A three-phase coupled discrete element modeling method for micp mineralized sand

Abstract

The application belongs to the technical field of geotechnical engineering numerical simulation, and particularly relates to a three-phase coupling discrete element modeling method for MICP mineralized sand soil. The method generates calcium carbonate particles by using a micro-particle filling method, restores the actual morphology of random deposition and crystal cluster formation based on scanning electron microscope test data, and overcomes the geometric distortion problem of traditional models; three types of contact, i.e. sand-sand, sand-calcium and calcium-calcium, are distinguished, and linear contact models and linear parallel bonding models are respectively used to accurately represent the combined mechanical behavior of sand particle friction and calcium carbonate cementation; the micro parameters are calibrated in reverse through indoor triaxial tests to ensure that the numerical simulation is consistent with the real material macro mechanical response, the peak strength error is less than 5%, and the model credibility is improved. The refined model can be used for MICP mineralized sand soil mechanical property analysis and seepage potential erosion simulation, and provides reliable numerical tools and theoretical basis for the optimized application of the microbial reinforcement technology in dam seepage prevention, foundation reinforcement and other geotechnical engineering scenes.

Description

Technical Field

[0001] This invention belongs to the field of numerical simulation technology in geotechnical engineering, specifically relating to a three-phase coupled discrete element modeling method for MICP mineralized sand. Background Technology

[0002] Microbially Induced Calcite Precipitation (MICP) is an environmentally friendly soil reinforcement method. It utilizes urease secreted by Bacillus pasteurellium to catalyze the hydrolysis of urea, which combines with calcium ions to form calcium carbonate precipitate. This process achieves cementation of sand particles and filling of pores, thereby improving soil strength and impermeability. It has broad application prospects in the field of geotechnical engineering seepage prevention and reinforcement.

[0003] When using the Discrete Element Method (DEM) to study the mechanical properties of MICP-reinforced soils, the key lies in constructing a numerical model that accurately reflects their cementation structure. Currently, commonly used modeling methods are often simplified: one is to directly apply a cementation model between sand particles to simulate cementation; the other is to generate a ring of regularly arranged particles at particle contact points to represent calcium carbonate precipitation. However, in actual MICP processes, calcium carbonate precipitates randomly and non-uniformly on the surface of sand particles and at contact points, forming a complex spatial distribution. Existing simplified models cannot accurately simulate this microstructure of calcium carbonate filling pores and adhering to the cementation on particle surfaces, leading to deviations in the model's prediction of the macroscopic mechanical behavior and failure mechanism of cemented sand. This is particularly true when dealing with seepage and undercutting problems involving multi-field coupling of fluid, particles, and cement, limiting its engineering applicability.

[0004] Therefore, there is an urgent need for a discrete element modeling method that can accurately characterize the microstructure and mechanical properties of MICP mineralized sand to overcome the shortcomings of existing technologies. Summary of the Invention

[0005] The purpose of this invention is to address existing problems by providing a three-phase coupled discrete element modeling method for MICP mineralized sand.

[0006] This invention is achieved through the following technical solution: A three-phase coupled discrete element modeling method for MICP mineralized sand includes the following steps: (1) Model particle generation: Based on the particle size distribution curve of the target discontinuous graded sand, a set of spherical sand particles with corresponding particle size and proportion is generated in the discrete element software to form an initial sand skeleton model; Based on the calcium carbonate content and scanning electron microscope morphology information obtained from physical experiments, the micro-particle filling method is used to randomly generate micro-spherical calcium carbonate particles in the pore space, near the contact point and on the surface of the sand particle model. The particle size range of calcium carbonate particles is 0.03~0.1mm, and the quantity is determined according to the calcium carbonate mass and density. The sand particles and calcium carbonate particles use different material density parameters. (2) Contact model definition: Clearly distinguish and define the three types of contact in the model, namely the contact between sand particles, the contact between sand particles and calcium carbonate particles, and the contact between calcium carbonate particles and calcium carbonate particles. (3) Contact model and parameter assignment: Differentiated contact models are adopted for the three contact types. The contact between sand particles is a linear contact model, and the contact between sand particles and calcium carbonate particles and calcium carbonate particles is a linear parallel bonding model. The contact between the wall boundary and the particles is a non-bonded linear contact model. (4) Micro-parameter calibration and verification: Macro-stress-strain curves of natural discontinuous graded sand and MIP mineralized sand were obtained through conventional triaxial compression tests in the laboratory; a numerical sample model with the same size, confining pressure and loading rate as the physical test was established in the discrete element software; the micro-mechanical parameters of various contact models were adjusted by trial and error method so that the stress-strain curve of the numerical simulation matches the results of the laboratory test, and the micro-parameter calibration was completed. (5) Model application: The calibrated three-phase coupled discrete element model is used to simulate the response of MICP mineralized sand under mechanical load, or as a solid phase basic model for fluid-particle coupled (CFD-DEM) seepage and undercut simulation studies.

[0007] Further, the particle size distribution of the discontinuously graded sand in step (1) includes coarse and fine particles, with the coarse particles ranging from 2 to 5 mm in diameter and the fine particles ranging from 0.25 to 0.6 mm in diameter; the number of calcium carbonate particles is calculated using the following formula: ; Where: m Calcium Carbonate For the mass of calcium carbonate crystals; C c R represents the mass fraction of calcium carbonate crystals. v The volume correction factor is set to 0.74. ρ Calcium Carbonate This refers to the density of calcium carbonate crystals. r Calcium Carbonate R is the radius of the calcium carbonate crystal.

[0008] Furthermore, the discrete element software mentioned in step (1) is PFC3D or PFC6.0, and the calculated size of the model is consistent with the actual sample size.

[0009] Furthermore, the formation of calcium carbonate particles in step (1) is based on scanning electron microscopy analysis results, simulating the actual morphology of calcium carbonate as crystal clusters attached to the surface of sand particles and filling pores.

[0010] Furthermore, the mesoscopic parameters of the linear contact model described in step (3) include the effective modulus. E stiffness ratio k coefficient of friction m .

[0011] The mesoscopic parameters of the linear parallel bond model include the bonding elastic modulus. E * Cemented stiffness ratio k * ,tensile strength s c * Cohesion c * internal friction angle f * .

[0012] Furthermore, in step (4), the specimen size for the indoor triaxial test is 39.1 mm in diameter and 80 mm in height. The confining pressure is set to 100 kPa, 200 kPa, and 300 kPa. The strain is loaded until it reaches 20%, and the stress-strain data is recorded.

[0013] Furthermore, the criterion for determining the micro-parameter calibration in step (4) is that the stress-strain curves of the numerical simulation and the indoor test show consistent trends, and the peak strength error is less than 5%.

[0014] Furthermore, in step (5), during the seepage and undercut simulation, the model is used to characterize the micromechanical behavior of solid phase particles and is coupled with computational fluid dynamics (CFD) software to achieve two-way fluid-structure interaction analysis.

[0015] The present invention has the following advantages over the prior art: 1. High geometric realism: The micro-particle filling method is used to generate calcium carbonate particles. Based on scanning electron microscopy experimental data, the actual morphology of calcium carbonate randomly deposited on the surface and pores of sand particles and forming crystal clusters is accurately restored, overcoming the distortion problem caused by the geometric simplification of traditional models. 2. Detailed mechanical characterization: By distinguishing three contact types—sand-sand, sand-calcium, and calcium-calcium—and using linear contact and linear parallel bonding models respectively, the frictional effect of unbonded sand particles and the cementing effect of calcium carbonate are accurately characterized, which is consistent with the composite mechanical behavior of MIP mineralized sand. 3. High model reliability: The micro-parameters are calibrated by reverse calibration through indoor triaxial tests to ensure that the macroscopic mechanical response of the numerical simulation is consistent with that of the real material, with a peak strength error of less than 5%, which improves the accuracy and reliability of the model prediction. 4. Wide applicability to engineering: The refined model established can be used for the mechanical property analysis and seepage erosion simulation of MIP mineralized sand, providing a reliable numerical tool and theoretical basis for the optimized application of microbial reinforcement technology in geotechnical engineering scenarios such as dam seepage prevention, foundation reinforcement, and slope protection. Attached Figure Description

[0016] Figure 1 Particle size distribution diagram for the test sand; Figure 2 SEM images of MICP mineralized sand at different magnifications, including (a) SEM image at 130x magnification; (b) SEM image at 250x magnification; (c) SEM image at 500x magnification; and (d) SEM image at 1000x magnification. Figure 3 Microstructure diagrams of discontinuous graded sand and MICP mineralized sand under SEM, where (a) sand particles with sand particles; (b) sand particles with calcium carbonate; (c) calcium carbonate with calcium carbonate. Figure 4 This is a schematic diagram of the linear contact model mechanism; Figure 5 This is a schematic diagram of the mechanism of parallel bonded contact model; Figure 6 It is a strain-controlled triaxial testing apparatus; Figure 7 For detailed parameter calibration flowchart; Figure 8 This is a schematic diagram of fluid-structure interaction. Figure 9 Numerical model of MICP mineralized discontinuous graded sand, where (a) numerical sample of MICP mineralized sand; (b) contact type of MICP mineralized sand model. Figure 10 The diagram shows a comparison of stress-strain curves for discontinuously graded sand, where (a) Gap-A3; (b) Gap-B1; and (c) Gap-C1. Figure 11 Comparison of stress-strain curves of discontinuous graded sand with MICP mineralization, where (a) MICP mineralization Gap-A3; (b) MICP mineralization Gap-B1; (c) MICP mineralization Gap-C1. Figure 12The diagram shows the force chain changes at different stages of the model with different fine particle contents, where (a) is the initial stage; (b) is the initiation stage; (c) is the development stage; and (d) is the failure stage. Figure 13 The changes in the permeation rate of samples with different fine particle contents over time are shown in the following figures: (a) the curves of the permeation rate of samples with different fine particle contents over time; (b) the curves of the permeation rate of samples with different fine particle contents over time after MIP treatment; (c) the comparison curves of the permeation rate over time; and (d) the trends of the permeation rate at 0s and 20s. Figure 14 The porosity of samples with different fine particle contents changes over time, including (a) porosity curves of samples with different fine particle contents over time; (b) porosity curves of samples with different fine particle contents over time after MICP treatment; (c) comparative curves of porosity changes over time; and (d) porosity change trends at 0s and 20s. Detailed Implementation

[0017] To further explain the present invention, the following specific embodiments are described.

[0018] Discontinuously graded soils, due to the lack of intermediate particle size distribution, typically exhibit an intermediate "plateau" in their particle size distribution curve, with two discontinuities.

[0019] 1. Model Particle Generation 1.1 Sand Particle Formation Based on the particle size distribution curve of the target discontinuously graded sand (e.g.) Figure 1 As shown in the figure, spherical sand particle sets were generated proportionally using the particle generation command in discrete element software (PFC3D or PFC6.0). The coarse particle size ranged from 2 to 5 mm, and the fine particle size ranged from 0.25 to 0.6 mm. The specific particle size distribution met the experimental design. Different sand types were prepared according to the discontinuous gradation of each grade as shown in Table 1.

[0020] Table 1 Classification of Sandy Soils at Various Levels ; The calculated dimensions of the model are consistent with those of the actual sample, namely a diameter of 39.1 mm and a height of 80 mm, ensuring the geometric similarity between the numerical model and the physical test sample.

[0021] 1.2 Formation of calcium carbonate particles The mass of calcium carbonate determined by the MIP mineralization test (Table 2) and the results of scanning electron microscopy analysis ( Figure 2 The particle size of calcium carbonate was determined to be in the range of 0.03~0.1 mm, and the morphology was an irregular crystal cluster.

[0022] Table 2. Calcium carbonate content after mineralization tests of sandy soils with different discontinuous gradations ; The "micro-particle filling method" was used to randomly generate micro-spherical calcium carbonate particles within the pore space of sand particles, near the contact points, and on the surface, simulating the actual deposition morphology of calcium carbonate. The number of calcium carbonate particles was calculated using formula (1): (1) In the formula: where m Calcium Carbonate For the mass of calcium carbonate crystals; C c The factor of 0.74 is taken to account for the difference in solid fraction between the most densely packed and closely packed calcium carbonate crystals with intergranular pores; ρ Calcium Carbonate This refers to the density of calcium carbonate crystals. r Calcium Carbonate R is the radius of the calcium carbonate crystal.

[0023] The density of sand particles is set at 2630 kg / m³ 3 The density of calcium carbonate particles is set at 3150 kg / m³. 3 To distinguish the physical properties of the two types of particles.

[0024] 2. Contact Model Definition Clearly distinguish the three contact model types in the model ( Figure 3 ), respectively corresponding to different microscopic mechanisms of action in MICP mineralized sand: Type (a): Contact between sand particles (sand-sand contact), contact between particles not cemented by calcium carbonate, mainly by friction and collision. Type (b): Base contact between sand particles and calcium carbonate particles (sand-calcium contact), where the surface of the sand particles is in cementation contact with the calcium carbonate crystals, transmitting cementing force; Type (c): basal contact between calcium carbonate particles (calcium-calcium contact), cementation contact between calcium carbonate crystals, forming a continuous cemented network.

[0025] 3. Contact Model and Parameter Assignment Differentiated contact models are used for the three contact types: Sand-to-sand contact: using a linear contact model ( Figure 4 This model only transmits normal and tangential forces, not torques, and conforms to the mechanical behavior of unconsolidated sand particles. Its core parameters include effective modulus. E stiffness ratio k (Normal stiffness) k n and tangential stiffness k s), coefficient of friction m .

[0026] Sand-calcium contact and calcium-calcium contact: A linear parallel bonding model was adopted ( Figure 5 This model, by constructing an adhesive layer in the contact area, can simultaneously transmit force and torque, and can characterize the formation and breakage process of cemented bonds. Core parameters include the cemented elastic modulus. E * Cemented stiffness ratio k * ,tensile strength s c * Cohesion c * internal friction angle f * .

[0027] Contact between wall boundaries and particles: A uniform, unbonded linear contact model is adopted, and the effective modulus of the wall is set to 1.0 × 10⁻⁶. 9 Pa, to avoid the boundary from interfering with the mechanical behavior of particles.

[0028] Based on existing research findings and empirical data, the initial parameter ranges are shown in Table 3 below: Table 3 Initial Parameters ; 4. Detailed parameter calibration and verification 4.1 Indoor triaxial compression test Sample preparation: Natural discontinuous graded sand and MICP mineralized sand were prepared in accordance with the "Standard for Geotechnical Testing Methods" (GB / T 50123-2019). The sample size was 39.1 mm in diameter and 80 mm in height. Three parallel samples were prepared for each group of samples to ensure the reliability of the data.

[0029] Experimental equipment: A strain-controlled triaxial testing apparatus (Nanjing Soil Instrument Factory Co., Ltd., model TSZ30-2.0) was used. Figure 6 ).

[0030] Test conditions: Confining pressures were set to 100 kPa, 200 kPa, and 300 kPa, respectively; loading rate was 0.01 mm / s; loading continued until the strain reached 20%; axial stress and axial strain data were recorded in real time; and stress-strain curves were plotted. Figure 10 , Figure 11 Both types of curves show a "linear growth-peak-softening" trend. The numerical simulation curves and experimental curves have a high degree of agreement, providing a direct comparative basis for the calibration of detailed parameters.

[0031] 4.2 Establishment of Numerical Triaxial Model Import the sand and calcium carbonate particle set generated in section 1.1 into the discrete element method software, and set the model size, confining pressure, and loading rate to be completely consistent with the indoor test.

[0032] Using the contact model and initial parameters defined above, confining pressure stabilization is achieved through servo control, and the loading program is started to simulate the triaxial compression process.

[0033] 4.3 Trial and Error Method Parameter Calibration The micromechanical parameters of various contact models were adjusted using a trial-and-error method (calibration process as follows). Figure 7 As shown in the flowchart of detailed parameter calibration, the stress-strain curves of the numerical simulation (including the slope of the elastic stage, peak strength, and post-peak softening / hardening characteristics) are consistent with the results of the laboratory test, and the peak strength error is controlled within 5%.

[0034] Calibration judgment criteria: The trend of change of the numerical curve is consistent with that of the test curve (including the slope of the elastic stage, the position of the peak strength, and the softening / hardening characteristics after the peak), and the peak strength error is less than 5%.

[0035] Typical parameters after calibration are shown in the following tables (Tables 4 to 9).

[0036] Table 4. Microscopic contact parameters of discontinuous graded sand. ; Table 5. Microscopic contact parameters of MICP-mineralized Gap-A1 ; Table 6. Microscopic contact parameters of MICP mineralized Gap-A2 ; Table 7. Microscopic contact parameters of MICP-mineralized Gap-A3 ; Table 8. Microscopic contact parameters of MICP-mineralized Gap-B1 ; Table 9. Microscopic contact parameters of MICP-mineralized Gap-C1 ; 5. Model Application 5.1 Simulation of Mechanical Properties The calibrated model was used to simulate the microscopic response of MICP mineralized sand under uniaxial compression and triaxial shear loads, and the evolution of parameters such as coordination number, porosity, and force chain network was analyzed.

[0037] 5.2 Simulation of seepage and undercutting This model is used as the basic solid phase model and coupled with computational fluid dynamics (CFD) software (such as OpenFOAM) to construct a CFD-DEM two-way fluid-structure interaction model. Figure 8 ).

[0038] Simulating the processes of fine particle loss, porosity change, and seepage channel evolution under seepage action provides numerical support for evaluating the anti-submarine corrosion effect of MICP technology.

[0039] The following describes the complete implementation process of the present invention in detail with reference to three typical embodiments, including experimental data, modeling process, parameter calibration, and application verification: Example 1: Modeling and Mechanical Property Simulation of MICP Mineralized Gap-A3 Type Sand 1. Experimental Data Collection Particle size distribution test: Gap-A3 sand contains 35% fine particles (0.60~0.45mm) and 65% coarse particles (5~2mm), with a uniformity coefficient of... C u =5.67, discontinuity ratio G r =3.33 ( Figure 1 (Table 2).

[0040] MICP mineralization test: using optimal mineralization parameters (bacterial solution concentration OD) 600 =1.0, cementing solution concentration 0.5mol / L, mineralization rounds 2), the cementing solution is prepared by mixing urea and calcium chloride in a 1:1 volume ratio, the mass of calcium carbonate was measured to be 5.53g, and the content was 2.95% (Table 2).

[0041] Scanning electron microscopy (SEM) showed that calcium carbonate particles, ranging in size from 0.03 to 0.1 mm, adhered to the surface of sand particles in the form of crystal clusters, filling the pores. Figure 2 ).

[0042] Indoor triaxial tests: Under confining pressures of 100 kPa, 200 kPa, and 300 kPa, the peak strengths of natural Gap-A3 were 0.28 MPa, 0.45 MPa, and 0.70 MPa, respectively; the peak strengths of MICP mineralized sand were 0.95 MPa, 1.42 MPa, and 1.80 MPa, respectively. The numerical simulation values ​​were 0.93 MPa, 1.39 MPa, and 1.77 MPa, respectively, with errors all less than 3%. Figure 11 ).

[0043] 2. Model Particle Generation Sand particles: In PFC3D, a collection of cylindrical sand particles with a diameter of 39.1 mm and a height of 80 mm is generated, and the particle size distribution conforms to the Gap-A3 gradation.

[0044] Calcium carbonate particles: According to formula (1), the number of particles is 20149, with an average radius of 0.05 mm. They are randomly filled in the pores and surface of the sand particles. The resulting numerical model is as follows. Figure 9 As shown.

[0045] 3. Contact Model Definition and Parameter Assignment Contact types: Define three types of contact: sand-sand, sand-calcium, and calcium-calcium. Figure 3 ).

[0046] Initial parameters: Sand-to-sand contact E = 1.0 × 10 8 Pa, κ = 1.0, μ = 1.2; Sand-calcium contact E ∗ =5.0×10 9 Pa、κ ∗ =1.0、σ c ∗ =94.0MPa, c ∗ =94.0MPa; Calcium-Calcium Contact E ∗ =5.0×10 9 Pa、κ ∗ =1.0、σ c ∗ =22.0MPa, c ∗ =22.0MPa (Table 7).

[0047] 4. Application of mechanical property simulation: Coordination number evolution: The initial coordination number was 2.30, which decreased to 1.75 when loaded to the peak strain. The coordination number stabilized at 0.35 during the failure stage, indicating that calcium carbonate cementation effectively improved particle contact stability.

[0048] Force chain network analysis: The proportion of strong contacts (red force chains) in mineralized sandy soil reached 32%, significantly higher than that in natural sandy soil (10%). Figure 12 This verified the effect of cementation on improving mechanical strength.

[0049] Example 2: Modeling and Comparative Analysis of MIP Mineralized Sand with Different Fine Particle Content 1. Test subjects: Discontinuously graded sandy soils with three types of fine particle content—Gap-A1 (15%), Gap-A2 (25%), and Gap-A3 (35%)—were selected (Table 2, ...). Figure 1 ).

[0050] 2. Modeling process: Following the procedure in Example 1, numerical models for three types of sandy soil were generated, with the number of calcium carbonate particles being 57,114, 45,493, and 20,149, respectively (calculated based on the data in Table 2).

[0051] Contact parameter calibration: The sand-sand contact parameters of the three types of sandy soils are consistent (Table 4), while the sand-calcium / calcium-calcium contact parameters increase with the increase of fine particle content (Tables 5-9).

[0052] 3. Comparative analysis application: Mechanical property comparison: Simulation results show that the peak strength (1.85 MPa, confining pressure 300 kPa) of Gap-A3 mineralized sand with a fine particle content of 35% is higher than that of Gap-A1 (1.48 MPa) and Gap-A2 (1.62 MPa), indicating that the increase in fine particle content can promote the cementing efficiency of calcium carbonate.

[0053] Detailed mechanistic analysis: The initial porosity of Gap-A3 is 0.38, lower than that of Gap-A1 (0.42) and Gap-A2 (0.40), indicating a more significant calcium carbonate filling effect and a denser force chain network. Figure 12 This study verified the correlation between fine particle content and mineralization effect.

[0054] Example 3: Application of CFD-DEM simulation of seepage and undercutting in MICP mineralized sand 1. Model preparation: The numerical model of Gap-A1 mineralized sand soil calibrated in Example 1 was used as the solid phase.

[0055] 2. CFD-DEM coupling settings: Fluid Domain: A 25mm×25mm×25mm fluid mesh was constructed in OpenFOAM with 125 meshes. The fluid viscosity was 0.001 Pa·s and the density was 1000 kg / m³. 3 .

[0056] Coupling parameters: Time step 1×10 -6 The fluid velocity is 0.1 m / s, and indicators such as fine particle loss, porosity, and coordination number are monitored.

[0057] 3. Results of erosion simulation: Fine particle loss: The fine particle erosion rate of MICP mineralized sand within 20 seconds was 1.55%, significantly lower than that of natural sand (1.77%). Figure 13 Calcium carbonate cementation effectively inhibits the migration of fine particles.

[0058] Porosity changes: The porosity of mineralized sand increased from the initial 0.42 to 0.46 (an increase of 9.5%), while that of natural sand increased from 0.45 to 0.54 (an increase of 20%), indicating that cementation slowed down pore expansion.

[0059] Force chain stability: During the erosion process, the force chain breakage rate of mineralized sand was 28%, while that of natural sand was 53%. Figure 12 This slowed down the process of latent erosion and damage.

[0060] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A three-phase coupled discrete element modeling method for MICP mineralized sand, characterized in that, Includes the following steps: (1) Model particle generation: Based on the particle size distribution curve of the target discontinuous graded sand, a set of spherical sand particles with corresponding particle size and proportion is generated in the discrete element software to form an initial sand skeleton model; Based on the calcium carbonate content and scanning electron microscope morphology information obtained from physical experiments, the micro-particle filling method is used to randomly generate micro-spherical calcium carbonate particles in the pore space, near the contact point and on the surface of the sand particle model. The particle size range of calcium carbonate particles is 0.03~0.1mm, and the quantity is determined according to the calcium carbonate mass and density. The sand particles and calcium carbonate particles use different material density parameters. (2) Contact model definition: Clearly distinguish and define the three types of contact in the model, namely, the contact between sand particles, the contact between sand particles and calcium carbonate particles, and the contact between calcium carbonate particles and calcium carbonate particles. (3) Contact model and parameter assignment: Differentiated contact models are adopted for the three contact types. The contact between sand particles is a linear contact model, and the contact between sand particles and calcium carbonate particles and calcium carbonate particles is a linear parallel bonding model. The contact between the wall boundary and the particles is a non-bonded linear contact model. (4) Micro-parameter calibration and verification: Macro-stress-strain curves of natural discontinuous graded sand and MIP mineralized sand were obtained through conventional triaxial compression tests in the laboratory; a numerical sample model with the same size, confining pressure and loading rate as the physical test was established in the discrete element software; the micro-mechanical parameters of various contact models were adjusted by trial and error method so that the stress-strain curve of the numerical simulation matches the results of the laboratory test, and the micro-parameter calibration was completed. (5) Model application: The calibrated three-phase coupled discrete element model is used to simulate the response of MICP mineralized sand under mechanical load, or as a solid phase basic model for fluid-particle coupled (CFD-DEM) seepage and undercut simulation studies.

2. The method according to claim 1, characterized in that, The particle size distribution of the discontinuously graded sand in step (1) includes coarse and fine particles, with the coarse particles ranging from 2 to 5 mm in diameter and the fine particles ranging from 0.25 to 0.6 mm in diameter; the number of calcium carbonate particles is calculated using the following formula: ； Where: m Calcium Carbonate For the mass of calcium carbonate crystals; C c R represents the mass fraction of calcium carbonate crystals. v The volume correction factor is set to 0.

74. ρ Calcium Carbonate This refers to the density of calcium carbonate crystals. r Calcium Carbonate R is the radius of the calcium carbonate crystal.

3. The method according to claim 1, characterized in that, The discrete element software mentioned in step (1) is PFC3D or PFC6.0, and the calculated size of the model is consistent with the actual sample size.

4. The method according to claim 1, characterized in that, The formation of calcium carbonate particles in step (1) is based on scanning electron microscopy analysis results, simulating the actual morphology of calcium carbonate as crystal clusters attached to the surface of sand particles and filling pores.

5. The method according to claim 1, characterized in that, The mesoscopic parameters of the linear contact model described in step (3) include the effective modulus. E stiffness ratio k coefficient of friction ； The mesoscopic parameters of the linear parallel bond model include the bonding elastic modulus. E * Cemented stiffness ratio k * ,tensile strength Cohesion c * internal friction angle .

6. The method according to claim 1, characterized in that, In step (4), the specimen size for the indoor triaxial test is 39.1 mm in diameter and 80 mm in height. The confining pressure is set to 100 kPa, 200 kPa, and 300 kPa. The strain is loaded until it reaches 20%, and the stress-strain data is recorded.

7. The method according to claim 1, characterized in that, The criteria for determining the micro-parameter calibration in step (4) are that the stress-strain curves of the numerical simulation and the indoor test show consistent trends, and the peak strength error is less than 5%.

8. The method according to claim 1, characterized in that, In step (5), during the seepage and undercut simulation, this model is used to characterize the micromechanical behavior of solid phase particles and is coupled with computational fluid dynamics (CFD) software to achieve two-way fluid-structure interaction analysis.

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