Marine soft soil tunnel construction disturbance induced surrounding rock energy dissipation classification evaluation method

Abstract

The present application relates to the technical field of underground engineering and geotechnical mechanics, and provides a marine soft soil tunnel construction disturbance induced surrounding rock energy dissipation grading evaluation method, comprising the following steps: step 1, establishing a marine soft soil energy dissipation constitutive model based on thermodynamics; step 2, determining the mechanical parameters of the constitutive model; step 3, establishing a tunnel construction mechanics model, embedding the constitutive model in step 1 and the mechanical parameters in step 2 into the tunnel construction mechanics model, and outputting energy sub-item output in real time; step 4, establishing a damage unit identification system; step 5, laying out a monitoring system to obtain monitoring data and feed back to the numerical model for verification; step 6, grading early warning through the closeness of the structural unit to the instability and failure energy threshold. The present application constructs a surrounding rock damage grading system from the perspective of energetics, and realizes rapid risk identification combined with multi-source monitoring data, thereby providing a new theory and engineering means for safe construction of marine soft soil tunnels.

Description

Technical Field

[0001] This invention relates to the fields of underground engineering and geotechnical mechanics, specifically to a method for classifying and evaluating energy dissipation in surrounding rock induced by disturbance during the construction of marine soft soil tunnels. Background Technology

[0002] Marine soft soils are widely distributed in coastal cities and offshore transportation corridors. Their high porosity, high water content, and weak structure make them prone to large deformations, instability, and water inrush during tunnel excavation. Especially in the construction of subways, submarine water pipelines, and cross-sea channels, shield tunneling or mining methods inevitably disturb the surrounding rock-strata system, inducing stress redistribution and rapid energy release.

[0003] Currently, existing design codes primarily assess stability based on limit equilibrium or equivalent elastoplastic theory, focusing on stress-strain indices and paying insufficient attention to energy changes. This makes it difficult to intuitively reflect the damage evolution and safety margin of the surrounding rock under excavation disturbance. Existing studies have attempted to introduce energy indicators (such as elastic strain energy density and plastic dissipation energy) to evaluate rock and soil failure, but these mainly focus on earthquake or slope slip scenarios, and research on the energy dissipation law of saturated soft clay tunnel surrounding rock is still limited.

[0004] Commonly used numerical post-processing methods have the following problems: (1) Incomplete energy breakdown. Most software defaults to outputting total external work or single strain energy, making it difficult to distinguish the contributions of elastic release, plastic dissipation, and pore water pressure. (2) Lack of classification standards. Even if energy data is obtained, there is a lack of quantitative thresholds corresponding to the damage level of the surrounding rock, making it impossible to quickly determine the risk level during construction. (3) Reliance on high-precision models. Accurate energy inversion often requires fine meshes and complex constitutive models, resulting in a large amount of computation, which is difficult to meet the needs of rapid iterative analysis during construction.

[0005] In summary, the core technological gaps in the current risk management of marine soft soil tunnel construction are as follows: There is a lack of a complete and efficient energy component calculation framework that can simultaneously consider elastic release, plastic dissipation, and seepage coupling effects, accurately quantifying the contribution of each energy component to surrounding rock damage; there is a lack of energy dissipation grading and evaluation standards that strictly match the surrounding rock damage mechanism, making it impossible to quantitatively convert energy indicators into risk levels that intuitively reflect safety margins; and there is a lack of energy-based real-time evaluation and early warning methods applicable to construction sites and capable of rapid implementation, making it difficult to effectively link numerical simulation, monitoring data, and energy analysis to guide support decisions and construction optimization.

[0006] Therefore, there is an urgent need to develop an innovative methodology to construct a graded evaluation mechanism for surrounding rock damage in marine soft soil tunnels from an energy perspective, and to combine multi-source information to achieve rapid identification and early warning of risks during construction, so as to provide new theoretical and engineering support for improving the safe construction level of tunnels in such complex strata. Summary of the Invention

[0007] To address the problems existing in the background technology, this invention proposes a graded evaluation method for energy dissipation of surrounding rock induced by disturbance during the construction of marine soft soil tunnels. It constructs a graded system for surrounding rock damage from an energy perspective and combines multi-source monitoring data to achieve rapid risk identification, providing new theoretical and engineering means for the safe construction of marine soft soil tunnels.

[0008] To achieve the above objectives, the present invention adopts the following solution:

[0009] The method for classifying and evaluating the energy dissipation of surrounding rock induced by disturbance during the construction of marine soft soil tunnels includes the following steps:

[0010] Step 1: Establish a thermodynamic constitutive model for energy dissipation in marine soft soil. The constitutive model defines the elastoplastic stress-strain relationship through yield conditions, flow rules, hardening laws, and elastic strain increments.

[0011] Step 2: Based on the geological survey data of the marine soft soil tunnel project, the mechanical parameters of the constitutive model are determined through experiments;

[0012] Step 3: Based on the dimensions of the marine soft soil tunnel project, establish a tunnel construction mechanics model. Embed the marine soft soil energy dissipation constitutive model established in Step 1 and the mechanical parameters obtained in Step 2 into the tunnel construction mechanics model, and output the energy component output, including damage variables, cumulative plastic strain and energy dissipation, in real time during the iteration process.

[0013] Step 4: Based on the energy component output obtained in Step 3, establish a damage unit identification system on the thermodynamic constitutive model of marine soft soil energy dissipation.

[0014] Step 5: Deploy a monitoring system at the tunnel excavation face to acquire monitoring data in real time and feed it back to the numerical model for verification.

[0015] Step 6: Based on the damage unit identification system established in Step 4, graded early warning is given by the degree of proximity of the structural unit to the instability failure energy threshold.

[0016] Optionally, in step 1, the method for establishing a thermodynamically based constitutive model for energy dissipation in marine soft soil includes the following steps:

[0017] Step 1.1, Initialization and Material Parameter Reading: Read elastic parameters, critical state parameters, initial hardening and initial hardening amount, and set convergence tolerance;

[0018] Step 1.2, Elastic Prediction: Calculate the elastic strain increment based on the generalized Hooke's law to generate the test stress. ,

[0019] Step 1.3, Yield Criterion: Using the yield function in the true stress space f Determine the state, if If the step is considered elastic, the elastic stiffness matrix is ​​directly output to update the stress; if If the yield function satisfies the mapping constraint between the dissipated stress space and the true stress space, then it enters the plastic correction stage; whereby the yield function satisfies the mapping constraint between the dissipated stress space and the true stress space.

[0020] The equation for the yield surface in the dissipated stress space is:

[0021]

[0022] The equation for the yield surface in true stress space is:

[0023]

[0024] In the formula, For effective average stress; It is a deviatoric stress invariant; Equivalent preconsolidation pressure / structural consolidation pressure; M The critical stress ratio; ;

[0025] ; All are structural parameters of the model, satisfying and This ensures the closure of the yield surface and positive energy definiteness.

[0026] Step 1.4, Plastic Flow Direction: Obtain the true stress based on the positive alternating current law of dissipative stress space.

[0027] Direction of spatial flow:

[0028]

[0029] In the formula, The expansion angle is the plastic potential function. For plastic volumetric strain; This is plastic shear strain;

[0030] Step 1.5, Plastic Correction and Consistency Conditions: Using plastic volumetric strain as the hardening parameter, the flow rules and consistency conditions of the dissipative stress space are coupled to derive a plastic multiplier compatible with energy dissipation, and the stress and hardening amount are updated to meet the requirements. ,

[0031] The formula for plastic multipliers is: ,

[0032] In the formula, For plastic hardening modulus, f Let be the yield function; These are stress components;

[0033] Step 1.6, Stress-Strain Relationship and Algorithm Tangent: Construct the output elastoplastic stiffness matrix for global Newton iteration. The elastoplastic stiffness matrix is ​​expressed as:

[0034] ,

[0035] In the formula, This is the elasto-plastic tangent stiffness matrix; Here is the elastic stiffness matrix; For plastic strain, the dual variable;

[0036] Step 1.7, Energy decomposition and threshold index online output, used to provide online indicators for graded early warning: decompose the external work increment into elastic strain energy, plastic dissipation energy and pore water work and output them in real time.

[0037] Optionally, in step 1.2, the elastic strain increment includes the elastic volumetric strain increment and the elastic shear strain increment, and the elastic volumetric strain increment is expressed as:

[0038]

[0039] The elastic shear strain increment is expressed as:

[0040]

[0041] In the formula, K is the bulk modulus of elasticity. It is the elastic shear modulus. , , is the porosity. It is Poisson's ratio.

[0042] Optionally, the structural parameters Adjustable, specifically:

[0043] when hour, The smaller the value, the flatter the yield surface. The larger the yield surface, the more it expands outward.

[0044] when At that time, by changing Controlling the direction of deviatoric stress propagation on the yield surface.

[0045] Optionally, in step 1.4, the flow rule is derived by naturally deriving the associated flow rule based on the dissipation increment function in the dissipation stress space, and then converting the flow direction to the real stress space through an explicit mapping relationship. The real stress space is generally not associated, only when... , , At that time, the true stress space becomes correlated, in which the shear dilatation angle for:

[0046]

[0047] In the formula, This is the equivalent average stress variable; The equivalent deviatoric stress variable; A and B are model parameters, derived from the yield surface form and structural parameters. Decide.

[0048] Optionally, in step 1.5, the hardening parameter satisfy:

[0049]

[0050] The coupling consistency condition yields:

[0051]

[0052] The flow law for coupled dissipative stress space is as follows:

[0053]

[0054] In the formula, H These are the hardening parameters; For plastic volumetric strain; This is the increment of the plastic multiplier.

[0055] Optionally, in step 2, the geological survey data includes soft soil distribution, pore pressure, and permeability coefficient; the step of determining the mechanical parameters of the constitutive model includes:

[0056] Step 2.1: Obtain the critical stress ratio M based on the consolidated undrained triaxial test, and determine the hardening modulus by combining it with the compression-rebound test. With the rebound index k;

[0057] Step 2.2: Construct a mean square error objective function based on triaxial test data, and use an improved genetic algorithm to invert and obtain structural parameters. .

[0058] Optionally, in step 4, the method for determining potential damage elements based on energy dissipation-strain threshold includes the following steps:

[0059] Step 4.1: Based on the basic equation of elastic-plastic-percolation coupling, combined with the energy dissipation constitutive model and Biot's percolation theory, the energy conservation relationship is derived, and the increment of external work is decomposed into the increment of elastic strain energy, the increment of plastic dissipation energy and the increment of work done by pore water.

[0060] Step 4.2: In ABAQUS, the energy component output from Step 3 is incorporated into the iterative solution process, and the numerical integration energy error is controlled within ±2% by comparing uniaxial compression and simple shearing.

[0061] Step 4.3: Design multiple sets of virtual tests with different combinations of burial depth, confining pressure, and tunneling rate; identify the characteristic points of the calculated energy-strain trajectory for each set; and use the least squares method to fit and obtain the empirical relationship between the critical value of plastic dissipation energy and the equivalent plastic shear strain. The empirical relationship is as follows:

[0062]

[0063] in, This is the critical value for plastic dissipation energy density. This is the critical value of the equivalent plastic shear strain;

[0064] Step 4.4, when any unit in the numerical calculation satisfies and When, it is determined to be a potential damage unit, among which, For plastic dissipation energy density, This is the equivalent plastic shear strain.

[0065] Optionally, in step 5, the monitoring system includes a distributed fiber optic strain sensor, a pore pressure gauge, and an inertial navigation attitude sensor; the monitoring data includes strain, pore pressure, and displacement data; the verification method specifically involves comparing the acquired monitoring data with the equivalent plastic shear strain and damage determination results obtained from the energy dissipation constitutive calculation in the numerical model, and if a deviation occurs, the model and threshold parameters are corrected by feedback.

[0066] Optionally, in step 6, the degree to which the structural unit is close to the instability failure energy threshold is determined by the ratio of the unit's current plastic dissipation energy density to the critical plastic dissipation energy density at the equivalent plastic shear strain level. The tiered early warning system includes:

[0067] The current alert level is Level 1: Normal tunneling, routine monitoring.

[0068] The alert level is Level II: slow down tunneling, increase grouting pressure, and strengthen monitoring frequency;

[0069] The warning level is Level 3: shutdown for inspection, localized advanced reinforcement, or extension of the pipe shed;

[0070] and The alert level is Level 4: Emergency shutdown; implementation of emergency plans such as secondary support, freezing / grouting, etc.

[0071] The beneficial effects of this invention are as follows: First, this scheme constructs a surrounding rock damage classification system from an energy perspective and combines multi-source monitoring data to achieve rapid risk identification, providing new theoretical and engineering methods for safe construction of marine soft soil tunnels. Specifically, step 1 establishes a constitutive model; step 2 determines mechanical parameters; and step 3 combines the constitutive model and mechanical parameters and embeds them into a specific tunnel construction finite element model, enabling the energy dissipation constitutive model to run in ABAQUS and output damage variables, cumulative plastic strain, and energy dissipation in real time during the iteration process, thereby supporting the simulation of the construction process and energy classification evaluation in engineering applications. Step 4 establishes a judgment system based on the "thermodynamically based marine soft soil energy dissipation constitutive model," using the energy component output in step 3 to make judgments and labels within the numerical calculation framework, forming a damage unit identification system. Step 5 is the verification and correction step for the "energy dissipation-strain threshold judgment system" proposed in this invention, forming a closed loop of monitoring-numerical prediction-feedback optimization, improving the accuracy and engineering applicability of the judgment system. Step 6 outlines engineering applications to enable rapid implementation of energy-based real-time evaluation and early warning systems on construction sites. Therefore, this method effectively links numerical simulation, monitoring data, and energy analysis to guide support decisions and construction optimization, providing new theoretical and engineering support for improving the safe construction level of tunnels in such complex geological formations.

[0072] Furthermore, the thermodynamic-based constitutive model for energy dissipation in marine soft soil established in this scheme possesses several advantages, including dual-space design, energy consistency, and adjustable shape. Moreover, this constitutive model starts from the dissipation function rather than directly assuming a real spatial yield surface, thus maintaining measurable energy decomposition and interpretable dilatation angle evolution. Additionally, it can be coupled with a graded evaluation method, and its model structural parameters... The adjustable nature of the model enables it to reflect the changes in the strength envelope caused by "disturbance / structural degradation", and then connect with the online measurement of plastic dissipation energy density to serve the "grading and early warning of surrounding rock energy dissipation". Attached Figure Description

[0073] Figure 1 This is a flowchart of the grading evaluation method of the present invention;

[0074] Figure 2 This is a flowchart of the UMAT constitutive model for energy dissipation in marine soft soil based on thermodynamics, as described in this invention.

[0075] Figure 3 This is an elliptical dissipated stress space diagram in an embodiment of the present invention;

[0076] Figure 4 As described in the embodiments of the present invention Schematic diagram of the effect on the yield surface;

[0077] Figure 5As described in the embodiments of the present invention Schematic diagram of the effect on the yield surface;

[0078] Figure 6 This is an energy consumption-strain curve diagram from an embodiment of the present invention;

[0079] Figure 7 This is a schematic diagram of the numerical model dimensions in an embodiment of the present invention;

[0080] Figure 8 The settlement of the soft soil layer under different working conditions in the embodiments of the present invention (the depth of the monitoring points is 4m underground).

[0081] Figure 9 This is an energy cloud map (SDV3: energy dissipation, SDV4: total energy input, SDV5: percentage) at a burial depth of 10m in this embodiment of the invention. Detailed Implementation

[0082] To make the present invention clearer and more understandable, the present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the given embodiments are only one implementation method and do not represent all embodiments.

[0083] Combination Figures 1-9 This invention provides a method for classifying and evaluating energy dissipation in surrounding rock induced by disturbance during the construction of marine soft soil tunnels, comprising the following steps:

[0084] Step 1: Establish a thermodynamic constitutive model for energy dissipation in marine soft soil. The constitutive model defines the elastoplastic stress-strain relationship through yield conditions, flow rules, hardening laws, and elastic strain increments.

[0085] First, the constitutive model in this embodiment possesses multiple characteristics, including dual-space, energy consistency, and shape adjustability. Furthermore, it starts from the dissipation function rather than directly assuming a real spatial yield surface, thus maintaining measurable energy decomposition and interpretable dilatation angle evolution. Additionally, it can be coupled with a hierarchical evaluation method, and its model structural parameters... , The adjustable nature of the model enables it to reflect the changes in the strength envelope caused by "disturbance / structural degradation", and then connect with the online measurement of plastic dissipation energy density to serve the "grading and early warning of surrounding rock energy dissipation".

[0086] Step 2: Based on the geological survey data of the marine soft soil tunnel project, the mechanical parameters of the constitutive model are determined through experiments. The geological survey data includes soft soil distribution, pore pressure, permeability coefficient, etc.

[0087] The steps for determining the mechanical parameters of the constitutive model include:

[0088] Step 2.1: Obtain the critical stress ratio M based on the consolidated undrained triaxial test, and determine the hardening modulus by combining it with the compression-rebound test. With the rebound index k; Step 2.2, construct the mean square error objective function based on the triaxial test data, and use an improved genetic algorithm to invert and obtain the structural parameters. .

[0089] Step 3: Based on the dimensions of the marine soft soil tunnel project, establish a tunnel construction mechanics model. Embed the marine soft soil energy dissipation constitutive model established in Step 1 and the mechanical parameters obtained in Step 2 into the tunnel construction mechanics model, so that the energy dissipation constitutive model can run in ABAQUS. During the iteration process, the STATEV array is used to output damage variables, cumulative plastic strain and energy dissipation in real time, thereby supporting the construction process simulation and energy classification evaluation for engineering applications.

[0090] Based on ABAQUS software, stress updates for elastoplastic constitutive relations are achieved through implicit integration algorithms, solving the convergence problem of strongly nonlinear problems. By dynamically updating damage variables, cumulative plastic strain, and energy dissipation using the STATEV array, real-time tracking of soil structure degradation under construction disturbances is realized, enabling the development of a UMAT subroutine for a thermodynamic isotropic constitutive model of marine soft soil.

[0091] Step 4: Based on the energy component output obtained in Step 3, establish a damage element identification system, namely the "energy dissipation-strain threshold" judgment system, on the thermodynamic-based constitutive model of marine soft soil energy dissipation. This specifically includes the following steps:

[0092] Step 4.1: Based on the basic equation of elastic-plastic-percolation coupling, combined with the energy dissipation constitutive model and Biot's percolation theory, the energy conservation relationship is derived, and the increment of external work is decomposed into the increment of elastic strain energy, the increment of plastic dissipation energy, and the increment of work done by pore water.

[0093] Step 4.2: In ABAQUS, the energy component output from step 3 is incorporated into the iterative solution process, and the numerical integration energy error is controlled within ±2% by comparing uniaxial compression and simple shearing, laying the foundation for subsequent threshold calibration.

[0094] Step 4.3: Design multiple sets of virtual tests with different combinations of burial depth, confining pressure, and tunneling rate; identify the characteristic points of the calculated energy-strain trajectory for each set; and use the least squares method to fit the empirical relationship between the critical value of plastic dissipation energy and the equivalent plastic shear strain.

[0095] The empirical relation is as follows:

[0096]

[0097] in, This is the critical value for plastic dissipation energy density. This is the critical value of the equivalent plastic shear strain;

[0098] Step 4.4, when any unit in the numerical calculation satisfies and When, it is determined to be a potential damage unit, among which, For plastic dissipation energy density, For equivalent plastic shear strain, it can be quickly located by highlighting in the energy dissipation contour map, such as... Figure 6 .

[0099] Step 5: Deploy a monitoring system at the tunnel excavation face to acquire monitoring data in real time and feed it back to the numerical model for verification. The monitoring system includes distributed fiber optic strain sensors, pore pressure gauges, and inertial navigation attitude sensors; the monitoring data includes strain, pore pressure, and displacement data; the verification method is as follows: compare the acquired monitoring data with the equivalent plastic shear strain and damage assessment results obtained from the energy dissipation constitutive calculation in the numerical model. If a deviation occurs, the model and threshold parameters are corrected, thus forming a closed loop of monitoring-numerical prediction-feedback optimization, improving the accuracy and engineering applicability of the assessment system.

[0100] Step 6: Based on the damage unit identification system established in Step 4, graded early warning is given by the degree of proximity of the structural unit to the instability failure energy threshold.

[0101] The degree to which the structural unit is close to the instability failure energy threshold is measured by the ratio of the unit's current plastic dissipation energy density to the critical plastic dissipation energy density at the equivalent plastic shear strain level. This indicates that it serves as the core criterion for tiered early warning systems. Among them, The plastic dissipation energy density (the energy consumed per unit volume by irreversible plastic deformation) is calculated in real time by the energy dissipation constitutive model in this embodiment during numerical integration. It reflects the degree of energy loss caused by microcrack propagation, plastic slip, etc., in the current stress-deformation stage of the surrounding rock structure. The critical value of plastic dissipation energy is obtained by a combination of indoor tests (such as triaxial shear and uniaxial compression) and numerical regression. It corresponds to the material or structural unit under a specific equivalent plastic shear strain. The energy threshold that leads to instability and failure.

[0102] when When the ratio approaches or exceeds 1, the unit is determined to be in a state of potential damage or destruction, and different levels of warnings are triggered accordingly, including:

[0103] The current alert level is Level 1: Normal tunneling, routine monitoring.

[0104] The alert level is Level II: slow down tunneling, increase grouting pressure, and strengthen monitoring frequency;

[0105] The warning level is Level 3: shutdown for inspection, localized advanced reinforcement, or extension of the pipe shed;

[0106] and The alert level is Level 4: Emergency shutdown; implementation of emergency plans such as secondary support, freezing / grouting, etc.

[0107] This method constructs a surrounding rock damage grading system from an energy perspective and combines multi-source monitoring data to achieve rapid risk identification, providing new theoretical and engineering means for safe construction of marine soft soil tunnels. Specifically, step 1 establishes a constitutive model; step 2 determines mechanical parameters; and step 3 combines the constitutive model and mechanical parameters, embedding them into a specific tunnel construction finite element model, enabling the energy dissipation constitutive model to run in ABAQUS. During the iteration process, damage variables, cumulative plastic strain, and energy dissipation are output in real time, supporting construction process simulation and energy grading evaluation in engineering applications. Step 4 establishes a judgment system based on the "thermodynamically based marine soft soil energy dissipation constitutive model." Using the energy component outputs from step 3, judgments and markings are performed within the numerical calculation framework, forming a damage unit identification system. Step 5 is the verification and correction step for the "energy dissipation-strain threshold judgment system" proposed in this embodiment, forming a closed loop of monitoring-numerical prediction-feedback optimization to improve the accuracy and engineering applicability of the judgment system. Step 6 is the engineering application, suitable for construction sites, enabling rapid implementation of energy-based real-time evaluation and early warning. Therefore, this method effectively links numerical simulation, monitoring data and energy analysis to guide support decisions and construction optimization, providing new theoretical and engineering support for improving the safe construction level of tunnels in such complex strata.

[0108] The present invention will be further explained below with reference to the specific implementation method of the energy dissipation constitutive model construction method.

[0109] The constitutive relation of soil is its stress-strain relationship. The constitutive relation used in this embodiment is based on the thermodynamic elastoplastic theory. The elastoplastic model employs an incremental method, dividing the strain increment into two parts: a recoverable elastic strain increment and an unrecoverable plastic strain increment. The elastic strain increment is calculated according to elastic theory, and the plastic strain increment is calculated according to plastic theory. Plastic theory is embodied in the yield condition, flow law, and hardening law. The yield condition determines the stress condition at which plastic deformation begins; the flow law determines the direction of the plastic strain increment; and the hardening law determines the magnitude of the plastic strain increment, i.e., it determines the hardening parameter. Therefore, the constitutive model in this embodiment defines the elastoplastic stress-strain relationship through the yield condition, flow law, hardening law, and elastic strain increment.

[0110] In this embodiment, the yield condition serves as the theoretical premise for "energy grading evaluation." This embodiment derives an elliptical yield surface in the dissipative stress space using a Collins-based dissipation increment function, and further provides the mapping to the actual stress space and explicit solutions. Simultaneously, it provides parameter constraints for closure and positive definiteness, forming a link that tightly connects thermodynamically consistent energy dissipation with the actual stress yield surface used in engineering. The specific derivation includes:

[0111] From the general expression of the dissipation increment function of Collins isotropic soil, we can obtain:

[0112]

[0113]

[0114]

[0115] In the formula, These are all structural parameters of the model; For plastic volumetric strain; For plastic shear strain; A and B are model parameters, derived from the yield surface form and structural parameters. Decide; For effective average stress; Equivalent preconsolidation pressure / structural consolidation pressure (hardening variable);

[0116] From the dissipation increment function dφ, we get:

[0117]

[0118]

[0119] In the formula, This is the equivalent average stress variable; This is the equivalent deviatoric stress variable;

[0120] Combining the two equations and eliminating the strain increment, we can obtain the elliptical yield surface in the dissipative stress space, as shown below. Figure 3 As shown.

[0121]

[0122] The yield equations were obtained above. Therefore, removing the strain yields the yield surface equation in the dissipative stress space:

[0123]

[0124]

[0125]

[0126] In the formula, is the yield function in the deviatoric stress space; It is a deviatoric stress invariant; This represents the static average effective stress component. This represents the static deviatoric stress component.

[0127] In constructing an isotropic model, the free energy function Part Two It depends only on plastic volumetric strain, not on plastic shear strain. In this case, only the volumetric migration force exists, and the migration stress of the deviatoric stress is:

[0128] ,Right now ,but .

[0129] In the formula, Let be the plastic potential function; Let represent the components of the plastic potential function related to the mean stress and the deviatoric stress, respectively; These are elastic strain components; This represents the plastic strain component.

[0130] The yield surface in the true stress space is then:

[0131]

[0132] untie The expression is:

[0133]

[0134] This yields the mapping and explicit solution to the true stress space. The condition for the existence of a solution to this equation is:

[0135] when Time (i.e.) ), This condition must be met. At this point, the range of p is 0 to... ( (If positive), the graph of the equation resembles an ellipse.

[0136] when Time (i.e.) ), This condition must be met. At this point, the range of values ​​for p is... Furthermore, the equation graph might be hyperbolic, but this case is discarded because it does not satisfy the actual stress characteristics of soil (tensile stress is not possible). Based on satisfying the yield criterion, the following is determined: .

[0137] If the model remains reasonable and the yield surface is closed... The value of must satisfy:

[0138]

[0139] The above Instead of an empirical "stretch curve," the closed ellipse is derived in the dissipative stress space and then explicitly mapped into the real stress space. Equation (12) provides the thermodynamic positive definite / closed criterion, ensuring that no parameter selection violates the energy consistency and numerical stability. This allows for physically interpretable control of the "flattening / bulging" and "deviatoric stress propagation direction" of the yield surface, uniformly covering both shear-dominated and volumetric deformation-dominated instability characteristics.

[0140] Furthermore, the structural parameters The adjustable nature of the model allows it to reflect changes in the strength envelope caused by "disturbance / structural degradation," thereby enabling online measurement and connection with plastic dissipation energy density to serve "grading and early warning of surrounding rock energy dissipation."

[0141] like Figure 4 ,when hour, The smaller the yield surface, the flatter it is, and the more it contracts inward. The larger the value (less than 2), the more the yield surface expands outward, exhibiting higher shear strength; most typically... It has a symmetrical "elliptical" shape, similar to the classic Drucker-Prager; exceeding... The range will lead to abnormal shapes and non-compliance. For example... Figure 5 ,when Time, change The main function is to regulate the direction of the "eccentric stress" propagation on the yield surface; The larger the value, the more the yield surface "bulges" in the q direction, indicating that the deviatoric stress is more likely to trigger yielding; The smaller the value, the more the yield surface "contracts" in the q direction, indicating that shear stress is less likely to trigger yielding. This embodiment starts from the dissipation function rather than directly assuming a real spatial yield surface, thus maintaining the quantifiability of energy decomposition and the interpretability of the evolution of the dilatation angle (see the flow rules described later).

[0142] The yield criterion is the condition used to determine whether an elasto-plastic material is under loading, unloading, or neutral loading after an applied stress increment; it is also a criterion for determining whether plastic deformation has occurred. During loading, both elastic and plastic strains may occur, but during unloading, only elastic strain is generated. Therefore, the loading and unloading states can be determined using the yield function, specifically:

[0143] (1) At that time, the stress state is on the yield surface.

[0144] Under loading conditions, both elastic strain increments and plastic strain increments occur simultaneously.

[0145] For neutral variable loads, only elastic deformation occurs;

[0146] For unloading, only elastic deformation occurs.

[0147] In the formula, For stress components.

[0148] (2) At this point, the stress state is within the yield surface, and minute stress changes only produce elastic strain.

[0149] for The state of yielding is theoretically nonexistent because a new yield surface would form as stress exceeds the yield surface. This judgment is primarily for yield determination when establishing the constitutive model later.

[0150] Therefore, the yield condition in this embodiment forms a derivation link of "dual space - provable closure - regressible special case", which enables the model to regress the special case of MCC / DP and to flexibly control the strength envelope and deformation boundary of marine soft soil under tunnel disturbance through structural parameters. The difference from the existing methods is that traditional DP / MCC often directly constructs the yield surface in the real stress space and rarely starts from the dissipated stress space and gives strict closure and positive definiteness criteria; this embodiment gives verifiable physical-thermodynamic constraints to the parameters through formula (12), avoiding numerical ill-conditions such as "false yield / non-closure / non-physical tensile stress region", which is more in line with the needs of soft soil energy characterization and construction period stability assessment.

[0151] Therefore, based on the yield condition, a thermodynamic constitutive model for energy dissipation in marine soft soil is constructed, and the specific methods include:

[0152] Step 1.1, Initialization and Material Parameter Reading: Read the elastic parameters, critical state parameters, initial hardening and initial hardening amount, and set the convergence tolerance to provide a basis for subsequent elasticity prediction and yield determination.

[0153] Step 1.2, Elastic Prediction: Calculate the elastic strain increment based on the generalized Hooke's law to generate the test stress. The elastic strain increment includes the elastic volumetric strain increment and the elastic shear strain increment, and the elastic volumetric strain increment is expressed as:

[0154]

[0155] The elastic shear strain increment is expressed as:

[0156]

[0157] In the formula, K is the bulk modulus of elasticity. It is the elastic shear modulus. , , is the porosity. It is Poisson's ratio.

[0158] Step 1.3, Yield Criterion: Using the yield function in the true stress space f Determine the state, if If the step is considered elastic, the elastic stiffness matrix is ​​directly output to update the stress; if Then it enters the plastic correction stage.

[0159] Step 1.4, Plastic Flow Direction: Obtain the true stress based on the positive alternating current law of dissipative stress space.

[0160] The direction of spatial flow includes:

[0161] Orthogonality law:

[0162]

[0163] According to the Drucker hypothesis, for stable materials:

[0164]

[0165] In the formula, This is the plastic potential function, used to determine the direction of the plastic strain increment.

[0166] In the dissipative stress space, the associated flow rule is naturally derived based on the dissipative increment function:

[0167]

[0168]

[0169]

[0170] in: , ,

[0171] Shear expansion angle for:

[0172]

[0173] Substituting (8) and (9), the flow direction is transformed to the real stress space through explicit mapping, yielding the real space flow rule:

[0174]

[0175] Furthermore, when At this time, the flow laws of dissipative stress space are interconnected, but at this time, the flow laws of the real stress space are different. They are not interconnected.

[0176] when , At that time, it is related to the actual stress space flow law and belongs to the modified Cambridge model.

[0177] The associated flow (orthogonal law) is naturally derived in the dissipative stress space, and after explicit transformation to the real stress space, a verifiable condition for when it is associated / unassociated is given. This is the key to unifying "energy consistency (dissipation)" and "engineering fitability (unassociated flow)" in the same model. The formula for the dilatation angle is derived from the energy-dissipation framework, rather than being empirically given; thus, it can self-consistently change with confining pressure, stress path, and structural parameters, better fitting the shrinkage / dilatation transformation of saturated soft soil. The difference from existing methods: traditional unassociated DP often treats the plastic potential function / dilatation angle as empirical parameters; the traditional Cambridge model MCC is associated flow, which is difficult to simultaneously approximate the measured volumetric-shear coupling under high disturbance conditions. This embodiment gives the criterion and bridging formula for "associated (dissipative space) ⇄ unassociated (real space)", and uses the energy term to constrain the evolution of the shear angle, taking into account both numerical stability and physical interpretability.

[0178] Step 1.5, Plastic Correction and Consistency Conditions: Using plastic volumetric strain as the hardening parameter, the flow rules and consistency conditions of the dissipative stress space are coupled to derive a plastic multiplier compatible with energy dissipation, and the stress and hardening amount are updated to meet the requirements. Specifically, it includes:

[0179] First, the hardening law uses plastic volumetric strain as the hardening parameter.

[0180]

[0181] Differentiation yields:

[0182] Right now In the formula, For volume,

[0183] Then, by the consistency condition, we get

[0184]

[0185]

[0186]

[0187]

[0188]

[0189] From (15), the flow rule of coupled dissipative stress space is transformed into:

[0190]

[0191] Then we can obtain:

[0192]

[0193] set up It is the plastic hardening modulus, expressed as:

[0194]

[0195] but:

[0196]

[0197] The above derivation guarantees convergence and positive energy dissipation under implicit integration, laying a computational foundation for the subsequent "online output of energy components + threshold determination". The difference from existing methods is that classical derivations often focus on the correlation in the real stress space; this embodiment couples the dual-space flow with the consistency condition to obtain a closed expression applicable to UMAT, facilitating stable and rapid engineering calculations.

[0198] Step 1.6, Stress-Strain Relationship and Algorithm Tangent: Constructing the output elastoplastic stiffness matrix for global Newton iteration ensures second-order convergence and numerical stability, which is a key step in solving efficiency and robustness. Its calculation derivation, through strain decomposition and stress increment relationships, yields the elastoplastic stiffness matrix and elastoplastic compliance matrix, specifically including the following:

[0199] Total strain equals elastic strain plus plastic strain.

[0200]

[0201] Multiply both sides simultaneously get,

[0202]

[0203] in, ,

[0204] Substituting,

[0205] Multiply both sides simultaneously Organized

[0206]

[0207] have to,

[0208]

[0209] in, That is, the elastic-plastic stiffness matrix.

[0210] Alternatively, another way of representing it can be used.

[0211]

[0212]

[0213]

[0214]

[0215]

[0216]

[0217]

[0218] The elastic-plastic flexibility matrix,

[0219]

[0220]

[0221] Step 1.7, Energy decomposition and threshold index online output, used to provide online indicators for graded early warning: The external work increment is decomposed into elastic strain energy, plastic dissipation energy and pore water work and output in real time, providing online indicators for graded early warning of "energy dissipation-strain threshold", which is the end point of this embodiment from constitutive to application.

[0222] Simulation Example:

[0223] To verify the rationality of the present invention, a subway tunnel project in Shenzhen was used as a case study. Based on its geological survey report, the mechanical parameters were selected as shown in Table 1 below:

[0224] Table 1 Parameters required for the UMAT subroutine

[0225]

[0226] A mechanical model for tunnel construction was established. Considering the influence of boundary effects, the model was selected with a height of 60m and a length of 120m. Figure 7 The tunnel has a circular cross-section, with a shield diameter of 6.2m. In the model, the tunnel lining has an outer diameter of 6.2m, an inner diameter of 5.5m, a thickness of 0.35m, and a width of 1.5m per ring. The boundary conditions are horizontal displacement constraints on both sides, vertical displacement constraints at the bottom, and a free boundary at the top. The geological strata mesh uses CPE4P elements, and the tunnel lining uses CPE4 elements.

[0227] When simulating the shield tunnel construction process in ABAQUS, it is necessary to comprehensively consider the dynamic interaction between soil and structure, material nonlinearity, and the temporal nature of construction steps. The excavated soil portion can be removed using the element birth and death function (*MODEL CHANGE) in ABAQUS.

[0228] The model calculation and analysis process is as follows: First, initial geostress equilibrium is performed. Initial geostress equilibrium is a crucial step that involves applying gravity and adjusting the initial stress field of the soil to eliminate spurious displacements caused by artificial modeling, ensuring that the simulated initial state matches the actual ground stress. In the Geostatic analysis step, geostress equilibrium is performed by applying gravity (if groundwater level changes are involved, body force is used to apply the gravity load), and the initial stress is balanced using *INITIAL CONDITIONS and STRESS to restore the initial stress field. The contact between the lining and the soil is set, defining the contact between the inner surface of the soil and the outer surface of the lining, and simulating the selection of Tie constraints. In the tunnel excavation analysis step, the element birth and death method is used to dynamically simulate the soil excavation process. The construction steps are implemented in stages according to the sequence of "initial geostress equilibrium → shield tunneling (removal of soil elements) → lining installation". Finally, the implicit solver (Standard) is used to analyze key indicators such as surface settlement, lining stress, and contact pressure, completing a refined simulation of the mechanical behavior of the shield tunnel construction.

[0229] Different burial depth conditions and response analyses were performed. Simulations were conducted for burial depths of 10 m, 15 m, 20 m, 25 m, and 30 m to extract surface settlement, lining stress, and energy dissipation distribution.

[0230] Regarding surface subsidence: When the burial depth increased from 10 meters to 30 meters, the maximum subsidence increased from 11.6 mm to 43.62 mm and then slightly decreased to 33.35 mm; the maximum uplift increased from 12.12 mm to 57.46 mm. Increased burial depth led to increased subsidence and uplift, but a turning point in subsidence occurred at a depth of 25 m. This indicates that as the burial depth increases, the self-weight stress of the overlying strata rises. On the one hand, this increases the stress release caused by excavation unloading, exacerbating uplift; on the other hand, it promotes the expansion of the plastic zone of the surrounding rock, leading to continuously increasing subsidence. However, when the burial depth exceeds the critical value of 25 m, the self-supporting capacity of the surrounding rock under high ground stress increases, inhibiting the continued development of subsidence and forming a turning point.

[0231] Regarding lining stress: As the burial depth increases from 10m to 20m, the maximum shear stress on the lining decreases, but then increases significantly again with increasing burial depth, exceeding 2300 kPa at a depth of 30m, reflecting the significant influence of the deep surrounding rock or the initial stress field. Both the shallow section (at 10m) and the deep section (at 25 to 30m) have a high risk of lining stress.

[0232] Regarding energy dissipation: Analysis of the energy dissipation cloud map shows that energy dissipation in marine soft soil mainly occurs near the area disturbed by the tunnel boring machine (TBM). At a depth of 15m, the TBM is about 4m away from the silty clay layer, with only the lowest part of the soil layer showing some energy dissipation. However, at depths of 20m and below, although there is total energy input, the silty clay layer shows almost no energy dissipation. At a depth of 10m, a high level of energy input and dissipation can be observed around the TBM, indicating that the marine soft soil has been severely disturbed and "damaged."

[0233] Therefore, this embodiment shows that in silt layers with a depth of 10-15m, the strata are weak and subject to significant disturbance. During shield tunnel construction, it is recommended to control the tunneling speed, strengthen support grouting, and, if necessary, perform pre-reinforcement to reduce potential engineering accidents. In hard rock layers with a depth of 25-30m, stress concentration and high shear stress are likely to occur, requiring increased lining thickness and optimized reinforcement arrangement to prevent lining failure.

[0234] This embodiment verifies the effectiveness of the energy dissipation classification evaluation method for identifying safety risks in marine soft soil tunnel construction through multi-depth working condition simulation, and provides a quantitative basis for dynamically adjusting support parameters and construction technology.

[0235] The specific embodiments of the present invention have been described in detail above with reference to the figures, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for classifying and evaluating energy dissipation in surrounding rock induced by disturbance during the construction of marine soft soil tunnels, characterized in that... Includes the following steps: Step 1: Establish a thermodynamic constitutive model for energy dissipation in marine soft soil. This constitutive model defines the elastoplastic stress-strain relationship through yield conditions, flow rules, hardening laws, and elastic strain increments. The method for establishing this constitutive model includes the following steps: Step 1.1, Initialization and Material Parameter Reading: Read elastic parameters, critical state parameters, initial hardening and initial hardening amount, and set convergence tolerance; Step 1.2, Elastic Prediction: Calculate the elastic strain increment based on the generalized Hooke's law to generate the test stress. , Step 1.3, Yield Criterion: Using the yield function in the true stress space f Determine the state, if If the step is considered elastic, the elastic stiffness matrix is ​​directly output to update the stress; if If the yield function satisfies the mapping constraint between the dissipated stress space and the true stress space, then it enters the plastic correction stage; whereby the yield function satisfies the mapping constraint between the dissipated stress space and the true stress space. The equation for the yield surface in the dissipated stress space is: The equation for the yield surface in true stress space is: In the formula, For effective average stress; It is a deviatoric stress invariant; Equivalent preconsolidation pressure / structural consolidation pressure; M The critical stress ratio; ; ; All are structural parameters of the model, satisfying and This ensures the closure of the yield surface and positive energy definiteness. Step 1.4, Plastic Flow Direction: Based on the positive alternating current law of dissipative stress space, the flow direction in the true stress space is obtained: In the formula, The expansion angle is the plastic potential function. For plastic volumetric strain; This is plastic shear strain; Step 1.5, Plastic Correction and Consistency Conditions: Using plastic volumetric strain as the hardening parameter, the flow rules and consistency conditions of the dissipative stress space are coupled to derive a plastic multiplier compatible with energy dissipation, and the stress and hardening amount are updated to meet the requirements. , The formula for plastic multipliers is: , In the formula, For plastic hardening modulus, f Let be the yield function; These are stress components; Step 1.6, Stress-Strain Relationship and Algorithm Tangent: Construct the output elastoplastic stiffness matrix for global Newton iteration. The elastoplastic stiffness matrix is ​​expressed as: ， In the formula, This is the elasto-plastic tangent stiffness matrix; Here is the elastic stiffness matrix; For plastic strain, the dual variable; Step 1.7, Energy decomposition and threshold index online output, used to provide online indicators for graded early warning: decompose the external work increment into elastic strain energy, plastic dissipation energy and pore water work and output them in real time; Step 2: Based on the geological survey data of the marine soft soil tunnel project, the mechanical parameters of the constitutive model are determined through experiments; Step 3: Based on the dimensions of the marine soft soil tunnel project, establish a tunnel construction mechanics model. Embed the marine soft soil energy dissipation constitutive model established in Step 1 and the mechanical parameters obtained in Step 2 into the tunnel construction mechanics model, and output the energy component output, including damage variables, cumulative plastic strain and energy dissipation, in real time during the iteration process. Step 4: Based on the energy component output obtained in Step 3, establish a damage unit identification system on the thermodynamic constitutive model of marine soft soil energy dissipation. Step 5: Deploy a monitoring system at the tunnel excavation face to acquire monitoring data in real time and feed it back to the numerical model for verification. Step 6: Based on the damage unit identification system established in Step 4, graded early warning is given by the degree of proximity of the structural unit to the instability failure energy threshold.

2. The method for classifying and evaluating energy dissipation of surrounding rock induced by disturbance during construction of marine soft soil tunnels according to claim 1, characterized in that: In step 1.2, the elastic strain increment includes the elastic volumetric strain increment and the elastic shear strain increment, and the elastic volumetric strain increment is expressed as: The elastic shear strain increment is expressed as: In the formula, K is the bulk modulus of elasticity. It is the elastic shear modulus. , , is the porosity. It is Poisson's ratio.

3. The method for classifying and evaluating energy dissipation of surrounding rock induced by disturbance during construction of marine soft soil tunnels according to claim 1, characterized in that: The structural parameters Adjustable, specifically: when hour, The smaller the value, the flatter the yield surface. The larger the yield surface, the more it expands outward. when At that time, by changing Controlling the direction of deviatoric stress propagation on the yield surface.

4. The method for classifying and evaluating energy dissipation of surrounding rock induced by disturbance during construction of marine soft soil tunnels according to claim 1, characterized in that: In step 1.4, the flow rule is as follows: in the dissipative stress space, the associated flow rule is naturally derived based on the dissipative increment function, and then the flow direction is transformed to the real stress space through an explicit mapping relationship. The real stress space is generally not associated, only when... , , At that time, the true stress space becomes correlated, in which the shear dilatation angle for: In the formula, This is the equivalent average stress variable; The equivalent deviatoric stress variable; A and B are model parameters, derived from the yield surface form and structural parameters. Decide.

5. The method for classifying and evaluating energy dissipation of surrounding rock induced by disturbance during construction of marine soft soil tunnels according to claim 4, characterized in that: In step 1.5, the hardening parameter satisfy: The coupling consistency condition yields: The flow law for coupled dissipative stress space is as follows: In the formula, H These are the hardening parameters; For plastic volumetric strain; This is the increment of the plastic multiplier.

6. The method for classifying and evaluating energy dissipation of surrounding rock induced by disturbance during construction of marine soft soil tunnels according to claim 1, characterized in that: In step 2, the geological survey data includes soft soil distribution, pore pressure, and permeability coefficient; the steps for determining the mechanical parameters of the constitutive model include: Step 2.1, obtaining the critical stress ratio M based on consolidated undrained triaxial tests, and determining the hardening modulus by combining compression-rebound tests. With the rebound index k; Step 2.2: Construct a mean square error objective function based on triaxial test data, and use an improved genetic algorithm to invert and obtain structural parameters. .

7. The method for classifying and evaluating energy dissipation of surrounding rock induced by disturbance during construction of marine soft soil tunnels according to claim 1, characterized in that: Step 4, establishing a method for determining potential damage elements based on energy dissipation-strain threshold, includes the following steps: Step 4.1: Based on the basic equation of elastic-plastic-percolation coupling, combined with the energy dissipation constitutive model and Biot's percolation theory, the energy conservation relationship is derived, and the increment of external work is decomposed into the increment of elastic strain energy, the increment of plastic dissipation energy and the increment of work done by pore water. Step 4.2: In ABAQUS, the energy component output from Step 3 is incorporated into the iterative solution process, and the numerical integration energy error is controlled within ±2% by comparing uniaxial compression and simple shearing. Step 4.3: Design multiple sets of virtual tests with different combinations of burial depth, confining pressure, and tunneling rate; identify the characteristic points of the calculated energy-strain trajectory for each set; and use the least squares method to fit and obtain the empirical relationship between the critical value of plastic dissipation energy and the equivalent plastic shear strain. The empirical relationship is as follows: in, This is the critical value for plastic dissipation energy density. This is the critical value of the equivalent plastic shear strain; Step 4.4, when any unit in the numerical calculation satisfies and When, it is determined to be a potential damage unit, among which, For plastic dissipation energy density, This is the equivalent plastic shear strain.

8. The method for classifying and evaluating energy dissipation of surrounding rock induced by disturbance during construction of marine soft soil tunnels according to claim 1, characterized in that, The monitoring system includes a distributed fiber optic strain sensor, a pore pressure gauge, and an inertial navigation attitude sensor; the monitoring data includes strain, pore pressure, and displacement data; the verification method specifically involves comparing the acquired monitoring data with the equivalent plastic shear strain and damage determination results obtained from the energy dissipation constitutive calculation in the numerical model, and if a deviation occurs, the model and threshold parameters are corrected accordingly.

9. The method for classifying and evaluating energy dissipation of surrounding rock induced by disturbance during construction of marine soft soil tunnels according to claim 1, characterized in that, In step 6, the degree to which the structural unit is close to the instability failure energy threshold is determined by the ratio of the unit's current plastic dissipation energy density to the critical plastic dissipation energy density at the equivalent plastic shear strain level. The tiered early warning system includes: The current alert level is Level 1: Normal tunneling, routine monitoring. The alert level is Level II: slow down tunneling, increase grouting pressure, and strengthen monitoring frequency; The warning level is Level 3: shutdown for inspection, localized advanced reinforcement, or extension of the pipe shed; and The alert level is Level 4: Emergency shutdown; Implementation of secondary support, freezing / grouting emergency plan.

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