A monolithic cement concrete pavement slab void state early warning method

Abstract

The application relates to a monolithic cement concrete pavement slab void state early warning method, which comprises the following steps: acquiring airport pavement measured data and airport operation data, judging whether the pavement is void, the void range and the void type; determining an evaluation machine type, the equivalent annual operation times of the evaluation machine type, the equivalent cumulative action times of the pavement and the allowable bending and tensile fatigue strength; constructing a finite element model of the pavement slab, and obtaining a void function relationship between the pavement slab void width and the maximum bending and tensile stress in the slab under different void types according to a simulation result; taking the cement concrete bending and tensile strength, the pavement design residual service life and the allowable bending and tensile fatigue strength corresponding to the evaluation period as dependent variables of the void function relationship, obtaining corresponding void widths as evaluation index threshold values; according to the void type and the corresponding threshold value, the void range is graded, the void state evaluation is completed, and early warning is carried out. Compared with the prior art, the application has the advantages of accurate evaluation, timely early warning and the like.

Description

Technical Field

[0001] This invention relates to the field of airport cement concrete pavement defects, and in particular to a method for early warning of voiding of a single cement concrete pavement panel. Background Technology

[0002] Airport concrete pavements are typically designed for a 30-year lifespan, but experience in my country shows that many airport concrete pavements require major overhauls after only 15-20 years. There are many causes of structural damage to pavements. Besides load-related factors such as rapid growth in air traffic and aircraft loads, a significant cause is the presence of voids between the pavement slab and the surface layer. Voiding is a common defect in airport concrete pavements. In its early stages, voiding manifests as separation between the pavement base layer and the surface layer, causing the surface layer to lose support from the base layer in certain areas. The surface layer slabs then operate under a cantilever beam-like stress pattern. Figure 1 As shown, this leads to a sharp increase in surface load stress, causing the pavement slab to crack. Furthermore, once voiding occurs, it will only worsen; it is an irreversible process that can only be eliminated or its development slowed down through specific treatment measures.

[0003] With the development of detection technology, it is now possible to determine whether pavement panels have become detached, and ground-penetrating radar (GPR) technology can accurately detect the location and extent of detachment. However, there is currently no method to evaluate the impact of detachment on the pavement, which means that GPR detection results cannot be effectively applied to pavement maintenance and detachment status assessment. Furthermore, the lack of a graded early warning system for pavement detachment in airport operations management makes it impossible to develop economical and reasonable maintenance plans for different detachment states of different pavement panels, resulting in wasted resources or a lack of safety assurance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for early warning of voiding in a single cement concrete pavement panel, which provides an early warning of voiding by accurately evaluating the voiding state of a single cement concrete pavement panel.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for early warning of voidage in a single cement concrete pavement slab includes the following steps:

[0007] S1: Acquire measured data of the airport pavement and airport operation data. Based on the detection results of ground-penetrating radar, determine whether the pavement is voided and the extent of voiding. Construct an circumscribed matrix for the voiding extent and determine the voiding type based on the positional relationship between the circumscribed matrix and the joints. The measured data of the airport pavement and airport operation data include the annual number of flights of each aircraft type at the tested airport, the remaining design service time of the pavement in the tested area, the evaluation period of the tested airport, and measured airport pavement structure data. The measured airport pavement structure data includes the flexural strength of cement concrete in the tested area, typical dimensional information of cement concrete pavement panels in the tested area, parameters of each operating aircraft type at the tested airport, reaction modulus of the base layer top surface, and joint load transfer capacity level.

[0008] S2: Determine the evaluation machine type, convert the annual operating frequency of each machine type into the equivalent annual operating frequency of the evaluation machine type, determine the equivalent cumulative number of pavement actions based on the equivalent annual operating frequency of the evaluation machine type, and determine the allowable flexural fatigue strength based on the equivalent cumulative number of pavement actions and the flexural strength of cement concrete.

[0009] S3: Based on the measured airport pavement structure data, a finite element model of the pavement panel is constructed. Various detachment conditions are set up so that the detachment width is within a pre-configured range and simulated with a pre-configured step size. The maximum bending tensile stress inside the pavement panel is calculated sequentially to obtain the corresponding data points of the detachment width and the maximum bending tensile stress inside the panel under different detachment types. The data points of the same detachment type are fitted to obtain the detachment function relationship between the detachment width and the maximum bending tensile stress inside the panel under different detachment types.

[0010] S4: The flexural strength of cement concrete, the allowable flexural fatigue strength of cement concrete pavement surface material corresponding to the remaining service time of pavement design, and the allowable flexural fatigue strength of cement concrete pavement surface material corresponding to the evaluation period are respectively used as the dependent variables of the void function relationship of a single cement concrete pavement panel, and the corresponding void width value is calculated in reverse, which is used as the threshold of the void size evaluation index.

[0011] S5: Based on the void type and void size evaluation index thresholds, classify the dimensions of the outer matrix of the void range into levels to complete the void status evaluation of a single cement concrete pavement slab. Based on the void evaluation results, determine the corresponding early warning level and take corresponding maintenance measures according to the early warning level and pre-configured rules.

[0012] The rectangle that forms the outer matrix of the vacated area encloses the entire vacated area with the smallest possible area, and one or two sides of the outer rectangle coincide with the joint of the slab panel where the vacated area is located.

[0013] The types of delamination include three types: corner delamination, edge delamination parallel to the aircraft's runway direction, and edge delamination perpendicular to the aircraft's runway direction.

[0014] The method for determining the type of void based on the positional relationship between the circumscribed matrix and the plate seam is as follows:

[0015] If two sides of the circumscribed rectangle coincide with mutually perpendicular board joints, or if only one side of the circumscribed rectangle coincides with a board joint, and the entire circumscribed rectangle is located on one side of the axis of symmetry of the overlapping board joint, and the distance from the axis of symmetry of the circumscribed rectangle to the nearest corner of the pavement board is less than 1 / 4 of the length of the overlapping board joint, then the void type is corner void; other voids are edge voids.

[0016] When a core sample test is available, the flexural strength of the cement concrete is determined based on the on-site core sample test; when no core sample test is available, the flexural strength of the cement concrete is set as the pavement design strength of the airport inspection area.

[0017] The remaining usable time of the pavement design in the detection area is obtained by subtracting the pavement usage time from the pavement design time.

[0018] The method for converting the annual operating frequency of various aircraft types into the equivalent annual operating frequency of the evaluation aircraft type is as follows:

[0019]

[0020]

[0021] Among them, P k Let G be the single wheel load on the main landing gear of the k-th aircraft type; G be the maximum takeoff weight of the aircraft; K ... type; K be the single wheel z Main landing gear load distribution factor; n c Number of main landing gear; n w m is the number of wheels on a main landing gear; m is the number of aircraft types operating at the airport; k is the kth aircraft type; n s To evaluate the number of tires on a main landing gear of an aircraft model; N k P represents the annual number of operations for the k-th model. s To evaluate the single-wheel load on the main landing gear of the aircraft; N s To evaluate the equivalent annual number of operations of the aircraft.

[0022] The method for determining the cumulative number of pavement equivalent effects based on the annual operating frequency of the evaluation engine type is as follows:

[0023]

[0024] Where, N ei To evaluate the model at time t i The equivalent cumulative number of actions within; when i=s, t s This represents the remaining service life of the pavement design. When i=p, t pThe evaluation period is indicated by T; the passage width is indicated by W; and the width of one wheel mark on the main landing gear of the evaluated aircraft is indicated by W.

[0025]

[0026] Among them, P s To evaluate the single-wheel load (kN) of the main landing gear of the aircraft model; q s To evaluate the main landing gear tire pressure (MPa) of the aircraft model.

[0027] The method for determining the allowable flexural fatigue strength based on the equivalent cumulative number of pavement action cycles and the flexural strength of cement concrete is as follows:

[0028] σ ri =f cm (0.885-0.0163lgN ei ), i=s,p

[0029] Where, σ ri f is the allowable flexural fatigue strength of the concrete pavement surface material; cm This refers to the flexural strength of cement concrete.

[0030] When constructing the finite element model of the runway panel, for corner detachment, the detachment shape is set as a square, and the detachment width is the side length of the square. A four-plate model considering the load transfer effect of the joint is adopted. The detachment position is set at the corner of the plate where the four plates intersect. The load application position is the tangent point where the edge of the main landing gear wheel mark of the evaluation model is perpendicular to the plate joint at the corner. For edge detachment, the detachment shape is set as a rectangle, the length of the rectangle is the same as the length of the plate joint, and the detachment width is the width of the rectangle. A two-plate model considering the load transfer effect of the joint is adopted. The edge detachment is located at the edge where the two plates meet, and it only occurs on one plate. Finite element models of two types of edge detachment are constructed, namely edge detachment parallel to the aircraft runway direction and edge detachment perpendicular to the aircraft runway direction.

[0031] The warning level for pavement detachment should be determined based on the evaluation results of pavement detachment status. When the pavement detachment status level is "Good," the pavement slab support is good, and no warning is required. When the pavement detachment status level is "Medium," slight detachment occurs at the bottom of the slab, warranting a Level 1 warning. However, pavement slabs at this warning level will not affect the normal operation of the runway in the short term, and grouting maintenance can be carried out at the bottom of the slab before the next evaluation period of the runway inspection. When the pavement detachment status level is "Poor," detachment occurs at the bottom of the slab, warranting a Level 2 warning. The most unfavorable load position has not reached the maximum flexural tensile stress of the cement concrete, and the airport can still operate normally, but the detachment will develop rapidly, therefore maintenance of the detached area is required in the short term. When the pavement detachment status level is "Poor," severe detachment occurs at the bottom of the slab, warranting a Level 3 warning. The most unfavorable load position has exceeded the maximum flexural tensile stress of the cement concrete, posing a significant safety hazard, and immediate maintenance is required.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) Ground penetrating radar has the advantages of high efficiency and high accuracy in detecting pavement detachment. It can detect the location and outline of the detachment at the bottom of the pavement panel. This invention establishes a reasonable evaluation method for the detachment state of pavement panel based on the shape of the detachment at the bottom of the pavement panel. It uses the detection results to accurately evaluate the detachment, which is mutually beneficial with ground penetrating radar technology. It fills the gap in the evaluation method for the detachment at the bottom of a single panel, thereby realizing the early warning of detachment.

[0034] (2) This invention, referencing existing design specifications, calculates the allowable flexural fatigue strength of the pavement panel corresponding to the remaining design time and evaluation period through rigorous theoretical derivation. The entire derivation process is clear and concise, with strong theoretical basis and high reliability. Based on relevant theories in this field, using the flexural strength and allowable flexural fatigue strength of the pavement panel as stress thresholds is highly reasonable.

[0035] (3) Based on the design and testing data of the pavement to be tested, this invention constructs a finite element model according to the actual pavement dimensions, pavement response modulus, and other data. The maximum flexural tensile stress within the slab is calculated using a step size of 0.25m for the void size. A functional relationship between the void size and the maximum flexural tensile stress within the slab is fitted. The entire model establishment and calculation process is based on the actual pavement condition, and the selection of the step size effectively reflects the entire process of void development at the bottom of the pavement slab. The theoretical derivation of the stress threshold is substituted into the functional relationship between the void size and the maximum flexural tensile stress within the slab to back-calculate the void size threshold. This process is logically rigorous, effectively utilizing the stress threshold and the finite element model calculation results. The final result meets the evaluation requirements for the void state of a single cement concrete pavement slab, and the evaluation results are authentic and reliable.

[0036] (4) This invention establishes corresponding early warning levels based on the evaluation results of pavement void status, and takes corresponding maintenance measures according to different early warning levels. The whole process is clear and concise, forming a targeted integrated management of "evaluation-early warning-maintenance", which is conducive to the timely treatment of pavement void defects. Practical application results show that the evaluation results of this evaluation method can reasonably reflect the pavement void status, conform to the development law of pavement void, and are accurate and reliable. Compared with traditional void evaluation methods, the accuracy is greatly improved. Attached Figure Description

[0037] Figure 1 This is a schematic diagram showing the bottom of the plate being hollowed out.

[0038] Figure 2 This is a flowchart of the method of the present invention;

[0039] Figure 3The diagram shows the case where the corner of the board is detached, where (a) represents the case where two sides coincide and (b) represents the case where one side coincides.

[0040] Figure 4 This is a schematic diagram showing the removal of the board edge.

[0041] Figure 5 The diagram shows the location of the load acting on the edge of the plate, where (a) is the case of a single wheel, (b) is the case of two wheels, (c) is the case of two axles and two wheels, and (d) is the case of three axles and two wheels.

[0042] Figure 6 The fitting curve for the edge void of the plate;

[0043] Figure 7 The fitting curve is for the corner of the plate being detached. Detailed Implementation

[0044] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0045] This embodiment provides a method for early warning of voids in a single cement concrete pavement slab, such as... Figure 2 As shown, it includes the following steps:

[0046] S1: Obtain actual measured data of the airport pavement and airport operation data, determine whether the pavement is delaminated and the range of delamination based on the detection results of ground penetrating radar, construct an outer matrix for the delamination range, and determine the type of delamination based on the positional relationship between the outer matrix and the slab gap.

[0047] In this embodiment, the measured data of the airport pavement and the airport operation data include the annual number of flights of each aircraft type at the tested airport, the remaining design service time of the pavement in the tested area, the evaluation period of the tested airport, and the measured airport pavement structure data. The measured airport pavement structure data includes the flexural strength of cement concrete in the tested area, the typical dimensional information of cement concrete pavement panels in the tested area, the parameters of each operating aircraft type at the tested airport, the reaction modulus of the top surface of the base layer, and the load transfer capacity level of the joints.

[0048] Airport evaluation period t p Evaluation of aircraft types and testing of the annual number of flights (N) for each aircraft type operating at the airport. i According to Articles 1 and 2 of D.0.6 in the "Technical Specification for Evaluation and Management of Civil Airport Pavement" (MH / T 5024-2019), it is determined as follows:

[0049] A1) The evaluation period is determined by the airport management agency or technical personnel according to the airport's usage requirements. In this embodiment, the evaluation period is the number of years the pavement has been in service since its construction and has met airworthiness requirements.

[0050] A2) Determine the airport's aircraft type combination and annual flight frequency using the following methods:

[0051] A21) Determine the aircraft type combination based on the actual operation of the airport, determine the average annual number of flights based on the airport's air traffic volume statistics for the past 5 years, and determine the annual number of flights for different aircraft types based on the average annual number of flights and the aircraft type combination.

[0052] A22) Determine the airport's aircraft type combination and the annual number of flights for different aircraft types based on the airport's master plan documents.

[0053] The remaining service life of the pavement in the inspection area (t) s (Year) is obtained by subtracting the time the pavement has been used from the pavement design time.

[0054] Flexural strength f of cement concrete cm (MPa) is determined according to the following method: when a core sample test is available, it is determined based on the on-site core sample test; when no core sample test is available, the flexural strength of the cement concrete is set as the pavement design strength of the airport testing area.

[0055] Typical dimensional information for the cement concrete pavement slab in the inspection area includes: pavement slab length *l* parallel to the aircraft taxiing direction, pavement slab length *w* perpendicular to the aircraft taxiing direction, and pavement slab thickness *h*. The pavement slab thickness is the effective thickness, which is used in finite element modeling.

[0056] The parameters for each aircraft type operating at the airport were obtained from Appendix A of the "Design Specification for Cement Concrete Pavement of Civil Airports" (MH / T 5004-2010).

[0057] The reaction modulus of the base course and the load transfer capacity level of the joints are determined by Appendix C and Section 7.4.4 of the "Technical Specification for Evaluation and Management of Civil Airport Pavement" (MH / T 5024-2019) based on the results of on-site deflection tests.

[0058] A rectangle that circumscribes the void area encloses the entire void area with the smallest possible area, and one or two sides of the circumscribed rectangle coincide with the joint of the slab panel where the void area is located.

[0059] There are three types of board edge separation: board corner separation, board edge separation parallel to the aircraft's runway direction, and board edge separation perpendicular to the aircraft's runway direction.

[0060] If two sides of the circumscribed rectangle coincide with mutually perpendicular slab joints, or if only one side of the circumscribed rectangle coincides with a slab joint, and the entire circumscribed rectangle is located on one side of the axis of symmetry of the overlapping slab joint, and the distance from the axis of symmetry of the circumscribed rectangle (perpendicular to the overlapping slab joint) to the nearest corner of the pavement slab is less than 1 / 4 of the length of the overlapping slab joint, then the void type is corner void. Figure 3 As shown; other gaps are gaps at the board edge, such as... Figure 4 As shown. For a corner gap, length a is the length of the longer side of the circumscribed rectangle, and width b is the length of the shorter side of the circumscribed rectangle; for an edge gap, length a is the length of the side of the circumscribed rectangle that coincides with the seam of the pavement panel, and width b is the length of the side of the circumscribed rectangle that is perpendicular to the seam of the pavement panel.

[0061] S2: Determine the evaluation model and convert the annual number of operations for each model into the equivalent annual number of operations N for the evaluation model. s The cumulative number of pavement equivalent actions (N) is determined based on the annual operating frequency of the evaluation model. es N ep The allowable flexural fatigue strength σ is determined based on the pavement equivalent cumulative number of loads and the flexural strength of cement concrete. rs σ rp .

[0062] S21: Determine the model to be evaluated.

[0063] The aircraft type for evaluation is determined according to Articles 1 and 2 of D.0.5 in the "Technical Specifications for the Evaluation and Management of Civil Airport Pavement" (MH / T 5024-2019), as shown below:

[0064] B1) Compile a table of current air traffic information for the airport, including information such as aircraft type name, maximum operating weight of the aircraft type, main landing gear tire pressure, annual takeoffs and landings, and ACN value.

[0065] B2) The technical personnel determine the evaluation aircraft type based on air traffic volume information. Generally, the evaluation aircraft type is selected from the one with the highest ACN value in the information table and whose annual takeoffs and landings account for no less than 5% of the airport's total annual takeoffs and landings.

[0066] Generally, the aircraft being evaluated is the largest aircraft operating within the airport.

[0067] S22: Convert the annual number of operations for various aircraft types into the equivalent annual number of operations for the evaluation aircraft type:

[0068]

[0069]

[0070] Among them, P k Let G be the single wheel load on the main landing gear of the k-th aircraft type (kN); G be the maximum takeoff weight of the aircraft (kN); K be the maximum takeoff weight of the aircraft (kN);z The main landing gear load distribution factor is taken as 0.95 in this embodiment; n c Number of main landing gear; n w m is the number of wheels on a main landing gear; m is the number of aircraft types operating at the airport; k is the kth aircraft type; n s To evaluate the number of tires on a main landing gear of an aircraft model; N k P represents the annual number of operations for the k-th model. s To evaluate the single-wheel load (kN) on the main landing gear of the aircraft; N s To evaluate the model-equivalent annual number of operations. In this embodiment, P i / P s Aircraft with a strength of less than 0.75 are not included.

[0071] S23: Determine the cumulative number of equivalent pavement action cycles based on the annual operating frequency of the evaluated engine type.

[0072]

[0073] Where, N ei To evaluate the model at time t i The equivalent cumulative number of actions within; when i=s, t s This represents the remaining service life of the pavement design. When i=p, t p The evaluation period is indicated by T, which represents the passage width; 11.4m is used for runways, and 2.3m can be used for taxiways and aprons. W represents the width of one wheel mark of the main landing gear of the evaluated aircraft.

[0074]

[0075] Among them, P s To evaluate the single-wheel load (kN) of the main landing gear of the aircraft model; q s To evaluate the main landing gear tire pressure (MPa) of the aircraft model.

[0076] S24: Determining the allowable flexural fatigue strength based on the equivalent cumulative number of pavement loads and the flexural strength of cement concrete:

[0077] σ ri =f cm (0.885-0.0163lgN ei ), i=s,p

[0078] Where, σ ri f is the allowable flexural fatigue strength of the concrete pavement surface material; cm This refers to the flexural strength of cement concrete.

[0079] S3: Based on the measured airport pavement structure data, a finite element model of the pavement panel is constructed. Three types of void conditions are set (corresponding to different void types), and the void width is simulated in a step size of 0.25m within the range of 0m to 2.0m. The maximum bending tensile stress σ in the pavement panel is calculated sequentially to obtain the corresponding data points of the pavement panel void width b′ and the maximum bending tensile stress σ in the panel under different void types. The data points of the same void type are fitted to obtain the void function relationship between the pavement panel void width and the maximum bending tensile stress in the panel under different void types.

[0080] Specifically, when constructing the finite element model of the pavement slab, the aircraft load is the main landing gear load of the evaluation aircraft type. The aircraft load parameters can be found in Appendix A of the "Design Specification for Cement Concrete Pavement of Civil Airports" (MH / T 5004-2010). The reaction modulus of the top surface of the base layer and the load transfer capacity of the joints are obtained through on-site deflection tests. The element type is selected as C3D8I. A suitable mesh density is required to ensure that the element size is less than half the thickness of the slab. In order to obtain accurate data, the element size is taken as 0.1m. In the delamination simulation, for corner delamination, the delamination shape is set as a square, and the delamination width b′ is the side length of the square. A four-plate model considering the load transfer effect of the joint is used. The delamination location is set at the corner of the plate where the four plates intersect. The load application location is the point where the edge of the main landing gear wheel mark of the evaluation aircraft is tangent to the plate joint perpendicular to the corner. For edge delamination, the delamination shape is set as a rectangle, the length a′ of the rectangle is the same as the length of the plate joint, and the delamination width b′ is the width of the rectangle. A two-plate model considering the load transfer effect of the joint is used. The edge delamination is located at the edge where the two plates intersect and occurs only on one plate. Finite element models for edge delamination parallel to the aircraft's runway direction and edge delamination perpendicular to the aircraft's runway direction are constructed respectively. Edge delamination can use a two-plate model considering the load transfer effect of the joint. The edge delamination is located at the edge where the two plates intersect and occurs only on one plate. The location of the load applied to the edge of the slab should be determined according to Article 5.0.1 of the "Design Code for Cement Concrete Pavement of Civil Airports" (MH / T 5004-2010). When evaluating the aircraft type with single-wheel, dual-wheel, or three-wheel main landing gear, the critical load position is as follows: Figure 5 As shown.

[0081] When fitting a function, the fitted functional relationship should guarantee the goodness of fit R. 2 The value should be greater than 0.95, and should reflect the relationship between the two. It should not be too complex and should allow the void width to be deduced from a given maximum bending tensile stress. This yields three functional relationships between the void width b′ of the slab and the maximum bending tensile stress σ within the slab:

[0082] σ=f j (b′),j=1,2,3

[0083] Where j=1 indicates the case where the corner of the board is detached, j=2 indicates the case where the edge of the board is detached parallel to the direction of the aircraft's runway, and j=3 indicates the case where the edge of the board is detached perpendicular to the direction of the aircraft's runway.

[0084] S4: The flexural strength f of cement concrete is respectively... xm The remaining service life of the pavement design (t) s The allowable flexural fatigue strength σ of the corresponding cement concrete pavement surface material rs Evaluation period t p The allowable flexural fatigue strength σ of the corresponding cement concrete pavement surface material rp As the dependent variable in the void function of a single cement concrete pavement panel, the corresponding void width value is calculated and used as the threshold for void size evaluation index.

[0085] Specifically, let:

[0086] f cm =f j (b j1 ′)

[0087] σ rs =f j (b j2 ′)

[0088] σ rp =f j (b j3 ′)

[0089] The solution yields that the internal stress of the detached pavement is equal to the flexural tensile strength f of the cement concrete. cm Threshold b for evaluating the size of the void at that time j1 The internal stress of the run-out surface is equal to the allowable flexural fatigue strength σ. rs Threshold b for evaluating the size of the void at that time j2 The internal stress of the run-out surface is equal to the allowable flexural fatigue strength σ. rp Threshold b for evaluating the size of the void at that time j3 ′.

[0090] S5: Based on the void type and void size evaluation index thresholds, classify the dimensions of the outer matrix of the void range into levels to complete the void status evaluation of a single cement concrete pavement slab. Based on the void status evaluation results, determine the corresponding warning level and take corresponding maintenance measures according to the warning level and pre-configured rules.

[0091] Specifically, the size classification of the outer matrix of the empty range is completed according to Table 1.

[0092] Table 1. Evaluation Criteria for De-emptying Status

[0093]

[0094] When the pavement slab void status level is "Good," the pavement slab bottom support is in good condition, and no warning is required. When the pavement slab void status level is "Medium," slight voids appear at the bottom of the slab, triggering a Level 1 warning. However, pavement slabs at this warning level will not affect the normal operation of the runway in the short term, and grouting maintenance can be carried out at the bottom of the slab before the next evaluation period of the runway. When the pavement slab void status level is "Poor," voids appear at the bottom of the slab, triggering a Level 2 warning. The most unfavorable load position has not reached the maximum flexural tensile stress of the cement concrete, and the airport can still operate normally. However, the voids will develop rapidly, so maintenance of the voided area is required in the short term. When the pavement slab void status level is "Poor," severe voids appear at the bottom of the slab, triggering a Level 3 warning. The most unfavorable load position has exceeded the maximum flexural tensile stress of the cement concrete, posing a huge safety hazard, and immediate maintenance is required.

[0095] This embodiment uses ground-penetrating radar detection results from the operational safety assurance department of a civil airport in eastern China as an example to evaluate the delamination status. The radar detection results show that there are delamination issues at the edge and corner of the pavement panels in some areas of the airport's runway 2, perpendicular to the aircraft's runway direction. The delamination status of a certain pavement panel in this area is as follows: the outer rectangle dimensions of the delamination at the edge perpendicular to the aircraft's runway direction are: length a = 2.56m and width b = 0.23m; the outer rectangle dimensions of the delamination at the corner are: length a = 0.65m and width b = 0.51m.

[0096] The airport's operational safety assurance department determined the reaction modulus of the base layer's top surface to be 103.56 MN / m using on-site deflection testing. 3 The load transfer capacity of the joint is rated as "poor".

[0097] According to information provided by the airport's operational safety assurance department, the airport pavement was designed 15 years ago and has been in service for 8 years; the pavement evaluation period is 4 years; the main operating aircraft parameters of the airport are shown in Table 2, and the airport pavement structural parameters are shown in Table 3.

[0098] Table 2 Aircraft Operating Parameters

[0099]

[0100] Table 3 Pavement Structure Parameters

[0101]

[0102]

[0103] According to information provided by the airport's operational safety department, the airport's cement concrete pavement is designed to have a remaining service life of 7 years.

[0104] According to the main parameters table of the aircraft, the B-767-300 is the largest aircraft and also the aircraft with the largest operating weight at the airport. Therefore, it was selected as the evaluation aircraft. The main parameters of the evaluation aircraft are shown in Table 4.

[0105] Table 4 Evaluation Model Load Parameters

[0106] Maximum takeoff weight (kN) 1596.5 <![CDATA[Number n of main landing gears e > 2 <![CDATA[Number of wheels n w > 4 Main landing gear load distribution factor p 0.95 <![CDATA[Single-wheel load P of the main landing gear s (kN)]]> 188.52 Tire pressure (MPa) 1.38 Wheel print size L (m) 0.5113 Wheelbase (m) 1.42 Coaxial wheel track (m) 1.14

[0107] The airport's remaining pavement service time (t) under the influence of the evaluated aircraft type s Evaluation period t p The allowable flexural fatigue strength σ of the corresponding cement concrete pavement surface material rs σ rp The calculation process is as follows:

[0108]

[0109]

[0110]

[0111]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[0118]

[0119]

[0120]

[0121]

[0122]

[0123] σ rs =5.0×(0.885-0.0163lg(9845.06))=4.10(MPa)

[0124] σ rp=5.0×(0.885-0.0163lg(5625.75))=4.12(MPa)

[0125] A finite element model was constructed using ABAQUS, with C3D8I element type and an element size of 0.1m. The finite element model has dimensions of 5m / 5m (length / width) and a thickness of 0.36m. The reaction modulus of the top surface of the base layer is 103.56MN / m². 3 The joint strength is 1.02 MPa, and the flexural strength of the cement concrete is 5 MPa. For corner detachment, a four-plate model considering the load transfer effect of the joint is used. The detachment is located at the corner of the intersecting plate, and the shape of the detachment is set as a square. The edge of the main landing gear wheel mark of the evaluated aircraft is tangent to the plate joint perpendicular to each other at the corner. At this time, the detachment width b′ is the side length of the square. For edge detachment perpendicular to the aircraft's runway direction, a two-plate model considering the load transfer effect of the joint is used. The edge detachment is located at the edge of the two intersecting plates and occurs only on one plate. The detachment length a′ is the same as the plate joint length, and the load application position of the edge detachment is set according to the critical load position.

[0126] In the finite element model, the widths of the plate corner detachment and the plate edge detachment perpendicular to the aircraft takeoff direction are calculated in increments of 0.25m, with the detachment widths ranging from 0m to 2.0m. The calculation results are shown in Table 5.

[0127] Table 5 Calculation results of maximum flexural tensile stress

[0128]

[0129]

[0130] Based on the data calculated using the finite element model, and according to the mapping relationship between the void size and the maximum bending tensile stress, the void size of a single cement concrete pavement slab and the maximum bending tensile stress within the slab are fitted to determine the functional relationship, such as... Figure 6 , Figure 7 As shown.

[0131] according to Figure 6 , Figure 7 The fitting results show that for the edge separation of the board in the direction perpendicular to the aircraft's runway, the sine function model is used for fitting, and the correlation coefficient R is [value missing]. 2 =0.99885 > 0.95, which meets the accuracy requirements. The fitted equation is y = -235.24765 + 240.35264sin(π(x + 37.01875) / 79.85347). For the corner gap, a sine function model is used for fitting, and the correlation coefficient R is 0.99885 > 0.95, which meets the accuracy requirements. 2=0.99942>0.95, which meets the accuracy requirements. The fitted equation is y=4.57588+1.38218sin(π(x-1.1261) / 2.2817).

[0132] The flexural strength f of the cement concrete of the airport cm Surface design remaining usage time t s The allowable flexural fatigue strength σ of the corresponding cement concrete pavement surface material rs Evaluation period t p The allowable flexural fatigue strength σ of the corresponding cement concrete pavement surface material rp Substituting "Tao" as the dependent variable into the functional relationship, as shown below:

[0133] 5.00=-235.24765+240.35264sin(π(b3′1+37.01875) / 79.85347)

[0134] 4.12=-235.24765+240.35264sin(π(b3′2+37.01875) / 79.85347)

[0135] 4.10=-235.24765+240.35264sin(π(b3′3+37.01875) / 79.85347)

[0136] 5.00=4.57588+1.38218sin(π(b1′1-1.1261) / 2.2817)

[0137] 4.12=4.57588+1.38218sin(π(b112-1.1261) / 2.2817)

[0138] 4.10=4.57588+1.38218sin(π(b1′3-1.1261) / 2.2817)

[0139] Calculating the above equation yields:

[0140] b3′1=2.03m, b3′2=0.61m, b3′3=0.58m

[0141] b1′1=1.31m, b1′2=0.83m, b1′3=0.81m

[0142] The evaluation criteria for the airport's board corner separation and board edge separation in the direction perpendicular to the aircraft's runway are shown in Table 6.

[0143] Table 6. Evaluation Criteria for Airport De-airing Status in Specific Embodiments

[0144]

[0145] The dimensions of the circumscribed rectangle of the board edge detached from the direction of the aircraft's runway are: length a = 2.56m and width b = 0.53m; the dimensions of the circumscribed rectangle of the board corner detached from the runway are: length a = 0.65m and width b = 0.51m.

[0146] For the board edge detachment in the direction perpendicular to the aircraft's runway: b = 0.53m < 0.58m, according to Table 6, the detachment status evaluation result is "good".

[0147] For the corner separation: 0.61m < a + b = 0.65 + 0.51 = 1.16m < 2.03m, according to Table 6, the evaluation result of the separation status is "times".

[0148] For this panel, the edge void status is rated as "good" and no warning is required; the corner void status is rated as "minor" and a level two warning is required, indicating a relatively serious void status. The most unfavorable load position has not reached the maximum bending tensile stress of the cement concrete, and the airport can still operate normally. However, the void will develop rapidly, so grouting maintenance of the void area is required in the short term.

[0149] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for early warning of voidage in a single cement concrete pavement slab, characterized in that, Includes the following steps: S1: Acquire measured data of the airport pavement and airport operation data. Based on the detection results of ground-penetrating radar, determine whether the pavement is voided and the extent of voiding. Construct an circumscribed matrix for the voiding extent and determine the voiding type based on the positional relationship between the circumscribed matrix and the joints. The measured data of the airport pavement and airport operation data include the annual number of flights of each aircraft type at the tested airport, the remaining design service time of the pavement in the tested area, the evaluation period of the tested airport, and measured airport pavement structure data. The measured airport pavement structure data includes the flexural strength of cement concrete in the tested area, typical dimensional information of cement concrete pavement panels in the tested area, parameters of each operating aircraft type at the tested airport, reaction modulus of the base layer top surface, and joint load transfer capacity level. S2: Determine the evaluation machine type, convert the annual operating frequency of each machine type into the equivalent annual operating frequency of the evaluation machine type, determine the equivalent cumulative number of pavement actions based on the equivalent annual operating frequency of the evaluation machine type, and determine the allowable flexural fatigue strength based on the equivalent cumulative number of pavement actions and the flexural strength of cement concrete. S3: Based on the measured airport pavement structure data, a finite element model of the pavement panel is constructed. Various detachment conditions are set up so that the detachment width is within a pre-configured range and simulated with a pre-configured step size. The maximum bending tensile stress inside the pavement panel is calculated sequentially to obtain the corresponding data points of the detachment width and the maximum bending tensile stress inside the panel under different detachment types. The data points of the same detachment type are fitted to obtain the detachment function relationship between the detachment width and the maximum bending tensile stress inside the panel under different detachment types. S4: The flexural strength of cement concrete, the allowable flexural fatigue strength of cement concrete pavement surface material corresponding to the remaining service time of pavement design, and the allowable flexural fatigue strength of cement concrete pavement surface material corresponding to the evaluation period are respectively used as the dependent variables of the void function relationship of a single cement concrete pavement panel, and the corresponding void width value is calculated in reverse, which is used as the threshold of the void size evaluation index. S5: Based on the void type and void size evaluation index threshold, classify the size of the outer matrix of the void range into levels, complete the void status evaluation of a single cement concrete pavement panel, issue an early warning based on the void status evaluation results, and take corresponding maintenance measures according to the early warning level and pre-configured measures rules. The method for converting the annual operating frequency of various aircraft types into the equivalent annual operating frequency of the evaluation aircraft type is as follows: in, For the first Single wheel load on the main landing gear of each aircraft model; This is the aircraft's maximum takeoff weight; Main landing gear load distribution factor; Number of main landing gears; The number of wheels on a main landing gear; To detect the number of different types of aircraft operating at the airport; For the first Individual models; To evaluate the number of tires on a main landing gear of an aircraft model; For the first Annual number of operations for each model; To evaluate the single wheel load on the main landing gear of the aircraft model; To evaluate the equivalent number of annual operations; The method for determining the cumulative number of pavement equivalent effects based on the annual operating frequency of the evaluation engine type is as follows: in, To evaluate the model's performance over time The cumulative number of equivalent actions within; when hour, Indicates the remaining service life of the pavement design, when hour, Indicates the evaluation period; This refers to the passage width; To evaluate the width of one wheel mark on the main landing gear of the aircraft model, in, To evaluate the single-wheel load of the main landing gear of the aircraft model; To evaluate the main landing gear tire pressure of the aircraft model; The method for determining the allowable flexural fatigue strength based on the equivalent cumulative number of pavement action cycles and the flexural strength of cement concrete is as follows: in, The allowable flexural fatigue strength of the concrete pavement surface material; This refers to the flexural strength of cement concrete.

2. The method for early warning of voidage in a single cement concrete pavement slab according to claim 1, characterized in that, The rectangle that forms the outer matrix of the vacated area encloses the entire vacated area with the smallest possible area, and one or two sides of the outer rectangle coincide with the joint of the slab panel where the vacated area is located.

3. The method for early warning of voidage in a single cement concrete pavement slab according to claim 1, characterized in that, The types of delamination include three types: corner delamination, edge delamination parallel to the aircraft's runway direction, and edge delamination perpendicular to the aircraft's runway direction.

4. The method for early warning of voidage in a single cement concrete pavement slab according to claim 3, characterized in that, The method for determining the type of void based on the positional relationship between the circumscribed matrix and the plate seam is as follows: If two sides of the circumscribed rectangle coincide with mutually perpendicular board joints, or if only one side of the circumscribed rectangle coincides with a board joint, and the entire circumscribed rectangle is located on one side of the axis of symmetry of the overlapping board joint, and the distance from the axis of symmetry of the circumscribed rectangle to the nearest corner of the pavement board is less than 1 / 4 of the length of the overlapping board joint, then the void type is corner void; other voids are edge voids.

5. The method for early warning of voidage in a single cement concrete pavement slab according to claim 1, characterized in that, When a core sample test is available, the flexural strength of the cement concrete is determined based on the on-site core sample test; when no core sample test is available, the flexural strength of the cement concrete is set as the pavement design strength of the airport inspection area.

6. The method for early warning of voidage in a single cement concrete pavement slab according to claim 1, characterized in that, The remaining usable time of the pavement design in the detection area is obtained by subtracting the pavement usage time from the pavement design time.

7. The method for early warning of voidage in a single cement concrete pavement slab according to claim 2, characterized in that, When constructing the finite element model of the runway panel, for corner detachment, the detachment shape is set as a square, and the detachment width is the side length of the square. A four-plate model considering the load transfer effect of the joint is adopted. The detachment position is set at the corner of the plate where the four plates intersect. The load application position is the tangent point where the edge of the main landing gear wheel mark of the evaluation model is perpendicular to the plate joint at the corner. For edge detachment, the detachment shape is set as a rectangle, the length of the rectangle is the same as the length of the plate joint, and the detachment width is the width of the rectangle. A two-plate model considering the load transfer effect of the joint is adopted. The edge detachment is located at the edge where the two plates meet, and it only occurs on one plate. Finite element models of two types of edge detachment are constructed, namely edge detachment parallel to the aircraft runway direction and edge detachment perpendicular to the aircraft runway direction.

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