Finite difference analysis-based reinforced soil structure design method considering anisotropy of rib material

Abstract

The invention discloses a reinforced soil structure design method based on finite difference analysis and considering anisotropy of a rib material, which comprises the following steps: establishing a roadbed reinforced soil corner slope three-dimensional model, simulating a roadbed layer by adopting a Duncan-Zhang nonlinear constitutive equation, simulating a foundation layer by adopting an elastic constitutive equation, and simulating a geogrid by adopting a Cable structure unit. A Geogrid structural unit is adopted to simulate the geotechnical cloth; on the basis of a verified model, different mechanical parameters are given to transverse and longitudinal ribs of the bidirectional geogrid to realize self-mechanical behavior anisotropy, the arrangement angle of a Cable unit and the center line of a reinforced soil structure is changed to realize the mechanical behavior anisotropy of a rib-soil interface, and meanwhile, other single or multiple variables can be adjusted, so that the mechanical behavior anisotropy of the rib-soil interface is realized. And testing the influence rule of the key factors on the mechanical properties of the reinforced soil structure. According to the method, the problem that the stress directions of the reinforced soil structure bars are inconsistent or uncertain under the complex geological condition can be solved, and more practical reinforced soil structure design parameters are effectively provided.

Description

Technical Field

[0001] The invention relates to the technical field of simulation design, and in particular to a reinforced soil structure design method based on finite difference analysis and considering the anisotropy of reinforcement materials. Background Art

[0003] Reinforced soil is an effective way to improve the bearing capacity and stability of soil. The core of the reinforcement is that the friction and interlocking between the soil and the reinforcement make up for the tensile and shear resistance defects of the soil. Compared with traditional building materials, the carbon emissions associated with the production of geosynthetics and the construction of reinforced soil structures are significantly higher. The bidirectional geogrid has the characteristics of bearing tension in both the longitudinal and transverse directions, and is one of the most commonly used reinforcement materials in geogrid reinforced soil structures. However, in the actual engineering application of reinforced soil structures, special terrain and soft foundation problems in valleys are frequently encountered. The force direction of the reinforcement under complex terrain or geological conditions is no longer clear, and local bulging and instability of reinforced soil structures often occur.

[0004] At present, the bottleneck problems in the application of reinforced soil structures include: 1. The stress levels of geogrids in different loading directions are significantly different, and the stability verification method based on the directional strength of the reinforcement ribs in the current design method has major safety hazards; 2. The relative displacement of the reinforcement-soil interface may not develop along the main rib layout direction, and it is urgent to fully examine the impact of the angle difference between the load and the main rib layout direction on the working performance of the reinforced soil structure. In the past, Geogrid structural units were often used to simulate the reinforcement layer in the analysis of reinforced structures, but there are the following defects: 1. As a continuous sheet structure, it is necessary to reduce the thickness of the reinforcement layer to achieve the purpose of equivalent stiffness and tensile performance; 2. The Geogrid structural unit is a linear elastic material with no failure limit; 3. The Geogrid structural unit has the same tensile, stiffness and interface mechanical properties in two directions. These shortcomings make the Geogrid structural unit not in line with the actual situation when simulating geogrids, and the bidirectional geogrid with orthotropic anisotropy is even more difficult to simulate, especially the interface friction resistance along the longitudinal ribs, the resistance along the transverse ribs, and the interlocking effect between the mesh and the soil particles cannot be simulated by it. Therefore, it is necessary to develop a three-dimensional model that reflects the basic characteristics of bidirectional geogrids and can simulate the anisotropic mechanical behavior of the reinforcement-soil interface in actual engineering, so as to obtain more practical design parameters of bidirectional geogrids and reinforced soil structures and provide more refined guidance for the application of reinforced soil structures. Summary of the invention

[0005] In response to the above problems, the present invention provides a reinforced soil structure design method based on finite difference analysis taking into account the anisotropy of reinforcement materials, simulating a bidirectional geogrid that is more in line with actual working conditions, pre-determining the stress characteristics of safe and efficient geogrids under complex geological conditions, and adjusting their laying methods, to provide refined guidance for design and construction, and to improve the safety and durability of reinforced soil structures.

[0006] In order to achieve the above-mentioned purpose and the technical advantages of the present invention, the present invention provides the following technical solutions:

[0007] A design method for reinforced soil structure based on finite difference analysis considering the anisotropy of reinforcement materials, comprising:

[0008] Step S1, establishing a three-dimensional model of the reinforced soil corner slope of the roadbed, obtaining the physical and mechanical parameters of the roadbed, foundation, bidirectional geogrid and geotextile of the finite difference model through indoor triaxial tests, bidirectional geogrid and geotextile single rib tensile tests, and performing model calibration;

[0009] Step S2, the three-dimensional model includes a roadbed backfill layer and a base layer from top to bottom, a bidirectional geogrid is set at the roadbed structure, a geotextile is set at the roadbed slope, a Cable structure unit is used to simulate the geogrid, and a Geogrid structure unit is used to simulate the geotextile, the material properties of the three-dimensional model are defined, and the grid is divided to obtain a finite difference model;

[0010] Step S3, horizontal layered loading is performed on the roadbed of the three-dimensional model to simulate the horizontal layered filling in the construction, and the ground stress balance calculation is performed after the filling is completed; static load and dynamic load are applied above the top of the slope to simulate the traffic load in the actual working condition, and the deformation and stress simulation data of the reinforced soil structure at different stages are obtained, and compared with the indoor model test results to verify the reliability of the model;

[0011] Step S4, based on the verified model, different mechanical parameters are given to the transverse and longitudinal ribs of the bidirectional geogrid to realize the anisotropic simulation of its own mechanical behavior, and the arrangement angle of the Cable unit with the center line of the reinforced soil structure is changed to realize the anisotropic simulation of the mechanical behavior of the reinforcement-soil interface;

[0012] Step S5, after adjusting other single or multiple variables, return to step S3 to test the influence of the key factors of the geogrid longitudinal and transverse tensile stiffness ratio, slope rotation angle and inclination, filler and reinforcement material parameters, load type, and the superposition effect of the anisotropy of the geogrid itself and the reinforcement-soil interface characteristics on the mechanical properties of the reinforced soil structure;

[0013] The method of simulating geogrids by using Cable structural units includes: the Cable structural unit is a linear structural unit with two nodes, which is composed of structural nodes and structural members, each node has an axial translational degree of freedom, and the structural unit members bear tension or compression; the bidirectional geogrid at the overlap is divided into two groups according to the horizontal and longitudinal rib directions, and is divided into multiple single structural members according to the actual mesh size, and multiple members are connected in series at the nodes by rigid connection to simulate the real geogrid;

[0014] The use of Geogrid structural units to simulate geotextiles includes: the Geogrid structural unit is a flexible plane shell-type structural unit with three nodes, used to simulate geomembranes or geotextiles flexible geosynthetics;

[0015] The Cable structure unit and Geogrid structure unit use interface units to simulate the interaction between soil-geogrid and geotextile-soil. The shear strength parameters of the soil-geogrid and geotextile-soil contact surfaces are simulated by the interface strength reduction factor RF. The specific equation is as follows:

[0016]

[0017] Where:

[0018] δ i is the friction angle of the contact surface;

[0019] c i is the cohesion of the contact surface;

[0020] φ is the friction angle of geogrid or geotextile;

[0021] c is the cohesion of geogrid or geotextile.

[0022] Preferably, the constitutive model of the road base layer is simulated using the Duncan-Zhang nonlinear constitutive equation, and the constitutive model of the ground base layer is simulated using the linear elastic constitutive equation.

[0023] Preferably, the Duncan-Zhang nonlinear constitutive equation is described by the hyperbolic model EB mode, and its tangent deformation modulus E t and the volume deformation modulus B can be expressed as:

[0024]

[0025] Where:

[0026] R f is the destruction ratio;

[0027] σ1-σ3 is the deviation stress at failure;

[0028] σ1, σ3 are the maximum and minimum principal stresses respectively;

[0029] K e is the elastic modulus coefficient;

[0030] n is the elastic modulus index;

[0031] P a is the atmospheric pressure;

[0032] K b is the bulk modulus coefficient;

[0033] m is the bulk modulus index.

[0034] The required model parameters are obtained through indoor triaxial tests;

[0035] The failure criterion adopts the Mohr-Coulomb yield criterion, and the yield function is as follows:

[0036]

[0037] Where:

[0038] is the friction angle of soil;

[0039] c is the cohesion of soil.

[0040] Preferably, the anisotropy of the bidirectional geogrid includes its own anisotropy and the anisotropy of the mechanical behavior of the reinforcement-soil interface. The own anisotropy is achieved by changing the tensile strength ratio of the orthogonal transverse and longitudinal ribs of the grid, and the anisotropy of the mechanical behavior of the reinforcement-soil interface is achieved by adjusting the laying angle of the grid and the center line of the reinforced soil structure. The laying angles of the geogrid include at least five common working conditions: 0°, 22.5°, 45°, 67.5° and 90°.

[0041] Preferably, the Cable structural unit is used to replace the original Geogrid unit for simulating geogrid to realize the anisotropic simulation of bidirectional geogrid. The Cable unit is defined by geometric parameters, material property parameters and interface bonding characteristics. The geometric parameters are calibrated in combination with the actual parameters of the grid. The elastic modulus E of the geogrid is g Determined by the tensile stiffness J of the geogrid's transverse and longitudinal ribs at 2% strain, the essence of the interaction between the geogrid and the soil is bonding and friction. The system is described by a spring-slider in the axial direction of the node. The interface bonding parameters include: shear stiffness K g , bonding strength C g , adhesive friction angle φ g , outer circumference P g , the calculation relationship is as follows:

[0042]

[0043] C g =P g ×C

[0044] tanφ g =0.67tanφ

[0045] Where:

[0046] is the shear force per length;

[0047] u s is the shear displacement per length;

[0048] c is the cohesion of soil;

[0049] φ is the friction angle of the soil.

[0050] Preferably, a Geogrid structural unit is used to simulate geotextiles to achieve flexible protection in engineering projects. The Geogrid unit is controlled by property parameters of unit area stiffness k, bonding strength C, and bonding friction angle φ, and the above parameters are obtained through tensile tests and pull-out tests of geotextiles.

[0051] Preferably, the calculation of the ground stress balance in step S3 is to impart soil gravity to the reinforced soil structure and impose constraints on the boundaries, so as to obtain an initial stress field under the action of the geogrid and the geotextile.

[0052] Preferably, when the static load is less than 100 kPa, a small bar load with an interval of 20 kPa is used, and when it is greater than 100 kPa, a large bar load with an interval of 50 kPa is used. The dynamic load is a half-sine wave with a frequency of 2 Hz and an amplitude of 0 to 120 kPa.

[0053] Preferably, in step S5, the reinforced soil structure considering the anisotropy of the reinforcement material is designed, that is, in step S4 of the specific modeling process, a function call and a Cable structure unit are used to form an anisotropic bidirectional geogrid, which is cyclically loaded until equilibrium.

[0054] Preferably, 2 to 3 or even multiple factors are selected from the key influencing factors to evaluate the stability of the complex reinforced soil structure under the coupling effect.

[0055] The beneficial effects of the present invention compared with the prior art are as follows:

[0056] 1) The present invention proposes a new three-dimensional model of a bidirectional geogrid reinforcement structure, which can take into account the relevant strength and stiffness characteristics of the geogrid reinforcement direction and the actual mesh structure.

[0057] 2) The bidirectional geogrid model constructed by the present invention can simulate the interaction between the geogrid reinforcement and soil, and reflect the anisotropic mechanical behavior characteristics of the bidirectional geogrid itself and the reinforcement-soil interface in different laying directions, successfully capture the actual load transfer mechanism between the geogrid ribs and the surrounding soil, and obtain the limit state of the bidirectional geogrid.

[0058] 3) The present invention takes into account the anisotropy of geogrids in actual engineering projects, and can invert the stability of reinforced structures based on key technical parameters such as the tensile strength ratio of transverse and longitudinal ribs, slope rotation angle and inclination, and load type. This can help clarify the service performance of reinforced soil structures under complex geological conditions where the force direction of the reinforcement is inconsistent or uncertain, thereby providing more practical reinforced soil structure design parameters for the project. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 A schematic diagram of a two-dimensional model of a road reinforcement structure section according to an embodiment of the present invention;

[0060] Figure 2 It is a schematic diagram of the reinforced soil corner slope of the above embodiment;

[0061] Figure 3 A top view of the reinforced soil corner slope of the above embodiment;

[0062] Figure 4 It is a schematic diagram of a three-dimensional model of the reinforced soil corner slope of the above embodiment;

[0063] Figure 5 It is a schematic diagram of the structure of the Cable structural unit in the three-dimensional model of the above embodiment;

[0064] Figure 6 A relationship diagram between shear force and shear displacement per length in the performance of the interface bonding material of the Cable structure unit of the above embodiment;

[0065] Figure 7 A diagram showing the relationship between the shear strength criterion in the performance of the interface bonding material of the Cable structure unit of the above embodiment;

[0066] Figure 8 It is a schematic diagram of the structure of the bidirectional geogrid in different laying directions in the three-dimensional model of the above embodiment;

[0067] Fig. 9 It is a schematic diagram of a bidirectional geogrid node in the three-dimensional model of the above embodiment;

[0068] Fig.10 A node displacement vector diagram of the reinforced soil corner slope in the above embodiment;

[0069] Fig.11The figures are the simulation results and test results of the reinforced soil corner slope of the above embodiment.

[0070] In the figure: base layer 1, road base layer 2, geogrid 3, geotextile 4, corner 5, longitudinal rib 6, transverse rib 7, node 8, first node 9, second node 10. DETAILED DESCRIPTION

[0071] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation instructions described herein are only used to explain the present invention and are not used to limit the present invention. The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings. Based on the implementation methods in the invention, all other implementation methods obtained by ordinary technicians in this field without creative work are within the scope of protection of the invention. In addition, in this specification, the drawings are not drawn to scale, and the same figure numerals represent the same parts.

[0072] The invention discloses a reinforced soil structure design method based on finite difference analysis considering the anisotropy of reinforcement material, characterized in that it includes: establishing a three-dimensional model of the corner slope of the roadbed reinforced soil, including a roadbed and a groundbed, setting a bidirectional geogrid at the roadbed structure, setting a geotextile at the roadbed slope, using the Duncan-Zhang nonlinear constitutive equation to simulate the roadbed, using the elastic constitutive method to simulate the groundbed, using the Cable structure unit to simulate the geogrid, using the Geogrid structure unit to simulate the geotextile, and verifying the reliability of the model by comparing with the indoor model test results; on the basis of the verified model, giving different mechanical parameters to the horizontal and longitudinal ribs of the bidirectional geogrid to realize the anisotropy of its own mechanical behavior, changing the arrangement angle of the Cable unit and the center line of the reinforced soil structure to realize the anisotropy of the mechanical behavior of the reinforcement-soil interface, and adjusting other single or multiple variables at the same time to test the influence of key factors on the mechanical characteristics of the reinforced soil structure. The invention can solve the problem of inconsistent or uncertain force direction of the reinforcement material of the reinforced soil structure under complex geological conditions, and effectively provide more practical reinforced soil structure design parameters.

[0073] Anisotropy refers to the phenomenon that the mechanical behaviors of the bidirectional geogrid itself and the reinforcement-soil interface are different in different directions. When the reinforced soil structure is subjected to complex forces and the force direction of the reinforcement is inconsistent or uncertain, the designed tensile strength may be much greater than the tensile strength in the actual force direction, which may pose a major safety hazard to the reinforced soil structure.

[0074] A design method for reinforced soil structure based on finite difference analysis considering the anisotropy of reinforcement materials, comprising:

[0075] Step S1, please refer to Figure 1-Figure 4, select typical reinforced soil engineering structures, establish a three-dimensional model of the reinforced soil corner slope of the roadbed, define material properties, divide the grid, and obtain a finite difference three-dimensional calculation model. The three-dimensional model includes a base layer 1, a roadbed 2, a geogrid 3, and a geotextile 4 from bottom to top, wherein the geogrid 3 is placed on the roadbed and is divided into three layers: upper, middle, and lower. The geogrid 3 and the geotextile 4 are rigidly connected and fixed. The physical and mechanical parameters of the base layer 1, roadbed 2, bidirectional geogrid 3, and geotextile 4 of the finite difference model are obtained through indoor triaxial tests, bidirectional geogrid and geotextile single rib tensile tests, and the model is calibrated.

[0076] Step S2, the three-dimensional model includes a foundation layer 1 and a roadbed backfill layer 2 from top to bottom, a bidirectional geogrid 3 is set at the roadbed structure, and a geotextile 4 is set at the roadbed slope. Cable structural units are used to simulate the geogrid 3, and Geogrid structural units are used to simulate the geotextile 4. Material properties are defined for the three-dimensional model, and the grid is divided to obtain a finite difference model.

[0077] Due to the complexity of the roadbed structure, a simple two-dimensional model is difficult to reflect the actual stress and deformation state of the reinforced structure. It is necessary to establish a three-dimensional numerical model through a finite difference platform and use solid units such as 4-nodes or 8-nodes with higher calculation accuracy to perform meshing and solving, such as the solid units provided in the FLAC3D (a geotechnical engineering finite difference three-dimensional analysis software) program.

[0078] The three-dimensional model uses Cable structural units to simulate geogrids 3, such as Figure 5 , Figure 6 As shown, the flat bidirectional geogrid 3 is divided into two groups of longitudinal ribs 6 and transverse ribs 7. A single node 8 is used to establish a rigid connection between the longitudinal and transverse ribs, thereby simulating the grid structure of the bidirectional geogrid. Figure 7 , the geogrid at the overlap is decomposed into multiple two-node cable structural unit straight segments according to the actual mesh size. Any curved geogrid can be composed of these units. Each structural unit has its own local coordinate system, which is defined by the positions of two nodes, such as Figure 7 The first and second nodes are shown. The Cable structural element has two degrees of freedom, and there is an axial force corresponding to each axial displacement. The stiffness matrix of the Cable element contains only one degree of freedom for the axial response of the anchor at each node. Therefore, the axial force of a single structural element can be monitored to observe the stress state of each part of the geogrid at any time.

[0079] The three-dimensional model uses Cable structural units to replace the original Geogrid units for simulating geogrids to achieve bidirectional geogrid anisotropy simulation. The Cable unit is defined by geometric parameters, material property parameters and interface bonding characteristics. The geometric parameters are calibrated in combination with the actual parameters of the grid. The elastic modulus E of the geogrid 3 is g Determined by the tensile stiffness J of the geogrid's transverse and longitudinal ribs at 2% strain, the essence of the interaction between the geogrid and the soil is bonding and friction. The system can be described by a spring-slider in the axial direction of the node. The interface bonding parameters mainly include: shear stiffness K g , bonding strength C g , adhesive friction angle φ g , outer circumference P g , see Figure 8 and Fig. 9 , the one-dimensional constitutive model can be used to describe the axial characteristics of the Cable structural unit. The specific calculation relationship is as follows:

[0080]

[0081] C g =P g ×C

[0082] tanφ g =0.67tanφ

[0083] Where:

[0084] is the shear force per length;

[0085] u s is the shear displacement per length;

[0086] c is the cohesion of soil;

[0087] φ is the friction angle of the soil.

[0088] The three-dimensional model uses Geogrid structural units to simulate geotextiles, including: Geogrid structural units are flexible plane shell structural units with three nodes, which can be used to simulate flexible geosynthetics such as geomembranes and geotextiles. Geogrid structural units behave as linear elastic materials with no damage limit, isotropic or orthotropic, and can be used to simulate the mechanical properties of flexible geotextiles. The Geogrid unit is controlled by property parameters such as unit area stiffness k, bond strength C, and bond friction angle φ, and the above parameters can be obtained through geotextile tensile tests and pull-out tests.

[0089] The Cable structure unit and Geogrid structure unit use interface units to simulate the interaction between soil-geogrid and geotextile-soil. The shear strength parameters of the soil-geogrid and geotextile-soil contact surfaces are simulated by the interface strength reduction factor (RF). The specific equation is as follows:

[0090]

[0091] Where:

[0092] δ i is the friction angle of the contact surface;

[0093] c i is the cohesion of the contact surface;

[0094] φ is the friction angle of geogrid or geotextile;

[0095] c is the cohesion of geogrid or geotextile.

[0096] The anisotropy of the bidirectional geogrid includes its own anisotropy and anisotropy of the mechanical behavior of the reinforcement-soil interface. The own anisotropy is achieved by changing the tensile strength ratio of the orthogonal transverse and longitudinal ribs of the grid, and the anisotropy of the mechanical behavior of the reinforcement-soil interface is achieved by adjusting the laying angle between the grid and the center line of the reinforced soil structure. The laying angle of the geogrid includes at least five common working conditions of 0°, 22.5°, 45°, 67.5° and 90°. The Cable structural unit is easy to set up and has high simulated real strength. For complex geogrid modeling, it can also be quickly classified and positioned through the external plug-in AutoCAD, and the three-dimensional model can be imported by function call.

[0097] The constitutive model of the roadbed abandons the Mohr-Coulomb constitutive model often used in previous simulations and instead adopts the Duncan-Zhang nonlinear constitutive equation simulation that can better reflect the shear strength characteristics of sand. Since the base layer is often made of crushed stone materials with no bonding ability, a linear elastic constitutive equation is used for simulation.

[0098] The Duncan-Zhang nonlinear constitutive equation can be described by the hyperbolic model EB mode, and its tangent deformation modulus E t and the volume deformation modulus B can be expressed as:

[0099]

[0100] Where:

[0101] R f is the destruction ratio;

[0102] σ1-σ3 is the deviation stress at failure;

[0103] σ1, σ3 are the maximum and minimum principal stresses respectively;

[0104] K e is the elastic modulus coefficient;

[0105] n is the elastic modulus index;

[0106] P a is the atmospheric pressure;

[0107] K b is the bulk modulus coefficient;

[0108] m is the bulk modulus index.

[0109] The required model parameters are obtained through indoor triaxial tests. The failure criterion adopts the Mohr-Coulomb yield criterion, and the yield function is as follows:

[0110]

[0111] Where:

[0112] is the friction angle of soil;

[0113] c is the cohesion of soil.

[0114] Step S3, horizontal layered loading is performed on the roadbed of the three-dimensional model to simulate the horizontal layered filling in construction, and the ground stress balance calculation is performed after the filling is completed. Static and dynamic loads are applied above the top of the slope to simulate the traffic load in actual working conditions, and the deformation and stress simulation data of the reinforced soil structure at different stages are obtained, which are compared with the indoor model test results to verify the reliability of the model;

[0115] The calculation of ground stress balance in step S3 is to give soil gravity to the reinforced soil structure and impose constraints on the boundaries, and obtain the initial stress field under the action of geogrids and geotextiles. A vertical load is applied above the top of the slope. The load is divided into static load and dynamic load. Preferably, when the static load is less than 100kPa, a small strip load with an interval of 20kPa is used, and when it is greater than 100kPa, a large strip load with an interval of 50kPa is used. The dynamic load is a half-sine wave with a frequency of 2Hz and an amplitude of 0-120kPa, thereby simulating the traffic load in the actual project. The specific formula is as follows:

[0116]

[0117] Step S4, based on the verified model, different mechanical parameters are given to the transverse and longitudinal ribs of the bidirectional geogrid to realize the anisotropic simulation of its own mechanical behavior, and the arrangement angle of the Cable unit with the center line of the reinforced soil structure is changed to realize the anisotropic simulation of the mechanical behavior of the reinforcement-soil interface;

[0118] Step S5, after adjusting other single or multiple variables, return to step S3 to test the influence of key factors such as the longitudinal and transverse tensile stiffness ratio of the geogrid, slope rotation angle and inclination, filler and reinforcement parameters, load type, and the superposition effect of the anisotropy of the geogrid itself and the reinforcement-soil interface characteristics on the mechanical properties of the reinforced soil structure.

[0119] In step S5, the reinforced soil structure considering the anisotropy of the reinforcement is designed, that is, in step S4 of the specific modeling process, a function call and a Cable structure unit are used to form an anisotropic bidirectional geogrid, and cyclic loading is performed until equilibrium. Fig.10 and Fig.11 , a three-dimensional model of reinforced soil corner slope considering anisotropy was established, and the node displacement vector diagram of the reinforced soil corner slope was obtained after the model was balanced. The settlement changes were monitored and compared with the test results. The fitting effect was good and it was operational. Furthermore, 2 to 3 or even multiple factors can be selected from the key influencing factors to evaluate the stability of complex reinforced soil structures under the coupling effect.

[0120] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A reinforced soil structure design method based on finite difference analysis considering the anisotropy of reinforcement materials, characterized in that: include: Step S1, establishing a three-dimensional model of the reinforced soil corner slope of the roadbed, obtaining the physical and mechanical parameters of the roadbed, foundation, bidirectional geogrid and geotextile of the finite difference model through indoor triaxial tests, bidirectional geogrid and geotextile single rib tensile tests, and performing model calibration; Step S2, the three-dimensional model includes a roadbed backfill layer and a base layer from top to bottom, a bidirectional geogrid is set at the roadbed structure, a geotextile is set at the roadbed slope, a Cable structure unit is used to simulate the geogrid, and a Geogrid structure unit is used to simulate the geotextile, the material properties of the three-dimensional model are defined, and the grid is divided to obtain a finite difference model; Step S3, horizontal layered loading is performed on the roadbed of the three-dimensional model to simulate horizontal layered filling during construction, and after the filling is completed, ground stress balance calculation is performed; By applying static and dynamic loads on the top of the slope to simulate the traffic load in actual working conditions, the deformation and stress simulation data of the reinforced soil structure at different stages were obtained, and compared with the indoor model test results to verify the reliability of the model; Step S4, based on the verified model, different mechanical parameters are given to the transverse and longitudinal ribs of the bidirectional geogrid to realize the anisotropic simulation of its own mechanical behavior, and the arrangement angle of the Cable unit with the center line of the reinforced soil structure is changed to realize the anisotropic simulation of the mechanical behavior of the reinforcement-soil interface; Step S5, after adjusting other single or multiple variables, return to step S3 to test the influence of the key factors of the geogrid longitudinal and transverse tensile stiffness ratio, slope rotation angle and inclination, filler and reinforcement material parameters, load type, and the superposition effect of the anisotropy of the geogrid itself and the reinforcement-soil interface characteristics on the mechanical properties of the reinforced soil structure; The method of simulating geogrids by using Cable structural units includes: the Cable structural unit is a linear structural unit with two nodes, which is composed of structural nodes and structural members, each node has an axial translational degree of freedom, and the structural unit members bear tension or compression; the bidirectional geogrid at the overlap is divided into two groups according to the horizontal and longitudinal rib directions, and is divided into multiple single structural members according to the actual mesh size, and multiple members are connected in series at the nodes by rigid connection to simulate the real geogrid; The use of Geogrid structural units to simulate geotextiles includes: the Geogrid structural unit is a flexible plane shell-type structural unit with three nodes, used to simulate geomembranes or geotextiles flexible geosynthetics; The Cable structure unit and Geogrid structure unit use interface units to simulate the interaction between soil-geogrid and geotextile-soil. The shear strength parameters of the soil-geogrid and geotextile-soil contact surfaces are simulated by the interface strength reduction factor RF. The specific equation is as follows: Where: δ i is the friction angle of the contact surface; c i is the cohesion of the contact surface; φ is the friction angle of geogrid or geotextile; c is the cohesion of geogrid or geotextile.

2. The reinforced soil structure design method based on finite difference analysis considering the anisotropy of reinforcement materials according to claim 1 is characterized in that: The constitutive model of the roadbed is simulated using the Duncan-Zhang nonlinear constitutive equation, and the constitutive model of the subgrade is simulated using the linear elastic constitutive equation.

3. The reinforced soil structure design method based on finite difference analysis considering the anisotropy of reinforcement materials according to claim 1 is characterized in that: The Duncan-Zhang nonlinear constitutive equation is described by the hyperbolic model EB mode, and its tangent deformation modulus E t and the volume deformation modulus B can be expressed as: Where: R f is the destruction ratio; σ1-σ3 is the deviation stress at failure; σ1, σ3 are the maximum and minimum principal stresses respectively; K e is the elastic modulus coefficient; n is the elastic modulus index; P a is the atmospheric pressure; K b is the bulk modulus coefficient; m is the bulk modulus index; The required model parameters are obtained through indoor triaxial tests; The failure criterion adopts the Mohr-Coulomb yield criterion, and the yield function is as follows: Where: is the friction angle of soil; c is the cohesion of soil.

4. The reinforced soil structure design method based on finite difference analysis considering the anisotropy of reinforcement materials according to claim 1 is characterized in that: The anisotropy of bidirectional geogrid includes its own anisotropy and the anisotropy of mechanical behavior of reinforcement-soil interface. The own anisotropy is achieved by changing the tensile strength ratio of the orthogonal transverse and longitudinal ribs of the grid. The anisotropy of mechanical behavior of reinforcement-soil interface is achieved by adjusting the laying angle between the grid and the center line of the reinforced soil structure. The laying angles of geogrid include at least five common working conditions: 0°, 22.5°, 45°, 67.5° and 90°.

5. The reinforced soil structure design method based on finite difference analysis considering the anisotropy of reinforcement materials according to claim 1 is characterized in that: The Cable structural unit is used to replace the original Geogrid unit for simulating geogrid to realize the anisotropic simulation of bidirectional geogrid. The Cable unit is defined by geometric parameters, material property parameters and interface bonding characteristics. The geometric parameters are calibrated in combination with the actual parameters of the grid. The elastic modulus E of the geogrid is g Determined by the tensile stiffness J of the geogrid's transverse and longitudinal ribs at 2% strain, the essence of the interaction between the geogrid and the soil is bonding and friction. The system is described by a spring-slider in the axial direction of the node. The interface bonding parameters include: shear stiffness K g , bonding strength C g , adhesive friction angle φ g , outer circumference P g , the calculation relationship is as follows: C g =P g ×C tanφ g =0.67tanφ Where: is the shear force per length; u s is the shear displacement per length; c is the cohesion of soil; φ is the friction angle of the soil.

6. The reinforced soil structure design method based on finite difference analysis considering the anisotropy of reinforcement materials according to claim 1 is characterized in that: The Geogrid structural unit is used to simulate the geotextile to realize the flexible protection function in the engineering. The Geogrid unit is controlled by the property parameters of unit area stiffness k, bond strength C, and bond friction angle φ. The above parameters are obtained through the tensile test and pull-out test of the geotextile.

7. The reinforced soil structure design method based on finite difference analysis considering the anisotropy of reinforcement materials according to claim 1 is characterized in that: The calculation of the ground stress balance in step S3 is to give the soil gravity to the reinforced soil structure and impose constraints on the boundaries, so as to obtain the initial stress field under the action of the geogrid and the geotextile.

8. The reinforced soil structure design method based on finite difference analysis considering the anisotropy of reinforcement materials according to claim 1 is characterized in that: When the static load is less than 100kPa, a small bar load with an interval of 20kPa is used. When it is greater than 100kPa, a large bar load with an interval of 50kPa is used. The dynamic load is a half-sine wave with a frequency of 2Hz and an amplitude of 0~120kPa.

9. The reinforced soil structure design method based on finite difference analysis considering the anisotropy of reinforcement materials according to claim 1, characterized in that: In the step S5, the reinforced soil structure considering the anisotropy of the reinforcement material is designed, that is, in the step S4 of the specific modeling process, a function call and a Cable structure unit are used to form an anisotropic bidirectional geogrid, which is cyclically loaded to equilibrium.

10. The reinforced soil structure design method based on finite difference analysis considering the anisotropy of reinforcement materials according to claim 1, characterized in that: Select at least 2 to 3 factors from the key influencing factors to evaluate the stability of complex reinforced soil structures under the coupling effect.

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