Method for determining differential settlement control indexes of new and old roadbeds of highway reconstruction and extension project based on material point method

Abstract

The invention discloses a method for determining differential settlement control indexes of new and old roadbeds of a highway reconstruction and extension project based on a material point method, which comprises the following steps of: drilling a pavement structure on a highway site, transporting a sample to a test room for storage, determining mechanical parameters of a pavement structure material under a non-damage condition, establishing a material point model of a corresponding size, and determining the difference settlement control indexes of the new and old roadbeds of the highway reconstruction and extension project. The method comprises the following steps: establishing a material point model, setting a constitutive relationship for the established material point model, applying a displacement load in the perfect material point model according to a roadbed differential settlement action form, calculating material points, performing post-processing by utilizing ParaView software, analyzing the influence of splicing seam expansion on pavement structure cracking, and determining a differential settlement control index of new and old roadbeds. According to the method, the problems of difficulty in sample manufacturing, high time consumption, high cost and the like in an indoor test method are solved, the influence of splicing seam expansion on pavement structure cracking is illustrated, and a new method is provided for determining differential settlement control indexes of new and old roadbeds in highway reconstruction and extension projects.

Description

Technical Field

[0001] The present invention relates to the technical field of road engineering, and particularly relates to a method for determining the differential settlement control index of new and old roadbeds in highway reconstruction and expansion projects based on the material point method. Background Technique

[0002] The cracking characteristics of the pavement structure under the influence of differential settlement between new and old roadbeds have always been the research focus of highway reconstruction and expansion projects. Usually, researchers will use indoor tests to analyze the cracking characteristics of structural materials. However, for pavement structures with large sizes, due to problems such as difficult sample production, long time consumption, and high costs, numerical simulation methods need to be used for research.

[0003] The finite element method is a numerical method based on the assumption of continuous media. It can simplify complex actual problems into many small units containing mathematical equations and calculate approximate solutions of the mathematical equations. In recent years, many scholars have used the finite element method to analyze the cracking characteristics of pavement structures under differential settlement. However, for widened pavement structures, there are obvious splicing joints between the new and old pavement structures, and there is still less research on considering the influence of the expansion of splicing joints on the cracking characteristics of pavement structures. At the same time, for pavement structures with splicing joints, the finite element method has problems such as mesh distortion, non-convergence of calculation, low efficiency, and high costs. Therefore, how to overcome the deficiencies of the finite element method in analyzing the cracking characteristics of complex cracked materials, realize the simulation of the whole cracking process of pavement structures with splicing joints under differential settlement, and determine the differential settlement control index of new and old roadbeds is an urgent problem to be solved. Summary of the Invention

[0004] Purpose of the Invention: The purpose of the present invention is to provide a method for determining the differential settlement control index of new and old roadbeds in highway reconstruction and expansion projects based on the material point method.

[0005] Technical Solution: The present invention includes the following steps:

[0006] (1) Drill holes in the pavement structure at the highway site and transport the samples to the laboratory for storage;

[0007] (2) Conduct indoor tests on the samples of the pavement structure to determine the mechanical parameters of the pavement structure materials under non-damaged conditions;

[0008] (3) Establish a material point model with corresponding dimensions in the PneBlast software according to the on-site pavement structure;

[0009] (4) Set the constitutive relationship for the material point model established in step (3) and assign the pavement structure material parameters obtained in step (2);

[0010] (5) Apply displacement loads to the improved material point model in step (4) according to the differential settlement action form of the subgrade, and perform material point calculations;

[0011] (6) Output the results obtained from the calculation in step (5), and perform post-processing using ParaView software;

[0012] (7) Based on the results obtained from the post-processing in step (6), analyze the influence of the expansion of the splicing joint on the cracking of the pavement structure, and determine the differential settlement control index of the new and old subgrades.

[0013] Further, in step (2), indoor tests are conducted on the samples of the pavement structure with reference to the highway pavement structure design specifications.

[0014] Further, the mechanical parameters in step (2) include elastic modulus, Poisson's ratio, and tensile strength.

[0015] Further, in step (3), the splicing joints of the pavement structure are represented by massless material points.

[0016] Further, it is characterized in that the material point model in step (4) adopts the following linear elastic model, expressed as:

[0017]

[0018] Among them, E, σ, and ε represent elastic modulus, stress, and strain respectively.

[0019] Further, it is characterized in that the differential settlement action form of the subgrade in step (5) is expressed as:

[0020]

[0021] Among them, δ represents the differential settlement, and its maximum value is δ max ; L represents the width of the pavement structure model.

[0022] Further, it is characterized in that the data obtained from the post-processing in step (6) is the horizontal stress data of the pavement structure model.

[0023] Further, it is characterized in that in step (7), the influence of the expansion of the splicing joint on the cracking of the pavement structure is analyzed by calculating the stress intensity factor at the tip of the splicing joint. The stress intensity factor K I The calculation formula is expressed as:

[0024]

[0025] Among them, r and σ v represent the distance from the front end of the splicing joint and the stress perpendicular to the crack surface respectively.

[0026] Further, the calculation method of the stress intensity factor includes:

[0027] According to the horizontal stress data of the pavement structure obtained in step (6), the vertical stress values of material points at different distances in front of the crack tip are taken by the extrapolation method, substituted into the stress intensity factor calculation formula, and regression analysis is carried out by the least square method to obtain the stress intensity factor K at the splicing joint tip I .

[0028] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0029] (1) Using the material point method to analyze the cracking characteristics of the pavement structure, overcoming the problems of difficult sample production, long time consumption and high cost in the indoor test method;

[0030] (2) Using the material point method, there is no need to consider the model mesh subdivision and complex shape functions, overcoming the problems of mesh distortion, calculation non-convergence, low efficiency and high cost in the analysis of the cracking of the pavement structure with splicing joints by the finite element method;

[0031] (3) Using the material point method to analyze the stress characteristics of the widened pavement structure under the condition of differential settlement, clarifying the influence of the splicing joint expansion on the cracking of the pavement structure, and providing a new method for determining the differential settlement control index of the new and old subgrades in the highway reconstruction and expansion project. Description of the drawings

[0032] Figure 1 is the flow chart of the numerical simulation method for the cracking of the pavement structure based on the material point;

[0033] Figure 2 is the cross-sectional schematic diagram of the widened pavement structure;

[0034] Figure 3 is the material point model of the widened pavement structure;

[0035] Figure 4 is the force model of the pavement structure under differential settlement;

[0036] Figure 5 is the horizontal stress nephogram of the pavement structure when the differential settlement is 10 cm. Specific embodiments

[0037] The technical solution of the present invention will be further described below with reference to the drawings.

[0038] This embodiment takes the reconstruction and expansion project of the Lianhuai section of the Changzhou-Shenyang Expressway as the background. Its widened pavement structure is an asphalt pavement structure with a width and thickness of 42 m and 0.8 m respectively. As Figure 1 shown, the method described in the present invention is now used to analyze the cracking characteristics of the pavement structure under different differential settlements of the new and old subgrades, including the following steps:

[0039] Step 1: Drill holes in the pavement structure at the highway site and transport the samples to the laboratory for storage.

[0040] Step 2: Conduct indoor tests on the pavement structure samples with reference to the "Code for Design of Highway Pavement Structure" (JTG D50-2017) to determine the elastic modulus, Poisson's ratio, and tensile strength of the pavement structure materials under non-damaged conditions. The results are shown in Table 1.

[0041] Table 1 Material parameters of the widened pavement structure layer

[0042]

[0043]

[0044] Step 3: According to the cross-section of the widened pavement structure as shown in Figure 2 , establish a material point model with corresponding dimensions in the PneBlast software, as shown in Figure 3 . In the figure, the white massless material points represent the splicing joints.

[0045] Step 4: Set a linear elastic model for the material point model established in Step 3 and assign the pavement structure material parameters obtained in Step 2. The formula of the linear elastic model is as follows:

[0046]

[0047] where e, σ, and ε represent the elastic modulus, stress, and strain respectively.

[0048] Step 5: According to the form of the subgrade differential settlement as shown in Figure 4 , apply displacement loads to the material point model perfected in Step 4 and conduct material point calculations.

[0049]

[0050] where δ represents the differential settlement, and its maximum value is δ max ; L represents the width of the pavement structure model.

[0051] Step 6: Output the results calculated in Step 5, and use ParaView software for post-processing to obtain the results as shown in Figure 5 . Table 2 shows the maximum tensile stress of the pavement surface layer under different differential settlements.

[0052] Table 2 Maximum tensile stress of the pavement surface layer under different differential settlements

[0053]

[0054] Step 7: According to the horizontal stress nephogram of the pavement structure obtained in Step 6, the vertical stress values of material points at different distances in front of the crack tip are taken by the extrapolation method, substituted into the following formula to calculate the stress intensity factor, and regression analysis is carried out by the least square method to obtain the stress intensity factor K at the tip of the splicing joint I .

[0055]

[0056] where r and σ v respectively represent the distance in front of the splicing joint and the stress perpendicular to the crack surface. Table 3 shows the stress intensity factors at the tips of the pavement structure splicing joints under different differential settlements. If the fracture toughness of the material is used as the cracking index, when the stress intensity factor at the tip of the splicing joint is greater than the fracture toughness of the surface layer material, the pavement surface layer will undergo cracking failure.

[0057] Table 3 Stress intensity factors at the tips of the pavement structure splicing joints under different differential settlements

[0058]

[0059] The present invention uses the pavement structure data obtained from indoor tests, establishes a pavement structure numerical model by the material point method and conducts analysis, can realize the full-process simulation of the cracking of the pavement structure with splicing joints under the action of differential settlement, and determine the differential settlement control index of the new and old subgrades.

Claims

1. A method for determining differential settlement control index of new and old roadbeds in highway reconstruction and expansion projects based on material point method, characterized in that: The steps include: (1) Drill holes in the pavement structure at the highway site and transport the samples to the laboratory for storage; (2) Conduct indoor tests on samples of pavement structures to determine the mechanical parameters of pavement structure materials under non-damage conditions; (3) Establish a material point model of corresponding size in PneBlast software according to the on-site pavement structure; (4) setting a constitutive relationship for the material point model established in step (3) and assigning the pavement structure material parameters obtained in step (2); (5) According to the differential settlement of the roadbed, displacement load is applied to the material point model improved in step (4), and material point calculation is performed; (6) Output the result calculated in step (5) and perform post-processing using ParaView software; (7) Based on the results obtained from post-processing in step (6), the effect of joint expansion on pavement structure cracking is analyzed, and the differential settlement control index of the new and old roadbeds is determined.

2. The method for determining the differential settlement control index of the new and old roadbeds in a highway reconstruction and expansion project based on the material point method according to claim 1 is characterized in that: In the step (2), indoor tests are performed on samples of the pavement structure with reference to the highway pavement structure design specifications.

3. The method for determining the differential settlement control index of new and old roadbeds in highway reconstruction and expansion projects based on the material point method according to claim 1 is characterized in that: The mechanical parameters in step (2) include elastic modulus, Poisson's ratio and tensile strength.

4. The method for determining the differential settlement control index of new and old roadbeds in highway reconstruction and expansion projects based on the material point method according to claim 1 is characterized in that: In the step (3), the joints of the pavement structure are represented by massless material points.

5. The method for determining the differential settlement control index of the new and old roadbeds in a highway reconstruction and expansion project based on the material point method according to claim 1 is characterized in that: The material point model in step (4) adopts the following linear elastic model, which is expressed as: Among them, E, σ and ε represent elastic modulus, stress and strain respectively.

6. The method for determining the differential settlement control index of new and old roadbeds in highway reconstruction and expansion projects based on the material point method according to claim 1 is characterized in that: The differential settlement effect of the roadbed in step (5) is expressed as follows: Among them, δ represents differential sedimentation, and its maximum value is δ max ; L represents the width of the pavement structure model.

7. The method for determining the differential settlement control index of new and old roadbeds in highway reconstruction and expansion projects based on the material point method according to claim 1 is characterized in that: The data obtained by post-processing in step (6) is the horizontal stress data of the pavement structure model.

8. The method for determining the differential settlement control index of the new and old roadbeds in a highway reconstruction and expansion project based on the material point method according to claim 1 is characterized in that: The step (7) analyzes the effect of joint expansion on pavement structure cracking by calculating the stress intensity factor at the joint tip. The stress intensity factor K I The calculation formula is expressed as: Among them, r and σ v They represent the distance to the front end of the joint and the stress perpendicular to the crack surface respectively.

9. The method for determining the differential settlement control index of the new and old roadbeds in a highway reconstruction and expansion project based on the material point method according to claim 8 is characterized in that: The calculation method of the stress intensity factor includes: According to the horizontal stress data of the pavement structure obtained in step (6), the vertical stress values ​​of material points at different distances from the front end of the crack tip are obtained by extrapolation, substituted into the stress intensity factor calculation formula, and the least squares method is used for regression analysis to obtain the stress intensity factor K at the tip of the joint: I .

Images