Semi-rigid base layer pre-cutting seam parameter optimization method considering combined action of vehicle load and temperature load

Abstract

The invention discloses a semi-rigid base layer pre-cut joint parameter optimization method considering the combined action of a vehicle load and a temperature load, relates to the field of road engineering, and aims to solve the problems that the determination of semi-rigid base layer pre-cut joint parameters only depends on engineering experience and an evaluation system is imperfect. Calculating the influence of the width, depth and spacing of the pre-cut joint on the internal stress of the semi-rigid base asphalt pavement, obtaining the change rule of the pre-cut joint parameters and the internal stress of the semi-rigid base asphalt pavement, proposing the selection rule of the optimal joint cutting parameters, and obtaining the optimal pre-cut joint parameters. According to the method, assistance can be provided for the pre-cut joint in the actual construction process.

Description

Technical Field

[0001] The present invention relates to the field of road engineering, and particularly relates to an optimization method for pre-cutting seam parameters of a semi-rigid base based on a finite element analysis method. Background Art

[0002] Most asphalt pavements adopt a pavement structure with a semi-rigid base because the semi-rigid base asphalt pavement has high strength, low cost, and good integrity and water stability of the pavement. However, the biggest drawback of the semi-rigid base is that it is prone to cracking under the influence of temperature shrinkage and fatigue damage, and the cracks will expand to the asphalt surface layer under the long-term influence of temperature and traffic load, thus forming reflection cracks in the semi-rigid base asphalt pavement. Such reflection cracks are generally transverse cracks and are one of the diseases of the semi-rigid base asphalt pavement.

[0003] A large number of studies have been conducted on the prevention and control measures for reflection cracks at home and abroad. The main prevention and control means include two aspects: structural design and material improvement. Among them, the structural design mainly includes increasing the thickness of the asphalt surface layer, setting a stress absorption layer, setting an anti-cracking structure layer, carrying out reinforcement, and setting pre-cutting seams; in terms of material improvement, the anti-cracking performance of the surface layer is improved by using modified asphalt, SMA, adding polyester fibers, improving the gradation of aggregates, etc. It is understood that among many prevention and control measures, the use of the pre-cutting seam technology is one of the better ones. After the pre-cutting seam technology was developed in China, many experts have tried the pre-cutting seam technology on different roads. For example, the pre-cutting seam technology has been used in sections such as the reconstruction project of the G217 line from Dushanzi to Kuruli and the S309 line from Linxia to Dahejia in China. After a period of observation, the occurrence rate of cracks has decreased significantly, and the cracks are concentrated near the pre-cutting seams, achieving good results. At home and abroad, a large number of studies have been conducted on the construction technology and pavement structure of the pre-cutting seam technology, and it has been relatively mature in this regard. After literature investigation, during the construction process of the domestic pre-cutting seam technology, a cutting seam spacing of 10 - 20 m, a cutting seam depth of 1 / 3 - 1 / 2 of the base thickness, and a cutting seam width of 3 - 5 mm are adopted. For the basis of its adoption, only qualitative descriptions are made and no quantitative calculations are carried out. The qualitative descriptions are mainly based on engineering experience, and the evaluation system is imperfect, resulting in poor evaluation results. Summary of the Invention

[0004] Aiming at the problem that the determination of the pre-cutting seam parameters of the semi-rigid base only relies on engineering experience and the evaluation system is imperfect, the present invention proposes a quantitative calculation method for the influence of the pre-cutting seam on the internal stress of the semi-rigid base asphalt pavement through the finite element method, and obtains the optimal cutting seam parameters through this method.

[0005] The method for optimizing the pre-cutting joint parameters of a semi-rigid base considering the combined action of vehicle load and temperature load according to the present invention comprises the following steps:

[0006] Step 1: Construct a two-dimensional finite element model of a semi-rigid base asphalt pavement, where the model includes model size, boundary conditions, load conditions, mesh division, and solution method; set the model size, boundary conditions, load conditions, and mesh division of the model;

[0007] Boundary condition setting: When calculating the stress distribution under load conditions, the lower boundary is completely fixed, and the left and right boundaries are symmetrically constrained; when calculating the temperature field, the upper boundary is applied with surface heat flux, the lower boundary is at a constant temperature, and the left and right boundaries are adiabatic;

[0008] Free mesh division is adopted for mesh division, and the solution method is implicit solution;

[0009] The calculation of the stress distribution under the load conditions is to calculate the stress distribution under different load conditions: vehicle load, temperature load, and the coupled load of both are applied respectively, the distribution law of the stress along the depth and horizontal direction is analyzed, and the maximum principal stresses on the surface of the surface layer, the bottom surface of the surface layer, and the bottom surface of the base layer are compared;

[0010] Step 2: Analysis of the influence of single-factor parameters: By the method of controlling variables, the pre-cutting joint width, depth, and spacing of the two-dimensional finite element model of the semi-rigid base asphalt pavement are changed respectively, the internal stress distribution of the semi-rigid base asphalt pavement under different pre-cutting joint parameter conditions is calculated, the relationship between the pre-cutting joint parameters and the stress is established, and the influence of the change of a single parameter on the internal stress of the base layer is calculated;

[0011] Step 3: Analysis of the interaction of two factors: Two pre-cutting joint parameters are changed simultaneously, and the added interaction evaluation value R of width-depth, width-spacing, and depth-spacing is calculated. The calculation formula of the evaluation value R is:

[0012] R = (R A+B+ - R A-B- ) - (R A+B- - R A-B- ) - (R A-B+ - R A-B- )

[0013] = R A+B+ - R A+B- - R A-B+ + R A-B-

[0014] where A+ and A- are the larger value and the smaller value of parameter A, B+ and B- are the larger value and the smaller value of parameter B, R>0 indicates a positive interaction, R = 0 indicates no interaction, and R<0 indicates a negative interaction;

[0015] Step 4. Orthogonal experiment optimization: Design a three-factor and five-level experiment, with the stress at the bottom of the semi-rigid base as the evaluation index. Calculate the sensitivity of each factor through range analysis and determine the optimal combination of pre-cutting joint parameters.

[0016] Further, the width, depth, and spacing of the pre-cutting joints described in Step 2 are 2 - 6 mm, 10 - 18 cm, and 5 - 25 m, respectively.

[0017] Further, the calculation of the temperature field is to calculate the internal temperature change of the pavement structure.

[0018] Further, the calculation of the temperature field is to calculate the internal temperature change of the pavement structure, which is to calculate the heating of the road surface by solar radiation, the inverse radiation from the road surface to the atmosphere, the heat convection exchange between the atmosphere and the road surface, and the heat transfer inside the road surface respectively; and obtain the temperature field inside the semi-rigid base asphalt pavement.

[0019] Further, the heating of the road surface by solar radiation, the inverse radiation from the road surface to the atmosphere, the heat convection exchange between the atmosphere and the road surface, and the heat transfer inside the road surface are realized through the definition of interaction and the user subroutines "FILM" and "DFLUX" respectively.

[0020] Further, in Step 4, calculating the sensitivity of each factor through range analysis is to calculate the mean value of each factor level to obtain the effect curve graph of the influencing factors, and calculate the range R of each factor j , to obtain the sensitivity of each influencing factor to the stress, where and R j are calculated as follows:

[0021]

[0022] K ij —— The sum of the test data results of level i corresponding to factor j;

[0023] —— The average value of the test data results of level i corresponding to factor j;

[0024] R j —— The range of the average values of the test data of r levels corresponding to factor j;

[0025] n is the number of test repetitions, and r is the number of levels.

[0026] Further, when calculating the temperature field, the surface heat flux applied to the upper boundary is dynamically adjusted by the solar radiation intensity and the heat convection coefficient.

[0027] Further, in Step 4, the orthogonal experiment is carried out to verify its stress reduction effect, the optimal cutting slot parameters are obtained, and the optimal cutting slot parameters are verified by comparing the stress distributions under the conditions of the optimal cutting slot parameters and without pre-cutting slots.

[0028] The present invention has the following beneficial effects:

[0029] In the present invention, the mechanical analysis models for reflective cracks at home and abroad are investigated. The vast majority of them adopt the finite element analysis method. At present, the technology for analyzing pavement stress by the finite element method at home and abroad is relatively mature. Therefore, by means of the finite element method, the present invention calculates the influence of the pre-cutting slot width, depth and spacing on the internal stress of the semi-rigid base asphalt pavement, obtains the variation law of the pre-cutting slot parameters and the internal stress of the semi-rigid base asphalt pavement, proposes the selection rules for the optimal cutting slot parameters, and obtains the optimal pre-cutting slot parameters. The present invention can provide assistance for the pre-cutting slot in the actual construction process.

[0030] 1) Analyze the distribution law of the internal stress of the semi-rigid base asphalt pavement under different load conditions

[0031] Using the finite element model of the semi-rigid base asphalt pavement established by the present invention, it is possible to analyze the distribution law of the internal stress of the semi-rigid base asphalt pavement under the action of vehicle load, temperature load, and the combined action of vehicle load and temperature load. Taking the maximum principal stress as the main evaluation index, the stress distribution law curves along the horizontal direction and the pavement depth direction are established. Secondly, by comparing the stress magnitudes and distribution conditions under different load conditions, the stress effects generated by different load conditions on the inside of the semi-rigid base asphalt pavement are explored.

[0032] 2) Consider the distribution law of the internal stress of the semi-rigid base asphalt pavement with pre-cutting slots

[0033] Pre-cutting slots are set on the finite element model of the semi-rigid base asphalt pavement established by the present invention. Using the experimental design method of controlling variables, the pre-cutting slot width, depth and spacing are respectively changed. Taking the maximum principal stress at the top surface of the surface layer, the bottom surface of the surface layer, and the bottom surface of the semi-rigid base as the evaluation indexes, the pre-cutting slot parameter-stress curves are established to analyze the influence law of different parameters on the internal stress of the semi-rigid base asphalt pavement. Secondly, two parameters in the pre-cutting slot are changed simultaneously, and the additive interaction evaluation values between the pre-cutting slot width and depth, width and spacing, and depth and spacing are calculated to analyze the influence of the interaction between the pre-cutting slot parameters on the internal stress of the semi-rigid base asphalt pavement.

[0034] 3) Optimization of the optimal cutting slot parameters for the semi-rigid base

[0035] Using the experimental design method of orthogonal experiment, and the three-factor five-level orthogonal table L 25 (5 3) Taking the maximum principal stress at the bottom surface of the semi-rigid base as the evaluation index, the range analysis was carried out on the calculation results, the effect curves of different influencing factors were drawn, the range values of different influencing factors were calculated, and the primary and secondary order of the influence of influencing factors on the internal stress of the semi-rigid base asphalt pavement was analyzed. Based on the results of the orthogonal test, the pre-cutting joint parameters were optimized to obtain the best cutting joint parameters. Description of the Drawings

[0036] Figure 1 It is a comparison diagram of stress magnitudes at different positions under different load conditions;

[0037] Figure 2 It is the effect curve diagram of three parameters of the pre-cutting joint;

[0038] Figure 3 It is the range diagram of influencing parameters of the pre-cutting joint. Detailed Implementation Modes

[0039] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer and more understandable, the spirit of what is disclosed in the present invention will be described in detail below. After any person skilled in the art in the technical field to which the present invention pertains understands the embodiments of the content of the present invention, the techniques taught by the content of the present invention can be changed and modified, which does not deviate from the spirit and scope of the content of the present invention.

[0040] The schematic embodiments of the present invention and their descriptions are used to explain the present invention, but do not limit the present invention.

[0041] Embodiment 1

[0042] In this embodiment, in combination with the drawings, taking the pavement structure of 4 cm upper surface layer (SMA-13), 6 cm middle surface layer (AC-20), 8 cm lower surface layer (AC-25), 36 cm cement stabilized graded crushed stone base, and 20 cm graded crushed stone subbase as an example, the present invention is described in detail.

[0043] Step 1: Creation of the finite element model of the semi-rigid base asphalt pavement

[0044] In China, the asphalt pavement structure type usually consists of the upper, middle and lower surface layers, the base, the subbase and the soil base. The semi-rigid base asphalt pavement structure type adopted and the material parameters of each structural layer are shown in Table 1. The modulus and Poisson's ratio of each structural layer are obtained by referring to the "Highway Asphalt Pavement Design Specification" (2017 edition).

[0045] Table 1 Parameters of each structural layer of the semi-rigid base asphalt pavement

[0046]

[0047]

[0048] Use the ABAQUS software to create components, define materials and their parameters, set analysis steps, define loads and boundary conditions, mesh, and create jobs in sequence. Then, call the implicit solver for calculation, enter the visualization module to obtain the corresponding stress nephogram, and select the stresses at three special positions (the midpoint of the surface layer surface, the midpoint of the bottom surface of the surface layer, and the midpoint of the bottom surface of the semi-rigid base) for comparison.

[0049] Step 2: Calculation and analysis of the internal stress distribution law of semi-rigid base asphalt pavement

[0050] Calculate the stress distributions under the conditions of vehicle load acting alone, temperature load acting alone, and the coupling action of vehicle load and temperature load respectively, and obtain the stress magnitudes at the three special positions under different load conditions as Figure 1 shown. It can be seen from the figure that the stress magnitudes are: coupling action of vehicle load and vehicle load > temperature load action > vehicle load action.

[0051] Step 3: Calculation and analysis of the internal stress distribution law of semi-rigid base asphalt pavement considering pre-cut joints

[0052] By changing the magnitudes of three parameters, obtain the variation laws of different pre-cut joint widths, depths, and spacings with the internal stress of the asphalt pavement, so as to analyze the influence of different pre-cut joint parameters on the stress of the asphalt pavement. Among them, five groups of parallel tests are set for the pre-cut joint width as 2mm, 3mm, 4mm, 5mm, and 6mm; five groups of parallel tests are set for the pre-cut joint depth as 10cm, 12cm, 14cm, 16cm, and 18cm; five groups of parallel tests are set for the pre-cut joint spacing as 5m, 10m, 15m, 20m, and 25m. Obtain the pre-cut joint parameter-stress curves, and the influence magnitudes of the pre-cut joint parameters on the stress can be known by calculating the difference between the maximum stress and the minimum stress of each curve as shown in Table 2. It can be Figure 2 seen that the influence of the pre-cut joints on the internal stresses at different positions of the semi-rigid base asphalt pavement is: bottom surface of the lower surface layer > bottom surface of the semi-rigid base > surface of the upper surface layer.

[0053] Table 2 Internal stress differences at different positions under different pre-cut joint parameters

[0054]

[0055] Step 4: Interaction between pre-cut joint parameters

[0056] By changing two parameters in the pre-cutting joint parameters simultaneously, the internal stress of the semi-rigid base asphalt pavement is obtained. The values of A+ / B+ and A- / B- in the calculation formula for the additive interaction are shown in Table 3. Substitute the corresponding stress calculation results into the calculation formula to obtain the additive interaction evaluation values under different combinations as shown in Table 4. It can be seen from the table that there is a negative additive interaction between the pre-cutting joint width and depth, no additive interaction between the pre-cutting joint width and spacing, and a positive additive interaction between the pre-cutting joint depth and pre-cutting joint spacing.

[0057] Table 3 Values of pre-cutting joint parameters

[0058]

[0059] Table 4 Additive interaction evaluation values under different combinations

[0060]

[0061] Step 5: Calculation and optimization of the best cutting joint parameters for the semi-rigid base

[0062] The value ranges of each influencing factor are as follows: the pre-cutting joint width is 2 - 6 mm, the pre-cutting joint depth is 10 - 18 cm, and the pre-cutting joint spacing is 5 - 25 m. Each influencing factor adopts five level values, and the orthogonal test method is used to analyze the best cutting joint parameters. The orthogonal test is a three-factor and five-level one, using the L 25 (5 3 ) type orthogonal table, without considering the interaction between factors, and a total of 25 groups of test results are calculated. The evaluation index adopted is the stress at the midpoint of the bottom of the semi-rigid base. After obtaining the stress magnitudes of 25 groups of tests through calculation, the range analysis method is used to calculate the average values of different factor levels, and the See Table 5, and based on this, draw the effect curves of each influencing factor (such as Figure 2 ), and then calculate the range magnitudes of different influencing factors according to the level values of different factors (such as Figure 3 ). It can be seen from Figure 2 that the stress decreases with the increase of the pre-cutting joint width, increases with the increase of the pre-cutting joint depth, and increases with the increase of the pre-cutting joint spacing. The order of the influence of pre-cutting joint parameters on stress is: pre-cutting joint spacing > pre-cutting joint depth > pre-cutting joint width. Through analysis, the best cutting joint parameters are obtained as: the pre-cutting joint width is 3 mm, the pre-cutting joint depth is 16 cm, and the pre-cutting joint spacing is 10 m.

[0063] Table 5 Different factor levels Calculation results

[0064]

[0065]

Claims

1. A method for optimizing parameters of semi-rigid base pre-cutting considering the combined effects of vehicle load and temperature load, characterized in that: The following steps are involved: Step 1: construct a two-dimensional finite element model of a semi-rigid base asphalt pavement, the model including model size, boundary conditions, load conditions, meshing and solution method; set the model size, boundary conditions, load conditions and meshing of the model; Boundary condition setting: When calculating stress distribution under load conditions, the lower boundary is completely fixed, and the left and right boundaries are symmetrical constraints; when calculating temperature field, the upper boundary is applied with surface heat flux, the lower boundary is kept at a constant temperature, and the left and right boundaries are insulated; The meshing method is free meshing, and the solution method is implicit solution; The stress distribution calculation under the load conditions is to calculate the stress distribution under different load conditions: apply vehicle load, temperature load and the coupled load of the two respectively, analyze the distribution law of stress along the depth and horizontal direction, and compare the maximum principal stress of the surface layer, the bottom surface of the surface layer and the bottom surface of the base layer; Step 2: Analysis of the influence of single factor parameters: By using the control variable method, the pre-cutting width, depth, and spacing of the two-dimensional finite element model of the semi-rigid base asphalt pavement are changed respectively, and the internal stress distribution of the semi-rigid base asphalt pavement under different pre-cutting parameters is calculated. The relationship between the pre-cutting parameters and stress is established, and the influence of a single parameter change on the internal stress of the base is calculated; Step 3, two-factor interaction analysis: change the two pre-cutting parameters at the same time, calculate the additive interaction evaluation value R of width-depth, width-spacing, and depth-spacing, and the calculation formula of the evaluation value R is: R=(R A+B+ -R A-B- )-(R A+B- -R A-B- )-(R A-B+ -R A-B- ) =R A+B+ -R A+B- -R A-B+ +R A-B- Among them, A+ and A- are the larger and smaller values ​​of parameter A, B+ and B- are the larger and smaller values ​​of parameter B, R>0 indicates a positive interaction, R=0 indicates no interaction, and R<0 indicates a negative interaction; Step 4: Orthogonal test optimization: Design a three-factor five-level test, use the bottom stress of the semi-rigid base as the evaluation index, calculate the sensitivity of each factor through range analysis, and determine the best pre-cutting parameter combination.

2. The method for optimizing parameters of semi-rigid base pre-cutting considering the combined effects of vehicle load and temperature load according to claim 1 is characterized in that The width, depth and spacing of the pre-cut slits described in step 2 are 2-6 mm, 10-18 cm and 5-25 m respectively.

3. The method for optimizing parameters of semi-rigid base pre-cutting considering the combined effects of vehicle load and temperature load according to claim 1 is characterized in that The temperature field calculation is to calculate and obtain the temperature changes inside the pavement structure.

4. The method for optimizing parameters of semi-rigid base pre-cutting considering the combined effects of vehicle load and temperature load according to claim 1 or 3, characterized in that The temperature field calculation is to calculate the temperature change inside the pavement structure, which comprehensively considers the heating of the road surface by solar radiation, the back radiation of the road surface to the atmosphere, the heat convection exchange between the atmosphere and the road surface, and the heat transfer inside the road surface; and obtains the temperature field inside the semi-rigid base asphalt pavement.

5. The method for optimizing parameters of semi-rigid base pre-cutting considering the combined effects of vehicle load and temperature load according to claim 4 is characterized in that The heating of the road surface by solar radiation, the back radiation of the road surface to the atmosphere, the heat convection exchange between the atmosphere and the road surface, and the heat transfer inside the road surface are respectively realized through the definition of interaction and the user subroutines "FILM" and "DFLUX".

6. The method for optimizing parameters of semi-rigid base pre-cutting considering the combined effects of vehicle load and temperature load according to claim 1 is characterized in that The sensitivity of each factor is calculated by range analysis in step 4 by calculating the average level of each factor. Obtain the effect curve of the influencing factors and calculate the range R of each factor j , to obtain the sensitivity of each influencing factor to stress, where and R j The calculation formula is as follows: K ij ——The sum of the test data results of level i corresponding to factor j; ——The average value of the test data results of level i corresponding to factor j; R j ——The range of the mean value of the test data of r levels corresponding to factor j; n is the number of experimental repetitions, and r is the number of levels.

7. The method for optimizing parameters of semi-rigid base pre-cutting considering the combined effects of vehicle load and temperature load according to claim 1 is characterized in that When calculating the temperature field, the surface heat flux applied on the upper boundary is dynamically adjusted through the solar radiation intensity and the heat convection coefficient.

8. The method for optimizing parameters of semi-rigid base pre-cutting considering the combined effects of vehicle load and temperature load according to claim 1 is characterized in that Step 4: Obtain the optimal slitting parameters by conducting orthogonal tests and verifying the stress reduction effect. Verify the optimal slitting parameters by comparing the stress distribution under the optimal slitting parameter conditions and without pre-slitting.

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