Salt-freeze thawing coupling damaged soil constitutive model construction method and system

Abstract

The invention discloses a salt-freeze thawing coupling damaged soil constitutive model construction method and system, and relates to the technical field of geotechnical engineering.The method comprises the steps that firstly, salt-containing and salt-free soil samples before and after freeze thawing are prepared, and the elastic modulus change rule of the soil samples is obtained through a static triaxial test; further defining and calculating salt damage variables, freeze-thaw damage variables and coupling damage factors of the salt damage variables and the freeze-thaw damage variables; secondly, on the basis of the Lemaitre strain equivalence principle, a damage factor reflecting infinitesimal strength Weibull distribution is introduced, and in combination with the generalized Hooke's law and the generalized Ewy Lade-Duncan damage criterion, a soil constitutive model capable of comprehensively representing the salt and freeze-thaw coupling damage effect is constructed; and finally, solving model parameters by utilizing peak value characteristics of the stress-strain curve. According to the method, the mechanical behaviors of the marine soft soil subjected to artificial freezing method construction can be predicted more accurately, and an effective theoretical tool is provided for design and safety evaluation of projects such as subsea tunnels in coastal regions.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering technology, and in particular to a method and system for constructing a constitutive model of soil with salt-freeze-thaw coupled damage. Background Technology

[0002] With the rapid development of infrastructure construction in my country's coastal areas, major projects such as undersea tunnels and rail transit are increasing. Coastal areas are widely covered with saline marine soft soils, which have complex mechanical properties and are significantly affected by freeze-thaw cycles, posing serious challenges to tunnel construction and long-term safety. Artificial freezing methods, due to their good water-stopping properties, high strength, and environmental friendliness, are widely used for soft soil foundation reinforcement and water-stopping in undersea tunnel construction. However, the thawing process after freezing causes the soil to undergo a complete freeze-thaw cycle, leading to damage phenomena such as internal structural reconstruction, porosity changes, and strength reduction, seriously affecting the long-term stability of the project.

[0003] Currently, research on soil mechanical behavior largely focuses on constitutive models considering only a single factor (such as freeze-thaw cycles or only salinity). However, in practical engineering, salinity and freeze-thaw cycles often have coupled effects. Existing models struggle to accurately describe the evolution of soil damage under the combined effects of salinity and freeze-thaw cycles, and its impact on stress-strain relationships. Especially in marine soft soil regions, the lack of a constitutive model that comprehensively considers the coupled effects of salinity and freeze-thaw damage limits the reliability and prediction accuracy of artificial freezing methods in these strata.

[0004] Therefore, it is urgent to establish a soil constitutive model that can reflect the coupling damage of salt content and freeze-thaw cycles, so as to more accurately predict the mechanical behavior of saline soft soil after freeze-thaw cycles, and provide theoretical basis and technical support for the design, construction and safety assessment of projects such as submarine tunnels in coastal areas. Summary of the Invention

[0005] To address this, embodiments of the present invention provide a method and system for constructing a constitutive model of soil damaged by salt-freeze-thaw coupling, which solves the problem in the prior art of lacking the ability to comprehensively consider the coupling effect of salt and freeze-thaw cycles, thereby accurately predicting the mechanical damage behavior of marine soft soil after artificial freezing construction.

[0006] To address the aforementioned technical problems, this invention provides a method for constructing a constitutive model of soil damaged by salt-freeze-thaw coupling, the method comprising the following steps: Step S1: Prepare saturated cylindrical soil samples and divide them into salt-containing sample groups and non-salt-containing sample groups; further process each group of samples to obtain samples in the pre-freeze-thaw state and samples in the post-freeze-thaw state after undergoing at least one complete freeze-thaw cycle. Step S2: Perform consolidation undrained static triaxial tests on the four types of samples obtained in Step S1 to obtain stress-strain curves under different salt contents, different freeze-thaw states and different confining pressures, and extract the distribution law of elastic modulus of the samples from them. Step S3: Based on the change in the elastic modulus, define a first damage variable characterizing salt damage and a second damage variable characterizing freeze-thaw damage, and calculate the coupling damage factor between salt and freeze-thaw based on the strain equivalence principle. Step S4: Based on the Lemaitre strain equivalence principle, establish the constitutive relationship between effective stress and total stress considering coupled damage; combine the assumption that the strength of soil micro-element follows the Weibull distribution, the generalized Hooke's law and the generalized Ewy-Lade-Duncan failure criterion, and construct a soil stress-strain constitutive model that reflects salt and freeze-thaw coupled damage. Step S5: Using the characteristic geometric conditions in the stress-strain curve obtained in step S2, solve for the undetermined parameters in the constitutive model constructed in step S4, and determine the final expression of the model.

[0007] Preferably, in step S1, the preparation of the sample specifically includes: selecting soil samples from the same location and preparing saturated samples of specified dimensions according to the "Standard for Geotechnical Testing Methods" GB / T50123-2019; controlling the target salt content of the sample by mixing NaCl solutions of different concentrations with the soil sample; molding the sample using the compaction method and then saturating it under vacuum; for samples in a freeze-thaw state, freezing them for a specified time in a preset negative temperature environment and then thawing them completely at room temperature.

[0008] Preferably, in step S2, a B-value test is required before the static triaxial test to ensure sample saturation. Subsequent consolidation and shear tests can only be carried out when the B-value is greater than 0.95. The test confining pressure is set to multiple levels to simulate different formation depths.

[0009] Preferably, in step S3, the first damage variable is defined as: ,in As the first damage variable, The elastic modulus is the value of the salt-containing, unfrozen sample. The elastic modulus of the unfrozen, salt-free sample is given; the second damage variable is defined as: ,in As the second damage variable, The elastic modulus of the salt-free freeze-thawed sample; the coupling damage factor is determined by... and It is calculated using the following formula: , in, This is the coupling damage factor.

[0010] Preferably, in step S4, the constitutive relationship between the effective stress and the total stress is expressed as: , in, For the total stress, The total stress matrix, For effective stress, For the effective stress matrix, As a damage factor, For elastic modulus, The elastic modulus matrix, In response, Here is the strain matrix.

[0011] Preferably, based on the assumption that the soil micro-element strength follows a Weibull distribution, the damage factor Represented as: , in, For soil micro-element strength based on effective stress, and These are the parameters of the Weibull distribution.

[0012] Preferably, in step S4, the core expression of the constitutive model is: , in, , These are axial stress and strain, respectively. For confining pressure, The elastic modulus is the value of the salt-containing, unfrozen sample. The elastic modulus is the unspecified, salt-free, unfrozen sample. The elastic modulus of the sample after freeze-thaw cycles without salt is given. Poisson's ratio, and For the Weibull distribution parameters, The soil micro-element strength is based on effective stress.

[0013] Preferably, the soil micro-element strength based on effective stress The expression is derived based on the generalized Ewy-Lade-Duncan violation criterion: , in, For material parameters of the generalized Ewy-Lade-Duncan failure criterion, This refers to the bonding stress.

[0014] Preferably, in step S5, the characteristic geometric condition is the peak point condition on the stress-strain curve, i.e., the peak stress. and its corresponding peak strain The conditions are satisfied that the function values ​​are equal and the first derivative is zero. Substituting these conditions into the constitutive model, the parameters are solved. : , in, The elastic modulus is the unspecified, salt-free, unfrozen sample. The elastic modulus is the value of the salt-containing, unfrozen sample. The elastic modulus of the sample after freeze-thaw cycles without salt is given. For material parameters of the generalized Ewy-Lade-Duncan failure criterion, For bonding stress, Poisson's ratio, For confining pressure.

[0015] This invention also provides a constitutive model construction system for soil with salt-freeze-thaw coupled damage. This system is used to implement the aforementioned method for constructing a constitutive model for soil with salt-freeze-thaw coupled damage, specifically including: The sample preparation and grouping module is used to prepare saturated cylindrical soil samples and divide them into salt-containing sample groups and non-salt-containing sample groups; each group of samples is further processed to obtain samples in the pre-freeze-thaw state and samples in the post-freeze-thaw state after undergoing at least one complete freeze-thaw cycle. The coupling effect mechanical parameter acquisition module is used to conduct consolidation undrained static triaxial tests on the four types of samples obtained by the sample preparation and grouping module, obtain stress-strain curves under different salt contents, different freeze-thaw states and different confining pressures, and extract the elastic modulus distribution law of the samples from them. The coupling damage factor definition module is used to define a first damage variable characterizing salt damage and a second damage variable characterizing freeze-thaw damage based on the change in the elastic modulus, and to calculate the coupling damage factor between salt and freeze-thaw based on the strain equivalence principle. The constitutive model construction module is used to establish the constitutive relationship between effective stress and total stress considering coupled damage based on the Lemaitre strain equivalence principle; and to construct a soil stress-strain constitutive model that reflects salt and freeze-thaw coupled damage by combining the assumption that the strength of soil micro-elements follows the Weibull distribution, the generalized Hooke's law and the generalized Ewy-Lade-Duncan failure criterion. The model parameter solution module is used to solve for the characteristic geometric conditions in the stress-strain curves obtained by the coupling action mechanical parameter acquisition module, and to solve for the undetermined parameters in the constitutive model constructed by the constitutive model construction module, thereby determining the final expression of the model.

[0016] As can be seen from the above technical solutions, this invention application has the following beneficial effects: (1) This invention creatively incorporates the coupling effect of salt damage and freeze-thaw damage into the constitutive model framework. This is achieved by defining and coupling two damage variables ( , Based on the Lemaitre strain equivalence principle and Weibull statistical distribution, this model was constructed, and for the first time, it theoretically unified the degradation mechanism of soil mechanical properties caused by the combined effects of salt and freeze-thaw cycles. This model can not only accurately predict the overall trend of the stress-strain curve, but also effectively capture key mechanical characteristics such as strain hardening and modulus degradation in saline freeze-thaw soils. Its agreement with experimental data is significantly higher than that of traditional models (such as the modified Cambridge model), making it particularly suitable for analyzing the mechanical behavior of marine soft soils in coastal artificial freezing projects.

[0017] (2) All parameters of the model (e.g.) , , , , , All parameters (e.g., ) have clear physical meaning and can be directly determined through conventional static triaxial shear tests and geotechnical tests. Key distribution parameters of the model. The solution relies on the peak characteristics of the stress-strain curve, and the method is intuitive and highly operable. This design avoids complex and obscure empirical parameters, greatly reducing the technical threshold and data acquisition cost for promoting the model in engineering practice.

[0018] (3) The constitutive model constructed in this invention directly addresses the two key damage factors that cannot be avoided in underground engineering projects in coastal areas (especially submarine tunnels using artificial freezing methods): "salinity" and "freeze-thaw cycles". This model can quantify and predict the attenuation of soil strength and deformation characteristics after experiencing freeze-thaw cycles, thereby providing a more reliable theoretical basis and calculation tool for assessing the stability of soil around tunnels, predicting deformation caused by construction, optimizing freezing scheme design, and ensuring the long-term safety of projects. It has important engineering application value. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Referring to the drawings will make the features and advantages of the present invention clearer. The drawings are illustrative and should not be construed as limiting the present invention in any way. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a flowchart of a method for constructing a constitutive model of soil with salt-freeze-thaw coupling damage provided by the present invention; Figure 2 This is a schematic diagram of the particle size distribution curve of the soil used in the experiment in this invention; Figure 3 This is a schematic diagram of stress-strain curves (0.4 MPa confining pressure) under different freeze-thaw conditions in this invention; Figure 4 This is a schematic diagram of the stress-strain curves (0.8 MPa confining pressure) under different salt contents before and after freeze-thaw cycles in this invention. Figure 5 This is a schematic diagram comparing the model's predicted values ​​with the experimental values ​​in this invention; Figure 6 This is a block diagram of a constitutive model construction system for soil with salt-freeze-thaw coupled damage provided by the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1: To address the lack of existing technologies that comprehensively consider the coupling effect of salinity and freeze-thaw cycles, thereby accurately predicting the mechanical damage behavior of marine soft soil after artificial freezing construction. For example... Figure 1 As shown, this invention proposes a method for constructing a constitutive model of soil with salt-freeze-thaw coupled damage, which includes the following steps: Step S1: Prepare saturated cylindrical soil samples and divide them into salt-containing sample groups and non-salt-containing sample groups; further process each group of samples to obtain samples in the pre-freeze-thaw state and samples in the post-freeze-thaw state after undergoing at least one complete freeze-thaw cycle. Step S2: Perform consolidation undrained static triaxial tests on the four types of samples obtained in Step S1 to obtain stress-strain curves under different salt contents, different freeze-thaw states and different confining pressures, and extract the distribution law of elastic modulus of the samples from them. Step S3: Based on the change in elastic modulus, define the first damage variable characterizing salt damage and the second damage variable characterizing freeze-thaw damage, and calculate the coupling damage factor between salt and freeze-thaw based on the strain equivalence principle. Step S4: Based on the Lemaitre strain equivalence principle, establish the constitutive relationship between effective stress and total stress considering coupled damage; combine the assumption that the strength of soil micro-element follows the Weibull distribution, the generalized Hooke's law and the generalized Ewy-Lade-Duncan failure criterion, and construct a soil stress-strain constitutive model that reflects salt and freeze-thaw coupled damage. Step S5: Using the characteristic geometric conditions in the stress-strain curve obtained in step S2, solve for the undetermined parameters in the constitutive model constructed in step S4, and determine the final expression of the model.

[0022] As can be seen from the above technical solution, this invention proposes a method for constructing a constitutive model of soil with salt-freeze-thaw coupled damage, which closely integrates experiments, theory, and engineering applications through a rigorous logical chain. Step S1 (sample preparation) scientifically sets up comparative groups with / without salt and before / after freeze-thaw, creating a material basis for revealing the coupled damage mechanism. Step S2 (static triaxial test) systematically obtains stress-strain curves and elastic modulus under different working conditions, providing key data support for model construction. Step S3 (damage factor definition) quantifies the individual and coupled damage of salt and freeze-thaw based on experimental data, realizing accurate characterization of the damage state. Step S4 (constitutive model construction) innovatively integrates the Lemaitre strain equivalence principle, Weibull statistical distribution, and generalized failure criterion to establish a theoretical model that can reflect the coupled damage effect from a mechanistic perspective. Step S5 (parameter solution) uses the characteristic points of the experimental curves for parameter calibration, ensuring that the model is not only theoretically rigorous but also has good operability and predictive accuracy. The entire scheme is interconnected, ultimately forming a high-precision constitutive model with clearly defined parameters that can directly serve the engineering mechanics analysis of coastal freeze-thaw soft soil.

[0023] This embodiment details the five core steps of the construction method, such as... Figure 1 The flowchart of the method is shown.

[0024] Further, in step S1, sample preparation and grouping are performed.

[0025] To ensure the consistency of the test results, silty clay from a typical site in the Yangtze River Delta region was selected as the test soil. Particle size distribution curves were analyzed using a Microtrac S3500 laser particle size analyzer. Figure 2 The basic physical properties are shown in Table 1, and the results of the main ion content are shown in Table 2. The content of each ion is less than 0.015%, and the total salt content is 0.03%, which is far below the experimental target value. Therefore, the influence of the initial salt content is ignored in the subsequent sample preparation process, and no additional salt washing operation is performed.

[0026] Table 1 Basic physical properties of the soil used in the experiment

[0027] Table 2. Main ion content of the soil used in the experiment

[0028] Note: Ion content is expressed as ion mass / dry soil mass, and the salt content ratios in the following tests are also mass ratios.

[0029] NaCl was selected as the representative for sample preparation, and the compaction method was used for sample preparation. At the same time, in order to avoid uneven density of the compacted sample and to restore the structural integrity of the sample as much as possible, and to be closer to the sedimentary state of marine soil, the soil sample was fully saturated after compaction, and then the sample was consolidated on the triaxial test device. The specific sample preparation process of the triaxial test is as follows: (1) The soil sample was dried, crushed and passed through a 2mm sieve; (2) NaCl was mixed with water to obtain salt solutions with different target salt contents (0%, 1%, 2%, 3%, 4%); (3) The salt solution was mixed with soil particles to make the water content reach 21%; (4) The mixed soil particles were placed in a sealed bag and left to stand for 24 hours to make the salt solution evenly distributed; (5) According to the "Standard for Geotechnical Testing Methods" (GB / T 50123-2019), the soil particles after standing were placed according to the maximum dry density of 1.65 g / cm³. 3 (6) The sample was immersed in water and vacuumed for 24 hours; (7) The sample was consolidated using a triaxial test device to simulate the actual burial depth of the strata.

[0030] During artificial freezing construction, the soil surrounding the tunnel will undergo one freeze-thaw cycle. To conform to actual engineering conditions and to compare the mechanical properties of samples before and after freeze-thaw, a portion of the samples were subjected to one freeze-thaw cycle before shearing. The consolidated samples were sealed with plastic wrap, and petroleum jelly was applied to the joints to prevent moisture loss during the freeze-thaw process. The samples were then placed in a low-temperature environment chamber and frozen at a preset temperature (e.g., -10℃, -20℃, -30℃) for 12 hours to ensure complete freezing and uniform temperature throughout the sample. After freezing, the samples were thawed at room temperature (approximately 20℃) for 12 hours to obtain a freeze-thawed sample.

[0031] Ultimately, four sample groups were obtained, consisting of two pairs: "salt-containing / salt-free" and "before / after freeze-thaw". Three to five parallel samples were prepared for each group.

[0032] Furthermore, in step S2, the mechanical parameters of the coupling effect are obtained through a static triaxial test.

[0033] The static properties of freeze-thawed chloride silty clay were studied using consolidated undrained static triaxial tests. The freezing temperatures of the samples were set at -10℃, -20℃, and -30℃, and the thawing temperature was approximately 20℃ (room temperature). The salt contents were selected as 0%, 1%, 2%, 3%, and 4%. The strain rate during the loading process of the consolidated undrained tests was set to 1.0 mm / min, and the confining pressures were selected as 0.2, 0.4, 0.6, and 0.8 MPa. The specific consolidated undrained test plan is shown in Table 3.

[0034] Table 3 Consolidation Undrained Test Plan

[0035] The experimental steps are as follows: (1) Test equipment inspection: Exhaust the top cap, base and internal circulation pipeline to ensure that the pipeline is unobstructed and free of air bubbles. Before the test begins, ensure that the confining pressure controller and back pressure controller are filled with 2 / 3 airless water.

[0036] (2) Sample installation: Filter paper is attached to both ends and around the sample. The rubber membrane is wrapped around the outside of the sample using a sleeve. The sample is installed on the base of the triaxial pressure chamber using a three-part mold. The confining pressure cylinder is then installed. After the initial value of the sensor is zeroed, an axial force is applied to finely adjust the position of the sensor so that it contacts the sample. When the axial force reaches 0.025kN, it indicates that the contact is good and loading can be stopped.

[0037] (3) Filling the confining pressure cylinder with water: Open the vent hole at the top and the valve at the bottom of the confining pressure cylinder to fill it with water, and then close the valve and the vent hole.

[0038] (4) B value detection: Use the B value to test the saturation. When the B value is less than 0.95, apply back pressure to saturate until the B value is greater than 0.95.

[0039] (5) Consolidation: Apply confining pressure to consolidate. Consolidation is complete when the deformation of the sample changes by no more than 0.01 mm per hour.

[0040] (6) Freeze-thaw: For samples that do not require freeze-thaw, skip this step and proceed directly to step (7) loading. For samples that require freeze-thaw, remove the sample from the triaxial pressure chamber and place it in a low-temperature environment chamber for freeze-thaw. After freeze-thaw, repeat (1)-(4) above. After confirming saturation, proceed to step (7) loading.

[0041] (7) Loading: Observe the real-time stress-strain curve. If there is a peak strain, stop the experiment 5% after the peak strain. If there is no peak strain, stop the experiment when the axial stress reaches 15%.

[0042] Taking a sample with 0% salt content under a confining pressure of 0.4 MPa as an example, Figure 3 The stress-strain curves before and after freeze-thaw are shown. The consolidated undrained test was conducted at room temperature; the temperature in the legend represents the freezing temperature set in the environmental chamber during the freezing process. The stress-strain curves show that stress develops rapidly in the initial loading stage, then continues to increase until failure, without a significant peak; all samples exhibit strain hardening. The elastic modulus parameter can be obtained from the slope of the stress-strain curve. Compared to the unfrozen samples, the elastic modulus of the frozen-thawed samples is significantly lower, which is caused by changes in the soil structure during the freeze-thaw process. During the freezing process of saturated samples, the ice-water phase transition leads to an increase in soil volume and expansion of pore size. After thawing, due to interparticle interactions, the sample volume cannot completely recover to its original state. The sample frozen at -20℃ has the lowest elastic modulus after freeze-thaw.

[0043] Taking a sample under a confining pressure of 0.8 MPa as an example, Figure 4 The stress-strain curves of samples with salt content ranging from 0% to 4% before and after freeze-thaw cycles at -10°C were presented. In the legend "X%-Y", "X%" and "Y" represent the salt content and the number of freeze-thaw cycles, respectively. The salt content does not change the failure mode of the stress-strain curve; the addition of salt only changes the peak stress of the curve. Figure 5 It can be seen that as the salt content increases, the elastic modulus of the soil first decreases and then increases.

[0044] Further, in step S3, a coupling damage factor is defined.

[0045] According to the principles of damage mechanics, the macroscopic mechanical effects of microscopic damage to a specimen can be reflected by changes in the elastic modulus. Therefore, the elastic modulus of a specimen can be used as a benchmark for measuring internal damage. First damage variable. Damage caused by salt is defined as follows: ,in The elastic modulus is the value of the salt-containing, unfrozen sample. The elastic modulus of the unfrozen, salt-free specimen; the second damage variable. Damage caused by freeze-thaw cycles is defined as follows: ;in The elastic modulus is the value of the sample after freeze-thaw cycles without salt.

[0046] Furthermore, based on the strain equivalence principle, considering the coupling effect of the two damage mechanisms, the salt-freeze-thaw coupled damage factor... Depend on and It can be calculated using the following formula: .

[0047] Further, in step S4, a constitutive model is constructed.

[0048] First, based on Lemaitre's strain equivalence principle, the total stress acting on the damaged soil... The resulting strain is equivalent to the effective stress. The strain generated on the undamaged soil. From this, the following constitutive relation is derived: , in, The total stress matrix, For the effective stress matrix, As a damage factor, For elastic modulus, The elastic modulus matrix, In response, Here is the strain matrix.

[0049] According to the extended strain equivalence principle, the strain caused by the effective stress in the first damage state acting on the second damage state is equivalent to the strain caused by the effective stress in the second damage state acting on the first damage state.

[0050] Assuming a salt-free and freeze-thaw-free state, the effective stress of the soil in its initial damaged state is: The elastic modulus is The effective stress of saline soil under damage state after freeze-thaw is The elastic modulus is The strain caused by salt and freeze-thaw cycles is The total strain is Damage factor is : , , , .

[0051] Similarly, assuming the effective stress of the damage state after loading is The elastic modulus is The strain caused by loading is The total strain is Damage factor is : , , , Among them, equivalent damage factor for: .

[0052] Then, assuming that the intensity of each infinitesimal element follows a Weibull distribution, the damage factor can be expressed as: , in, For soil micro-element strength based on effective stress, and These are the parameters of the Weibull distribution.

[0053] Furthermore, it can be deduced that: .

[0054] Next, the stress-strain relationship of the undamaged soil element obeys the generalized Hooke's law, which can be obtained as follows: , in, , These are the axial stress (first principal stress) and strain, respectively. This is the second principal stress. This is the confining pressure (third principal stress). It is Poisson's ratio.

[0055] Furthermore, it can be deduced that: .

[0056] Secondly, the expression for the strength of the infinitesimal element is derived based on the generalized Ewy-Lade-Duncan failure criterion. This criterion is stated as: , in: , , , , in, For the effective first stress invariant, For the effective third stress invariant, For cohesion, It is the internal friction angle. For bonding stress, For the material parameters of the generalized Ewy-Lade-Duncan failure criterion, is a material constant.

[0057] The principal stress relationship at failure can be derived as follows: .

[0058] Therefore, the soil micro-element strength function is defined as: Its effective stress form is: .

[0059] Furthermore, from the constitutive relations of effective stress and total stress, we can obtain: ; Therefore, we can conclude that: .

[0060] Furthermore, it can be deduced that: .

[0061] Further, in step S5, the model parameters are solved.

[0062] In the stress-strain curve, the peak stress and its corresponding peak strain The following geometric conditions must be met: , , , .

[0063] Parameters in the constitutive model All can be determined by conventional triaxial testing and the Mohr-Coulomb strength criterion, as detailed in Table 4.

[0064] Table 4. Methods for determining parameters of the coupled damage model

[0065] Key distribution parameters The solution is obtained by using the peak points of the stress-strain curve. The slope is zero. The geometric conditions are then determined. Substituting these conditions along with the peak point coordinates into the model expression, the following can be derived: Analytical solution: .

[0066] At this point, all parameters of the constitutive model can be determined, and the complete constitutive relation can be established.

[0067] Furthermore, to verify the effectiveness of this model, the stress-strain curves predicted by the model are compared with the actual experimental data obtained in step S2 of the embodiment, and also compared with the prediction results of the widely used modified Cambridge model, such as... Figure 5 As shown, the legend “X%-Y MPa-Z” consists of three parts, representing the salinity, confining pressure, and number of freeze-thaw cycles, respectively.

[0068] The comparative results show that under low confining pressures (0.2 MPa, 0.4 MPa), both the model of this invention and the modified Cambridge model can predict the trend well, but the model of this invention has a higher degree of agreement with the experimental values. Under high confining pressures (0.6 MPa, 0.8 MPa), the prediction deviations of both models increase, but the model of this invention still outperforms the modified Cambridge model in predicting curve morphology and failure modes, and is closer to the experimental data. This indicates that the salt-freeze-thaw coupled damage constitutive model proposed in this invention can accurately reflect the mechanical behavior of saline soil after freeze-thaw cycles, especially in capturing its damage evolution process.

[0069] Example 2: Figure 6 As shown, this invention provides a constitutive model construction system for soil with salt-freeze-thaw coupled damage. This system is used to implement the constitutive model construction method for soil with salt-freeze-thaw coupled damage in Embodiment 1 above, specifically including: The sample preparation and grouping module 100 is used to prepare saturated cylindrical soil samples and divide them into salt-containing sample groups and non-salt-containing sample groups; each group of samples is further processed to obtain samples in the pre-freeze-thaw state and samples in the post-freeze-thaw state after undergoing at least one complete freeze-thaw cycle. The coupling effect mechanical parameter acquisition module 200 is used to conduct consolidation undrained static triaxial tests on the four types of samples obtained by the sample preparation and grouping module 100, obtain stress-strain curves under different salt contents, different freeze-thaw states and different confining pressures, and extract the elastic modulus distribution law of the samples from them. The coupling damage factor definition module 300 is used to define a first damage variable characterizing salt damage and a second damage variable characterizing freeze-thaw damage based on the change of elastic modulus, and to calculate the coupling damage factor between salt and freeze-thaw based on the strain equivalence principle. Constitutive model construction module 400 is used to establish the constitutive relationship between effective stress and total stress considering coupled damage based on the Lemaitre strain equivalence principle; and to construct a soil stress-strain constitutive model reflecting salt and freeze-thaw coupled damage by combining the assumption that the strength of soil micro-elements follows the Weibull distribution, the generalized Hooke's law and the generalized Ewy-Lade-Duncan failure criterion. The model parameter solving module 500 is used to solve the undetermined parameters in the constitutive model constructed by the constitutive model construction module by utilizing the characteristic geometric conditions in the stress-strain curve obtained by the coupling mechanical parameter acquisition module 200, and to determine the final expression of the model.

[0070] This embodiment provides a constitutive model construction system for soil with salt-freeze-thaw coupling damage, used to implement the aforementioned constitutive model construction method for soil with salt-freeze-thaw coupling damage. Therefore, the specific implementation of the constitutive model construction system for soil with salt-freeze-thaw coupling damage can be found in the embodiment section of the constitutive model construction method for soil with salt-freeze-thaw coupling damage described above. For example, the sample preparation and grouping module 100, the coupling mechanical parameter acquisition module 200, the coupling damage factor definition module 300, the constitutive model construction module 400, and the model parameter solving module 500 are used to implement steps S1, S2, S3, S4, and S5 in the above-mentioned constitutive model construction method for soil with salt-freeze-thaw coupling damage, respectively. Therefore, the specific implementation can be referred to the description of the corresponding embodiments. To avoid redundancy, it will not be repeated here.

[0071] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0072] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0073] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The functions specified in one or more boxes. These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable apparatus for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0074] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for constructing a constitutive model of soil damaged by salt-freeze-thaw coupling, characterized in that, Includes the following steps: Step S1: Prepare saturated cylindrical soil samples and divide them into salt-containing sample groups and non-salt-containing sample groups; further process each group of samples to obtain samples in the pre-freeze-thaw state and samples in the post-freeze-thaw state after undergoing at least one complete freeze-thaw cycle. Step S2: Perform consolidation undrained static triaxial tests on the four types of samples obtained in Step S1 to obtain stress-strain curves under different salt contents, different freeze-thaw states and different confining pressures, and extract the distribution law of elastic modulus of the samples from them. Step S3: Based on the change in the elastic modulus, define a first damage variable characterizing salt damage and a second damage variable characterizing freeze-thaw damage, and calculate the coupling damage factor between salt and freeze-thaw based on the strain equivalence principle. Step S4: Based on the Lemaitre strain equivalence principle, establish the constitutive relationship between effective stress and total stress considering coupled damage; combine the assumption that the strength of soil micro-element follows the Weibull distribution, the generalized Hooke's law and the generalized Ewy-Lade-Duncan failure criterion, and construct a soil stress-strain constitutive model that reflects salt and freeze-thaw coupled damage. Step S5: Using the characteristic geometric conditions in the stress-strain curve obtained in step S2, solve for the undetermined parameters in the constitutive model constructed in step S4, and determine the final expression of the model.

2. The method for constructing a constitutive model of soil with salt-freeze-thaw coupled damage according to claim 1, characterized in that, In step S1, the preparation of the sample specifically includes: selecting soil samples from the same location and preparing saturated samples of specified dimensions according to the "Standard for Geotechnical Testing Methods" GB / T50123-2019; controlling the target salt content of the sample by mixing NaCl solutions of different concentrations with the soil sample; molding the sample using the compaction method and then saturating it under vacuum; for samples in a freeze-thaw state, freezing them for a specified time in a preset negative temperature environment and then thawing them completely at room temperature.

3. The method for constructing a constitutive model of soil with salt-freeze-thaw coupled damage according to claim 1, characterized in that, In step S2, the B-value needs to be tested before the static triaxial test to ensure sample saturation. The subsequent consolidation and shear tests can only be carried out when the B-value is greater than 0.

95. The test confining pressure is set to multiple levels to simulate different formation depths.

4. The method for constructing a constitutive model of soil with salt-freeze-thaw coupled damage according to claim 1, characterized in that, In step S3, the first damage variable is defined as: ,in As the first damage variable, The elastic modulus is the value of the salt-containing, unfrozen sample. The elastic modulus of the unfrozen, salt-free sample is given; the second damage variable is defined as: ,in As the second damage variable, The elastic modulus of the salt-free freeze-thawed sample; the coupling damage factor is determined by... and It is calculated using the following formula: ， in, This is the coupling damage factor.

5. The method for constructing a constitutive model of soil with salt-freeze-thaw coupled damage according to claim 1, characterized in that, In step S4, the constitutive relationship between the effective stress and the total stress is expressed as: ， in, For the total stress, The total stress matrix, For effective stress, For the effective stress matrix, As a damage factor, For elastic modulus, The elastic modulus matrix, In response, Here is the strain matrix.

6. The method for constructing a constitutive model of soil with salt-freeze-thaw coupled damage according to claim 5, characterized in that, Based on the assumption that the strength of soil micro-elements follows a Weibull distribution, the damage factor... Represented as: ， in, For soil micro-element strength based on effective stress, and These are the parameters of the Weibull distribution.

7. The method for constructing a constitutive model of soil with salt-freeze-thaw coupled damage according to claim 1, characterized in that, In step S4, the core expression of the constitutive model is: ， in, , These are axial stress and strain, respectively. For confining pressure, The elastic modulus is the value of the salt-containing, unfrozen sample. The elastic modulus is the unspecified, salt-free, unfrozen sample. The elastic modulus of the sample after freeze-thaw cycles without salt is given. Poisson's ratio, and For the Weibull distribution parameters, This refers to the soil micro-element strength based on effective stress.

8. The method for constructing a constitutive model of soil with salt-freeze-thaw coupled damage according to claim 7, characterized in that, The soil micro-element strength based on effective stress The expression is derived based on the generalized Ewy-Lade-Duncan violation criterion: ， in, For material parameters of the generalized Ewy-Lade-Duncan failure criterion, This refers to the bonding stress.

9. The method for constructing a constitutive model of soil with salt-freeze-thaw coupled damage according to claim 1, characterized in that, In step S5, the characteristic geometric condition is the peak point condition on the stress-strain curve, i.e., the peak stress. and its corresponding peak strain The conditions are satisfied that the function values ​​are equal and the first derivative is zero. Substituting these conditions into the constitutive model, the parameters are solved. : ， in, The elastic modulus is the unspecified, salt-free, unfrozen sample. The elastic modulus is the value of the salt-containing, unfrozen sample. The elastic modulus of the sample after freeze-thaw cycles without salt is given. For material parameters of the generalized Ewy-Lade-Duncan failure criterion, For bonding stress, Poisson's ratio, For confining pressure.

10. A system for constructing constitutive models of soil damaged by salt-freeze-thaw coupling, characterized in that, The system is used to implement the constitutive model construction method for salt-freeze-thaw coupled damage soil as described in any one of claims 1 to 9, specifically including: The sample preparation and grouping module is used to prepare saturated cylindrical soil samples and divide them into salt-containing sample groups and non-salt-containing sample groups; each group of samples is further processed to obtain samples in the pre-freeze-thaw state and samples in the post-freeze-thaw state after undergoing at least one complete freeze-thaw cycle. The coupling effect mechanical parameter acquisition module is used to conduct consolidation undrained static triaxial tests on the four types of samples obtained by the sample preparation and grouping module, obtain stress-strain curves under different salt contents, different freeze-thaw states and different confining pressures, and extract the elastic modulus distribution law of the samples from them. The coupling damage factor definition module is used to define a first damage variable characterizing salt damage and a second damage variable characterizing freeze-thaw damage based on the change in the elastic modulus, and to calculate the coupling damage factor between salt and freeze-thaw based on the strain equivalence principle. The constitutive model construction module is used to establish the constitutive relationship between effective stress and total stress considering coupled damage based on the Lemaitre strain equivalence principle; and to construct a soil stress-strain constitutive model that reflects salt and freeze-thaw coupled damage by combining the assumption that the strength of soil micro-elements follows the Weibull distribution, the generalized Hooke's law and the generalized Ewy-Lade-Duncan failure criterion. The model parameter solution module is used to solve for the characteristic geometric conditions in the stress-strain curves obtained by the coupling action mechanical parameter acquisition module, and to solve for the undetermined parameters in the constitutive model constructed by the constitutive model construction module, thereby determining the final expression of the model.

Images