determination in tunnels with adverse alteration zones.

[0006] To achieve the above objectives, in a first aspect, this application provides a method for determining the instability of tunnels in adverse alteration zones based on multi-energy competition driving theory, comprising the following steps:

[0007] S10, Obtain the core parameters of the adverse alteration zone and surrounding rock mass, including geometric parameters, mechanical parameters, seepage parameters and geological property parameters;

[0008] S20, Based on the aforementioned core parameters, calculate the uniformly distributed forces exerted by the alteration zone and water on the tunnel arch slab after tunnel excavation. q ;

[0009] S30, based on the uniformly distributed force q The displacements of the alteration zone under both the natural state and the tunnel excavation and unloading state are calculated. Based on the displacements and the core parameters, the gravitational potential energy difference between the two states is calculated. Elastic potential energy difference Poor osmotic kinetic energy and frictional energy loss ;

[0010] S40, based on gravitational potential energy difference Elastic potential energy difference Poor osmotic kinetic energy and frictional energy loss The change in kinetic energy caused by alteration is calculated using the energy equation. Based on the geological attribute parameters, it is determined whether the adverse alteration zone is in a stable state, a large deformation unstable state, or a mudflow instability state.

[0011] As a further preferred embodiment, in step S10, the geometric parameters include the thickness of the alteration zone. t Maximum burial depth d ,inclination Thickness of rock slab between tunnel arch and alteration zone h and the length of the alteration zone along its direction L ;

[0012] The mechanical parameters include the effective cohesion of the altered zone rock mass. Effective internal friction angle Natural density Buoyancy Young's modulus E Young's modulus of slab and moment of inertia per unit width of bending section I ;

[0013] The seepage parameters include the hydraulic gradient of groundwater in the alteration zone after tunnel excavation. i ;

[0014] The geological property parameters include clay mineral content. M Moisture content w and pore connectivity k .

[0015] As a further preferred embodiment, in step S20, the uniformly distributed force is calculated. q include:

[0016] Through formula Calculate the frictional force of the alteration zone. F ;in, g It is the acceleration due to gravity;

[0017] Through formula Calculate the buoyancy of the alteration zone. G ;

[0018] The overall equilibrium equations for alteration zones and water in the sliding direction Solve for the uniformly distributed force. q ;in, This is the density of water.

[0019] As a further preferred option, in step S30, the natural state refers to the state in which the alteration zone, the surrounding rock mass, and the groundwater are in static equilibrium before the tunnel is excavated, without external disturbance, the displacement of the bottommost unit is 0, and the permeability is 0.

[0020] The tunnel excavation unloading state refers to the situation after tunnel excavation where the original equilibrium state is broken, water-bearing structures are exposed, or water-resistant slabs leak, and the tunnel arch slab is subjected to uniformly distributed forces. q The action causes bending deformation, which in turn causes displacement at the bottom of the alteration zone.

[0021] As a further preferred embodiment, in step S30, the displacement in the natural state... u 1. Based on the boundary condition that the bottom displacement is 0, combined with the differential equation of axial force in the alteration zone. The solution is obtained; where, N This refers to the axial force at the end of the alteration zone. x The coordinates are along the direction of the alteration zone. g It is the acceleration due to gravity. This is the density of water.

[0022] As a further preferred embodiment, in step S30, the displacement of the alteration zone under the unloading state of tunnel excavation is calculated. u Step 2, specifically:

[0023] Based on the theory of beams with fixed ends, through the formula Calculate the maximum bending moment of the rock slab And through the formula Calculate the maximum deflection of the rock slab ;

[0024] With the maximum deflection As the displacement boundary condition at the bottom of the alteration zone, it is determined by the formula... Calculate the displacement at the bottom of the alteration zone, where x The coordinates are along the direction of the alteration zone;

[0025] Combined with the axial force at the end of the alteration zone N With uniformly distributed force q relational equations The mixed boundary conditions are obtained by combining the equations. ;in, uThis represents the displacement of the undesirable alteration zone;

[0026] Based on the aforementioned mixed boundary conditions, and combined with the differential equation of axial force in the alteration zone... The displacement is obtained by solving. u 2; among which, g It is the acceleration due to gravity. This is the density of water.

[0027] As a further preferred option, step S30 also includes:

[0028] Calculate the critical elastic strain energy of the poorly altered zone. The calculation formula is: ,in The yield stress of the alteration zone is denoted as . V The volume of the alteration zone per unit width. E Young's modulus;

[0029] When the elastic potential energy difference is greater than or equal to the critical elastic strain energy When instability is determined, step S40 is performed.

[0030] As a further preferred embodiment, in step S40, the energy equation is:

[0031] .

[0032] As a further preferred embodiment, in step S40, the determination of the instability type includes:

[0033] The criteria for determining the condition of an undesirable alteration zone are as follows:

[0034] when >( + When the alteration zone is in a stable state, it is determined that the alteration zone is in a stable state.

[0035] when <( + )and = ( + - When the alteration zone is in a stable state, it is determined that the alteration zone is in a stable state.

[0036] when <( + )and <( + - When the alteration zone is in an unstable state, it is determined that the alteration zone is in an unstable state; when it is in an unstable state, if the clay mineral content in the core parameters is simultaneously satisfied... MThe moisture content is greater than or equal to the first threshold and the core parameter is greater than or equal to the first threshold. w If the value is less than or equal to the second threshold, it is determined to be a large deformation instability state; if the clay mineral content is also satisfied... M Greater than or equal to the first threshold, the moisture content w The pore connectivity in the core parameters is greater than the second threshold. k The hydraulic gradient in the core parameters is greater than or equal to the third threshold. i If the value is greater than or equal to the fourth threshold, it is determined to be a mudflow instability state.

[0037] Secondly, this application provides a stability control method for tunnel construction, which, using the method described in any one of the above statements, includes the following steps:

[0038] Before tunnel construction, risk prediction is made for the surrounding rock of the tunnel containing the unfavorable alteration zone based on the instability criterion of the tunnel's unfavorable alteration zone.

[0039] During tunnel construction, based on the instability type determined by prediction or real-time assessment, corresponding reinforcement measures are formulated and implemented.

[0040] The undesirable alteration zone is a weak geological body formed by the transformation of primary rocks by later geological hydrothermal alteration, with internally distributed alteration minerals. The alteration minerals include one or more of sericitization, chloritization, and kaolinization.

[0041] The beneficial effects of the technical solution provided in this application are:

[0042] By combining the "three-energy competition" with key geological parameters such as clay mineral content and water content, the energy balance relationship is considered, while also taking into account the essential properties of the alteration zone, thus adapting to complex geological conditions.

[0043] By establishing a critical elastic strain energy calculation method and a multi-parameter coupling criterion, the energy threshold and geological condition threshold for stability-instability are clarified, thus avoiding the bias of judgment based on a single factor.

[0044] Based on the dual constraints of energy-dominant relationship and geological parameters, we can accurately distinguish between two types of instability: large deformation and mudslide inrush, providing a direct basis for formulating differentiated reinforcement measures.

[0045] All parameters are conventional survey and testing indicators for tunnel engineering, and the calculation steps are clear, which can be directly applied to pre-construction risk assessment and dynamic monitoring during construction.

[0046] Predicting the type and level of instability in advance can help avoid landslides and sudden surges caused by sudden instability, thereby reducing project safety costs and schedule losses. Attached Figure Description

[0047] Figure 1 This is a flowchart of the tunnel instability criterion based on multi-energy competition driving theory provided in the embodiments of this application;

[0048] Figure 2 This is a schematic diagram illustrating the influence of cohesion and internal friction angle on frictional energy consumption provided in the embodiments of this application;

[0049] Figure 3 This is a schematic diagram of the stress analysis of the unit width alteration zone provided in the embodiments of this application;

[0050] Figure 4 This is a schematic diagram of the undesirable alteration zone in state 1 (natural state) provided in the embodiments of this application;

[0051] Figure 5 This is a schematic diagram of the adverse corrosion zone in state 2 (tunnel excavation unloading state) provided in the embodiments of this application;

[0052] Figure 6 This is a schematic diagram illustrating the relationship between multi-energy competition drive and instability state provided in the embodiments of this application. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0054] This application found through research that the inaccuracy of existing instability criteria for tunnel adverse alteration zones is due to the following reasons: (1) Single factor-dominated judgment ignores the synergistic effect of multiple energies: Existing criteria focus on single factors such as gravity or seepage, without considering the competitive balance between gravitational potential energy, elastic potential energy, seepage kinetic energy and frictional energy consumption, resulting in a large deviation in instability judgment; (2) Lack of quantification of energy conversion process: There is a lack of quantitative calculation of energy changes in alteration zones under different states, making it difficult to accurately define the critical conditions of "stability-instability"; (3) Failure to distinguish instability types: It is impossible to effectively predict whether instability is "large deformation" or "sudden mudflow", which is not conducive to the formulation of targeted reinforcement measures.

[0055] Therefore, there is an urgent need for a criterion for instability in tunnels with adverse alteration zones that can comprehensively consider multiple energy competition relationships, quantify critical conditions, and distinguish instability types, in order to overcome the shortcomings of existing technologies.

[0056] In response, this application provides a method for determining the instability of tunnels in adverse alteration zones based on the multi-energy competition driving theory, achieving the following objectives: (1) comprehensively considering the competitive balance relationship between gravitational potential energy, elastic potential energy, permeation kinetic energy and frictional energy consumption to improve the comprehensiveness of instability judgment; (2) establishing quantitative energy equations and instability critical conditions to improve the accuracy of judgment results; (3) distinguishing between the two types of "large deformation instability" and "mudslide surge instability" to provide a basis for targeted reinforcement; (4) simplifying the calculation process to ensure the engineering operability of the technical solution.

[0057] Specifically, the instability criterion method for tunnel adverse alteration zones based on multi-energy competition driving theory provided in this application includes steps S10 to S40, which are detailed below:

[0058] Step S10: Obtain the core parameters of the adverse alteration zone and the surrounding rock mass. The core parameters include geometric parameters, mechanical parameters, seepage parameters and geological property parameters.

[0059] Specifically, the geometric parameters may include the thickness of the alteration zone. t Maximum burial depth d ,inclination Thickness of rock slab between tunnel arch and alteration zone h and the length of the alteration zone along its direction L Mechanical parameters include the effective cohesion of the altered zone rock mass. Effective internal friction angle Natural density Buoyancy Young's modulus E Young's modulus of slab and moment of inertia per unit width of bending section I Seepage parameters may include the hydraulic gradient of groundwater in the alteration zone after tunnel excavation. i Geological property parameters may include clay mineral content. M Moisture content w and pore connectivity k .

[0060] This step systematically collects and defines multi-dimensional basic data that affect the stability of the alteration zone, providing a complete and unified input basis for subsequent stress and energy calculations and the establishment of comprehensive criteria. Specifically, it can cover key information from the geometry of the alteration zone, rock mechanical properties, groundwater seepage conditions to its material composition.

[0061] Step S20: Based on the core parameters, calculate the uniformly distributed forces exerted by the alteration zone and water on the tunnel arch slab after tunnel excavation. q .

[0062] Specifically, this application can quantitatively solve the load acting on the key bearing structure (arch rock slab) after excavation and unloading by comprehensively considering the balance relationship of buoyancy, friction and permeability, thus characterizing the complex rock-water interaction as a clear mechanical boundary condition, laying the foundation for analyzing the deformation of the rock slab and the displacement response of the alteration zone.

[0063] Step S30, based on uniformly distributed force q The displacement of the alteration zone under natural and tunnel excavation unloading conditions is calculated respectively. Based on the displacement and core parameters, the differences in gravitational potential energy, elastic potential energy, permeability kinetic energy, and frictional energy consumption between the two conditions are calculated.

[0064] In this application, state 1 (natural state) is defined as follows: before tunnel excavation, the alteration zone, surrounding rock mass, and groundwater are in a state of static equilibrium, with no external disturbance, the displacement of the bottommost unit is 0, and the permeability is 0 (hydraulic gradient). =0);

[0065] State 2 (Tunnel Excavation and Unloading State) is as follows: After tunnel excavation, the original equilibrium state is broken, and there is exposure of water storage structures or leakage of water-resistant panels (hydraulic gradient). i >0), the tunnel arch rock slab is subjected to uniformly distributed load. q The action causes bending deformation, which in turn causes displacement at the bottom of the alteration zone.

[0066] This step quantifies the changes in the displacement field caused by engineering activities by simulating the state changes before and after excavation. Furthermore, it combines displacement with mechanical and seepage parameters to transform them into core physical quantities that characterize the energy conversion and consumption of the system, namely gravitational potential energy difference, elastic potential energy difference, seepage kinetic energy difference, and frictional energy consumption, thereby elevating the mechanical analysis to the level of energy competition and balance.

[0067] Specifically, the displacement of the alteration zone in its natural state u 1. Based on the boundary conditions of state 1 (the displacement of the bottom element is 0), combined with the differential equation of axial force in the alteration zone, The solution is obtained.

[0068] Displacement of the alteration zone under tunnel excavation and unloading conditions u 2 can be obtained through the following steps:

[0069] First, based on the theory of beams with fixed ends, through the formula... Calculate the maximum bending moment of the rock slab And through the formula Calculate the maximum deflection of the rock slab ;

[0070] With maximum deflection As the displacement boundary condition at the bottom of the alteration zone, it is determined by the formula... Calculate the displacement at the bottom of the alteration zone, wherex The coordinates are along the direction of the alteration zone;

[0071] Combined with the axial force at the end of the alteration zone N With uniformly distributed force q relational equation The mixed boundary conditions are obtained by combining the equations. ;in, u This represents the displacement of the undesirable alteration zone;

[0072] Based on mixed boundary conditions, combined with the differential equation of axial force in the alteration zone The displacement is obtained by solving. u 2; among which, g It is the acceleration due to gravity. This is the density of water.

[0073] Step S40, based on the gravitational potential energy difference Elastic potential energy difference Poor osmotic kinetic energy and frictional energy loss Through the energy equation Calculate the change in kinetic energy caused by alteration. Based on geological attribute parameters, it is determined whether the adverse alteration zone is in a stable state, a large deformation unstable state, or a mudflow instability state.

[0074] In this step, the gravitational potential energy difference The displacement difference between state 1 and state 2 can be used to determine the displacement difference between them. u 2- u 1) Derived from buoyancy and gravity; difference in penetration kinetic energy. hydraulic gradient i The density of water Thickness of alteration zone t The derivation yields the following: frictional energy dissipation. From frictional force and displacement difference ( u 2- u 1) It is derived.

[0075] Specifically, the determination of the instability type can be as follows:

[0076] (1) When the frictional energy dissipation of the alteration zone is greater than the sum of the gravitational potential energy change and the seepage kinetic energy change caused by tunnel excavation, the elastic potential energy change and kinetic energy change of the alteration zone are both 0, and the alteration zone is in a stable state.

[0077] (2) When the frictional energy dissipation of the alteration zone is less than the sum of the gravitational potential energy change and the permeation kinetic energy change caused by tunnel excavation, if the elastic potential energy change of the alteration zone is exactly equal to the sum of the gravitational potential energy change and the permeation kinetic energy change minus the frictional energy dissipation, then the kinetic energy of the alteration zone is 0, and the alteration zone is in a stable state.

[0078] (3) When the frictional energy dissipation of the altered zone is less than the sum of the changes in gravitational potential energy and seepage kinetic energy caused by tunnel excavation, if the elastic potential energy change of the altered zone is less than the sum of the changes in gravitational potential energy and seepage kinetic energy minus the frictional energy dissipation, then the kinetic energy of the altered zone is greater than 0, and the altered zone is in an unstable state. In this case, it can be further divided into two situations:

[0079] ① When the alteration zone is in an unstable state, and simultaneously satisfies the clay mineral content requirement... Moisture content At that time, it was determined that the alteration zone had undergone large deformation and instability;

[0080] ② When the alteration zone is in an unstable state, and simultaneously satisfies the clay mineral content requirement... Moisture content Pore ​​connectivity Hydraulic gradient At that time, it was determined to be a sudden instability caused by a mudflow.

[0081] Furthermore, the criterion also needs to consider two factors that affect instability: (1) the softening of the alteration zone upon contact with water leads to a decrease in effective cohesion. Effective internal friction angle and Young's modulus E This reduces the elastic potential energy difference. Energy loss due to friction (2) The thickness of the rock slab between the alteration zone and the tunnel top. h When the energy difference is insufficient, the elastic potential energy difference decreases, while the gravitational potential energy difference and the permeation kinetic energy difference increase, inducing instability and failure.

[0082] Therefore, step S30 also requires calculating the critical elastic strain energy of the poorly altered zone. When the elastic potential energy difference of the alteration zone When the elastic deformation reaches its limit and the instability trend cannot be restrained by elastic recovery, the instability determination in step S40 is carried out.

[0083] This step establishes an energy balance equation driven by multi-energy competition, using kinetic energy change as a direct criterion for whether the system tends to become unstable. It also couples in geological properties such as clay mineral content and water content, enabling the identification of stable states and the precise distinction between two different instability mechanisms and forms: large deformation and mudflow surge.

[0084] The instability criterion method for adverse alteration zones in tunnels based on multi-energy competition-driven theory provided in this application has the following effects: By acquiring a comprehensive parameter system covering geometric, mechanical, seepage, and geological properties, and calculating the displacement of the alteration zone before and after engineering disturbance, as well as the resulting changes in gravitational potential energy, elastic potential energy, seepage kinetic energy, and frictional energy consumption, the method quantifies the kinetic energy change by constructing a multi-energy competition-driven energy equation and coupling geological parameters for comprehensive judgment. This method breaks through the limitations of traditional single-factor analysis, comprehensively considers the competitive balance between multiple energies driving instability and hindering instability, and can subdivide the instability type according to the energy-dominant mode and geological conditions, thereby more comprehensively reflecting the complex dynamic response of the surrounding rock system during tunnel excavation and effectively improving the accuracy of instability judgment.

[0085] In one embodiment, the technical solution to achieve the above objective can be as follows: Addressing the problem that existing instability criteria for tunnel adverse alteration zones only focus on single forces, displacements, and pore pressures, leading to insufficient accuracy, this application analyzes the force and energy changes of adverse alteration zones in their natural state and under tunnel excavation unloading conditions. It establishes a multi-energy competition-driven energy equation, quantifies the conversion relationships between gravitational potential energy, elastic potential energy, permeation kinetic energy, frictional energy dissipation, and kinetic energy, and thus forms an instability criterion. This criterion can accurately distinguish between the stable state, large deformation instability state, and debris flow instability state of adverse alteration zones, providing a scientific basis for risk prediction before tunnel construction and the formulation of reinforcement measures during construction, effectively reducing safety accidents caused by instability of adverse alteration zones during tunnel excavation. The technical solution of this application is logically rigorous, computationally feasible, and applicable to the stability evaluation of surrounding rock in various tunnels containing adverse alteration zones.

[0086] like Figure 1 As shown in this embodiment, the instability criterion for tunnel adverse alteration zones based on multi-energy competition driving theory includes the following steps:

[0087] S1: Core Definitions and Parameter Descriptions

[0088] The key parameters for defining undesirable alteration zones are shown in Table 1:

[0089] Table 1 Key Parameters

[0090]

[0091] In this embodiment, buoyancy density The value is Effective cohesion Effective internal friction angle Young's modulus E is taken as the softened value when the alteration zone softens upon contact with water; clay mineral content M The water content was determined by X-ray diffraction. wThe pore connectivity was determined by drying test. k Determined by mercury porosimetry.

[0092] Moment of inertia per unit width of the slab bending section I Due to the thickness of the rock slab h The calculation is as follows: I = h 3 / 12 is used to characterize the flexural bearing capacity of rock slabs.

[0093] S2: Establishment of Instability Criterion

[0094] This embodiment proposes a multi-energy competition-driven theory and establishes an instability criterion for undesirable alteration zones. The solution steps are as follows:

[0095] S21: Stress analysis of alteration zone per unit width

[0096] By selecting a unit width of undesirable alteration band as the research object, the interference of the width dimension on the calculation is avoided, thus simplifying the model.

[0097] like Figure 2 As shown, friction is the core force hindering the sliding of the alteration zone, and it is determined by the effective cohesion of the rock mass, the internal friction angle, and the buoyancy density, as shown in the following formula:

[0098] (1)

[0099] Buoyancy is one of the core driving forces for sliding in alteration zones. The buoyancy of groundwater must be considered. The formula is as follows:

[0100] (2)

[0101] Calculate the forces exerted by the alteration zone and water on the bottom rock slab, taking into account buoyancy, friction, and permeability. q ,like Figure 3 As shown, the overall equilibrium equation for the alteration zone and water in the sliding direction is established as follows:

[0102] (3)

[0103] S22: Two key states defining the alteration zone

[0104] Clarifying the stress and boundary conditions of the alteration zone before and after tunnel excavation lays the foundation for subsequent energy calculations, such as... Figure 4 and Figure 5 As shown: State 1 (Natural State): Before tunnel excavation, the alteration zone, surrounding rock mass, and groundwater are in a state of static equilibrium, with no external disturbance. The displacement at the bottom is 0, and the seepage force is 0 (hydraulic gradient). i=0); State 2 (Tunnel Excavation Unloading State): After tunnel excavation, the original equilibrium state is broken, and two working conditions may exist: ① The water-retaining structure is directly exposed; ② The water-retaining plate leaks, causing groundwater to carry away the clay minerals in the alteration zone (hydraulic gradient). i >0); at the same time, the tunnel arch rock slab bends and deforms under the load, causing displacement at the bottom of the alteration zone.

[0105] S23: Calculate the displacement and elastic force of the alteration zone under two conditions.

[0106] (1) Since the displacement of the bottom of the alteration zone in state 1 is 0, and the undesirable alteration zone is not disturbed, the displacement of the bottom of the alteration zone is 0, that is By combining the differential equation of axial force in the alteration zone (see equation (4)), the displacement of the alteration zone in its natural state can be obtained. u 1; where the axial force differential equation reflects the relationship between the axial pressure of the alteration zone and the displacement and Young's modulus.

[0107] Assuming the axial force inside the alteration zone is N Then the axial force satisfies the differential equation:

[0108] (4)

[0109] Assuming the alteration zone is in an elastic state, then , E The Young's modulus of the undesirable alteration zone. u This represents the displacement of the undesirable alteration zone.

[0110] (2) For state 2, according to the theory of beams with fixed ends, uniformly distributed load q The maximum bending moment (Equation (5)) and maximum deflection (Equation (6)) under the action are:

[0111] (5)

[0112] (6)

[0113] In the formula Let be the moment of inertia of the bending section per unit width. Returning to the problem of undesirable alteration zones, the displacement at the bottom of the undesirable alteration zone is:

[0114] (7)

[0115] Axial force at the end of the alteration zone and q The relationship satisfies:

[0116] (8)

[0117] Combining (7) and (8), we get:

[0118] (9)

[0119] Based on the mixed boundary conditions (9) and the axial force differential equation (4), the displacement of the alteration zone under state 2 can be obtained, denoted as: u 2.

[0120] Before tunnel excavation, the water-retaining structure formed by the alteration zone is in a static state. Therefore, for state 1, the seepage force on the alteration zone is: For state 2, due to excavation disturbance, the water-reservoir structure is directly exposed, or leakage occurs between the tunnel and the impermeable slab of the water-reservoir structure. Assume the hydraulic gradient of the alteration zone is as follows: i The magnitude of the penetrating force on the alteration zone is the penetrating force. .

[0121] S24: Critical elastic strain energy

[0122] (10)

[0123] In the formula, The yield stress (kPa) of the alteration zone. The volume of the alteration zone per unit width (m³); The Young's modulus of the undesirable alteration zone.

[0124] When the elastic potential energy difference of the alteration zone When this occurs, it indicates that the elastic deformation has reached its limit and the instability trend cannot be restrained by elastic recovery; other energy terms must be considered to determine the type of instability. For adverse alteration zones, the yield stress should be taken. Young's modulus Then the critical elastic strain energy of the poor alteration zone can be calculated. .

[0125] S25: Establishing the energy equation driven by multi-energy competition

[0126] According to the kinetic energy theorem, the change in kinetic energy of the alteration zone is equal to the algebraic sum of the changes in all energies, encompassing the gravitational potential energy difference, elastic potential energy difference, penetration kinetic energy difference, and frictional energy loss, forming the core energy equation (Equation (11)):

[0127] (11)

[0128] In the formula, The kinetic energy of the alteration zone; The difference in gravitational potential energy between state 1 and state 2. Due to the difference in elastic potential energy, Due to poor osmotic kinetic energy, This represents the frictional energy loss from state 1 to state 2. Essentially, this equation represents a competitive balance between "driving energy" and "impeding energy."

[0129] S3: Instability Criterion Based on Energy Equation

[0130] Formula (11) gives the multi-energy competition driving relationship among kinetic energy, elastic potential energy, gravitational potential energy, permeation kinetic energy, and frictional energy dissipation. Based on this formula and combined with key geological parameters such as material conditions (clay mineral content, water content) and channel conditions (pore connectivity), the state of the alteration zone is divided into three cases, such as... Figure 6 As shown in Table 2, they are respectively:

[0131] (1) When the frictional energy dissipation of the alteration zone is greater than the sum of the gravitational potential energy change and the seepage kinetic energy change caused by tunnel excavation, the elastic potential energy change and kinetic energy change of the alteration zone are both 0, and the alteration zone is in a stable state.

[0132] (2) When the frictional energy dissipation of the alteration zone is less than the sum of the gravitational potential energy change and the seepage kinetic energy change caused by tunnel excavation, if the elastic potential energy change of the alteration zone is exactly equal to the sum of the gravitational potential energy change and the seepage kinetic energy change minus the frictional energy dissipation, then the kinetic energy of the alteration zone is 0 and the alteration zone is in a stable state.

[0133] (3) When the frictional energy dissipation of the altered zone is less than the sum of the changes in gravitational potential energy and seepage kinetic energy caused by tunnel excavation, if the elastic potential energy change of the altered zone is less than the sum of the changes in gravitational potential energy and seepage kinetic energy minus the frictional energy dissipation, then the kinetic energy of the altered zone is greater than 0, and the altered zone is in an unstable state. In this case, it can be further divided into two situations:

[0134] ① When the alteration zone is in an unstable state, and simultaneously satisfies the clay mineral content requirement... Moisture content At that time, it was determined that the alteration zone had undergone large deformation and instability;

[0135] ② When the alteration zone is in an unstable state, and simultaneously satisfies the clay mineral content requirement... Moisture content Pore ​​connectivity Hydraulic gradient At that time, it was determined to be a sudden instability caused by a mudflow.

[0136] It is important to note that the softening of the alteration zone upon contact with water may lead to a decrease in its effective cohesion, internal friction angle, and stiffness. This, in turn, reduces the elastic potential energy and frictional energy dissipation of the alteration zone, potentially causing instability. Furthermore, when the thickness of the rock slab between the alteration zone and the tunnel roof is insufficient, the elastic potential energy of the alteration zone decreases, while the changes in gravitational potential energy and permeation kinetic energy increase, which can also lead to instability and failure of the alteration zone.

[0137] Table 2. Classification and Comparison of Instability Criteria

[0138]

[0139] The beneficial effects of the technical solution provided in this embodiment are:

[0140] By combining the "three-energy competition" with key geological parameters such as clay mineral content and water content, the energy balance relationship is considered, while also taking into account the essential properties of the alteration zone, thus adapting to complex geological conditions.

[0141] By establishing a critical elastic strain energy calculation method and a multi-parameter coupling criterion, the energy threshold and geological condition threshold for stability-instability are clarified, thus avoiding the bias of judgment based on a single factor.

[0142] Based on the dual constraints of energy-dominant relationship and geological parameters, we can accurately distinguish between two types of instability: large deformation and mudslide inrush, providing a direct basis for formulating differentiated reinforcement measures.

[0143] All parameters are conventional survey and testing indicators for tunnel engineering, and the calculation steps are clear, which can be directly applied to pre-construction risk assessment and dynamic monitoring during construction.

[0144] Predicting the type and level of instability in advance can help avoid landslides and sudden surges caused by sudden instability, thereby reducing project safety costs and schedule losses.

[0145] The key point of this embodiment is:

[0146] Breaking through the traditional mechanical analysis framework, we establish a three-energy competition and release theory of "strain energy - water potential energy - gravitational potential energy", revealing the energy driving mechanism of mud bursts and large deformations, and solving the defect of traditional criteria that ignore the synergistic effect of multiple energies;

[0147] A coupled model of clay mineral content, water content, pore connectivity and energy term is constructed to combine geological essential properties with energy characteristics, so as to achieve accurate differentiation of instability types and overcome the limitation of traditional criteria that "emphasize mechanics and neglect geology".

[0148] A quantitative calculation method for critical elastic strain energy is proposed, clarifying the critical energy threshold of elastic constraints, transforming the fuzzy judgment of "stability-instability" into a quantitative standard, and improving the accuracy of the judgment in engineering applications.

[0149] The following is a specific implementation example of this application:

[0150] A tunnel traverses igneous rock strata. Due to regional tectonic movements and long-term groundwater action, a local granite alteration zone has developed. This alteration zone, characterized primarily by chloritization and kaolinization, extends in a banded pattern and forms a certain angle with the tunnel axis, representing a typical section of weak geological risk. Through advanced geological exploration, borehole sampling, laboratory mechanical tests, and in-situ testing, complete parameters of the alteration zone and surrounding rock mass were obtained: the average thickness of the alteration zone... t =7m, maximum burial depth d =200m, Inclination angleα =27°; the groundwater level penetrates the lower part of the alteration zone, and the natural density of the alteration zone is... ρ =2600 kg / m³, buoyant density ρ =1600kg / m³; Effective cohesion c =30 kPa, effective internal friction angle =25°, after softening in water, the mechanical parameters decreased to 27 kPa and 23° respectively; Young's modulus of the alteration zone. E =3.0GPa, softened to 2.7GPa; the rock slab between the tunnel arch and the alteration zone is an unaltered, intact rock mass with an average thickness of 3.0GPa. h =9m, Young's modulus E =29GPa, moment of inertia per unit width of the bending section I =0.068m 4 / m; Hydraulic gradient of the alteration zone under natural conditions i =0, expected leakage after tunnel excavation. i It rose to 0.33.

[0151] When the tunnel construction reached 10m from the leading edge of the alteration zone, on-site monitoring revealed an abnormally increased deformation rate of the surrounding rock and fluctuations in groundwater pressure. Therefore, the stability assessment was conducted using the criteria outlined in this application. First, the alteration zone per unit width was selected as the research object, and force calculations were performed based on the aforementioned parameters: According to indicators such as rock mass cohesion, internal friction angle, and buoyancy density, the frictional force per unit width of the alteration zone was calculated to be 178 kPa; combining buoyancy density, thickness, and dip angle, the component of buoyancy gravity along the sliding direction was determined to be 162 kPa; substituting the hydraulic gradient parameters, the uniformly distributed forces exerted by the alteration zone and water on the bottom rock slab were solved using equilibrium equations. q =205kPa.

[0152] Subsequently, displacement calculations were performed under two states: State 1 (natural state) with no external disturbance and zero bottom displacement. Combining the axial force differential equation and the Young's modulus of the alteration zone, the displacement of the natural state was obtained. u State 1 = 0.002m, representing the elastic deformation of the rock mass; State 2 (after excavation), based on the theory of fixed beams at both ends, calculates the maximum bending moment of the arch-top rock slab as 236kPa. With a maximum deflection of 0.017 m and a maximum deflection of 0.017 m, these were used as the boundary conditions for the displacement at the bottom of the alteration zone. The displacement after excavation was obtained by solving the relevant equations simultaneously. u 2 =0.043m, which is significantly larger than the natural state, indicating that the excavation has disrupted the original balance.

[0153] In the core energy equation solution stage, the energy terms were calculated as follows: gravitational potential energy difference 13.8 kJ / m, elastic potential energy difference 7.9 kJ / m, infiltration kinetic energy difference 20.2 kJ / m, and frictional energy loss 7.5 kJ / m. Substituting these values ​​into the energy balance relationship, the alteration kinetic energy was calculated to be 13.8 + 20.2 - 7.9 - 7.5 = 18.6 kJ / m > 0. Furthermore, the infiltration kinetic energy difference is greater than the gravitational potential energy difference, and this also satisfies the clay mineral content requirement. M =35% > 30%, moisture content w =32% > 30%, Pore connectivity k =0.65>0.6, hydraulic gradient i =0.33>0.3, the criterion determines that the alteration zone is "unstable state - mud flow sudden instability".

[0154] Based on the judgment results, a comprehensive treatment plan of "water blocking reinforcement + drainage and pressure reduction + dynamic monitoring" was formulated: Double-liquid grouting was used to reinforce the altered zone and surrounding rock mass to improve its cohesion and internal friction angle; drainage steel pipes were installed to divert groundwater and reduce the hydraulic gradient; and the frequency of monitoring surrounding rock deformation and seepage pressure was increased. After reinforcement, a recalculation showed that the hydraulic gradient decreased to 0.05, the mechanical parameters of the altered zone returned to pre-softening levels, the activity of clay minerals decreased, and the water content... w Reduced to 22%, pore connectivity k The energy level was reduced to 0.45. The updated energy terms were: gravitational potential energy difference 11.2 kJ / m, infiltration kinetic energy difference 2.9 kJ / m, and frictional energy consumption 17.8 kJ / m. The energy equations showed that the kinetic energy was ≤0, and the frictional energy consumption was greater than the sum of the gravitational potential energy difference and the infiltration kinetic energy difference. The criteria indicated that the alteration zone had stabilized. During subsequent tunnel excavation, the deformation rate of the surrounding rock remained stable within the safety threshold, showing no signs of instability. The tunnel successfully passed through this risky section, fully validating the accuracy and engineering guidance value of the criteria proposed in this application.

[0155] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for determining the instability of tunnels in adverse alteration zones based on multi-energy competition driving theory, characterized in that, Includes the following steps: S10, Obtain the core parameters of the adverse alteration zone and surrounding rock mass, including geometric parameters, mechanical parameters, seepage parameters and geological property parameters; S20, Based on the aforementioned core parameters, calculate the uniformly distributed forces exerted by the alteration zone and water on the tunnel arch slab after tunnel excavation. q ; S30, based on the uniformly distributed force q The displacements of the alteration zone under both the natural state and the tunnel excavation and unloading state are calculated. Based on the displacements and the core parameters, the gravitational potential energy difference between the two states is calculated. Elastic potential energy difference Poor osmotic kinetic energy and frictional energy loss ; S40, based on gravitational potential energy difference Elastic potential energy difference Poor osmotic kinetic energy and frictional energy loss The change in kinetic energy caused by alteration is calculated using the energy equation. Based on the geological attribute parameters, it is determined whether the adverse alteration zone is in a stable state, a large deformation unstable state, or a mudflow surge unstable state. In step S40, the energy equation is: ； In step S40, the determination of the instability type includes: The criteria for determining the condition of an undesirable alteration zone are as follows: when >( + When the alteration zone is in a stable state, it is determined that the alteration zone is in a stable state. when <( + )and = ( + - When the alteration zone is in a stable state, it is determined that the alteration zone is in a stable state. when <( + )and <( + - When the alteration zone is in an unstable state, it is determined that the alteration zone is in an unstable state; when it is in an unstable state, if the clay mineral content in the core parameters is simultaneously satisfied... M The moisture content is greater than or equal to the first threshold and the core parameter is greater than or equal to the first threshold. w If the value is less than or equal to the second threshold, it is determined to be a large deformation instability state; if the clay mineral content is also satisfied... M Greater than or equal to the first threshold, the moisture content w The pore connectivity in the core parameters is greater than the second threshold. k The hydraulic gradient in the core parameters is greater than or equal to the third threshold. i If the value is greater than or equal to the fourth threshold, it is determined to be a mudflow instability state.

2. The method for determining instability of tunnels in adverse alteration zones based on multi-energy competition driving theory as described in claim 1, characterized in that, In step S10, the geometric parameters include the thickness of the alteration zone. t Maximum burial depth d ,inclination Thickness of rock slab between tunnel arch and alteration zone h and the length of the alteration zone along its direction L ; The mechanical parameters include the effective cohesion of the altered zone rock mass. Effective internal friction angle Natural density Buoyancy Young's modulus E Young's modulus of slab and moment of inertia per unit width of bending section I ; The seepage parameters include the hydraulic gradient of groundwater in the alteration zone after tunnel excavation. i ; The geological property parameters include clay mineral content. M Moisture content w and pore connectivity k .

3. The method for determining instability of tunnels in adverse alteration zones based on multi-energy competition driving theory as described in claim 2, characterized in that, In step S20, the uniformly distributed force is calculated. q include: Through formula Calculate the frictional force of the alteration zone. F ;in, g It is the acceleration due to gravity; Through formula Calculate the buoyancy of the alteration zone. G ; The overall equilibrium equations for alteration zones and water in the sliding direction Solve for the uniformly distributed force. q ;in, This is the density of water.

4. The method for determining instability of tunnels in adverse alteration zones based on multi-energy competition driving theory as described in claim 1, characterized in that, In step S30, the natural state refers to the state before tunnel excavation where the alteration zone, surrounding rock mass, and groundwater are in static equilibrium, without external disturbance, with the bottom unit displacement being 0 and the permeability being 0. The tunnel excavation unloading state refers to the situation after tunnel excavation where the original equilibrium state is broken, water-bearing structures are exposed, or water-resistant slabs leak, and the tunnel arch slab is subjected to uniformly distributed forces. q The action causes bending deformation, which in turn causes displacement at the bottom of the alteration zone.

5. The method for determining instability of tunnels in adverse alteration zones based on multi-energy competition driving theory as described in claim 2, characterized in that, In step S30, the displacement in the natural state u 1. Based on the boundary condition that the bottom displacement is 0, combined with the differential equation of axial force in the alteration zone. The solution is obtained; where, N The axial force at the end of the alteration zone. x The coordinates are along the direction of the alteration zone. g It is the acceleration due to gravity. This is the density of water.

6. The method for determining instability of tunnels in adverse alteration zones based on multi-energy competition driving theory as described in claim 2, characterized in that, In step S30, the displacement of the alteration zone under the unloading state of tunnel excavation is calculated. u Step 2, specifically: Based on the theory of beams with fixed ends, through the formula Calculate the maximum bending moment of the rock slab And through the formula Calculate the maximum deflection of the rock slab ; With the maximum deflection As the displacement boundary condition at the bottom of the alteration zone, it is determined by the formula... Calculate the displacement at the bottom of the alteration zone, where x The coordinates are along the direction of the alteration zone; Combined with the axial force at the end of the alteration zone N With uniformly distributed force q relational equations The mixed boundary conditions are obtained by combining the equations. ;in, u This represents the displacement of the undesirable alteration zone; Based on the aforementioned mixed boundary conditions, and combined with the differential equation of axial force in the alteration zone... The displacement is obtained by solving. u 2; among which, g It is the acceleration due to gravity. This is the density of water.

7. The method for determining instability of tunnels in adverse alteration zones based on multi-energy competition driving theory as described in claim 1, characterized in that, Step S30 also includes: Calculate the critical elastic strain energy of the poorly altered zone. The calculation formula is: ,in The yield stress of the alteration zone is denoted as . V The volume of the alteration zone per unit width. E Young's modulus; When the elastic potential energy difference is greater than or equal to the critical elastic strain energy When instability is determined, step S40 is performed.

8. A stability control method in tunnel construction, characterized in that, The method for determining instability in tunnels with adverse alteration zones based on multi-energy competition driving theory, as described in any one of claims 1 to 7, includes the following steps: Before tunnel construction, risk prediction is made on the surrounding rock of the tunnel containing the unfavorable alteration zone based on the instability criterion of the tunnel's unfavorable alteration zone. During tunnel construction, based on the instability type determined by prediction or real-time assessment, corresponding reinforcement measures are formulated and implemented. The undesirable alteration zone is a weak geological body formed by the transformation of primary rocks by later geological hydrothermal alteration, with internally distributed alteration minerals. The alteration minerals include one or more of sericitization, chloritization, and kaolinization.

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