Root-soil mixture impact penetration sounding dynamic response prediction method

Abstract

The invention provides a root-soil mixture impact penetration sounding dynamic response prediction method. The method comprises the following steps: firstly, constructing a discrete element model of a root-soil mixture, and constructing a root system structure with high simulation characteristics in the discrete element model; and fine simulation of interaction of the root system and the soil particles under the impact penetration power load is realized in combination with a contact model for simulating mechanical properties of the root-soil mixture, so that impact penetration penetration prediction of the root-soil mixture is finally realized. According to the method, various behaviors such as contact, friction, stripping and tearing between root-soil particles can be dynamically simulated on a microcosmic level, the behaviors are coupled into an integral model of impact penetration sounding, and the penetration resistance mechanism of a root-soil mixed medium can be accurately captured through the method, so that the penetration resistance of the root-soil mixed medium is accurately determined. And a reference is provided for abnormal identification and correction of the penetration signal.

Description

Technical Field

[0001] The present invention relates to the technical field of remote ground mechanics surveying, and in particular to a method for predicting dynamic response of impact penetration testing of a root-soil mixture. Background Art

[0002] Existing remote ground mechanics survey methods mostly rely on space-based remote sensing and airborne geophysical prospecting to obtain surface geological information. Space-based remote sensing offers advantages in large-scale data collection and can more intuitively identify surface vegetation distribution and geological structures. However, its non-contact measurement method is limited in extracting mechanical parameters within soil layers. Furthermore, due to factors such as spatial resolution and weather conditions, its real-time performance and data accuracy are insufficient for applications requiring high timeliness and precision, such as post-disaster emergency response. Airborne geophysical prospecting, which typically relies on aircraft-borne geological exploration equipment, can delineate geological structures and identify material properties. However, it suffers from insufficient vertical resolution, low precision in inversion results, and significant limitations in measuring specific soil mechanical characteristics. Since neither of these methods can directly and accurately obtain internal soil mechanical parameters (such as the internal friction angle and cohesion), they struggle to provide targeted mechanical information for emergency response and subsequent engineering decisions in geological disaster scenarios.

[0003] In order to make up for the shortcomings of non-contact remote sensing and geophysical exploration technology in measuring soil mechanics parameters, the Institute of Mechanics of the Chinese Academy of Sciences proposed the use of impact penetration probing to quickly and remotely explore the characteristics of underground soil layers, such as Figure 1 This approach is similar to the story of "throwing a stone to test the water": a penetrometer is dropped into the target area via drone, and the gravitational potential energy of free fall is used to achieve impact penetration. During the penetration process, dynamic signals such as acceleration and resistance are recorded in real time, and key mechanical parameters such as the soil's cohesion and internal friction angle are determined through data inversion. Compared to traditional static penetration and sampling tests, this method offers greater maneuverability and ease of operation in geological disaster areas, significantly improving measurement efficiency.

[0004] However, with the deepening of research and application, it was 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 mechanical signals collected by the penetrometer often produce significant fluctuations, making it difficult for subsequent soil mechanics parameter inversion methods to process the disturbance signals caused by these "root-soil coupling effects".

[0005] The reason for this is that plant roots have high toughness and tensile strength. Their random distribution and complex contact with soil particles can significantly affect the dynamic response during impact penetration. Traditional analytical or semi-analytical models, primarily based on the assumption of homogeneous soil, struggle to account for the multiple coupling effects of transient shear, plastic deformation, and root fracture within 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 can lead to significant deviations in the inversion of soil mechanical parameters.

[0006] Therefore, there is an urgent need for a prediction tool for the impact penetration process of root-soil mixtures 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] In response to the technical problems existing in the above-mentioned background technology, the present invention proposes a method for predicting the dynamic response of root-soil mixture impact penetration sounding. The method has a reasonable conception and can dynamically simulate various behaviors such as contact, friction, peeling, and tearing between root-soil particles at the microscopic level, and couple it to the overall model of impact penetration sounding. It can more accurately capture the changes in the resistance mechanism of the root-soil mixture medium to the penetrometer, and provide a reference for the abnormal identification and correction of the penetration signal.

[0008] In order to solve the above technical problems, the present invention provides a method for predicting the dynamic response of impact penetration testing of a root-soil mixture, which first constructs a discrete element model of the root-soil mixture and constructs a root structure with high simulation characteristics in the discrete element model; then, combined with a contact model for simulating the mechanical properties of the root-soil mixture, a detailed simulation of the interaction between the roots and soil particles under the impact penetration dynamic load is achieved, so as to finally realize the impact penetration testing prediction of the root-soil mixture.

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

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

[0011] (1.1.1) Model construction of soil area

[0012] The particle refinement method is introduced in the discrete element calculation domain of the root-soil mixture, i.e., the simulation domain. The simulation domain refers to the three-dimensional DEM spatial area within the impact range of the penetrometer, which contains all discrete units of soil particles. The diameter of the soil particles is partitioned and scaled according to the distance from the penetration center, so as to obtain the soil particle domain Ω. s ;

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

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

[0015] Then, the root system is moderately idealized: the root system is regarded as consisting of a series of spherical micro-element discrete units, and the corresponding parallel bonding contact model is applied to the root-root contact interface to ensure that its overall mechanical strength matches the measured strength of the real vegetation root system, thereby obtaining the root system particle domain Ω. r ;

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

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

[0018] Ω=Ω s ∪Ω r ;

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

[0020] (1.2) Establishing the penetrometer model

[0021] With reference to the actual penetrometer shape, the root-soil mixture is considered as a rigid body in the discrete element geometric model, and the corresponding body density and size are set; the Coulomb friction-slip relationship is used between the penetrometer and the soil:

[0022]

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

[0024] When the tangential friction F t Reach critical value μF n After that, relative slip is triggered and the dynamic friction state 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 mixed particles can be truly reproduced.

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

[0026] Domain division: With 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 particle scaling factor α to each subdomain i (i=1:N), and maintain 1<α1<α2<…<α N ,

[0028] Particle size scaling: to the 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 is used to fill particles of different sizes into each subdomain. A gravity field is then applied iteratively until the contact force converges, obtaining an initial static equilibrium state consistent with the measured porosity.

[0030] The method for predicting the dynamic response of impact penetration probing of a root-soil mixture is described, wherein the parallel bond 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 a strength threshold, the bond breaks instantaneously, allowing the root particles to slip or rotate relative to each other, thereby simulating the breaking, bending, and shear instability of the root fibers.

[0031] The method for predicting the dynamic response of impact penetration testing of a root-soil mixture, wherein: the contact model for simulating the mechanical properties of the root-soil mixture includes a rolling resistance linear 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 rolling resistance linear model, the linear contact bond model, and the linear parallel bond model, the following can be realized in a discrete element environment: ① rolling, shear, and bond failure between soil particles; ② the subtle processes of root-soil interpenetration, pulling, and peeling; and ③ the local breakage or deformation of the root itself under the impact force of penetration.

[0033] The method for predicting the dynamic response of impact penetration testing of a root-soil mixture includes: a linear rolling resistance model for soil-soil contact, based on a traditional linear contact model, which adds an inter-particle rolling resistance parameter to simulate the energy dissipation of sand or similar granular soils during mutual rolling and shearing; and a relatively weak bonding force can be applied between particles when a certain degree of bonding effect is taken into account;

[0034] The linear contact bond model can simulate the bond and failure between roots and soil during tension and shear. If the tension or shear force exceeds the bond strength, root-soil peeling occurs.

[0035] The linear parallel bonding model is used to simulate the tension, bending and a certain degree of shear strength of the root itself, and can provide the combined force of axial tension and bending moment, approximately reflecting the bendability and strength of real herbaceous roots.

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

[0037] (3.1) Initial gravity balance and compaction

[0038] To ensure that the initial state of the simulation conforms to natural gravity conditions, a downward gravitational acceleration vector g is applied to all root particles and soil particles contained within the discrete element computational domain Ω. After gravity loading, explicit dynamic relaxation iterations are used to allow the root-soil particle system to automatically adjust its position and contact force, so that the contact force network and particle displacement within the computational domain tend to be stable. This means that the initial stress field distribution is considered to be similar to the actual situation.

[0039] (3.2) Loading the penetrometer

[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 downward under the combined action of gravity and inertia and gradually penetrates the root-soil mixture.

[0041] (3.3) Recording dynamic response

[0042] During the penetration process of the root-soil mixture, the resistance, penetration depth, and acceleration curve of the penetrometer are recorded in real time through the DEM solver. At the same time, the motion state of soil particles and roots, as well as the number and location of damaging 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 of soil density, internal friction angle, cohesion, and root strength parameters provides support for rapid identification of the mechanical characteristics of the root-soil system.

[0045] The root-soil mixture impact penetration test dynamic response prediction method, wherein the sensitivity analysis process in step (3.4) is:

[0046] With the help of the dynamic curve of the penetration process, the key constitutive parameter vector of the root-soil system θ=[E * μ* κ * F0] to perform sensitivity evaluation, where E * is the effective modulus, μ * is the inter-particle friction coefficient, κ * is the ratio of normal to tangential stiffness between particles, F0 is the attraction between particles;

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

[0048]

[0049] Among them, R is the resistance peak or energy dissipation index; the sensitivity ranking results can be used to determine the priority of subsequent tests 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 method for predicting the dynamic response of the root-soil mixture impact penetration sounding of the present invention is rationally conceived and can dynamically simulate various behaviors such as contact, friction, peeling, and tearing between root-soil particles at the microscopic level, and couple them to the overall model of the impact penetration sounding. The prediction method of the present invention can more accurately capture the changes in the resistance mechanism of the root-soil mixture medium to the penetrometer, and provide a reference for the abnormal identification and correction of the penetration signal. It can be seen that the present invention has extremely important technical value and broad promotion prospects in disaster rescue surveys, mountain slope stability assessments, and other application scenarios that require high-efficiency and high-precision ground mechanical data.

[0052] The present invention can more accurately capture transient mechanical fluctuations caused by root tearing, squeezing or peeling, thereby effectively reducing the error in judging the mechanical characteristics of the soil.

[0053] The present invention adopts a root-soil hybrid discrete element model, which can accurately locate the temporal and spatial location of root damage, reducing the difficulty of judging the source of mechanical signal mutation.

[0054] This method uses numerical simulation based on the discrete element method to perform a large number of virtual experiments on a computer, reducing the number and cost of field exploration experiments. Furthermore, by simulating different root-soil mixture configurations, the mechanical properties under different conditions can be quickly determined, providing guidance for field exploration.

[0055] The present invention is not only applicable to herbaceous root systems, but can also be used to simplify and model tree roots or rock and soil inclusions. It has a wide range of applications and provides technical support for various disaster environments or engineering scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0057] Figure 1 A schematic diagram of the construction of an impact penetration test model for a rootless soil mass involved in the method for predicting the dynamic response of impact penetration test of a root-soil mixture according to the present invention;

[0058] Figure 2 Schematic diagram of extraction and simplification of root geometry involved in the method for predicting the dynamic response of impact penetration testing of a root-soil mixture according to the present invention;

[0059] Figure 3 Schematic diagram of the selection of contact models involved in the method for predicting the dynamic response of impact penetration testing of a root-soil mixture according to the present invention;

[0060] Figure 4 This is a diagram showing the effect of the impact penetration test of a root-soil mixture involved in the method for predicting the dynamic response of the impact penetration test of a root-soil mixture according to the present invention;

[0061] Figure 5 This is a diagram of the existing impact penetration test site. DETAILED DESCRIPTION

[0062] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall 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 impact penetration testing of a root-soil mixture. It constructs a root structure with high simulation characteristics in a discrete element model, combines multiple contact models such as rolling resistance, linear bonding and parallel bonding, and realizes a detailed simulation of the interaction between roots and soil particles under impact penetration dynamic loads, thereby realizing the prediction of impact penetration testing of root-soil mixtures.

[0065] S100, construction of discrete element model

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

[0067] S111. Model construction of soil area

[0068] In order to balance computational efficiency and simulation accuracy, the present invention adopts a particle refinement method to construct a discrete element method model. This method amplifies the particle size by applying different scaling factors within the simulation domain, which can ensure high computational accuracy while effectively controlling the number of calculated particles within a reasonable range. Figure 1 As shown in the figure, the simulation domain is divided into multiple concentric regions, and the particle size is scaled according to the soil particle size distribution. For example, at the center of the soil trough, a scaling factor of 6 is used 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 into the larger particle area and ensure the rationality of the simulation, the scaling factor ratio between adjacent regions is kept below 1.5.

[0069] To significantly reduce the computational effort while maintaining accuracy, the present 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 within the penetrometer's impact range, encompassing all discrete soil particle units. The core of the particle refinement method is to partition and scale the soil particle diameter according to the distance from the penetration center, thereby obtaining the soil particle domain Ω. s The specific process is as follows:

[0070] Domain division: With 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 particle scaling factor α to each subdomain i (i=1:N), and maintain 1<α1<α2<…<α N ,

[0072] Particle size scaling: to the reference particle size d ref (taken from the measured particle size distribution of soil) i =α i d ref ,i=1:N;

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

[0074] S112. Extraction and model construction of root geometry

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

[0076] b) Moderately idealize the root system: consider the root system as consisting of a series of spherical micro-units, and apply the corresponding parallel bonding contact model at the root-root contact interface to ensure that its overall mechanical strength matches the measured strength of the real vegetation root system, thereby obtaining the root system particle domain Ω r . Figure 2 The discrete element root system models of different forms are shown.

[0077] The above parallel bonded contact model application process is:

[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 bond stiffness in the linear elastic stage is composed of normal stiffness and tangential stiffness; when the interfacial 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 breaking, bending and shear instability of root fibers.

[0079] S113. Assembly of the root-soil complex

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

[0081] Ω=Ω s ∪Ω r ;

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

[0083] S120, build penetrometer model

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

[0085]

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

[0087] When the tangential friction F t Reach critical value μFn After that, relative slip is triggered and the dynamic friction state 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 mixed particles can be truly reproduced.

[0088] S200, selection of contact model

[0089] In order to accurately simulate the mechanical properties of the root-soil mixture, the present invention adopts a combination of multiple contact models (such as Figure 3 The core includes:

[0090] S210, Soil-Soil Contact: Rolling Resistance Linear Model (RRLM)

[0091] Based on the traditional linear contact model, the rolling resistance parameter between particles is added to simulate the energy dissipation of sand or similar soil particles during 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 to possess a combination of cohesive and frictional forces. Roots adhere to surrounding soil particles; at the same time, the root surface exhibits a certain degree of frictional resistance. LCBM simulates the bond and failure between roots and soil during tension and shear. If the tension or shear force exceeds the bond strength, root-soil debonding occurs.

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

[0095] To simulate the root's own tension, bending, and a certain degree of shear strength, the present invention uses a parallel bonding model within the root system (root-root contact); this model can provide the combined forces 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 better reproduced in a discrete element environment: rolling, shearing and bonding failure between soil particles; the subtle processes of root-soil interpenetration, pulling and peeling; and the local breakage or deformation of the root itself under the impact force of penetration.

[0097] S300, numerical simulation steps of impact penetration process

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

[0099] S310, initial gravity balance and compaction

[0100] To ensure that the initial state of the simulation conforms to natural gravity conditions, a downward gravitational acceleration vector g is applied to all root and soil particles 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 forces, stabilizing the contact force network and particle displacements within the computational domain. This allows the initial stress field distribution to approximate the actual situation.

[0101] S320, Loading Penetrometer

[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 inertia and gradually penetrates into the soil layer (root-soil mixture).

[0103] S330, record dynamic response

[0104] During the penetration process of the root-soil mixture, the resistance, penetration depth, acceleration curve, etc. encountered by the penetrometer are recorded in real time through the DEM solver; at the same time, the movement state of soil particles and roots in the discrete element model of the root-soil mixture, as well as the number and location of destructive contacts, are tracked.

[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 is performed to provide support for rapid identification of the mechanical characteristics of the root-soil system;

[0107] And the sensitivity analysis process is:

[0108] With the help of the measured dynamic curve of the penetration process, the key constitutive parameter vector of the root-soil system can be calculated:

[0109] θ=[E * μ * κ * F0];

[0110] Perform sensitivity evaluation. * Effective modulus; μ * Interparticle friction coefficient; κ * The ratio of normal to tangential stiffness between particles; F0 is the attraction between particles.

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

[0112]

[0113] where R is the peak resistance value or energy dissipation index. The sensitivity ranking results can be used to determine the priority of subsequent tests and model calibration, thus providing a quantitative basis for interpreting penetration signal anomalies and modifying parameters.

[0114] Implementation effect:

[0115] 100 plant roots are embedded in the soil area in a dispersed manner, and the impact penetration test dynamics evolution of the root-soil system is simulated by the present invention. Figure 4 As shown in the figure, the results show that when the penetrometer gradually passes through the root-dense area, the tearing, stripping and fracture processes of the local roots increase, resulting in significant fluctuations in the penetration resistance curve. This additional interaction between roots and soil particles will cause more frequent pulse peaks in the acceleration signal.

[0116] Therefore, the present invention can more accurately capture transient mechanical fluctuations caused by root tearing, squeezing or peeling, thereby effectively reducing the error in judging the mechanical characteristics of the soil.

[0117] The present invention can dynamically simulate various behaviors such as contact, friction, peeling, and tearing between root-soil particles at the microscopic level, and couple them to the overall model of impact penetration probing. Through this method, the changes in the resistance mechanism of the root-soil mixed medium to the penetrometer can be captured more accurately, and a reference can be provided for the abnormal 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, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 root-soil mixture impact penetration testing, characterized in that : First, 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; then, combined with a contact model used to simulate the mechanical properties of the root-soil mixture, a detailed simulation of the interaction between the roots and soil particles under the impact penetration dynamic load is achieved, so as to finally realize the impact penetration sounding prediction of the root-soil mixture.

2. The root-soil mixture impact penetration test dynamic response prediction method according to claim 1, characterized in that: 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 in the discrete element model is as follows: (1.1) Establishing a discrete element geometric model of the root-soil mixture (1.1.1) Model construction of soil area The particle refinement method is introduced in the discrete element calculation domain of the root-soil mixture, i.e., the simulation domain. The simulation domain refers to the three-dimensional DEM spatial area within the impact range of the penetrometer, which contains all discrete units of soil particles. The diameter of the soil particles is partitioned and scaled according to the distance from the penetration center, so as to obtain the soil particle domain Ω. s ; (1.1.2) Extraction and model construction of root geometry First, obtain the typical root morphology of the vegetation type to be tested; Then, the root system is moderately idealized: the root system is regarded as consisting of a series of spherical micro-element discrete units, and the corresponding parallel bonding contact model is applied to the root-root contact interface to ensure that its overall mechanical strength matches the measured strength of the real vegetation root system, thereby obtaining the root system particle domain Ω. r ; (1.1.3) Assembly of the root-soil complex After completing the soil area model, i.e. the soil particle domain Ω constructed in step (1.1.1), s The idealized root model, that is, the root particle domain Ω obtained in step (1.1.2) r After the construction of , the two are merged into the same three-dimensional discrete element numerical domain Ω: Oh=Oh s ∪Ω r ; In the initialization stage of soil samples, random deposition or compaction is used to make the root-soil system reach a relatively stable force balance state, which serves as the initial configuration for subsequent impact penetration simulation. (1.2) Establishing the penetrometer model With reference to the actual penetrometer shape, the root-soil mixture is considered as a rigid body in the discrete element geometric model, and the corresponding body density and size are set; the Coulomb friction-slip relationship is used between the penetrometer and the soil: Among them, F n is the normal contact force, F t is the tangential friction resistance, μ is the equivalent friction coefficient between the penetrometer and soil particles; When the tangential friction F t Reach critical value μF n After that, relative slip is triggered and the dynamic friction state 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 mixed particles can be truly reproduced.

3. The root-soil mixture impact penetration test dynamic response prediction method according to claim 2, characterized in that: The specific process of the step (1.1.1) is as follows: Domain division: With the penetration point as the axis, the simulation domain is divided into N concentric ring regions Ω1, Ω2,…,Ω N ; Scaling factor setting: assign a particle scaling factor α to each subdomain i (i=1:N), and maintain 1<α1<α2<…<α N , Particle size scaling: to the reference particle size d ref Execute d i =α i d ref ,i=1:N; Numerical filling and gravity pre-compaction: A random deposition-compaction cycle is used to fill particles of different sizes into each subdomain. A gravity field is then applied iteratively until the contact force converges, obtaining an initial static equilibrium state consistent with the measured porosity.

4. The root-soil mixture impact penetration test dynamic response prediction method according to claim 2, characterized in that: The parallel bonding 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 bonding 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 breaking, bending, and shear instability of the root fibers.

5. The method for predicting the dynamic response of a root-soil mixture impact penetration test according to claim 1, characterized in that: The contact model for simulating the mechanical properties of the root-soil mixture includes a rolling resistance linear model for soil-soil contact, a linear contact bond model for root-soil contact, and a linear parallel bond model for root-root contact; By combining the rolling resistance linear model, the linear contact bond model, and the linear parallel bond model, the following can be realized in a discrete element environment: ① rolling, shear, and bond failure between soil particles; ② the subtle processes of root-soil interpenetration, pulling, and peeling; and ③ the local breakage or deformation of the root itself under the impact force of penetration.

6. The method for predicting the dynamic response of a root-soil mixture impact penetration test according to claim 5, characterized in that: The soil-soil contact rolling resistance linear model is based on the traditional linear contact model, adding the rolling resistance parameter 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 bond model can simulate the bond and failure between roots and soil during tension and shear. If the tension or shear force exceeds the bond strength, root-soil peeling occurs. The linear parallel bonding model is used to simulate the tension, bending and a certain degree of shear strength of the root itself, and can provide the combined force of axial tension and bending moment, approximately reflecting the bendability and strength of real herbaceous roots.

7. The root-soil mixture impact penetration test dynamic response prediction method according to claim 1, characterized in that: The specific process of achieving a detailed simulation of the interaction between roots and soil particles under impact penetration dynamic load is as follows: (3.1) Initial gravity balance and compaction To ensure that the initial state of the simulation conforms to natural gravity conditions, a downward gravitational acceleration vector g is applied to all root particles and soil particles contained within the discrete element computational domain Ω. After gravity loading, explicit dynamic relaxation iterations are used to allow the root-soil particle system to automatically adjust its position and contact force, so that the contact force network and particle displacement within the computational domain tend to be stable. This means that the initial stress field distribution is considered to be similar to the actual situation. (3.2) Loading the penetrometer 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 downward under the combined action of gravity and inertia and gradually penetrates the root-soil mixture. (3.3) Recording dynamic response During the penetration process of the root-soil mixture, the resistance, penetration depth, and acceleration curve of the penetrometer are recorded in real time through the DEM solver. At the same time, the motion state of soil particles and roots, as well as the number and location of damaging contacts, are tracked in the discrete element model of the root-soil mixture. (3.4) Data post-processing and parameter inversion Sensitivity analysis of soil density, internal friction angle, cohesion, and root strength parameters provides support for rapid identification of the mechanical characteristics of the root-soil system.

8. The method for predicting the dynamic response of root-soil mixture impact penetration testing according to claim 7, characterized in that: The sensitivity analysis process in step (3.4) is as follows: With the help of the dynamic curve of the penetration process, the key constitutive parameter vector of the root-soil system θ=[E * μ * κ * F0] to perform sensitivity evaluation, where E * is the effective modulus, μ * is the inter-particle friction coefficient, κ * is the ratio of normal to tangential stiffness between particles, F0 is the attraction between particles; Apply ±10% normalized perturbation to the obtained θ, and use Morris local increment method to calculate the relative sensitivity coefficient of each parameter: Among them, R is the resistance peak or energy dissipation index; the sensitivity ranking results can be used to determine the priority of subsequent tests and model calibration, thereby providing a quantitative basis for the interpretation of penetration signal anomalies and parameter correction.

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