Decision-making method for estimating remaining life of asphalt pavement and pre-maintenance

Abstract

The present invention discloses a decision-making method for estimating the remaining life of an asphalt pavement and pre-maintenance, and belongs to the technical field of highway asphalt pavement detection. From the beginning of the operation of the expressway, the pavement condition is assessed before any disease occurs on the highway asphalt pavement; the road section preventive maintenance judgment is made through the PQI and its sub-item indicators. When 96>PQI≥90, preventive maintenance judgment is introduced, core sampling is performed on typical sections in the road section, and then a series of semicircular bending tests are performed to measure the dynamic modulus, fatigue life and bending tensile strength. Combined with the traffic volume survey, the remaining life of the asphalt pavement is estimated, the maintenance time is determined, and maintenance decisions are made. The present invention can assess the pavement condition before any disease occurs on the asphalt pavement. After comprehensive comparison and analysis of multiple data, the scientificity and accuracy of the preventive maintenance decision of the pavement are improved, the real situation of the pavement performance is reflected, high-quality maintenance is achieved, and a more scientific reference basis is provided for the construction of long-life highways.

Description

Technical Field

[0001] The invention relates to the technical field of highway asphalt pavement detection, and in particular to a decision-making method for estimating the remaining life of an asphalt pavement and pre-maintenance. Background Art

[0002] With the rapid development of China's highway construction, the total mileage of highways in the country has reached nearly 6 million kilometers, of which 177,000 kilometers are expressways. Most of the expressways use asphalt concrete pavement, and its maximum design life is currently only 15 years. my country's high-speed highway construction has gradually entered a new stage of "maintenance as the main and construction as the auxiliary". The pavement needs to adopt the concept of full life cycle cost control, promote the preventive maintenance of asphalt pavement, and timely maintain and treat micro-diseases of the pavement to promote a virtuous cycle of preventive maintenance and pavement life extension. At the same time, my country's logistics and transportation industries are developing rapidly. The traffic volume and the number of heavy vehicles on many highway trunk networks have increased rapidly, resulting in excessive traffic load on asphalt pavements. Some asphalt pavement diseases appear in advance, affecting the road's traffic capacity and normal use. In order to solve the contradiction between the increase in highway traffic volume and the extension of pavement life, more scientific and accurate decisions need to be made in terms of the timing of preventive maintenance of asphalt pavements.

[0003] At present, there are schemes to predict the service life of pavements with different disease characteristics, and provide certain theoretical support for when to carry out pavement maintenance after the disease appears. However, the existing technology lacks certain preventive maintenance, and does not consider that the condition of asphalt pavements can be assessed and preventive maintenance methods can be decided before the disease appears. Although preventive maintenance requires earlier investment, it is a maintenance measure with the best cost-effectiveness ratio. Therefore, the present invention intends to provide a set of decision-making methods for estimating the remaining life of asphalt pavements and preventive maintenance, so as to provide a reliable basis for the timing and decision-making of preventive maintenance. Summary of the invention

[0004] The purpose of the present invention is to provide a decision-making method for estimating the remaining life of asphalt pavement and pre-maintenance, which can evaluate the pavement condition before the asphalt pavement is damaged. Through comprehensive comparison and analysis of multiple data, the scientificity and accuracy of pavement preventive maintenance decisions are improved, the actual situation of pavement performance is reflected, high-quality maintenance is achieved, and a more scientific reference basis is provided for the construction of long-life highways.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The decision-making method for estimating the remaining life of asphalt pavement and pre-maintenance includes the following steps:

[0007] S1. Evaluate highway sections: Combined with routine maintenance, evaluate the road surface condition from the beginning of the highway’s operation and before any damage occurs on the highway’s asphalt pavement;

[0008] S2. Use the asphalt pavement technical condition index PQI and its sub-item indicators to make judgments on road section preventive maintenance:

[0009] (1) When PQI ≥ 96, follow routine maintenance;

[0010] (2) When PQI < 90, repair and maintenance measures should be taken;

[0011] (3) When 96>PQI≥90, preventive maintenance judgment is introduced, core sampling is carried out on typical sections of the road section, and then a series of semicircular bending tests are carried out;

[0012] Typical sections include filled sections, half-filled and half-cut sections, turning sections, and entrance and exit speed change sections;

[0013] The number of core samples shall be no less than 1 complete core sample per 1 km;

[0014] Semicircular bending tests include dynamic modulus test, bending tensile failure test, and three-point bending fatigue test;

[0015] S3. Traffic volume survey: Conduct direct and indirect surveys on the evaluated highways, monitor the actual roads and obtain the annual traffic volume Q i ;

[0016] S4. Estimation of the remaining life of asphalt pavement: By defining the remaining life ratio ρ j , according to the number N of semicircular standard samples prepared by drilling core, take the average remaining life ratio And calculate the predicted number of residual equivalent axle load actions N f ;

[0017] S5. Determine the timing of maintenance and make maintenance decisions, including preventive maintenance, minor repairs, major repairs, and reconstruction.

[0018] Preferably, the dynamic modulus of each structural layer of the asphalt pavement can be obtained through the semicircular bending dynamic modulus test, and used for the finite element analysis of the asphalt pavement structure to obtain the stress distribution of each layer of the asphalt pavement structure under the 100kN double-wheel standard axle load; the specific process of the dynamic modulus test is:

[0019] S201. Install the matching sensor limiting devices on the semicircular specimen, with the spacing between the limiting devices being 5 cm;

[0020] S202, install a displacement sensor with a measuring range of ±1mm and an accuracy of 0.1μm, use a fixture for three-point bending test, and the bottom support spacing of the fixture is 0.8 times the diameter of the specimen;

[0021] S203. Use the UTM multifunctional testing machine and the supporting test program to measure the semicircular bending and tensile dynamic modulus of the specimen; during the modulus test, the bending and tensile deformation of the bottom of the specimen does not exceed 1500με, and each set of dynamic modulus data is 20 to 40με of the recoverable bending and tensile deformation of the specimen, and the irrecoverable bending and tensile strain does not exceed 100με.

[0022] Preferably, the semicircular bending fatigue test is used to determine the fatigue life, and a displacement sensor of ±5 mm is used to record the displacement response of the specimen during the failure process. The specific process is as follows:

[0023] S211. Divide the test specimens into three groups according to the order of pavement structure layers: upper layer, middle layer, and lower layer. Select one test specimen from each group to perform a semicircular bending fatigue test. The fixture installation and support spacing are the same as those for the semicircular bending dynamic modulus test.

[0024] S212. Use finite element software to simulate the stress-strain response of each structural layer of the asphalt pavement under the standard axle load and obtain the maximum horizontal tensile stress σ caused by it. max ;

[0025] S213, based on the fact that the semicircular bending failure strength of the same graded specimen is about 4 times the splitting failure strength, the tensile stress at the bottom center of the semicircular bending specimen is selected as σ≈4σ max The corresponding applied load is taken as fatigue load.

[0026] Preferably, the semicircular bending failure test is used to determine the bending tensile strength, and the specific process is: select another specimen in the semicircular bending fatigue test, the test loading rate is 50mm / min, the test environment is an environmental box at 20°C, and the test fixture and sensor are the same as the semicircular bending fatigue test.

[0027] Preferably, in step S3, the traffic volume survey method is specifically:

[0028] Direct survey method: sensors are buried in each lane to count the number of vehicle axles on the asphalt road since it was opened to traffic;

[0029] Indirect investigation method: Obtain traffic records at the toll booths, analyze and process them to obtain the vehicle axle count.

[0030] Preferably, in step S4:

[0031] Define the remaining life ratio ρ j :

[0032]

[0033] Where N 新 The service life of the fresh asphalt mixture is the semicircular bending fatigue test life of the fresh asphalt mixture with the same gradation as the old asphalt mixture with core drilling;

[0034] Average remaining life ratio

[0035]

[0036] Predicted number of residual equivalent axle load actions N f :

[0037]

[0038] Where DDF is the direction factor, LDF is the lane factor, m is the vehicle type number, VCDF is m is the distribution coefficient of vehicle type m, EALF m is the equivalent design axle load conversion factor of class m vehicles, t is the number of years of traffic, and its remaining service life n is predicted as follows:

[0039]

[0040] The derivation process of the above formula is as follows:

[0041]

[0042] Average annual growth rate of traffic volume

[0043]

[0044]

[0045] Finally, the following remaining life discriminant is obtained:

[0046]

[0047] Therefore, the present invention adopts the above-mentioned decision-making method for estimating the remaining life of asphalt pavement and pre-maintenance, and the beneficial effects achieved are:

[0048] 1. The present invention improves the scientificity and accuracy of existing preventive maintenance decisions for asphalt pavements. It can assess the pavement condition of asphalt pavements when no disease occurs on the asphalt pavement, and determine whether and when preventive maintenance is needed.

[0049] 2. The dynamic modulus, flexural strength, and fatigue life measured by the indoor semicircular bending test are combined with the monitored traffic volume, environmental conditions, etc., and a multi-data analysis is performed to construct an asphalt pavement remaining life prediction model, thereby obtaining an asphalt pavement preventive maintenance decision-making evaluation system, which can scientifically and accurately predict the remaining life of the pavement, achieve high-quality maintenance, delay the development of pavement diseases, and maintain or improve the functional condition of the pavement.

[0050] 3. The present invention uses a semicircular bending test, and its specimen preparation and test process are very simple and cost-effective; during the test, the stress state of the specimen is closer to the stress state of the actual pavement structure, truly reflects the pavement performance, and scientifically decides the maintenance time of the asphalt pavement, providing a more scientific and systematic reference basis for the construction of long-life highways in my country.

[0051] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a flow chart of the decision-making method of the present invention;

[0053] Figure 2 This is a schematic diagram of a semicircular bending test specimen of the present invention;

[0054] Figure 3 This is a schematic diagram of a semicircular bending dynamic modulus test of the present invention;

[0055] Figure 4 This is a schematic diagram of fatigue load determined by finite element software simulation in the present invention;

[0056] Figure 5 This is a schematic diagram of a semicircular bending fatigue test of the present invention;

[0057] Figure 6 This is a schematic diagram of the semicircular bending fatigue life estimation of the present invention;

[0058] Figure 7 This is a schematic diagram of the decision-making for pre-maintenance of asphalt pavement according to the present invention. DETAILED DESCRIPTION

[0059] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0060] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the usual meanings understood by persons with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. The words "include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, but do not exclude other elements or objects. The terms "set", "install" and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the internal connection of two elements. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0061] Example

[0062] like Figure 1-7 As shown, the present invention provides a decision-making method for estimating the remaining life of an asphalt pavement and pre-maintenance, comprising the following steps:

[0063] 1 (Step S1), evaluate the highway section: In combination with daily maintenance, the road surface condition is evaluated from the beginning of the opening of the highway to traffic, before any disease occurs on the asphalt road surface (at the same time, the highway management and maintenance department will perform daily maintenance on the asphalt road surface, and organize a road surface condition evaluation of the asphalt road surface every year).

[0064] Typical asphalt pavement diseases include cracking, block cracks, longitudinal cracks, transverse cracks, potholes, looseness, subsidence, rutting, ripples, oil spills, and repairs.

[0065] Second (step S2), the preventive maintenance of the road section is judged by the asphalt pavement technical condition index PQI and its sub-item indicators.

[0066] The pavement performance index (PQI) is calculated by evaluating the scores of the asphalt pavement sub-indicators of pavement damage (PCI), smoothness (RQI), rutting (RDI) and skid resistance (SRI), and comprehensively calculating the weights of the asphalt pavement PQI sub-indicators. The specific calculation formula is PQI = w PCI PCI+w RQI RQI+w RDI RDI+w SRI SRI. The weight of the asphalt pavement PQI sub-index is: PCI (High speed) = 0.35, w RQI (High speed) = 0.40, w RDI (High speed) = 0.15, wSRI (High speed) = 0.10.

[0067] The current "Technical Specifications for Maintenance of Asphalt Pavements on Highways" (JTG 5142-2019) requires that the PQI of asphalt pavements be ≥ 90, otherwise the asphalt pavement needs to be maintained. The "Technical Specifications for Preventive Maintenance of Asphalt Pavements on Highways" (JTG / T 5142-01-2021), an industry recommended standard of the People's Republic of China, also does not give clear indicators for the timing of preventive maintenance. Therefore, the present invention combines the PQI index to provide a scientific decision-making method for the timing of preventive maintenance:

[0068] 1. When PQI ≥ 96, perform routine maintenance;

[0069] 2. When PQI < 90, repair and maintenance shall be carried out;

[0070] 3. When 96>PQI≥90, preventive maintenance judgment is introduced, core sampling is carried out on typical sections of the road section, and then a series of semicircular bending tests are carried out.

[0071] (1) Typical sections include filled sections, half-filled and half-cut sections, turning sections, and entrance and exit speed change sections. When 96>PQI≥90 in the section, the number of core samples shall be no less than 1 complete core sample per 1 km.

[0072] Core sampling is to use a mobile coring machine to drill cylindrical core samples of the asphalt layer and the water-stabilizing layer on the asphalt pavement lane. The diameter of the core sample is 10cm, and the integrity and representativeness of the core sample are guaranteed as much as possible. The drilled core samples are cut indoors, and the core samples are cut in layers according to the thickness of the structural layer of the original pavement; for example, the structural layer of the asphalt pavement of the expressway is generally 4cm for the upper layer, 6cm for the middle layer, and 8cm for the lower layer; the specimens are cut using a 0.3mm thick saw blade cutting machine, which has little loss during the cutting process and can effectively improve the cutting accuracy of the specimens. The saw blade runs smoothly and the cutting surface is flat; the specimens are cut into cylindrical specimens of 4cm, 5cm, and 5cm in height; each cylindrical specimen is cut into two semicircular specimens along the diameter; the radius of the two semicircular specimens perpendicular to the cutting diameter does not differ by more than 1mm.

[0073] (2) Figure 2-6 The semicircular bending test includes dynamic modulus test, bending-tension failure test and three-point bending fatigue test.

[0074] a) If Figure 3-4 As shown in the figure, through the semicircular bending dynamic modulus experiment, the dynamic modulus of each structural layer of the asphalt pavement can be obtained, and used in the finite element analysis of the asphalt pavement structure to obtain the stress distribution of each layer of the asphalt pavement structure under the 100kN double-wheel standard axle load;

[0075] The specific process of dynamic modulus experiment is as follows:

[0076] S201. Install the matching sensor limiting devices on the semicircular specimen, with the spacing between the limiting devices being 5 cm;

[0077] S202, install a displacement sensor with a measuring range of ±1mm and an accuracy of 0.1μm, use a three-point bending test fixture, and the bottom support spacing of the fixture is 0.8 times the diameter of the specimen, that is, 8cm;

[0078] S203. Use the UTM multifunctional testing machine and the supporting test program to measure the semicircular bending and tensile dynamic modulus of the specimen; during the modulus test, the bending and tensile deformation of the bottom of the specimen does not exceed 1500με, and each set of dynamic modulus data is 20 to 40με of the recoverable bending and tensile deformation of the specimen, and the irrecoverable bending and tensile strain does not exceed 100με.

[0079] b) If Figure 5-6 As shown in the figure, the semicircular bending fatigue test is used to determine the fatigue life. The displacement sensor with a range of ±5 mm can effectively record the displacement response of the specimen during the failure process. The specific process is as follows:

[0080] S211. Divide the test specimens into three groups according to the order of pavement structure layers: upper layer, middle layer, and lower layer. Select one test specimen from each group to perform a semicircular bending fatigue test. The fixture installation and support spacing are the same as those for the semicircular bending dynamic modulus test.

[0081] S212. Use finite element software to simulate the stress-strain response of each structural layer of the asphalt pavement under the standard axle load and obtain the maximum horizontal tensile stress σ caused by it. max ;

[0082] S213, based on the fact that the semicircular bending failure strength of the same graded specimen is about 4 times the splitting failure strength, the tensile stress at the bottom center of the semicircular bending specimen is selected as σ≈4σ max The corresponding applied load is taken as fatigue load.

[0083] c) The semicircular bending destructive test is used to determine the bending tensile strength. The specific process is: select another specimen in the semicircular bending fatigue test, the test loading rate is 50mm / min, the test environment is an environmental chamber at 20℃, and the test fixture and sensor are the same as the semicircular bending fatigue test.

[0084] Step 3 (S3): Traffic volume survey: Conduct direct and indirect surveys on the evaluated highway, monitor the actual roads and obtain the annual traffic volume Q i .

[0085] Direct survey method: sensors are buried in each lane to count the number of vehicle axles on the asphalt road since it was opened to traffic;

[0086] Indirect investigation method: Obtain traffic records at the toll booths, analyze and process them to obtain the vehicle axle count.

[0087] Step 4: Estimation of the remaining life of the asphalt pavement (e.g. Figure 6 shown).

[0088] (1) By defining the remaining life ratio ρ j :

[0089]

[0090] Where N 新 The service life of the fresh asphalt mixture is the semicircular bending fatigue test life of the fresh asphalt mixture with the same gradation as the old asphalt mixture with core drilling;

[0091] According to the number N of semicircular standard samples prepared by drilling core, take the average remaining life ratio

[0092]

[0093] (2) Calculate and predict the number of residual equivalent axle load actions N f :

[0094]

[0095] Where DDF is the direction factor, LDF is the lane factor, m is the vehicle type number, VCDF is m is the distribution coefficient of vehicle type m, EALF m is the equivalent design axle load conversion factor of class m vehicles, t is the number of years of traffic, and its remaining service life n is predicted as follows:

[0096]

[0097] The derivation process of the above formula is as follows:

[0098]

[0099] Average annual growth rate of traffic volume

[0100]

[0101] Finally, the following remaining life discriminant is obtained:

[0102]

[0103] 5. (Step S5) Determine the maintenance opportunity and make maintenance decisions, including preventive maintenance, minor repairs, major repairs, and reconstruction.

[0104] During the fatigue test, the displacement response under each cyclic load is measured. Under the premise that the load size remains unchanged and the bending and tensile deformation at the bottom of the specimen is a small deformation, the semicircular bending and tensile dynamic modulus of the specimen at any time can be obtained; based on the test data of the fatigue test of the standard specimen made indoors, the semicircular bending dynamic modulus, fatigue test and destruction test data of the standard specimen can be obtained; the on-site core sample test data and the constructed remaining life estimation model data are compared and analyzed to determine the pavement performance of the original asphalt pavement and judge whether pre-maintenance treatment is required.

[0105] Therefore, the present invention adopts the above-mentioned asphalt pavement remaining life estimation and pre-maintenance decision-making method, which can evaluate the pavement condition before the asphalt pavement is damaged. Through comprehensive comparison and analysis of multiple data, the scientificity and accuracy of pavement preventive maintenance decisions are improved, the actual situation of pavement performance is reflected, high-quality maintenance is achieved, and a more scientific reference basis is provided for the construction of long-life highways.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A decision-making method for estimating the remaining life of an asphalt pavement and pre-maintenance, characterized in that: The following steps are involved: S1. Evaluate highway sections: Combined with routine maintenance, evaluate the road surface condition from the beginning of the highway’s operation and before any damage occurs on the highway’s asphalt pavement; S2. Use the asphalt pavement technical condition index PQI and its sub-item indicators to make judgments on road section preventive maintenance: (1) When PQI ≥ 96, follow routine maintenance; (2) When PQI < 90, repair and maintenance measures should be taken; (3) When 96>PQI≥90, preventive maintenance judgment is introduced, core sampling is carried out on typical sections of the road section, and then a series of semicircular bending tests are carried out; Typical sections include filled sections, half-filled and half-cut sections, turning sections, and entrance and exit speed change sections; The number of core samples shall be no less than 1 complete core sample per 1 km; Semicircular bending tests include dynamic modulus test, bending tensile failure test, and three-point bending fatigue test; S3. Traffic volume survey: Conduct direct and indirect surveys on the evaluated highways, monitor the actual roads and obtain the annual traffic volume Q i ; S4. Estimation of the remaining life of asphalt pavement: By defining the remaining life ratio ρ j , according to the number N of semicircular standard samples prepared by drilling core, take the average remaining life ratio And calculate the predicted number of residual equivalent axle load actions N f ; The calculation process and formula are: Define the remaining life ratio ρ j : Where N 新 The service life of the fresh asphalt mixture is the semicircular bending fatigue test life of the fresh asphalt mixture with the same gradation as the old asphalt mixture with core drilling; Average remaining life ratio Predicted number of residual equivalent axle load actions N f : Where DDF is the direction factor, LDF is the lane factor, m is the vehicle type number, VCDF is m is the vehicle type distribution coefficient of category m, EALF m is the equivalent design axle load conversion factor of class m vehicles, t is the number of years of traffic, and its remaining service life n is predicted as follows: The derivation process of the above formula is as follows: Average annual growth rate of traffic volume Finally, the following remaining life discriminant is obtained: S5. Determine the timing of maintenance and make maintenance decisions, including preventive maintenance, minor repairs, major repairs, and reconstruction.

2. The decision-making method for estimating the remaining life of asphalt pavement and pre-maintenance according to claim 1 is characterized in that: Through the semicircular bending dynamic modulus test, the dynamic modulus of each structural layer of the asphalt pavement can be obtained, and used for the finite element analysis of the asphalt pavement structure to obtain the stress distribution of each layer of the asphalt pavement structure under the 100kN double-wheel standard axle load; the specific process of the dynamic modulus test is as follows: S201. Install the matching sensor limiting devices on the semicircular specimen, with the spacing between the limiting devices being 5 cm; S202, install a displacement sensor with a measuring range of ±1mm and an accuracy of 0.1μm, use a fixture for three-point bending test, and the bottom support spacing of the fixture is 0.8 times the diameter of the specimen; S203. Use the UTM multifunctional testing machine and the supporting test program to measure the semicircular bending and tensile dynamic modulus of the specimen; during the modulus test, the bending and tensile deformation of the bottom of the specimen does not exceed 1500με, and each set of dynamic modulus data is 20 to 40με of the recoverable bending and tensile deformation of the specimen, and the irrecoverable bending and tensile strain does not exceed 100με.

3. The decision-making method for estimating the remaining life of asphalt pavement and pre-maintenance according to claim 2 is characterized in that: The semicircular bending fatigue test is used to determine the fatigue life. A ±5mm displacement sensor is used to record the displacement response of the specimen during the failure process. The specific process is as follows: S211. Divide the test specimens into three groups according to the order of pavement structure layers: upper layer, middle layer, and lower layer. Select one test specimen from each group to perform a semicircular bending fatigue test. The fixture installation and support spacing are the same as those for the semicircular bending dynamic modulus test. S212. Use finite element software to simulate the stress-strain response of each structural layer of the asphalt pavement under the standard axle load and obtain the maximum horizontal tensile stress σ caused by it. max ; S213, based on the fact that the semicircular bending failure strength of the same graded specimen is 4 times the splitting failure strength, the tensile stress at the bottom center of the semicircular bending specimen σ≈4σ is selected. max The corresponding applied load is taken as fatigue load.

4. The decision-making method for estimating the remaining life of an asphalt pavement and pre-maintenance according to claim 3 is characterized in that: The semicircular bending failure test is used to determine the bending tensile strength. The specific process is: select another specimen in the semicircular bending fatigue test, the test loading rate is 50mm / min, the test environment is an environmental chamber at 20℃, and the test fixture and sensor are the same as the semicircular bending fatigue test.

5. The decision-making method for estimating the remaining life of asphalt pavement and pre-maintenance according to claim 4 is characterized in that: In step S3, the traffic volume survey method is specifically as follows: Direct survey method: sensors are buried in each lane to count the number of vehicle axles on the asphalt road since it was opened to traffic; Indirect investigation method: Obtain traffic records at the toll booths, analyze and process them to obtain the vehicle axle count.

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