A method for predicting dynamic response of root-soil complex impact penetration sounding

Abstract

The application provides a root-soil mixture impact penetration sounding power response prediction method, which comprises the following steps: firstly, a discrete element model of the root-soil mixture is constructed, and a root structure with high simulation characteristics is constructed in the discrete element model; and then, a contact model used for simulating the mechanical characteristics of the root-soil mixture is combined to realize fine simulation of the interaction between the root and the soil particles under the impact penetration dynamic load, so that the impact penetration sounding prediction of the root-soil mixture is finally realized. The application can dynamically simulate the contact, friction, peeling and tearing behaviors between the root and the soil particles at the mesoscopic level, and couple the behaviors to the overall model of the impact penetration sounding. Through the method, the penetration resistance mechanism of the root-soil mixed medium can be accurately captured, and the reference for the abnormal identification and correction of the penetration signal can be provided.

Description

Technical Field

[0001] This invention relates to the field of remote ground mechanics surveying technology, specifically to a method for predicting the dynamic response of impact penetration testing of root-soil mixtures. Background Technology

[0002] Existing ground-based remote mechanical survey methods primarily rely on space-based remote sensing and airborne geophysical exploration to acquire surface geological information. Space-based remote sensing excels in large-scale data collection, enabling relatively intuitive identification of surface vegetation distribution and geological structures. However, its non-contact measurement capabilities are limited in extracting internal soil mechanical parameters. Furthermore, its real-time performance and data accuracy are hampered by factors such as spatial resolution and weather conditions, making it difficult to meet the high-timeliness and high-precision requirements of post-disaster emergency response. Airborne geophysical exploration typically relies on airborne geological exploration equipment to classify geological structures and identify material properties. However, it suffers from insufficient vertical resolution, low precision in inversion results, and significant deficiencies in the specific measurement of soil mechanical characteristics. Since neither of these methods can directly and accurately obtain internal soil mechanical parameters (such as internal friction angle and cohesion), they are ill-suited to providing targeted mechanical information for disaster relief and subsequent engineering decisions in geological disaster scenarios.

[0003] To compensate for the shortcomings of non-contact remote sensing and geophysical exploration technologies in measuring soil mechanics parameters, the Institute of Mechanics, Chinese Academy of Sciences, proposed using impact penetration testing to rapidly and remotely determine the properties of underground soil layers, such as... Figure 1 As shown in the diagram. This approach is similar to the ancient Chinese proverb "testing the waters with a stone": a drone is used to deploy the penetrator to the target area, utilizing the gravitational potential energy of free fall to achieve impact penetration; during penetration, dynamic signals such as acceleration and resistance are recorded in real time, and then key mechanical parameters of the soil layer, such as cohesion and internal friction angle, are determined through data inversion. Compared to traditional static cone penetration and sampling tests, this method offers greater mobility and ease of operation in geologically hazardous areas, significantly improving measurement efficiency.

[0004] However, as research and application have deepened, it has been found that this technology still faces challenges in complex field environments: when there are a large number of plant root components in the target soil layer, the impact mechanics signals collected by the penetrator often fluctuate significantly, making it difficult for subsequent soil mechanics parameter inversion methods to handle these disturbance signals caused by "root-soil coupling".

[0005] The reason for this is that plant roots possess high toughness and tensile strength, and their random distribution and complex contact with soil particles significantly affect the dynamic response during impact penetration. Traditional analytical or semi-analytical models are mainly based on the assumption of homogeneous soil, which makes it difficult to cover the multiple coupled effects of transient shear, plastic deformation, and root fracture in the root-soil composite medium. Without accurate modeling and numerical simulation of this process, relying solely on single impact penetration acceleration or stress measurement data is likely to result in significant deviations when inverting soil mechanical parameters.

[0006] Therefore, there is an urgent need for a predictive tool for the impact penetration process of root-soil mixtures, in order to accurately characterize the mechanical contribution of plant roots during high-speed penetration and to separate soil parameters from root disturbance signals. Summary of the Invention

[0007] To address the technical problems existing in the background art, this invention proposes a method for predicting the dynamic response of root-soil mixture impact penetration testing. Its concept is reasonable and can dynamically simulate various behaviors between root and soil particles, such as contact, friction, peeling, and tearing, at the microscopic level. It can also couple these behaviors into the overall model of impact penetration testing, which can accurately capture the changes in the resistance mechanism of the root-soil mixture to the penetrometer and provide a reference for the anomaly identification and correction of the penetration signal.

[0008] To address the aforementioned technical problems, this invention provides a method for predicting the dynamic response of root-soil mixtures under impact penetration testing. First, a discrete element model of the root-soil mixture is constructed, and a root system structure with high simulation characteristics is built within the discrete element model. Then, a contact model is combined to simulate the mechanical properties of the root-soil mixture, achieving a precise simulation of the interaction between the root system and soil particles under impact penetration dynamic loads, ultimately enabling the prediction of the impact penetration test response of the root-soil mixture.

[0009] The method for predicting the dynamic response of a root-soil mixture during impact penetration testing, wherein the specific process of first constructing a discrete element model of the root-soil mixture and then constructing a root system structure with high simulation characteristics within the discrete element model is as follows:

[0010] (1.1) Establish the discrete element geometric model of the root-soil mixture

[0011] (1.1.1) Model construction of soil region

[0012] A particle refinement method is introduced into the discrete element computational domain (DEM) of the root-soil mixture, i.e., the simulation domain. The simulation domain refers to the three-dimensional DEM spatial region of the penetrometer impact range, containing all discrete soil particle elements. The diameter of the soil particles is scaled and partitioned according to their distance from the penetration center, thereby obtaining the soil particle domain Ω. s ;

[0013] (1.1.2) Extraction and model construction of root system geometry

[0014] First, for the type of vegetation to be tested, obtain its typical root morphology;

[0015] The root system is then appropriately idealized: it is considered to be composed of a series of spherical discrete micro-element units, and a corresponding parallel adhesive contact model is applied to the root-root contact interface to ensure that its overall mechanical strength matches the measured strength of the actual vegetation root system, thereby obtaining the root particle domain Ω. r ;

[0016] (1.1.3) Assembly of root-soil complex

[0017] After completing the model of the soil region, i.e., the soil particle domain Ω constructed in step (1.1.1), s The root granular domain Ω obtained in step (1.1.2) is compared with the idealized root system model. r After construction, the two are merged into the same three-dimensional discrete element numerical domain Ω:

[0018] Ω=Ω s ∪Ω r ;

[0019] In the soil sample initialization stage, the root-soil system is brought to a relatively stable force balance state through random deposition or compaction, which serves as the initial configuration for subsequent impact penetration simulation.

[0020] (1.2) Establishing the penetrator model

[0021] Referring to the actual shape of the penetrometer, it is treated as a rigid body in the discrete element geometric model of the root-soil mixture, and the corresponding volume density and dimensions are set; the Coulomb friction-slip relationship is used between the penetrometer and the soil contact surface:

[0022]

[0023] Among them, F n For normal contact force, F t The frictional resistance is tangential, and μ is the equivalent friction coefficient between the penetrometer and the soil particles.

[0024] When the tangential friction F t Reaching the critical value μF n After that, relative slip is triggered and dynamic friction is entered; by implementing this friction-slip criterion in the DEM contact pair, the shear friction process between the actual probe and the root-soil mixture particles can be realistically reproduced.

[0025] The method for predicting the dynamic response of root-soil mixture impact penetration testing, wherein the specific process of step (1.1.1) is as follows:

[0026] Domain partitioning: Using the penetration point as the axis, the simulation domain is divided into N concentric ring regions Ω1, Ω2, ..., Ω N ;

[0027] Scaling factor setting: Assign a granular scaling factor α to each subdomain. i (i = 1:N), and keep 1 < α1 < α2 < ... < α N ,

[0028] Particle size scaling: for reference particle size d ref Execute d i =α i d ref i = 1:N;

[0029] Numerical filling and gravity pre-compaction: A random deposition-compaction cycle was used to fill each subdomain with particles of different sizes; then a gravity field was applied iteratively until the contact force converged, and an initial static equilibrium state consistent with the measured porosity was obtained.

[0030] The method for predicting the dynamic response of the root-soil mixture impact penetration test includes the following steps: The parallel bonded contact model in step (1.1.2) is applied as follows: The contact interface between the two particles is regarded as a thin layer of adhesive material that can simultaneously transmit normal force, tangential force, bending moment and torque; the bond stiffness in the linear elastic stage consists of normal stiffness and tangential stiffness; when the normal stress or shear stress at the contact interface between the two particles exceeds the strength threshold, the bond breaks instantaneously, allowing the root particles to slip or rotate relative to each other, thereby simulating the tensile breakage, bending and shear instability of the root fibers.

[0031] The method for predicting the dynamic response of the root-soil mixture during impact penetration testing includes the following contact models for simulating the mechanical properties of the root-soil mixture: a linear rolling resistance model for soil-soil contact, a linear contact bonding model for root-soil contact, and a linear parallel bonding model for root-root contact.

[0032] By combining the aforementioned linear rolling resistance model, linear contact bonding model, and linear parallel bonding model, the following can be achieved in a discrete element environment: ① rolling, shearing, and bonding failure between soil particles; ② the subtle processes of root-soil interlocking, pulling, and peeling; ③ the local fracture or deformation of the root itself under penetration impact force.

[0033] The method for predicting the dynamic response of the root-soil mixture impact penetration test includes: the linear model of rolling resistance in soil-soil contact is based on the traditional linear contact model, with the addition of rolling resistance parameters between particles to simulate the energy dissipation of sand or similar granular soils during mutual rolling and shearing; when considering a certain degree of bonding effect, a weaker bonding force can be applied between particles.

[0034] The linear contact bonding model can simulate the bonding and failure between roots and soil during tensile and shear processes; if the tensile or shear force exceeds the bonding strength, root-soil debonding occurs.

[0035] The linear parallel bonding model is used to simulate the tensile, bending and shear strength of the root itself, and can provide the combined force of axial tension and bending moment, which approximately reflects the bendability and strength of real herbaceous root systems.

[0036] The method for predicting the dynamic response of root-soil mixtures under impact penetration testing, wherein the specific process for achieving a detailed simulation of the interaction between roots and soil particles under impact penetration dynamic load is as follows:

[0037] (3.1) Initial gravitational equilibrium and compaction

[0038] To ensure that the initial state of the simulation conforms to the natural gravity conditions, a downward gravitational acceleration vector g needs to be applied to all root particles and soil particles contained in the discrete element computational domain Ω. After the gravity loading, the root-soil particle system automatically adjusts its position and contact force through explicit dynamic relaxation iteration, so that the contact force network and particle displacement in the computational domain tend to stabilize, that is, the initial stress field distribution is considered to be approximately the same as the actual situation.

[0039] (3.2) Loading Penetrator

[0040] The initial position and initial velocity of the penetrometer are set at the top of the discrete element model of the root-soil mixture. After the simulation starts, the penetrometer accelerates down under the combined action of gravity and inertial force and gradually penetrates the root-soil mixture.

[0041] (3.3) Record the dynamic response

[0042] During the penetration of the root-soil mixture, the resistance, penetration depth, and acceleration curves experienced by the penetrometer are recorded in real time using the DEM solver; at the same time, the motion state of soil particles and roots, as well as the number and location of failure contacts, are tracked in the discrete element model of the root-soil mixture.

[0043] (3.4) Data post-processing and parameter inversion

[0044] Sensitivity analysis was performed on soil density, internal friction angle, cohesion, and root strength parameters to provide support for the rapid identification of the mechanical characteristics of the root-soil system.

[0045] The method for predicting the dynamic response of root-soil mixture impact penetration testing, wherein the sensitivity analysis process in step (3.4) is as follows:

[0046] Using the dynamic measured curves of the penetration process, the key constitutive parameter vector θ=[E] of the root-soil system is determined. * μ* κ * Sensitivity assessment is performed using F0], where E * For effective modulus, μ * κ is the coefficient of friction between particles. * The ratio of the normal to the tangential stiffness between particles is given by F0, where F0 is the attractive force between particles.

[0047] Apply a ±10% normalized perturbation to the obtained θ, and calculate the relative sensitivity coefficient of each parameter using the Morris local increment method:

[0048]

[0049] Where R is the peak resistance or energy dissipation index; the sensitivity ranking results can be used to determine the priority of subsequent experiments and model calibration, thereby providing a quantitative basis for the interpretation of penetration signal anomalies and parameter correction.

[0050] By adopting the above technical solution, the present invention has the following beneficial effects:

[0051] The present invention presents a well-conceived method for predicting the dynamic response of root-soil mixtures during impact penetration testing. It dynamically simulates various behaviors between root and soil particles, such as contact, friction, peeling, and tearing, at the microscopic level and couples these simulations into the overall impact penetration test model. This prediction method can accurately capture the changes in the resistance mechanism of the root-soil mixture to the penetrometer and provides a reference for the anomaly identification and correction of penetration signals. Therefore, this invention has significant technical value and broad prospects for application in disaster relief surveys, mountain slope stability assessments, and other scenarios requiring high-timeliness and high-precision ground mechanical data.

[0052] This invention provides more accurate capture of transient mechanical fluctuations caused by root tearing, compression, or peeling, thereby effectively reducing errors in judging soil mechanical characteristics.

[0053] This invention employs a root-soil hybrid discrete element model, which can accurately locate the spatiotemporal position of root damage, reducing the difficulty in determining the source of sudden changes in mechanical signals.

[0054] This invention enables numerous virtual experiments to be conducted on a computer through numerical simulation based on the discrete element method, reducing the number of experiments and costs associated with field exploration. Furthermore, by simulating different root-soil mixture configurations, the mechanical properties under various conditions can be quickly obtained, providing guidance for field exploration.

[0055] This invention is not only applicable to herbaceous root systems, but can also be used to simplify and model tree roots or soil-rock mixtures, making it widely applicable and providing technical support for various disaster environments or engineering scenarios. Attached Figure Description

[0056] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0057] Figure 1 This is a schematic diagram of the construction of the impact penetration test model for rootless soil involved in the root-soil mixture impact penetration dynamic response prediction method of the present invention.

[0058] Figure 2 This is a schematic diagram illustrating the extraction and simplification of root geometry involved in the root-soil mixture impact penetration dynamic response prediction method of the present invention.

[0059] Figure 3 This is a schematic diagram illustrating the selection of the contact model involved in the root-soil mixture impact penetration dynamic response prediction method of the present invention.

[0060] Figure 4 This is a diagram illustrating the effect of impact penetration testing of a root-soil mixture, which is part of the method for predicting the dynamic response of impact penetration testing of a root-soil mixture in this invention.

[0061] Figure 5 This is a diagram illustrating the existing impact penetration test site. Detailed Implementation

[0062] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0063] The present invention will be further explained below with reference to specific embodiments.

[0064] This embodiment provides a method for predicting the dynamic response of root-soil mixtures under impact penetration testing. By constructing a root system structure with high simulation characteristics in a discrete element model and combining various contact models such as rolling resistance, linear bonding, and parallel bonding, it achieves a fine simulation of the interaction between the root system and soil particles under impact penetration dynamic load, thereby realizing the prediction of impact penetration testing of root-soil mixtures.

[0065] S100, Construction of Discrete Element Model

[0066] S110. Establish the discrete element geometric model of the root-soil mixture.

[0067] S111, Model Construction of Soil Region

[0068] To balance computational efficiency and simulation accuracy, this invention employs a particle refinement method to construct the discrete element method model. This method increases the particle size by applying different scaling factors within the simulation domain, ensuring both high computational accuracy and effectively controlling the number of computational particles within a reasonable range. For example... Figure 1 As shown, the simulation domain is divided into multiple concentric regions, and the particle size is scaled according to the soil particle size distribution. For example, a scaling factor of 6 is used at the center of the soil trough to ensure sufficient contact between the particles and the penetrometer. As the particles move away from the center, the scaling factor gradually increases, reaching 30 at the outer boundary. To prevent small particles from migrating to areas with larger particles and to ensure the rationality of the simulation, the scaling factor ratio between adjacent regions is kept below 1.5.

[0069] To significantly reduce computational complexity while maintaining accuracy, this invention introduces a particle refinement method within the discrete element computational domain (hereinafter referred to as the "simulation domain") of the root-soil mixture. The simulation domain refers to the three-dimensional DEM spatial region of the penetrometer's impact range, containing all discrete soil particle elements. The core of the particle refinement method is to partition and scale the soil particle diameter according to its distance from the penetration center, thereby obtaining the soil particle domain Ω. s The specific process is as follows:

[0070] Domain partitioning: Using the penetration point as the axis, the simulation domain is divided into N concentric ring regions Ω1, Ω2, ..., Ω N ;

[0071] Scaling factor setting: Assign a granular scaling factor α to each subdomain. i (i = 1:N), and keep 1 < α1 < α2 < ... < α N ,

[0072] Particle size scaling: for reference particle size d ref (Taken from measured particle size distribution of soil) Execute d i =α i d ref i = 1:N;

[0073] Numerical filling and gravity pre-compaction: A random deposition-compaction cycle was used to fill each subdomain with particles of different sizes; then a gravity field was applied iteratively until the contact force converged, and an initial static equilibrium state consistent with the measured porosity was obtained.

[0074] S112. Extraction and Model Construction of Root System Geometry

[0075] a) Obtain the typical root morphology for the vegetation type to be tested;

[0076] b) Appropriately idealize the root system: Treat the root system as a series of spherical discrete micro-element units, and apply a corresponding parallel adhesive contact model at the root-root interface to ensure that its overall mechanical strength matches the measured strength of the actual vegetation root system, thereby obtaining the root particle domain Ω. r . Figure 2 Different forms of discrete element root system models are illustrated.

[0077] The above-mentioned parallel bond contact model application process is as follows:

[0078] The contact interface between the two particles is regarded as a thin layer of adhesive material that can simultaneously transmit normal force, tangential force, bending moment and torque; the bonding stiffness in the linear elastic stage consists of normal stiffness and tangential stiffness; when the interface normal stress or shear stress exceeds the strength threshold, the bond breaks instantaneously, allowing the root particles to slip or rotate relative to each other, thereby simulating the tensile breakage, bending and shear instability of the root fibers.

[0079] S113, Assembly of root-soil complex

[0080] After completing the model of the soil region (the soil particle domain Ω constructed in step S111), s ) and the idealized root system model (root granular domain Ω obtained in step S112) r After constructing the first two, they are merged into the same three-dimensional discrete element numerical domain Ω:

[0081] Ω=Ω s ∪Ω r ;

[0082] In the soil sample initialization stage, the root-soil system is brought to a relatively stable force balance state through random deposition or compaction, which serves as the initial configuration for subsequent impact penetration simulation.

[0083] S120. Establish the penetrator model.

[0084] Referring to the actual shape of the penetrometer, it is treated as a rigid body in the discrete element geometric model of the root-soil mixture (see step S110), and the corresponding volume density and dimensions are set. The Coulomb friction-slip relationship is used between the penetrometer and the soil contact surface to simulate the friction between the actual probe and soil particles, such as... Figure 1 As shown; the Coulomb friction-slip relationship is:

[0085]

[0086] Among them, F n For normal contact force, F t The frictional resistance is tangential, and μ is the equivalent friction coefficient between the penetrometer and the soil particles.

[0087] When the tangential friction F t Reaching the critical value μFn After that, relative slip is triggered and dynamic friction is entered; by implementing this friction-slip criterion in the DEM contact pair, the shear friction process between the actual probe and the root-soil mixture particles can be realistically reproduced.

[0088] S200, Selection of Contact Model

[0089] To accurately simulate the mechanical properties of root-soil mixtures, this invention employs a combination of various contact models (such as...). Figure 3 As shown), the core includes:

[0090] S210, Soil-to-soil contact: Linear rolling resistance model (RRLM)

[0091] Based on the traditional linear contact model, a rolling resistance parameter between particles is added to simulate the energy dissipation of sand or similar granular soils during mutual rolling and shearing. When a certain degree of bonding effect (such as the viscosity formed by soil moisture and fine particles) is taken into account, a weaker bonding force can be applied between particles.

[0092] S220, Root-Soil Contact: Linear Contact Bond Model (LCBM)

[0093] The root-soil interface is considered as a combination of cohesion and friction. Roots adhere to the surrounding soil particles; simultaneously, the root surface exhibits frictional resistance. LCBM (Low-Low Pressure Mesh) can simulate the bonding and failure between roots and soil during tensile and shear processes. Root-soil debonding occurs when the tensile or shear force exceeds the bond strength.

[0094] S230, Root-to-Root Contact: Linear Parallel Bonding Model (LPBM)

[0095] To simulate the tensile, bending, and shear strength of the root itself, this invention employs a parallel bonding model within the root system (root-to-root contact); this model can provide the combined force of axial tension and bending moment, approximately reflecting the bendability and strength of real herbaceous roots.

[0096] By combining the above contact models, the following can be reproduced well in the discrete element environment: rolling, shearing and bonding failure between soil particles; the subtle processes of root-soil interlocking, pulling and peeling; and the local fracture or deformation of the root itself under the penetrating impact force.

[0097] S300, Numerical Simulation Steps for Impact Penetration Process

[0098] After establishing the discrete element model and the contact model, the specific prediction process is as follows:

[0099] S310, Initial Gravitational Equilibrium and Compaction

[0100] To ensure the initial state of the simulation conforms to natural gravity conditions, a downward gravitational acceleration vector g needs to be applied to all root and soil particles contained within the discrete element computational domain Ω. After gravity loading, explicit dynamic relaxation iterations allow the root-soil particle system to automatically adjust its position and contact force, stabilizing the contact force network and particle displacements within the computational domain. This ensures that the initial stress field distribution approximates the actual situation.

[0101] S320, Loading Penetrator

[0102] The initial position and initial velocity of the penetrometer are set at the top of the discrete element model of the root-soil mixture. After the simulation starts, the penetrometer accelerates down under the combined action of gravity and inertial force and gradually penetrates the soil layer (root-soil mixture).

[0103] S330, Recording Dynamic Response

[0104] During the penetration of the root-soil mixture, the resistance, penetration depth, acceleration curves, etc. experienced by the penetrometer are recorded in real time using the DEM solver; at the same time, the motion state of soil particles and roots, as well as the number and location of failure contacts, are tracked in the discrete element model of the root-soil mixture.

[0105] S340, Data Post-processing and Parameter Inversion

[0106] Inversion or sensitivity analysis of parameters such as soil density, internal friction angle, cohesion, and root strength provides support for the rapid identification of the mechanical characteristics of the root-soil system.

[0107] The sensitivity analysis process is as follows:

[0108] Using the dynamic measured curves of the penetration process, the key constitutive parameter vectors of the root-soil system can be determined:

[0109] θ=[E * μ * κ * F0];

[0110] Sensitivity assessment was conducted. Among them, E * Effective modulus; μ * interparticle friction coefficient; κ * The ratio of normal to tangential stiffness between particles; F0 interparticle attraction.

[0111] Apply a ±10% normalized perturbation to the obtained θ, and calculate the relative sensitivity coefficient of each parameter using the Morris local increment method:

[0112]

[0113] Where R represents the peak drag or energy dissipation index. The sensitivity ranking results can be used to determine the priority of subsequent experiments and model calibration, thereby providing a quantitative basis for the interpretation of penetration signal anomalies and parameter correction.

[0114] Implementation results:

[0115] One hundred plant roots were embedded in the soil in a dispersed manner, and the impact penetration dynamics of the root-soil system were simulated using this invention. Figure 4 As shown, the results indicate that as the penetrometer gradually passes through the dense root zone, the tearing, peeling, and fracture processes of local roots increase, resulting in significant fluctuations in the penetration resistance curve. This additional interaction between the roots and soil particles leads to more frequent pulse peaks in the acceleration signal.

[0116] Therefore, this invention is more accurate in capturing transient mechanical fluctuations caused by root tearing, compression or stripping, thereby effectively reducing the error in judging the mechanical characteristics of soil.

[0117] This invention can dynamically simulate various behaviors such as contact, friction, peeling, and tearing between root and soil particles at the microscopic level, and couple them into the overall model of impact penetration testing. In this way, the resistance mechanism changes of the root-soil mixed medium on the penetrometer can be captured more accurately, and a reference can be provided for the anomaly identification and correction of the penetration signal.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for predicting the dynamic response of a root-soil mixture through impact penetration testing, characterized in that... First, a discrete element model of the root-soil mixture is constructed, and a root system structure with high simulation characteristics is built in the discrete element model. Then, a contact model is used to simulate the mechanical properties of the root-soil mixture to realize the fine simulation of the interaction between the root system and soil particles under impact penetration dynamic load, so as to finally realize the impact penetration test prediction of the root-soil mixture. The specific process of first constructing a discrete element model of the root-soil mixture and then constructing a root system structure with high simulation characteristics within the discrete element model is as follows: (1.1) Establish the discrete element geometric model of the root-soil mixture (1.1.1) Model construction of soil region A particle refinement method is introduced into the discrete element computational domain (DEM) of the root-soil mixture, i.e., the simulation domain. The simulation domain refers to the three-dimensional DEM spatial region of the penetrometer impact range, containing all discrete soil particle elements. Based on the distance from the penetration center, the diameter of the soil particles is partitioned and scaled to obtain the soil particle domain. ; (1.1.2) Extraction and model construction of root system geometry First, for the type of vegetation to be tested, obtain its typical root morphology; The root system is then appropriately idealized: it is considered to be composed of a series of spherical discrete micro-element units, and a corresponding parallel adhesive contact model is applied to the root-root contact interface to ensure that its overall mechanical strength matches the measured strength of the actual vegetation root system, thereby obtaining the root granular domain. ; (1.1.3) Assembly of root-soil complex After completing the model of the soil region, i.e., the soil particle domain obtained in step (1.1.1), The root granular domain obtained in step (1.1.2) Then, the two are merged into the same three-dimensional discrete element numerical domain. : ； In the soil sample initialization stage, the root-soil system is brought to a relatively stable force balance state through random deposition or compaction, which serves as the initial configuration for subsequent impact penetration simulation. (1.2) Establish the penetrator model Referring to the actual shape of the penetrometer, it is treated as a rigid body in the discrete element geometric model of the root-soil mixture, and the corresponding volume density and dimensions are set; the Coulomb friction-slip relationship is used between the penetrometer and the soil contact surface: ； Among them, F n For normal contact force, F t The frictional resistance is tangential, and μ is the equivalent friction coefficient between the penetrometer and the soil particles. When the tangential friction F t Reaching the critical value μF n After that, relative slip is triggered and dynamic friction is entered; by implementing this friction-slip criterion in the DEM contact pair, the shear friction process between the actual probe and the root-soil mixture particles can be realistically reproduced. The specific process of step (1.1.1) is as follows: Domain partitioning: Using the penetration point as the axis, the simulation domain is divided into N concentric ring regions. ; Scaling factor setting: Assign a granular scaling factor to each subdomain and keep ; Particle size scaling: for reference particle size implement ; Numerical filling and gravity pre-compaction: A random deposition-compaction cycle was used to fill each subdomain with particles of different sizes; then a gravity field was applied iteratively until the contact force converged, and an initial static equilibrium state consistent with the measured porosity was obtained.

2. The method for predicting the dynamic response of root-soil mixture impact penetration testing as described in claim 1, characterized in that, The application process of the parallel bonded contact model in step (1.1.2) is as follows: the contact interface between the two particles is regarded as a thin layer of adhesive material that can simultaneously transmit normal force, tangential force, bending moment and torque; the bond stiffness in the linear elastic stage consists of normal stiffness and tangential stiffness; when the normal stress or shear stress at the contact interface between the two particles exceeds the strength threshold, the bond breaks instantaneously, allowing the root particles to slip or rotate relative to each other, thereby simulating the breakage, bending and shear instability of the root fiber.

3. The method for predicting the dynamic response of root-soil mixture impact penetration testing as described in claim 1, characterized in that: The contact models used to simulate the mechanical properties of root-soil mixtures include a linear rolling resistance model for soil-soil contact, a linear contact bonding model for root-soil contact, and a linear parallel bonding model for root-root contact. By combining the aforementioned linear rolling resistance model, linear contact bonding model, and linear parallel bonding model, the following can be achieved in a discrete element environment: ① rolling, shearing, and bonding failure between soil particles; ② the subtle processes of root-soil interlocking, pulling, and peeling; ③ the local fracture or deformation of the root itself under penetration impact force.

4. The method for predicting the dynamic response of root-soil mixture impact penetration testing as described in claim 3, characterized in that: The linear model of rolling resistance in soil-soil contact is based on the traditional linear contact model, with the addition of rolling resistance parameters between particles to simulate the energy dissipation of sand or similar granular soils during mutual rolling and shearing. When a certain degree of bonding effect is taken into account, a weaker bonding force can be applied between particles. The linear contact bonding model can simulate the bonding and failure between roots and soil during tensile and shear processes; if the tensile or shear force exceeds the bonding strength, root-soil debonding occurs. The linear parallel bonding model is used to simulate the tensile, bending and shear strength of the root itself, and can provide the combined force of axial tension and bending moment, which approximately reflects the bendability and strength of real herbaceous root systems.

5. The method for predicting the dynamic response of root-soil mixture impact penetration testing as described in claim 1, characterized in that, The specific process for achieving a detailed simulation of the interaction between roots and soil particles under impact penetration dynamic load is as follows: (3.1) Initial gravitational equilibrium and compaction To ensure that the initial state of the simulation conforms to the natural gravity condition, it is necessary to perform the simulation in the discrete element computational domain. Within the system, a downward gravitational acceleration vector g is applied to all root particles and soil particles contained therein. After gravity loading, the root-soil particle system is automatically adjusted in position and contact force through explicit dynamic relaxation iteration, so that the contact force network and particle displacement in the computational domain tend to stabilize, that is, the initial stress field distribution is considered to be approximately the same as the actual situation; (3.2) Loading penetrator The initial position and initial velocity of the penetrometer are set at the top of the discrete element model of the root-soil mixture. After the simulation starts, the penetrometer accelerates down under the combined action of gravity and inertial force and gradually penetrates the root-soil mixture. (3.3) Record the dynamic response During the penetration of the root-soil mixture, the resistance, penetration depth, and acceleration curves experienced by the penetrometer are recorded in real time using the DEM solver; at the same time, the motion state of soil particles and roots, as well as the number and location of failure contacts, are tracked in the discrete element model of the root-soil mixture. (3.4) Data post-processing and parameter inversion Sensitivity analysis was performed on soil density, internal friction angle, cohesion, and root strength parameters to provide support for the rapid identification of the mechanical characteristics of the root-soil system.

6. The method for predicting the dynamic response of root-soil mixture impact penetration testing as described in claim 5, characterized in that, The sensitivity analysis process in step (3.4) is as follows: Using the dynamic measured curves of the penetration process, the key constitutive parameter vectors of the root-soil system are determined. Sensitivity assessment was conducted, in which... For effective modulus, The coefficient of friction between particles. The ratio of the normal to the tangential stiffness between particles. For interparticle attraction; On the income Apply a ±10% normalized perturbation and calculate the relative sensitivity coefficient for each parameter using the Morris local increment method: ； Where R is the peak resistance or energy dissipation index; the sensitivity ranking results can be used to determine the priority of subsequent experiments and model calibration, thereby providing a quantitative basis for the interpretation of penetration signal anomalies and parameter correction.

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