Method and system for evaluating permeability of cement stabilized recycled aggregate pervious base

Abstract

The application provides a cement stabilized recycled aggregate permeable base layer permeability evaluation method and system, and belongs to the technical field of road engineering material numerical simulation and performance evaluation. The method comprises the following steps: a discrete element environment is constructed, a virtual aggregate is generated, a particle crushing model and a double-shell medium contact model are introduced in gravity settlement and static compaction, and a virtual sample is obtained; according to the volume relationship between cement paste and aggregate, a double-shell medium geometric model composed of aggregate and its surface cement paste is constructed; an equivalent ball is used to replace the aggregate, a virtual cement bridge geometric model between aggregates is constructed according to volume conservation; the inherent gap of solid-liquid particles in smooth particle hydrodynamics is considered, and geometric scaling correction is performed on the double-shell medium and the virtual cement bridge; the corrected solid phase is introduced into a seepage model, fluid flow is simulated to obtain a stable flow, and a permeability coefficient is calculated. The application can quickly and accurately evaluate the material permeability, and provide a fine numerical basis for pore clogging mechanism analysis.

Description

Technical Field

[0001] This invention relates to the field of numerical simulation and performance evaluation technology for road engineering materials, and in particular to a method and system for evaluating the permeability of cement-stabilized recycled aggregate permeable base course. Background Technology

[0002] With the increasing frequency of extreme rainfall events, the construction of sponge cities has placed higher demands on urban road drainage systems. Cement-stabilized recycled aggregate permeable base course material (CRPB) has become an important candidate material for permeable road base courses due to its combination of load-bearing capacity, permeability, and resource reuse value.

[0003] CRPB materials are typically composed of natural coarse aggregates, recycled aggregates, and cementitious materials. During construction and molding, significant compaction is required, which can easily lead to aggregate particle breakage, cement paste migration, and the formation of inter-aggregate bridging structures. This results in a complex microporous structure and highly tortuous seepage channels within the material. During service, these materials may also experience pore blockage due to fine particle deposition, cement paste filling, and localized pore closure, leading to a decline in permeability or even failure.

[0004] Currently, the evaluation of the permeability of CRPB materials still mainly relies on laboratory tests, such as porosity testing and constant head permeability coefficient testing. Although these methods can directly obtain measured data, they usually have problems such as long test cycles, high testing costs, and a large workload of repeated tests under different mix ratios and compaction conditions. Moreover, they can only obtain macroscopic permeability results and cannot reveal the microscopic mechanisms of pore connectivity, local blockage, and seepage evolution within the material.

[0005] To further analyze the internal pore structure of materials, existing studies have also employed computed tomography (CT) to observe and characterize the pore distribution of permeable materials or similar porous materials. While this method is beneficial for analyzing the static pore structure characteristics of materials, it is generally difficult to achieve dynamic simulation of the seepage process and is also difficult to directly apply to the rapid prediction of permeability coefficients under different operating conditions.

[0006] With the development of computer technology, numerical simulation methods have gradually become an important tool for assessing the permeability of permeable materials. Computational fluid dynamics (CFD) is one of the more common approaches, but existing methods generally suffer from the following shortcomings: First, they often simplify aggregates to spherical particles, making it difficult to reflect the actual morphology of aggregates and their impact on pore structure. Second, most methods are only applicable to low compaction conditions, making it difficult to describe the crushing and fragmentation behavior of aggregate particles under high compaction conditions. Third, when using traditional mesh methods to solve fluid motion, it is difficult to accurately capture the existence and migration characteristics of fluids in complex pores, resulting in insufficient geometric realism of the model. Fourth, existing methods lack a unified technical approach that can simultaneously consider the actual morphology of aggregates, particle crushing, the geometry of cement bridges, and seepage boundary correction within the same modeling framework, thus limiting the in-depth understanding of the pore blockage mechanism of CRPB materials.

[0007] Furthermore, while existing artificial intelligence methods can be used to predict material properties, they typically rely on fitting existing sample data and lack sufficient physical mechanism constraints. The results are insufficient in terms of physical interpretability, and are particularly unfavorable for explaining potential pore blockage and seepage failure mechanisms during the material design stage.

[0008] Therefore, there is an urgent need to provide a new method for assessing the permeability of cement-stabilized recycled aggregate permeable base courses. This method can simultaneously consider the actual morphology of aggregates, compaction and crushing behavior, and cement slurry contact with aggregate surfaces during the virtual sample generation stage. It can also rationally construct the geometry of virtual cement bridges during the aggregate bonding characterization stage and perform geometric corrections on the double-shell medium and cement bridges during the seepage solution stage. This improves the accuracy of numerical assessment of material permeability and provides a reliable microscopic numerical basis for the analysis of pore blockage mechanisms. Summary of the Invention

[0009] To address the aforementioned problems, the present invention aims to provide a method and system for rapidly evaluating and analyzing the permeability of cement-stabilized recycled aggregate permeable base courses.

[0010] In a first aspect, the present invention provides a method for evaluating the permeability of cement-stabilized recycled aggregate permeable base courses, comprising the following steps:

[0011] Step S100: Construct a discrete element simulation environment, generate virtual aggregate particles with preset particle size distribution and real morphology, apply gravity settling, and introduce a particle crushing model and a double-shell medium contact model during static compaction to simulate the crushing behavior of aggregate particles and the contact, compression, separation and bridging effects of cement paste on the aggregate surface. After parameter calibration, compact to a stable state to obtain a compacted virtual sample.

[0012] Step S200: Based on the compacted virtual sample, determine the average thickness of the cement slurry layer on the surface of the aggregate according to the volume relationship between the cement slurry and the aggregate, and construct a double-shell medium geometric model composed of the aggregate and its surface cement slurry.

[0013] Step S300: Based on the double-shell medium geometric model, an equivalent sphere with the same volume as the actual aggregate is used to replace the actual aggregate, the cement slurry contact between the aggregates is determined, and a virtual cement bridge geometric model between the aggregates is constructed according to the volume conservation relationship and the geometric relationship of the equivalent sphere.

[0014] Step S400: Considering the inherent gap between solid particles and fluid particles in the smooth particle hydrodynamics method, perform geometric scaling correction on the double-shell medium geometric model and the virtual cement bridge geometric model to obtain the corrected solid phase geometric model;

[0015] Step S500: Import the corrected solid phase geometric model into the smooth particle fluid dynamics seepage model, regard the aggregate, surface hardened cement slurry and virtual cement bridge as solid phases, discretize the fluid into smooth particle fluid dynamics particles, simulate the flow behavior of the fluid in the pores, and obtain the fluid flow rate under stable seepage state.

[0016] Step S600: Calculate the permeability coefficient of the cement-stabilized recycled aggregate permeable base course material based on the fluid flow rate under the stable seepage state.

[0017] A second aspect of the present invention provides a permeability assessment system for cement-stabilized recycled aggregate permeable base courses, comprising:

[0018] The Discrete Element Virtual Sample Preparation Module is used to construct a discrete element simulation environment, generate virtual aggregate particles with preset particle size distribution and real morphology, apply gravity settling, and introduce a particle crushing model and a double-shell medium contact model during static compaction to simulate the crushing behavior of aggregate particles and the contact, compression, separation and bridging effects of cement paste on the aggregate surface. After parameter calibration, it is compacted to a stable state to obtain the compacted virtual sample.

[0019] The double-shell medium geometric model construction module is used to determine the average thickness of the cement slurry layer on the surface of the aggregate based on the compacted virtual sample and the volume relationship between the cement slurry and the aggregate, and to construct a double-shell medium geometric model composed of the aggregate and its surface cement slurry.

[0020] The virtual cement bridge geometric model construction module is used to construct a virtual cement bridge geometric model between aggregates based on the double-shell medium geometric model, using an equivalent sphere with the same volume as the actual aggregate to replace the actual aggregate, determining the cement slurry contact between aggregates, and constructing the virtual cement bridge geometric model between aggregates based on the volume conservation relationship and the geometric relationship of the equivalent sphere.

[0021] The geometric scaling correction module is used to consider the inherent gap between solid particles and fluid particles in the smooth particle hydrodynamics method, and to perform geometric scaling correction on the double-shell medium geometric model and the virtual cement bridge geometric model to obtain the corrected solid phase geometric model.

[0022] The smooth particle fluid dynamics seepage simulation module is used to import the corrected solid phase geometric model into the smooth particle fluid dynamics seepage model, regard aggregate, surface hardened cement paste and virtual cement bridge as solid phase, discretize the fluid into smooth particle fluid dynamics particles, simulate the flow behavior of fluid in pores, and obtain the fluid flow rate under stable seepage state.

[0023] The permeability coefficient calculation module is used to calculate the permeability coefficient of cement-stabilized recycled aggregate permeable base course material based on the fluid flow rate under the stable seepage state.

[0024] The present invention has the following advantages or beneficial effects:

[0025] 1. In the discrete element compaction modeling stage, not only is the true morphology of the aggregate incorporated, but the continuous crushing behavior of particles during compaction and the contact suction effect of fresh cement paste on the aggregate surface are also considered. Parameter calibration makes the model more closely resemble the actual material properties, thus realistically reproducing the particle movement, stress evolution, and microstructure formation process of cement-stabilized recycled aggregate permeable base course materials during the forming process. Compared to traditional modeling methods that simplify aggregates to spherical shapes and ignore compaction crushing and paste contact, the virtual specimens obtained by this invention are closer to the actual material state in terms of pore structure, particle interlocking relationships, and contact networks.

[0026] 2. In the geometric modeling stage of the virtual cement bridge, based on the volume relationship between cement paste and aggregate, equivalent sphere substitution, and the principle of volume conservation, the volume, cross-sectional radius, and height of the cement bridge are accurately calculated. The shape of the cement bridge—cylindrical or frustum—is determined based on the relative size of the cross-sectional radius and the equivalent radius of the connecting aggregates. This approach accurately reflects the asymmetric bonding state when aggregates of different sizes are joined, avoiding systematic errors introduced by uniformly adopting a single geometric assumption, and providing a more realistic solid boundary for subsequent seepage simulation.

[0027] 3. By fully considering the inherent gaps between solid and fluid particles in the smooth particle hydrodynamics method, geometric scaling correction is applied to the double-shell medium composed of aggregate and its surface-hardened cement slurry, as well as the virtual cement bridge, effectively compensating for porosity loss caused by limited particle resolution. Compared with directly using the original, uncorrected geometric model, this correction strategy significantly reduces the problems of underestimated pore size and excessive shrinkage of permeability channels, thereby improving the reliability of the numerical simulation results of the permeability coefficient.

[0028] 4. By organically integrating discrete element compaction sampling, geometric modeling of cement bridges, and smooth particle fluid dynamics seepage simulation, the permeability performance of materials can be rapidly predicted without requiring extensive physical experiments for each mix proportion and compaction condition. This significantly reduces the workload of repetitive laboratory tests, shortens the evaluation cycle, and lowers testing costs. Furthermore, comparing the numerical simulation results with laboratory constant head permeability test results demonstrates that the method has good predictive accuracy under conditions such as cement content below 20%, providing a reliable basis for engineering applications.

[0029] 5. The modeling approach established in this invention does not rely on a single aggregate source or a specific mix design. By adjusting aggregate parameters, cement paste parameters, geometric model parameters, and boundary conditions, it can be easily adapted to assess the seepage performance of other permeable road base courses or similar porous engineering materials. Its core advantage lies in unifying particle crushing, slurry bridging, and seepage calculation within a framework driven by the same physical mechanism. This not only outputs the macroscopic permeability coefficient but also allows for numerical observation of the fluid distribution, retention areas, and main flow channels within the sample under stable seepage conditions, providing a microscopic numerical basis for analyzing the mechanisms of local pore blockage and overall seepage failure. Attached Figure Description

[0030] The above and other features and advantages of the present invention will become more apparent from a detailed description of exemplary embodiments thereof with reference to the accompanying drawings.

[0031] Figure 1 This is a flowchart of a method for evaluating the permeability of cement-stabilized recycled aggregate permeable base course according to the present invention;

[0032] Figure 2 This is a schematic diagram of the settlement-compaction-crushing process.

[0033] Figure 3 A schematic diagram of the geometric modeling of a double-shell medium and a cement bridge;

[0034] Figure 4 This is a schematic diagram of the seepage boundary and geometric correction.

[0035] Figure 5 This is a schematic diagram of the structure of a cement-stabilized recycled aggregate permeable base course permeability assessment system according to the present invention;

[0036] Figure 6 This is a schematic diagram of the structure of an electronic device according to the present invention;

[0037] Figure 7 This is a schematic diagram of the structure of a computer-readable storage medium according to the present invention. Detailed Implementation

[0038] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that the invention will be thorough and complete, and the concept of the exemplary embodiments will be fully conveyed to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore their detailed description will be omitted.

[0039] The terms “a,” “one,” “the,” and “the” are used to indicate the existence of one or more elements / components / etc.; the terms “including” and “having” are used to indicate an open-ended meaning of inclusion and that other elements / components / etc. may exist in addition to the listed elements / components / etc.

[0040] Example 1

[0041] like Figures 1 to 4 As shown, this invention also provides a Discrete Element Method - Smoothed Particle Hydrodynamics (DEM-SPH) hybrid modeling method for permeability assessment of cement-stabilized recycled aggregate permeable base (CRPB). This method mainly includes steps such as virtual sample preparation, virtual cement bridge geometry modeling, geometric scaling correction of the double-shell medium and cement bridge, SPH seepage simulation, and permeability coefficient calculation. Details are as follows:

[0042] Step S100: Discrete Element Virtual Sample Preparation and Parameter Calibration. A virtual sample that can realistically reflect the microstructure of CRPB material is constructed using the discrete element method. Its specific implementation includes the following sub-steps:

[0043] Step S101: Constructing a Discrete Element Simulation Platform and Sample Formation: Construct a discrete element simulation platform and determine the size, boundary conditions, and aggregate placement range of the simulation sample formation domain. In a preferred embodiment, the diameter of the sample formation domain is 140 mm and the height is greater than 300 mm, corresponding to the forming scale of the actual CRPB sample. Subsequently, virtual aggregate particles with different particle sizes and true morphologies are randomly generated within the sample formation domain. The aggregate particles preferably adopt polyhedral or other discrete element particle forms that can characterize the actual aggregate shape, rather than simple spherical particles, to reduce geometric errors caused by aggregate shape simplification. After the aggregate particles are generated, gravitational acceleration is applied to the particle system, allowing the aggregate particles to settle freely within the sample formation domain. During the free settling stage, the particle breakage model is not activated; only the aggregate particles are allowed to rearrange under gravity until the particle system reaches a kinetically stable state. The so-called "kinetically stable state" refers to the overall kinetic energy of the particle system dropping below a preset threshold, the particle displacement change stabilizing, and the contact network no longer experiencing significant abrupt changes. At this point, the initial particle packing structure after gravity deposition is considered to have been obtained.

[0044] Step S102: Simulating Static Compaction and Particle Crushing: A rigid loading plate is generated on top of the aggregate mixture to simulate the static compaction effect applied during the actual CRPB molding process. During the compaction stage, a particle crushing model is activated, and the tensile stress on each aggregate particle is calculated in real time based on Griffith strength theory. For any aggregate particle, if the real-time calculated Griffith tensile stress exceeds the preset single-particle strength of that aggregate particle, the aggregate particle is considered to have crushed. To make the crushing behavior closer to the actual compaction process, the orientation of the fracture surface of the aggregate particle is related to the direction of the dominant contact force, and multiple consecutive crushing of particles is allowed during continuous loading. In this way, the crushing refinement, particle rearrangement, and fragment interlocking behavior of the aggregate during the compaction process can all be numerically reflected.

[0045] Step S103: Constructing a double-shell medium contact model: To consider the contact and bridging effects of fresh cement paste on the aggregate surface in the discrete element simulation, this embodiment introduces a suction component to construct a double-shell medium contact model based on the basic linear rolling resistance contact model between aggregate particles. Specifically, the aggregate encased in cement paste is considered as a double-shell medium consisting of an "aggregate core + an outer cement paste shell". Thus, when two aggregates approach or separate, not only the mechanical contact between the aggregate bodies is considered, but also the rheological contact and liquid-like bridging suction effect of the fresh cement paste on the surface.

[0046] In a preferred embodiment, the double-shell dielectric contact model satisfies the following relationship:

[0047] a. When the fresh cement paste on the surfaces of the two aggregates just comes into contact, the normal displacement between the two shell media is defined as zero, and at this time an initial suction force is generated between the two shell media;

[0048] b. As the two bishell media continue to approach each other, the suction gradually decreases and approaches zero. When the bishell media continue to approach each other, the cement slurry is slightly squeezed, thus generating normal compressive force.

[0049] c. When the core of the double-shell medium, i.e. the aggregate body, is in contact, the contact force between particles degenerates into a linear rolling resistance contact model for calculation;

[0050] d. Conversely, when the two bilayer media separate from each other from the contact state, the compressive normal force gradually decreases to zero, forming suction between the cement pastes and undergoing a process of first increasing and then decreasing until the cement pastes are completely separated and the suction drops to zero. This mechanical description can well characterize the microscopic bridging behavior exhibited by fresh cement paste during aggregate contact and separation.

[0051] Step S104, Parameter Calibration and Compaction Completion: The key parameters involved in the above model are calibrated. Specifically, the friction coefficient, rolling resistance friction coefficient, and stiffness ratio of different types of aggregates are calibrated through laboratory angle of repose tests; the single-particle strength and stiffness parameters of different types of aggregates are obtained through single-particle crushing tests; and the initial suction parameters in the double-shell medium contact model are determined through multiple rounds of compaction simulation and parameter adjustment. The calibrated parameters are substituted into the compaction simulation, and compaction continues until the preset compaction force is reached, and the kinetic energy, displacement, and contact force network of the particle system tend to stabilize, thus determining that the compaction process is complete and obtaining a compacted virtual sample. At this point, the particle structure, fragments, pore morphology, and particle contact relationships in the virtual sample can realistically reflect the microstructure of the actual material after compaction.

[0052] In the discrete element compaction modeling stage, this invention not only improves geometric realism by generating aggregate particles with realistic morphology, but more importantly, it introduces a particle breakage model and a double-shell medium contact model, while simultaneously considering the aggregate breakage behavior during compaction and the contact suction effect of fresh cement paste on the aggregate surface. This enables a more realistic reproduction of the particle movement, stress evolution, and microstructure formation process of CRPB materials during actual molding, making the constructed virtual specimens closer to the actual material state in terms of pore structure, particle interlocking relationships, and contact networks, laying a solid foundation for subsequent accurate seepage analysis.

[0053] Step S200: Constructing a double-shell medium geometric model. After obtaining the compacted virtual sample, this step is used to construct a double-shell medium geometric model composed of aggregates and their surface-hardened cement paste. Specifically, firstly, based on the volume relationship between the cement paste and the aggregates, the average thickness of the cement paste layer on the aggregate surface is calculated. Preferably, the cement paste volume is obtained by converting the mass and density of cement and water, and the aggregate volume is obtained by converting the mass and density of the aggregates. Then, the average thickness of the cement paste layer when the aggregate surface is uniformly coated is obtained by combining the relationship between the average radius and volume of the aggregates. Thus, each aggregate and the cement paste layer attached to its surface can be regarded as a whole double-shell medium geometric model.

[0054] Step S300: Construct a virtual cement bridge geometric model, used to build a virtual cement bridge geometric model connecting adjacent aggregates based on the double-shell medium geometric model. The specific implementation includes the following sub-steps:

[0055] Step S301, Equivalent Sphere Substitution: To facilitate the derivation of the geometric parameters of the virtual cement bridge, this embodiment uses an equivalent sphere with the same volume as the actual aggregate to replace the actual aggregate. It should be emphasized that at the connection points of the cement bridge, the contour of the equivalent sphere should correspond to the contour of the actual aggregate to avoid distortion of the local connection shape due to geometric substitution.

[0056] Step S302, Cement Bridge Judgment and Parameter Calculation: Based on this, when the distance between the surfaces of two aggregates is less than or equal to twice the average cement paste layer thickness, it is determined that the cement paste on the surfaces of the two aggregates has come into contact, and after hardening, a virtual cement bridge with a specific volume is formed. Based on the volume conservation relationship, the equivalent sphere overlap relationship, and the geometric continuity relationship, the volume, cross-sectional radius, and height of the virtual cement bridge are calculated. When the gap between the aggregate surfaces approaches zero, if the solution is directly calculated according to the ideal cylindrical relationship, it may lead to the cross-sectional radius of the cement bridge approaching infinity, which obviously does not conform to the actual physical situation. In this regard, this embodiment introduces a correction relationship: when the gap between the aggregate surfaces is less than a certain preset threshold, the height of the cement bridge is limited to a finite value to reflect the real state of the cement paste being squeezed out around the contact area to form a finite-height bridge.

[0057] Step S303, Determination of the geometric shape of the cement bridge: When determining the geometric shape of the cement bridge, this embodiment does not simply adopt a uniform cylindrical shape, but determines it based on the relative size between the cross-sectional radius of the cement bridge and the equivalent radius of the connecting aggregate.

[0058] a. When the equivalent radii of the connecting aggregates are similar and the cross-sectional radius of the cement bridge is not greater than the equivalent radius of the connecting aggregates, the cement bridge is regarded as a cylindrical cement bridge;

[0059] b. When the cross-sectional radius of the cement bridge is larger than the equivalent radius of one of the connecting aggregates, to more accurately reflect the asymmetry of the connection shape, the cement bridge is considered as a frustum-shaped cement bridge. In this case, the reference radius obtained under the cylindrical assumption is used as the mid-section radius of the frustum, and one end face radius is matched with the smaller equivalent radius aggregate, while the other end face radius is calculated based on geometric continuity. This can more accurately adapt to bridging connections between aggregates of different particle sizes.

[0060] This invention does not simply treat the bonding between aggregates as a fixed form. Instead, based on the volume relationship, equivalent sphere relationship, and volume conservation relationship between cement paste and aggregates, it first calculates the geometric parameters of the cement bridge, and then intelligently determines whether the cement bridge is cylindrical or frustum-shaped according to the relative size of the cross-sectional radius and the aggregate radius. This approach can more accurately reflect the asymmetric bonding state when aggregates of different particle sizes are bonded, avoiding systematic errors introduced by uniformly adopting a single geometric assumption, and making the description of solid boundaries more precise.

[0061] Step S400: Geometric scaling correction, used to perform geometric scaling correction on the double-shell medium and the virtual cement bridge to compensate for the inherent gaps between solid and fluid particles in the Smooth Particle Hydrodynamics (SPH) method. The reason is that there are inherent gaps between solid and fluid particles in the SPH method. If the original aggregate / cement paste / cement bridge geometry model is used directly without correction, the pore size will be underestimated due to incomplete resolution of tiny pores, resulting in a lower simulation result for the permeability coefficient.

[0062] The specific correction method is as follows:

[0063] (1) Double-shell medium correction: Let the equivalent radius of the aggregate be R, the thickness of the surface cement slurry layer be δ, and the inherent gap between solid particles and fluid particles be ε. Then, the outer contour of the double-shell medium formed by the aggregate and its surface hardened cement slurry is corrected according to R, δ and ε. Under the premise of keeping the original position and overall geometry unchanged, the scaled double-shell medium is equivalently compensated for the porosity loss caused by the limited particle resolution, so as to obtain the scaled outer contour of the double-shell medium.

[0064] (2) Virtual cement bridge correction: For the virtual cement bridge, geometric correction is carried out according to the same idea. The equivalent radius is corrected according to the inherent gap ε to complete the corresponding geometric correction.

[0065] This invention creatively recognizes the problem of underestimated pore size caused by the inherent gaps between solid and fluid particles in the SPH method. Specifically, before importing the model into the SPH model, geometric scaling corrections are applied to both the double-shell medium composed of aggregate and surface-hardened cement slurry, as well as the virtual cement bridge. This strategy effectively compensates for the influence of finite particle resolution on pore characterization and overcomes the defect of underestimating the calculated permeability coefficient due to directly using the original geometric model, thereby significantly improving the reliability of the numerical simulation results for the permeability coefficient.

[0066] Step S500: Smooth particle hydrodynamic seepage simulation, used to simulate the flow behavior of fluid in the pores of the sample based on the geometrically scaled solid phase geometric model. The specific steps are as follows:

[0067] Step S501: Constructing a seepage model: The aggregate, surface-hardened cement slurry, and virtual cement bridge are considered as solid phases. The fluid is discretized into a series of SPH particles, and the smoothed particle fluid dynamics method is used to simulate the flow behavior of the fluid in the pores of the CRPB material. Regarding boundary condition settings, this embodiment preferably sets an inflow end, an outflow end, and impermeable boundaries. The inflow end and outflow end can be set as periodic boundaries to achieve continuous seepage circulation. At the initial stage of the simulation, a cylindrical fluid column with a preset height is placed at the top of the model to provide stable head conditions.

[0068] Step S502, Numerical Parameter Setting: For numerical parameter setting, the Wendland kernel function is preferably used to solve the SPH. More preferably, the particle spacing can be set to 1.0 × 10⁻⁶. -4 m, the smoothing length is taken as twice the interparticle distance, the fluid viscosity is taken as 0.001 Pa·s, and the calculation time step is taken as 1.0 × 10⁻⁶. -5 s, the acceleration due to gravity is taken as 9.81 m / s².

[0069] Step S600: Calculate the permeability coefficient, used to calculate the material's permeability coefficient based on the fluid flow rate under steady-state seepage conditions. After the seepage simulation begins, the fluid gradually establishes a steady flow process within the sample pores. As time progresses, when the inflow and outflow rates tend to stabilize, and the fluid distribution inside the sample no longer changes significantly, the seepage is considered to have reached a steady state. Subsequently, the steady-state flow rate of the fluid exiting the sample under steady-state seepage conditions is monitored, and the material's permeability coefficient is calculated based on the constant head method.

[0070] This invention constructs a complete virtual testing platform by organically combining DEM compaction, geometric modeling of cement bridges, and SPH seepage simulation. This platform enables numerical evaluation of the permeability performance of CRPB materials without requiring extensive physical testing for every material mix and compaction condition. This significantly reduces the workload of repetitive laboratory tests, shortens the evaluation cycle, and lowers testing costs, making it particularly suitable for rapid screening during material design and parameter comparison stages.

[0071] Step S700: Method Validation. To verify the effectiveness of the method of this invention, the permeability coefficient can be compared with the results of laboratory constant head permeability tests. CRPB samples with different cement contents and different pressures can be designed, and laboratory constant head permeability tests and DEM-SPH numerical simulations can be carried out respectively, comparing the permeability coefficients obtained from the two methods. For example, the model is validated using combined working conditions with cement contents of 5%, 10%, and 20% and pressures of 100 kN, 150 kN, and 200 kN. The results show that, within a certain range, the numerical simulation results obtained by this method have good consistency with the laboratory test results. In particular, when the cement content is below 20%, the model generally has good predictive ability; however, when the cement content increases to 20%, the error of some samples increases significantly, indicating that under high cement content, the error caused by the geometric simplification of the slurry and cement bridge will be enhanced.

[0072] The modeling approach established in this invention does not rely on a single aggregate source or a single mix proportion system. It can be adapted to assess the seepage performance of other permeable road base courses or similar porous engineering materials by adjusting aggregate parameters, cement paste parameters, geometric model parameters, and boundary conditions. Furthermore, comparison with laboratory test results ensures the accuracy of the model's predictions, making it a reliable, physics-driven analytical tool. Its core advantage lies in unifying particle crushing, slurry bridging, and seepage calculation within a single technical framework through a physics-driven approach, thus exhibiting good method transferability.

[0073] Example 2

[0074] like Figure 5 As shown, the present invention also provides a permeability assessment system for cement-stabilized recycled aggregate permeable base courses, including...

[0075] The Discrete Element Virtual Sample Preparation Module is used to construct a discrete element simulation environment, generate virtual aggregate particles with preset particle size distribution and real morphology, apply gravity settling, and introduce a particle crushing model and a double-shell medium contact model during static compaction to simulate the crushing behavior of aggregate particles and the contact, compression, separation and bridging effects of cement paste on the aggregate surface. After parameter calibration, it is compacted to a stable state to obtain the compacted virtual sample.

[0076] The double-shell medium geometric model construction module is connected to the discrete element virtual sample preparation module. It is used to determine the average cement slurry layer thickness on the aggregate surface based on the compacted virtual sample and the volume relationship between cement slurry and aggregate, and to construct a double-shell medium geometric model composed of aggregate and its surface cement slurry.

[0077] The virtual cement bridge geometric model construction module is connected to the double-shell medium geometric model construction module. It is used to construct a virtual cement bridge geometric model between aggregates based on the double-shell medium geometric model, using an equivalent sphere with the same volume as the actual aggregate to replace the actual aggregate, determining the cement slurry contact between aggregates, and constructing the virtual cement bridge geometric model between aggregates based on the volume conservation relationship and the geometric relationship of the equivalent sphere.

[0078] The geometric scaling correction module, connected to the virtual cement bridge geometric model construction module, is used to perform geometric scaling correction on the double-shell medium geometric model and the virtual cement bridge geometric model, taking into account the inherent gap between solid particles and fluid particles in the smooth particle hydrodynamics method, to obtain the corrected solid phase geometric model.

[0079] The smooth particle fluid dynamics seepage simulation module, connected to the geometric scaling correction module, is used to import the corrected solid phase geometric model into the smooth particle fluid dynamics seepage model. Aggregate, surface-hardened cement slurry, and virtual cement bridge are regarded as solid phases, and the fluid is discretized into smooth particle fluid dynamics particles to simulate the flow behavior of the fluid in the pores and obtain the fluid flow rate under stable seepage conditions.

[0080] The permeability coefficient calculation module, connected to the smooth particle fluid dynamics seepage simulation module, is used to calculate the permeability coefficient of the cement-stabilized recycled aggregate permeable base course material based on the fluid flow rate under the stable seepage state.

[0081] The verification module, connected to the permeability coefficient calculation module, is used to compare the permeability coefficient with the results of laboratory constant head permeability tests to verify the accuracy of the system's prediction of the permeability of cement-stabilized recycled aggregate permeable base course materials under different cement contents and different pressure conditions.

[0082] The specific methods by which the modules in the above embodiments perform their operations have been described in detail in Embodiment 1, and will not be elaborated upon here.

[0083] Example 3

[0084] like Figure 6As shown, the present invention also provides an electronic device, including a processor 101, a communication interface 102, a memory 103, and a communication bus 104. The processor 101, communication interface 102, and memory 103 communicate with each other via the communication bus 104. The memory 103 is used to store computer programs. In this embodiment, when the processor 101 executes the program stored in the memory 103, it implements the steps of the method in Embodiment 1.

[0085] The electronic device provided in this embodiment of the invention has a similar implementation principle and technical effect to the above embodiments, and will not be described again here.

[0086] The aforementioned memory 103 may be an electronic memory such as flash memory, EEPROM (Electrically Erasable Programmable Read-Only Memory), EPROM, hard disk, or ROM. Memory 103 has storage space for program code used to perform any of the method steps described above. For example, the storage space for program code may include individual program codes for implementing the various steps in the methods described above. This program code can be read from or written to one or more computer program products. These computer program products include program code carriers such as hard disks, optical discs (CDs), memory cards, or floppy disks. Such computer program products are typically portable or fixed storage units. The storage unit may have storage segments or storage spaces arranged similarly to memory 103 in the aforementioned electronic device. The program code may be compressed, for example, in a suitable form. Typically, the storage unit includes programs for performing the method steps according to embodiments of the invention, i.e., code that can be read by a processor such as 101, which, when run by the electronic device, causes the electronic device to perform the various steps in the methods described above.

[0087] Example 4

[0088] like Figure 7 As shown, the present invention also provides a computer-readable storage medium. The computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the method described above.

[0089] The computer-readable storage medium may be included in the device / apparatus described in the above embodiments; or it may exist independently and not assembled into the device / apparatus. The computer-readable storage medium carries one or more programs that, when executed, implement the method according to the embodiments of the present invention.

[0090] According to embodiments of the present invention, the computer-readable storage medium may be a non-volatile computer-readable storage medium, such as including, but not limited to: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof. In the present invention, the computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0091] In this embodiment of the invention, the term "multiple" refers to two or more, unless otherwise explicitly defined. The terms "install," "connect," and "fix" should be interpreted broadly. For example, "connect" can mean a fixed connection, a detachable connection, or an integral connection. Those skilled in the art can understand the specific meaning of the above terms in this embodiment of the invention based on the specific circumstances.

[0092] In the description of the embodiments of the present invention, it should be understood that the terms "upper" and "lower" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or unit referred to must have a specific orientation or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0093] In the description of this specification, the terms "an embodiment," "a preferred embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0094] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. For those skilled in the art, the embodiments of the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of the present invention should be included within the protection scope of the embodiments of the present invention.

Claims

1. A method for evaluating the permeability of cement-stabilized recycled aggregate permeable base course, characterized in that, Includes the following steps: Step S100: Construct a discrete element simulation environment, generate virtual aggregate particles with preset particle size distribution and real morphology, apply gravity settling, and introduce a particle crushing model and a double-shell medium contact model during static compaction to simulate the crushing behavior of aggregate particles and the contact, compression, separation and bridging effects of cement paste on the aggregate surface. After parameter calibration, compact to a stable state to obtain a compacted virtual sample. Step S200: Based on the compacted virtual sample, determine the average thickness of the cement slurry layer on the surface of the aggregate according to the volume relationship between the cement slurry and the aggregate, and construct a double-shell medium geometric model composed of the aggregate and its surface cement slurry. Step S300: Based on the double-shell medium geometric model, an equivalent sphere with the same volume as the actual aggregate is used to replace the actual aggregate, the cement slurry contact between the aggregates is determined, and a virtual cement bridge geometric model between the aggregates is constructed according to the volume conservation relationship and the geometric relationship of the equivalent sphere. Step S400: Considering the inherent gap between solid particles and fluid particles in the smooth particle hydrodynamics method, perform geometric scaling correction on the double-shell medium geometric model and the virtual cement bridge geometric model to obtain the corrected solid phase geometric model; Step S500: Import the corrected solid phase geometric model into the smooth particle fluid dynamics seepage model, regard the aggregate, surface hardened cement slurry and virtual cement bridge as solid phases, discretize the fluid into smooth particle fluid dynamics particles, simulate the flow behavior of the fluid in the pores, and obtain the fluid flow rate under stable seepage state. Step S600: Calculate the permeability coefficient of the cement-stabilized recycled aggregate permeable base course material based on the fluid flow rate under the stable seepage state.

2. The method according to claim 1, characterized in that, Also includes: Step S700: Compare the permeability coefficient with the results of laboratory constant head permeability tests to verify the accuracy of the method in predicting the permeability of cement-stabilized recycled aggregate permeable base course materials under different cement contents and different compressive strengths.

3. The method according to claim 1, characterized in that, The simulated crushing behavior of aggregate particles includes: During the compaction process, the contact force on the surface of the aggregate particles is identified, and the Griffith tensile stress of the aggregate particles is calculated in real time based on the three-dimensional stress state of the particles. When the Griffith tensile stress exceeds the preset single particle strength, the aggregate particle is determined to have broken. The orientation of the fracture surface of the aggregate particles is related to the direction of the dominant contact force, and the same aggregate particle is allowed to break multiple times continuously during the continuous loading process.

4. The method according to claim 1, characterized in that, The double-shell dielectric contact model satisfies the following relationship: When fresh cement paste just comes into contact between the surfaces of two aggregates, the normal displacement between the two shell media is defined as zero, and an initial suction force is generated between the two shell media. As the two-shell media continue to approach each other, the suction force gradually decreases to zero, and if they continue to approach, a normal compressive force is generated. When the core of the double-shell medium, i.e. the aggregate body, is in contact, the interparticle force degenerates into a linear rolling resistance contact model. When the two bilayer media separate, the compressive normal force gradually decreases to zero, and then a suction force is generated between the fresh cement slurry and gradually changes until the cement slurry is completely separated and the suction force decreases to zero.

5. The method according to claim 1, characterized in that, The parameter calibration includes: The friction coefficient, rolling resistance friction coefficient, and stiffness ratio of different types of aggregates were calibrated through laboratory angle of repose tests. The strength and stiffness parameters of aggregate particles were determined by single-particle crushing tests. The initial suction parameters in the double-shell medium contact model were determined through multiple rounds of compaction simulation and parameter adjustment.

6. The method according to claim 1, characterized in that, The geometric model for constructing the virtual cement bridge between aggregates includes: The average thickness of the cement paste layer on the aggregate surface is calculated based on the ratio of cement paste volume to aggregate volume. An equivalent sphere with the same volume as the aggregate is used to replace the actual aggregate, and the equivalent sphere is made to correspond to the outline of the actual aggregate at the connection position of the cement bridge. When the distance between the surfaces of two aggregates is less than or equal to twice the average thickness of the cement paste layer, it is determined that the cement paste on the surfaces of the two aggregates is in contact and forms a virtual cement bridge after hardening. The volume, cross-sectional radius, and height parameters of the virtual cement bridge are calculated based on the volume conservation relationship, the equivalent sphere overlap relationship, and the geometric continuity relationship.

7. The method according to claim 1 or 6, characterized in that, When constructing the geometric model of the virtual cement bridge between aggregates, the determination of its geometric shape includes: When the cross-sectional radius of the cement bridge is not greater than the equivalent radius of the connecting aggregate, the cement bridge is constructed as a cylindrical cement bridge. When the cross-sectional radius of the cement bridge is greater than the equivalent radius of one of the connecting aggregates, the cement bridge is constructed as a frustum-shaped cement bridge, and the mid-section radius is taken as the reference radius obtained based on the cylindrical assumption. One end face radius is matched with the smaller equivalent radius aggregate, and the other end face radius is calculated based on geometric relationships.

8. The method according to claim 1, characterized in that, The geometric scaling correction includes: Let the equivalent radius of the aggregate be R, the thickness of the cement paste layer on the aggregate surface be δ, and the inherent gap between solid particles and fluid particles in the smooth particle hydrodynamic simulation be ε. Then, the outer contour of the double-shell medium formed by the aggregate and its surface hardened cement paste is corrected according to R, δ and ε to obtain the scaled outer contour of the double-shell medium. Alternatively, the equivalent radius of the virtual cement bridge can be corrected based on the inherent gap ε to complete the corresponding geometric correction.

9. The method according to claim 1, characterized in that, In step S500, the seepage model is configured with an inflow end, an outflow end, and an impermeable boundary. The inflow end and the outflow end are configured as periodic boundaries. In the initial state of seepage, a fluid column with a preset height is set at the top of the model to form a stable head condition.

10. A permeability assessment system for cement-stabilized recycled aggregate permeable base courses, characterized in that, include: The Discrete Element Virtual Sample Preparation Module is used to construct a discrete element simulation environment, generate virtual aggregate particles with preset particle size distribution and real morphology, apply gravity settling, and introduce a particle crushing model and a double-shell medium contact model during static compaction to simulate the crushing behavior of aggregate particles and the contact, compression, separation and bridging effects of cement paste on the aggregate surface. After parameter calibration, it is compacted to a stable state to obtain the compacted virtual sample. The double-shell medium geometric model construction module is used to determine the average thickness of the cement slurry layer on the surface of the aggregate based on the compacted virtual sample and the volume relationship between the cement slurry and the aggregate, and to construct a double-shell medium geometric model composed of the aggregate and its surface cement slurry. The virtual cement bridge geometric model construction module is used to construct a virtual cement bridge geometric model between aggregates based on the double-shell medium geometric model, using an equivalent sphere with the same volume as the actual aggregate to replace the actual aggregate, determining the cement slurry contact between aggregates, and constructing the virtual cement bridge geometric model between aggregates based on the volume conservation relationship and the geometric relationship of the equivalent sphere. The geometric scaling correction module is used to consider the inherent gap between solid particles and fluid particles in the smooth particle hydrodynamics method, and to perform geometric scaling correction on the double-shell medium geometric model and the virtual cement bridge geometric model to obtain the corrected solid phase geometric model. The smooth particle fluid dynamics seepage simulation module is used to import the corrected solid phase geometric model into the smooth particle fluid dynamics seepage model, regard aggregate, surface hardened cement paste and virtual cement bridge as solid phase, discretize the fluid into smooth particle fluid dynamics particles, simulate the flow behavior of fluid in pores, and obtain the fluid flow rate under stable seepage state. The permeability coefficient calculation module is used to calculate the permeability coefficient of cement-stabilized recycled aggregate permeable base course material based on the fluid flow rate under the stable seepage state.

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