Classification evaluation method for surrounding rock energy dissipation induced by marine facies soft soil tunnel construction disturbance

Abstract

The invention relates to the technical field of underground engineering and geotechnical mechanics, and provides a marine facies soft soil tunnel construction disturbance induced surrounding rock energy dissipation grading evaluation method which comprises the following steps: step 1, establishing a marine facies soft soil energy dissipation constitutive model based on thermodynamics; 2, determining mechanical parameters of the constitutive model; 3, establishing a tunnel construction mechanical model, embedding the constitutive model in the step 1 and the mechanical parameters in the step 2 into the tunnel construction mechanical model, and outputting an energy subitem output quantity in real time; step 4, establishing a damage unit identification system; 5, arranging a monitoring system to obtain monitoring data and feeding the monitoring data back to the numerical model for verification; and step 6, performing graded early warning according to the closeness degree of the structural unit to the instability failure energy threshold value. According to the scheme, a surrounding rock damage grading system is constructed through an energetic perspective, rapid risk identification is realized in combination with multi-source monitoring data, and a new theoretical and engineering means is provided for safe construction of the marine soft soil tunnel.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of underground engineering and geotechnical mechanics, and particularly relates to a method for grading evaluation of energy dissipation of surrounding rock induced by construction disturbance of marine soft soil tunnel. BACKGROUND

[0002] Marine soft soil is widely distributed in coastal cities and offshore transportation corridors. Its characteristics of high void ratio, high water content and weak structure make it prone to large deformation, instability and water gushing during tunnel excavation. Especially in the construction of subways, underwater water transportation corridors and cross-sea passages, shield or mining method construction inevitably causes disturbance to the surrounding rock-stratum system, inducing stress redistribution and rapid energy release.

[0003] At present, the existing design specifications mainly evaluate stability based on limit equilibrium or equivalent elastic-plastic theory, focusing on stress-strain indicators and paying insufficient attention to energy changes, which makes it difficult to intuitively reflect the damage evolution and safety margin of surrounding rock under excavation disturbance. Existing research attempts to introduce energy indicators (such as elastic strain energy density and plastic dissipation energy) to evaluate rock and soil damage, but mainly focuses on earthquake or slope sliding scenarios, and there is limited research on the energy dissipation law of saturated soft clay tunnel surrounding rock.

[0004] The commonly used numerical post-processing methods have the following problems: (1) incomplete energy components, most software defaults to output total external work or single strain energy, making it difficult to distinguish the contribution of elastic release, plastic dissipation and pore water pressure work. (2) Lack of grading standards. Even if energy data is obtained, there is a lack of quantitative threshold corresponding to the damage level of surrounding rock, making it impossible to quickly determine the risk level during construction. (3) Dependence on high-precision models. Accurate energy inversion often requires fine grids and complex constitutive relations, which is computationally intensive and difficult to meet the needs of rapid iterative analysis during construction.

[0005] In summary, the core technical gaps in the current risk management and control of marine soft soil tunnel construction are: lack of a complete and efficient energy component calculation framework that can consider the coupling effects of elastic release, plastic dissipation and seepage, accurately quantify the contribution of each energy component to surrounding rock damage; lack of energy dissipation grading evaluation standards strictly matched with the damage mechanism of surrounding rock, which cannot quantitatively convert energy indicators into risk levels that intuitively reflect safety margins; lack of a real-time evaluation and early warning method based on energy that is suitable for construction sites and can be quickly implemented, making it difficult to effectively link numerical simulation, monitoring data and energy analysis to guide support decision-making and construction optimization.

[0006] Therefore, it is urgent to develop an innovative method system to construct a grading evaluation mechanism for marine soft soil tunnel surrounding rock damage from the perspective of energy science, and to realize rapid identification and early warning of construction risks by combining multi-source information, providing new theories and engineering support for improving the safety level of such complex stratum tunnels. SUMMARY

[0007] To solve the problems in the background art, the application provides a marine soft soil tunnel construction disturbance induced surrounding rock energy dissipation grading evaluation method, a surrounding rock damage grading system is constructed from the perspective of energy, and multi-source monitoring data is combined to realize rapid risk identification, thereby providing a new theory and engineering means for marine soft soil tunnel safety construction.

[0008] To achieve the above-mentioned purpose, the application adopts the following scheme: The marine soft soil tunnel construction disturbance induced surrounding rock energy dissipation grading evaluation method comprises the following steps: Step 1, a marine soft soil energy dissipation constitutive model based on thermodynamics is established, and the constitutive model defines the elastoplastic stress-strain relationship through a yield condition, a flow rule, a hardening law and an elastic strain increment; Step 2, based on the geological survey data of the marine soft soil tunnel engineering, the mechanical parameters of the constitutive model are determined through experiments; Step 3, a tunnel construction mechanical model is established based on the size of the marine soft soil tunnel engineering, the marine soft soil energy dissipation constitutive model established in step 1 and the mechanical parameters obtained in step 2 are embedded into the tunnel construction mechanical model, and energy sub-item output quantities including damage variables, cumulative plastic strain and energy dissipation quantities are output in real time in the iteration process; Step 4, based on the energy sub-item output quantities obtained in step 3, a damage unit identification system is established based on the marine soft soil energy dissipation constitutive model based on thermodynamics; Step 5, a monitoring system is arranged on the tunnel excavation face, which is used to obtain monitoring data in real time and feed back to the numerical model for verification; Step 6, based on the damage unit identification system established in step 4, the proximity of the structural unit to the instability and failure energy threshold is used for grading early warning.

[0009] Optionally, in step 1, the method for establishing the marine soft soil energy dissipation constitutive model based on thermodynamics comprises the following steps: Step 1.1, initialization and material parameter reading: reading elastic parameters, critical state parameters, initial hardening and initial hardening quantity, and setting convergence tolerance; Step 1.2, elastic prediction: calculating the elastic strain increment according to the generalized Hooke's law to generate a trial stress , Step 1.3, yield discrimination: judging the state through a true stress space yield function f If , the step is considered as elastic, and the elastic stiffness matrix is directly output to update the stress; if , plastic correction is entered; wherein the yield function satisfies the mapping constraint of the dissipation stress space and the true stress space; The yield surface equation in the dissipative stress space is:

[0010] The yield surface equation in real stress space is:

[0011] Where, is the effective mean stress; is the deviatoric stress invariant; is the equivalent pre-consolidation pressure / structural consolidation pressure; M is the critical state stress ratio; ; ; are all structural parameters of the model, satisfying and , ensuring the closure of the yield surface and the positivity of energy; Step 1.4, Plastic flow direction: Get the true stress based on the orthogonal flow law in the dissipative stress space Flow direction of space:

[0012] Where, is the expansion angle of the plastic potential function; is the plastic volume strain; is the plastic shear strain; Step 1.5, plastic correction and consistency condition: Using plastic volume strain as the hardening parameter, couple the flow law and consistency condition of the dissipative stress space, derive the plastic multiplier compatible with energy dissipation, and update the stress and hardening amount to meet , The plastic multiplier formula is: , Where, is the plastic hardening modulus, f is the yield function; is the stress component; Step 1.6, stress-strain relationship and algorithm tangent: Construct the output elastic-plastic stiffness matrix for global Newton iteration. The elastic-plastic stiffness matrix is ​​expressed as: , Where, is the elastic-plastic tangent stiffness matrix; is the elastic stiffness matrix; is the plastic strain dual variable; Step 1.7. Energy decomposition and threshold indicator online output for providing online indicators for hierarchical early warning: decompose the external work increment into elastic strain energy, plastic dissipation energy and pore water work and output in real time.

[0013] Optionally, in step 1.2, the elastic strain increment includes an elastic volumetric strain increment and an elastic shear strain increment, and the elastic volumetric strain increment is represented as:

[0014] The elastic shear strain increment is represented as:

[0015] In the formula, K is the elastic bulk modulus, is the elastic shear modulus, , is the void ratio, is the Poisson's ratio.

[0016] Optionally, the structural parameter is adjustable, specifically: When , the smaller the yield surface is, the flatter the yield surface is, the larger the yield surface is, the outwardly bulging the yield surface is; When , adjust the deviatoric stress extension direction of the yield surface by changing

[0017] Optionally, in step 1.4, the flow rule is that, in the dissipation stress space, the associated flow rule is derived based on the dissipation increment function, and the flow direction is converted to the real stress space through an explicit mapping relationship. The real stress space is generally unassociated, and only when , , , the real stress space becomes associated, wherein the shear dilatancy angle is:

[0018] In the formula, is the equivalent average stress variable; is the equivalent deviatoric stress variable; A and B are model parameters determined by the yield surface form and the structural parameter .

[0019] Optionally, in step 1.5, the hardening parameter satisfies:

[0020] Coupling consistency condition, we have:

[0021] Coupled with the flow law in the dissipative stress space, we get:

[0022] Where, H is the hardening parameter; is the plastic volume strain; is the plastic multiplier increment.

[0023] Optionally, in step 2, the geological survey data includes soft soil distribution, pore pressure, and permeability coefficient; and the step of determining the mechanical parameters of the constitutive model includes: Step 2.1: Obtain the critical stress ratio M based on the consolidated undrained triaxial test and determine the hardening modulus by combining the compression-rebound test. and the rebound index k; Step 2.2: Based on the triaxial test data, the mean square error objective function is constructed and the structural parameters are obtained by inversion using the improved genetic algorithm. .

[0024] Optionally, in step 4, establishing a method for determining potentially damaged units based on energy dissipation-strain thresholds includes the following steps: Step 4.1: Based on the basic equation of elastic-plastic-seepage coupling, combined with the energy dissipation constitutive model and Biot seepage theory, the energy conservation relationship is derived, and the external work increment is decomposed into the elastic strain energy increment, the plastic dissipation energy increment, and the pore water work increment; Step 4.2: In ABAQUS, the energy output from step 3 is embedded in the iterative solution process and verified by comparing uniaxial compression and simple shear to control the numerical integration energy error to ±2%. Step 4.3: Design multiple virtual tests with different combinations of burial depth, confining pressure, and excavation rate. Identify the characteristic points of the energy-strain trajectory for each set of calculations. Use the least squares method to fit the empirical relationship between the critical value of plastic dissipated energy and the equivalent plastic shear strain. The empirical relationship is:

[0025] in, is the critical value of plastic dissipation energy density, is the critical value of equivalent plastic shear strain; Step 4.4, when any unit in the numerical calculation satisfies and When , it is determined to be a potential damaged unit, where is the plastic dissipated energy density, is the equivalent plastic shear strain.

[0026] Optionally, in step 5, the monitoring system comprises a distributed optical fiber strain sensor, a pore pressure gauge and an inertial navigation attitude sensor; the monitoring data comprises strain, pore pressure and displacement data; and the verification method specifically comprises: comparing the obtained monitoring data with equivalent plastic shear strain and damage determination results calculated based on the energy dissipation constitutive model in the numerical model, and feeding back the model and threshold parameters for correction if a deviation occurs.

[0027] Optionally, in step 6, the proximity of the structural unit to the instability failure energy threshold is determined by the ratio of the current plastic dissipation energy density of the unit to the critical plastic dissipation energy density at the equivalent plastic shear strain level It is indicated that the hierarchical early warning comprises: When the value is 0, it is a first-level warning: normal tunneling, normal monitoring; When the value is 1, it is a second-level warning: reduced tunneling speed, increased grouting pressure, and increased monitoring frequency; When the value is 2, it is a third-level warning: stop for inspection, local advanced reinforcement or pipe roof lengthening; When the value is 3, it is a fourth-level warning: emergency stop; and secondary support, freezing / grouting and other emergency solutions are performed.

[0028] The present application has the beneficial effects that: first, the present application constructs a surrounding rock damage grading system from the perspective of energy, 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, specifically: step 1, establishing a constitutive model, step 2, determining mechanical parameters, step 3, combining the constitutive model and the mechanical parameters, embedding them into a specific tunnel construction finite element model, enabling the energy dissipation constitutive model to run in ABAQUS, and outputting damage variables, cumulative plastic strain and energy dissipation in real time during the iteration process, thereby supporting construction process simulation and energy grading evaluation for engineering application. Step 4 establishes a judgment system based on the “thermodynamic-based energy dissipation constitutive model of marine soft soil”, uses the energy sub-item output from 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 link of the “energy dissipation-strain threshold judgment system” proposed by the present application, to form a closed loop of monitoring-numerical prediction-feedback optimization, and to improve the accuracy and engineering applicability of the judgment system. Step 6 is the engineering application, which is suitable for the construction site and can quickly implement real-time evaluation and early warning based on energy. Therefore, the present method effectively links numerical simulation, monitoring data and energy analysis to guide support decision-making and construction optimization, and provides a new theory and engineering support for improving the safety construction level of such complex stratum tunnels.

[0029] ​Moreover, the thermodynamically based marine soft soil energy dissipation constitutive model established in this scheme has multiple characteristics of dual space, energy consistency and adjustable shape. Moreover, the constitutive model starts from the dissipation function rather than directly assuming the real space yield surface, so it can keep the energy decomposition quantifiable and the shear dilation angle evolution interpretable. In addition, it can be coupled with the graded evaluation method, and its model structural parameters The adjustability enables the model to reflect the changes in strength envelope caused by "disturbance / structural degradation", and then connect with the online measurement of plastic dissipation energy density to serve the "surrounding rock energy dissipation graded early warning". BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flow chart of the hierarchical evaluation method of the present invention; Figure 2 This is a flow chart of the UMAT constitutive model for energy dissipation of marine soft soil based on thermodynamics of the present invention; Figure 3 is an elliptical dissipative stress space diagram in an embodiment of the present invention; Figure 4 In the embodiment of the present invention Schematic diagram of the impact on the yield surface; Figure 5 In the embodiment of the present invention Schematic diagram of the impact on the yield surface; Figure 6 This is an energy consumption-strain curve diagram in an embodiment of the present invention; Figure 7 Schematic diagram of the size of the numerical model in the embodiment of the present invention; Figure 8 is the settlement of the soft soil layer under different working conditions in the embodiment of the present invention (the depth of the monitoring point is 4m underground); Figure 9 This is the energy cloud diagram (SDV3: energy dissipation, SDV4: total energy input, SDV5: proportion) at a burial depth of 10m in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the present invention clearer and more understandable, the present invention is described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the embodiment given is only one implementation method and does not represent all embodiments.

[0032] Combine Figures 1-9 The embodiment of the present invention provides a method for grading and evaluating surrounding rock energy dissipation induced by construction disturbance in marine soft soil tunnels, comprising the following steps: Step 1: Establish an energy dissipation constitutive model of marine soft soil based on thermodynamics. The constitutive model defines the elastic-plastic stress-strain relationship through yield conditions, flow laws, hardening laws and elastic strain increments.

[0033] Firstly, the constitutive model in this embodiment has the characteristics of dual space-energy-shape adjustment, and is derived from the dissipation function rather than directly assuming the real space yield surface, so it can keep the energy decomposition measurable and the shear dilatancy angle evolution explainable. In addition, it can be coupled with the hierarchical evaluation method, and the adjustable structural parameters of the model , can reflect the strength envelope change caused by "disturbance / structural deterioration", and then be connected with the online measurement of plastic dissipation energy density to serve the "surrounding rock energy dissipation hierarchical warning".

[0034] Step 2, based on the geological survey data of marine soft soil tunnel engineering, the mechanical parameters of the constitutive model are determined by test. The geological survey data includes soft soil distribution, pore pressure, permeability coefficient and the like.

[0035] The step of determining the mechanical parameters of the constitutive model comprises: Step 2.1, based on the consolidation undrained triaxial test, the critical state stress ratio M is obtained, and the hardening modulus and the resilience index k are determined by combining the compression resilience test; step 2.2, based on the triaxial test data, the mean square error objective function is constructed, and the structural parameters are obtained by inversion using the improved genetic algorithm.

[0036] Step 3, based on the size of marine soft soil tunnel engineering, a tunnel construction mechanical model is established, the marine soft soil energy dissipation constitutive model established in step 1 and the mechanical parameters obtained in step 2 are embedded into the tunnel construction mechanical model, so that the energy dissipation constitutive model can run in ABAQUS, and the damage variable, cumulative plastic strain and energy dissipation are output in real time in the iteration process by using the STATEV array, thereby supporting the construction process simulation and energy hierarchical evaluation of engineering application.

[0037] Based on the ABAQUS software, the stress update of the elastoplastic constitutive relation is realized by the implicit integration algorithm, solving the convergence problem of strong nonlinearity. The damage variable, cumulative plastic strain and energy dissipation are dynamically updated by using the STATEV array, realizing the real-time tracking of soil structure degradation under construction disturbance, and then the UMAT subprogram of the thermodynamic isotropic constitutive model of marine soft soil can be developed.

[0038] Step 4, based on the energy item output obtained in step 3, a damage element identification system, i.e. "energy dissipation-strain threshold" judgment system, is established on the basis of the thermodynamic marine soft soil energy dissipation constitutive model. It specifically includes the following steps: Step 4.1, based on the basic equations of elastoplasticity-seepage coupling, combined with the energy dissipation constitutive model and Biot seepage theory, the energy conservation relationship is derived, and the external work increment is decomposed into elastic strain energy increment, plastic dissipation energy increment and pore water work increment.

[0039] Step 4.2, in ABAQUS, the energy item output in step 3 is implanted into the iterative solution process, and is verified by uniaxial compression and simple shear, so that the numerical integral energy error is controlled within ±2%, which lays a foundation for subsequent threshold calibration.

[0040] Step 4.3, design a virtual test of multiple groups of different buried depths, confining pressures and excavation rates, identify the characteristic points of energy-strain trajectory of each group of calculations, 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, The empirical relationship is:

[0041] wherein, is the critical value of plastic dissipation energy density, is the critical value of equivalent plastic shear strain; Step 4.4, when any element in numerical calculation satisfies and , it is determined as a potential damage element, wherein, is the plastic dissipation energy density, is the equivalent plastic shear strain, which can be displayed in highlight in the energy dissipation cloud diagram to realize rapid positioning, such as Figure 6 .

[0042] Step 5, a monitoring system is arranged on the tunnel excavation face for real-time acquisition of monitoring data and feedback to the numerical model for verification. The monitoring system includes distributed optical fiber strain sensors, pore pressure gauges and inertial navigation attitude sensors; the monitoring data includes strain, pore pressure and displacement data; the verification method is specifically: comparing the acquired monitoring data with the equivalent plastic shear strain and damage determination results calculated based on the energy dissipation constitutive model in the numerical model, if there is deviation, then feedback to modify the model and threshold parameters, so as to form a closed loop of monitoring-numerical prediction-feedback optimization, and improve the accuracy and engineering applicability of the determination system.

[0043] Step 6, based on the damage element identification system established in step 4, the proximity of the structural element to the instability and failure energy threshold is used for hierarchical early warning.

[0044] The proximity of the structural element to the instability and failure energy threshold is represented by the ratio of the current plastic dissipation energy density of the element to the critical plastic dissipation energy density at the equivalent plastic shear strain level , which is the core criterion for hierarchical early warning. Wherein, The plastic dissipation energy density (energy consumed by non-recoverable plastic deformation per unit volume) is calculated in real time by the energy dissipation constitutive model of the embodiment during numerical integration, reflecting the degree of energy loss of the surrounding rock structure due to micro-crack expansion, plastic slip, etc. in the current stress-deformation stage. The plastic dissipation energy critical value is obtained by calibration through laboratory tests (such as triaxial shear, uniaxial compression, etc.) and numerical regression, which is the energy threshold value corresponding to the specific equivalent plastic shear strain The energy threshold value below which the unit enters an unstable failure state.

[0045] When When the ratio is close to or exceeds 1, the unit is determined to be in a potential damage or failure state, and different levels of early warning are triggered accordingly, including: When the ratio is less than 0.5, it is a first-level warning: normal tunneling, normal monitoring; When the ratio is between 0.5 and 1, it is a second-level warning: slow down tunneling, increase grouting pressure, and increase monitoring frequency; When the ratio is between 0.5 and 1, it is a second-level warning: slow down tunneling, increase grouting pressure, and increase monitoring frequency; When the ratio is greater than 1, it is a third-level warning: stop and check, local advanced reinforcement or pipe roof lengthening; When the ratio is greater than 1, it is a third-level warning: stop and check, local advanced reinforcement or pipe roof lengthening;

[0046] The method establishes a surrounding rock damage grading system from an energy perspective and realizes rapid risk identification combined with multi-source monitoring data, providing new theories and engineering methods for safe construction of marine soft soil tunnels. Specifically, step 1 establishes the constitutive model, step 2 determines the mechanical parameters, 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 iteration, thereby supporting construction process simulation and energy grading evaluation for engineering applications. Step 4 establishes a judgment system based on the "thermodynamic-based energy dissipation constitutive model of marine soft soil", uses the energy sub-item output from step 3 to make judgments and markings within the numerical calculation framework, forming a damage unit identification system. Step 5 is the verification and correction of the "energy dissipation-strain threshold judgment system" proposed in this embodiment to form a closed loop of monitoring-numerical prediction-feedback optimization, improving the accuracy and engineering applicability of the judgment system. Step 6 is the engineering application, which is suitable for construction sites and can quickly implement real-time evaluation and early warning based on energy. Therefore, this method effectively links numerical simulation, monitoring data and energy analysis to guide support decision-making and construction optimization, providing new theories and engineering support for improving the safety construction level of such complex stratum tunnels.

[0047] The application will be further described in combination with the specific embodiments of the construction method of the energy dissipation constitutive model.

[0048] The constitutive relation of soil, i.e. the stress-strain relation of soil. The constitutive relation adopted in the embodiment is based on the elastoplastic theory of thermodynamics. The elastoplastic model adopts the incremental method, and the strain increment is divided into two parts, i.e. the recoverable elastic strain increment and the unrecoverable plastic strain increment. The elastic strain increment is calculated according to the elastic theory, and the plastic strain increment is calculated according to the plastic theory. The plastic theory is embodied in the yield condition, the flow rule and the hardening law. The yield condition is the stress condition for determining the start of plastic deformation; the flow rule is the rule for determining the direction of plastic strain increment; and the hardening law is the law for determining the size of plastic strain increment, i.e. the hardening parameter. Therefore, the constitutive model in the embodiment defines the elastoplastic stress-strain relation through the yield condition, the flow rule, the hardening law and the elastic strain increment.

[0049] Among them, the yield condition is the theoretical premise of the "energy grading evaluation" in the embodiment. The embodiment derives the elliptical yield surface in the dissipation stress space based on the dissipation increment function of Collins, and further gives the mapping to the real stress space and the explicit solution, while giving the parameter constraint of closure and positive definiteness, forming a link that strictly connects the energy dissipation consistent with thermodynamics and the real stress yield surface used in engineering. The specific derivation includes: The general expression of the isotropic soil dissipation increment function of Collins can be obtained as follows:

[0050]

[0051]

[0052] In the formula, are model structural parameters; is the plastic volumetric strain; is the plastic shear strain; A and B are model parameters, which are determined by the yield surface form and the structural parameters ; is the effective mean stress; is the equivalent pre-consolidation pressure / structural consolidation pressure (hardening variable); is obtained from the dissipation increment function dφ:

[0053]

[0054] In the formula, is the equivalent mean stress variable; is the equivalent deviatoric stress variable; Two equations are combined, and the strain increment is eliminated, so that the elliptical yield surface in the dissipation stress space can be obtained, as shown in Figure 3 .

[0055]

[0056] The yield combination is obtained above, and then the strain is removed to obtain the yield surface equation in the dissipation stress space:

[0057]

[0058]

[0059] In the formula, is the yield function in the deviatoric stress space; is the deviatoric stress invariant; is the static average effective stress component; is the static deviatoric stress component.

[0060] In the isotropic model, the second part of the free energy function only depends on the plastic volumetric strain and does not depend on the plastic shear strain. At this time, only the volumetric migration force, and the deviatoric stress migration stress is: That is, , .

[0061] In the formula, is the plastic potential function; is the plastic potential function component representing the average stress and deviatoric stress, respectively; is the elastic strain component; is the plastic strain component.

[0062] Then the yield surface in the true stress space is:

[0063] The expression of is:

[0064] Thus, the mapping and explicit solution in the true stress space are obtained. The solution of the equation exists under the following conditions: When (i.e. ), must be satisfied. At this time, the value range of p is 0 to ( is positive), and the equation graph is similar to an ellipse.

[0065] When , i.e. , must be satisfied. At this time, the value range of p is , the equation graph may be a hyperbola, but it is abandoned because it does not satisfy the stress characteristics of the real soil body (cannot pull stress). According to the satisfaction of the yield condition, the value of p is determined .

[0066] If the model is reasonable and the yield surface is closed, the value of p must satisfy:

[0067] The above non-experience 'pulling curve', and after deducing the closed ellipse in the dissipation stress space, it is mapped into the real stress space by an explicit mapping, and then the thermodynamic positive / closed criterion is given by equation (12), which ensures that any parameter selection does not damage the energy consistency and numerical stability. In order to physically explain the 'flat / outer drum' and 'deviatoric stress expansion direction' of the yield surface, it covers both shear and volume dominated instability characteristics.

[0068] Further, the structural parameter can be adjusted, so that the model can reflect the strength envelope change caused by 'disturbance / structural deterioration', and then be connected with the online metering of plastic dissipation energy density, serving'surrounding rock energy dissipation grading early warning'.

[0069] As Figure 4 , when , is smaller, the yield surface is more 'flat' and shrinks inward, is larger (less than 2), the yield surface expands outward, showing higher shear strength; the most typical is , which is a symmetric 'ellipse', similar to the classical Drucker-Prager; beyond range, it will lead to abnormal shape, which does not conform. For example Figure 5 , when , changing mainly controls the 'deviatoric stress' expansion direction of the yield surface; is larger, the yield surface is more 'drummed' in the q direction, indicating that the deviatoric stress is more likely to trigger yield; is smaller, the yield surface is more'shrunk' in the q direction, indicating that the shear stress is not easy to trigger yield. The present embodiment starts from the dissipation function rather than directly assuming the yield surface in the real space, so it can maintain the energy decomposition and the shear dilatancy angle evolution can be explained (see the flow rule described later).

[0070] The yield criterion is the condition for the elastic-plastic material to judge whether it is loaded or unloaded, or neutral variable load after the stress increment is applied, and is also the criterion for judging whether plastic deformation occurs. When loaded, both elastic and plastic strain can occur, but only elastic strain occurs when unloaded. Therefore, through the yield function, the loading and unloading state can be judged, which is specifically: (1) When the stress state is on the yield surface, It is a loading state, and both elastic strain increment and plastic strain increment occur; It is a neutral variable load, and only elastic deformation occurs; It is unloaded, and only elastic deformation also occurs.

[0071] In the formula, is the stress component.

[0072] (2) When the stress state is in the yield surface, only elastic strain occurs with a small stress change.

[0073] For the state of , because a new yield surface will be formed as the stress exceeds the yield surface, it does not exist in theory. The above judgment is mainly for the subsequent establishment of the constitutive model to make yield discrimination.

[0074] Therefore, the yield condition of this embodiment forms a "double space-provable closed-regressible special case" derivation link, so that the model can regress the special case of MCC / DP, and can also flexibly regulate the strength envelope and deformation boundary of marine soft soil under tunnel disturbance through structural parameters. The difference from the existing method is that the traditional DP / MCC directly constructs the yield surface in the real stress space, and rarely starts from the dissipation stress space and gives strict closedness and positive definiteness criteria; this embodiment gives the parameters through formula (12) a testable physical-thermodynamic constraint, avoiding "false yield / non-closed / non-physical tensile stress region" and other numerical pathologies, and better meeting the needs of soft soil energy characterization and construction period stability evaluation.

[0075] Therefore, based on the yield condition, a marine soft soil energy dissipation constitutive model based on thermodynamics is constructed, and the specific method includes: 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, which provides a basis for subsequent elastic prediction and yield discrimination.

[0076] Step 1.2, elastic prediction: calculate the elastic strain increment according to the generalized Hooke's law to generate the trial stress , the elastic strain increment includes an elastic volumetric strain increment and an elastic shear strain increment, the elastic volumetric strain increment is expressed as:

[0077] The elastic shear strain increment is expressed as:

[0078] wherein K is an elastic bulk modulus, G is an elastic shear modulus, , is a void ratio, is a Poisson's ratio.

[0079] Step 1.3, yield criterion: the real stress space yield function f is used to judge the state, if , the step is considered as elastic, and the elastic stiffness matrix is directly output to update the stress; if , the plastic correction is entered.

[0080] Step 1.4, plastic flow direction: the flow direction of the real stress space is obtained based on the positive flow rule of the dissipation stress space, including: Orthogonal law:

[0081] According to the Drucker hypothesis, for stable materials:

[0082] wherein is a plastic potential function, used to determine the plastic strain increment direction.

[0083] In the dissipation stress space, the associated flow rule is naturally derived based on the dissipation increment function:

[0084]

[0085]

[0086] wherein: , , The shear dilatancy angle is:

[0087] Substituting (8) and (9), the flow direction is converted to the real stress space through an explicit mapping relationship, and the real space flow rule is obtained: ​

[0088] Further, when , the flow rule in the deviatoric stress space is correlated, but at this time, the flow rule in the true stress space is uncorrelated except

[0089] When , , the flow rule in the true stress space is correlated, belonging to the modified Cam-Clay model.

[0090] The checkable conditions of when to be correlated / uncorrelated are given after the correlated flow (orthogonal law) is naturally obtained in the deviatoric stress space and explicitly transformed to the true stress space. The key is to unify the "energy consistency (dissipation)" and "engineering fitting (uncorrelated flow)" in the same model. The formula expression of the dilatancy angle is derived from the energy-dissipation framework, rather than being given empirically; thus, it can change self-consistently with the confining pressure, stress path, and structural parameters, and is more consistent with the shrinkage / dilatancy transformation of saturated soft soil. The difference from existing methods: the traditional uncorrelated DP often takes the plastic potential function / dilatancy angle as an empirical parameter; the traditional Cam-Clay model MCC is a correlated flow, which is difficult to simultaneously approximate the measured volume-shear coupling under high disturbance conditions. The embodiment gives the criterion and bridging formula of "correlation (deviatoric stress space) ⇄ uncorrelation (true stress space)", and uses the energy term to constrain the evolution of the shear angle, taking into account numerical stability and physical interpretability.

[0091] Step 1.5, plastic modification and consistency condition: using the plastic volumetric strain as the hardening parameter, coupling the flow rule in the deviatoric stress space and the consistency condition, deriving the plastic multiplier compatible with energy dissipation, updating the stress and hardening quantity to satisfy . Specifically, it includes: First, the hardening law takes the plastic volumetric strain as the hardening parameter,

[0092] Differential, get:

[0093] That is , in the formula, is the specific volume,

[0094] Then, from the consistency condition, get

[0095]

[0096]

[0097] ​

[0098]

[0099] By (15), the flow rule transformation of coupling dissipative stress space is:

[0100] Then we can get:

[0101] Let be the plastic hardening modulus, expressed as:

[0102] Then:

[0103] The above derivation ensures the convergence and energy dissipation under implicit integration, and lays the computational foundation for subsequent "energy item online output + threshold judgment". The difference from existing methods: the classical derivation mostly stays in the correlation case of true stress space; this embodiment couples the double-space flow with the consistency condition to obtain a closed expression that can be used in UMAT, which is convenient for stable and fast engineering calculation.

[0104] Step 1.6, stress-strain relationship and algorithm tangent: constructing the output elastoplastic stiffness matrix for global Newton iteration to ensure second-order convergence and numerical stability, which is the key node of solving efficiency and stability. Its calculation derivation is obtained by strain decomposition and stress increment relationship to obtain the elastoplastic stiffness matrix and elastoplastic flexibility matrix, which specifically includes the following: The total strain is equal to the elastic strain plus the plastic strain,

[0105] Multiply both sides by Get,

[0106] Where, ,

[0107] Substituting,

[0108] Multiply both sides by , and rearrange to get,

[0109] Get,

[0110] Where, That is, the elastoplastic stiffness matrix, Another representation method can also be used,

[0111]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117] The elastic-plastic compliance matrix matrix,

[0118]

[0119] Step 1.7, energy decomposition and threshold index online output, used for providing online index for hierarchical early warning: decomposing the external work increment into elastic strain energy, plastic dissipation energy and pore water work and outputting in real time, providing online index for "energy dissipation-strain threshold" hierarchical early warning, which is the landing point of this embodiment from the constitutive relation to the application.

[0120] Simulation embodiment: In order to verify the rationality of the scheme, a subway tunnel engineering in Shenzhen is taken as an example, according to the geological survey report, the mechanical parameters are selected as shown in the following table 1: Table 1 Parameters required by UMAT subroutine

[0121] A tunnel construction mechanics model is established. Considering the influence of boundary effect, the height of the model is selected as 60m, and the length is selected as 120m, such as Figure 7 The tunnel cross section is circular, the shield diameter is 6.2m, the lining outer diameter of the tunnel in the model is 6.2m, the inner diameter is 5.5m, the thickness is 0.35m, and the ring width is 1.5m. The boundary conditions are two sides of horizontal displacement constraint, bottom vertical displacement constraint, and top free boundary of ground surface. The stratum grid adopts CPE4P unit, and the tunnel lining adopts CPE4 unit.

[0122] When simulating the shield tunnel construction process in ABAQUS, the dynamic interaction between soil and structure, material nonlinearity and time sequence of construction steps need to be considered comprehensively, and the unit birth and death function (*MODEL CHANGE) in ABAQUS is used to remove the excavated soil part.

[0123] The model calculation analysis process is: first, initial stress balance. Initial stress balance is a key step to eliminate the false displacement of the model caused by artificial modeling by applying gravity and adjusting the initial stress field of the soil body, so that the simulation starting state is consistent with the actual stratum stress. In the Geostatic analysis step, the geostress balance operation is performed, the gravity is applied (if the groundwater level changes, the body force is used to apply the gravity load), the initial stress is balanced by INITIAL CONDITIONS, STRESS, and the initial stress field is restored. Set the contact between the lining and the soil, define the contact between the inner surface of the soil and the outer surface of the lining, and simulate the Tie constraint. 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 in the order of "initial geostress balance → shield propulsion (remove soil elements) → lining installation". Finally, the key indicators such as ground settlement, lining stress and contact pressure are analyzed by the implicit solver (Standard) to complete the fine simulation of the mechanical behavior of shield tunnel construction.

[0124] Different buried depth conditions are set and response analysis is performed. The buried depths of 10 m, 15 m, 20 m, 25 m and 30 m are simulated, and the ground settlement, lining stress and energy dissipation distribution are extracted: Regarding ground settlement: when the buried depth increases from 10 m to 30 m, the maximum settlement increases from 11.6 mm to 43.62 mm and then slightly decreases to 33.35 mm; the maximum heave increases from 12.12 mm to 57.46 mm. The increase of buried depth leads to the increase of settlement and heave, but the settlement appears an inflection point at the buried depth of 25 m. It shows that with the increase of buried depth, the overburden stress increases, on the one hand, it increases the stress release caused by excavation unloading, and intensifies the heave; on the other hand, it promotes the expansion of the plastic zone of surrounding rock, and the settlement increases continuously, but when the buried depth exceeds the critical value of 25 m, the self-bearing capacity of surrounding rock under high stress is enhanced, which inhibits the continuous development of settlement, forming an inflection point. Regarding lining stress: with the increase of buried depth from 10 m to 20 m, the maximum shear stress of lining decreases, but then it increases significantly with the increase of buried depth to more than 2300 kPa at the buried depth of 30 m, reflecting the significant influence of deep surrounding rock or initial stress field. There is a high risk of lining stress in both shallow section (10 m) and deep section (25 to 30 m).

[0125] Regarding energy dissipation: from the energy dissipation cloud analysis, the energy dissipation of marine soft soil mainly occurs near the construction shield disturbance, when the buried depth is 15 m, the shield tunnel is about 4 m away from the silt silty clay layer, only the lower part of the soil layer has a little energy dissipation influence, and when the buried depth is 20 m and below, although there is total energy input, the silt silty clay layer has almost no energy dissipation display. When the buried depth is 10 m, it can be seen that there is a circle around the shield tunnel, there is high energy input, and there is also high energy dissipation, indicating that the marine soft soil has been seriously disturbed and "destroyed".

[0126] Therefore, the present embodiment shows that the silt layer with a buried depth of 10-15 m is weak in stratum, and is significantly disturbed, so it is suggested to control the advancing speed during shield tunnel construction, to strengthen support grouting, and to perform advanced reinforcement if necessary, to reduce possible engineering accidents. The hard rock layer with a buried depth of 25-30 m is prone to stress concentration and high shear stress risk, so it is necessary to improve the lining thickness and optimize the steel bar arrangement to cope with the lining damage.

[0127] The present embodiment verifies the effectiveness of the energy dissipation grading evaluation method for the safety risk identification of marine soft soil tunnel construction through multi-buried depth working condition simulation, and provides a quantitative basis for dynamically adjusting the support parameters and construction technology.

[0128] The specific embodiments of the present application are described in detail above in combination with the drawings, but the present application is not limited to the described embodiments. For those skilled in the art, various changes, modifications, replacements and variations of these embodiments can be made without departing from the principles and spirits of the present application, and still fall within the protection scope of the present application.

Claims

1. A classification evaluation method for surrounding rock energy dissipation induced by construction disturbance in marine soft soil tunnels, characterized by: The steps include: Step 1: Establishing a thermodynamically based constitutive model for energy dissipation of marine soft soil, wherein the constitutive model defines the elastic-plastic stress-strain relationship through yield conditions, flow laws, hardening laws, and elastic strain increments; Step 2: Based on geological survey data of a marine soft soil tunnel project, determine the mechanical parameters of the constitutive model through experiments; Step 3: Establish a tunnel construction mechanics model based on the engineering dimensions of the marine soft soil tunnel. 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. Output energy sub-items, including damage variables, accumulated plastic strain, and energy dissipation, are generated in real time during the iteration process. Step 4: Based on the energy output obtained in step 3, a damage element identification system is established on the thermodynamically based marine soft soil energy dissipation constitutive model; Step 5: Deploy a monitoring system on the tunnel excavation face to obtain real-time monitoring data and feed it back to the numerical model for verification; Step 6: Based on the damaged unit identification system established in step 4, a graded warning is issued according to the degree to which the structural unit is close to the instability damage energy threshold.

2. The method for grading and evaluating surrounding rock energy dissipation induced by construction disturbance in marine soft soil tunnels according to claim 1 is characterized by: In step 1, a method for establishing a thermodynamically based constitutive model of marine soft soil energy dissipation 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 the convergence tolerance; Step 1.2, Elasticity Prediction: Calculate the elastic strain increment based on the generalized Hooke's law and generate the test stress , Step 1.3, yield determination: through the real stress space yield function f Judge the status, if , then the step is considered elastic and the elastic stiffness matrix is ​​directly output to update the stress; if , then enter the plastic correction; wherein, the yield function satisfies the mapping constraints between the dissipative stress space and the real stress space; The yield surface equation in the dissipative stress space is: The yield surface equation in real stress space is: Where, is the effective mean stress; is the deviatoric stress invariant; is the equivalent pre-consolidation pressure / structural consolidation pressure; M is the critical state stress ratio; ; ; are all structural parameters of the model, satisfying and , ensuring the closure of the yield surface and the positivity of energy; Step 1.4, plastic flow direction: Based on the orthogonal flow law in the dissipative stress space, the flow direction in the real stress space is obtained: Where, is the expansion angle of the plastic potential function; is the plastic volume strain; is the plastic shear strain; Step 1.5, plastic correction and consistency condition: Using plastic volume strain as the hardening parameter, couple the flow law and consistency condition of the dissipative stress space, derive the plastic multiplier compatible with energy dissipation, and update the stress and hardening amount to meet , The plastic multiplier formula is: , Where, is the plastic hardening modulus, f is the yield function; is the stress component; Step 1.6, stress-strain relationship and algorithm tangent: Construct the output elastic-plastic stiffness matrix for global Newton iteration. The elastic-plastic stiffness matrix is ​​expressed as: ， Where, is the elastic-plastic tangent stiffness matrix; is the elastic stiffness matrix; is the plastic strain dual variable; Step 1.7, energy decomposition and threshold index online output, used to provide online indicators for graded warning: decompose the external work increment into elastic strain energy, plastic dissipated energy, and pore water work and output them in real time.

3. The method for grading and evaluating surrounding rock energy dissipation induced by construction disturbance in marine soft soil tunnels according to claim 2 is characterized by: In step 1.2, the elastic strain increment includes the elastic volume strain increment and the elastic shear strain increment, and the elastic volume strain increment is expressed as: The elastic shear strain increment is expressed as: Where K is the elastic bulk modulus, is the elastic shear modulus, , , is the void ratio, is Poisson's ratio.

4. The method for grading and evaluating surrounding rock energy dissipation induced by construction disturbance in marine soft soil tunnels according to claim 2 is characterized by: The structural parameters Adjustable, specifically: when hour, The smaller it is, the flatter the yield surface is. The larger it is, the more the yield surface expands outward; when When, by changing Control the deviatoric stress extension direction of the yield surface.

5. The method for grading and evaluating surrounding rock energy dissipation induced by construction disturbance in marine soft soil tunnels according to claim 2 is characterized by: In step 1.4, the flow law is to derive the associated flow law naturally based on the dissipative increment function in the dissipative stress space, and then convert the flow direction to the real stress space through an explicit mapping relationship. The real stress space is generally non-associated and only when , , When the real stress space becomes related, the dilatancy angle for: Where, is the equivalent mean stress variable; is the equivalent deviatoric stress variable; A and B are model parameters, which are determined by the yield surface form and structural parameters. Decide.

6. The method for grading and evaluating surrounding rock energy dissipation induced by construction disturbance in marine soft soil tunnels according to claim 4 is characterized by: In step 1.5, the hardening parameter satisfy: Coupling consistency conditions, we get: Coupled with the flow law in the dissipative stress space, we get: Where, H is the hardening parameter; is the plastic volume strain; is the plastic multiplier increment.

7. The method for grading and evaluating surrounding rock energy dissipation induced by construction disturbance in marine soft soil tunnels according to claim 1 is characterized by: 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: step 2.1, obtaining the critical state stress ratio M based on the consolidated undrained triaxial test, and determining the hardening modulus in combination with the compression-rebound test and the rebound index k; Step 2.2: Based on the triaxial test data, the mean square error objective function is constructed and the structural parameters are obtained by inversion using the improved genetic algorithm. .

8. The method for grading and evaluating surrounding rock energy dissipation induced by construction disturbance in marine soft soil tunnels according to claim 1 is characterized by: In step 4, establishing a method for determining potential damage units based on energy dissipation-strain thresholds includes the following steps: Step 4.1: Based on the basic equation of elastic-plastic-seepage coupling, combined with the energy dissipation constitutive model and Biot seepage theory, the energy conservation relationship is derived, and the external work increment is decomposed into the elastic strain energy increment, the plastic dissipation energy increment, and the pore water work increment; Step 4.2: In ABAQUS, the energy output from step 3 is embedded in the iterative solution process and verified by comparing uniaxial compression and simple shear to control the numerical integration energy error to ±2%. Step 4.3: Design multiple virtual tests with different combinations of burial depth, confining pressure, and excavation rate. Identify the characteristic points of the energy-strain trajectory for each set of calculations. Use the least squares method to fit the empirical relationship between the critical value of plastic dissipated energy and the equivalent plastic shear strain. The empirical relationship is: in, is the critical value of plastic dissipation energy density, is the critical value of equivalent plastic shear strain; Step 4.4, when any unit in the numerical calculation satisfies and When , it is determined to be a potential damaged unit, where is the plastic dissipated energy density, is the equivalent plastic shear strain.

9. The method for grading and evaluating surrounding rock energy dissipation induced by construction disturbance of marine soft soil tunnels according to claim 1 is characterized in that: The monitoring system includes a distributed optical fiber 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 is specifically: comparing the acquired monitoring data with the equivalent plastic shear strain and damage judgment results obtained based on the energy dissipation constitutive calculation in the numerical model, and if any deviation occurs, feedback is provided to correct the model and threshold parameters.

10. The method for grading and evaluating surrounding rock energy dissipation induced by construction disturbance of marine soft soil tunnels according to claim 1, characterized in that: In step 6, the proximity of the structural unit 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 graded warnings include: Level 1 warning: normal excavation and routine monitoring; It is a Level 2 warning: slow down excavation, increase grouting pressure, and strengthen monitoring frequency; The third level warning is: stop the machine for inspection, carry out local advance reinforcement or extend the pipe shed; and It is a level 4 warning: emergency shutdown; implement secondary support, freezing / grouting emergency plans.

Images