| Weishi Xuchang expressway is an important part of Rizhao Nanyang national key highway.During the construction period of Wei Xu expressway,the "long-life composite asphalt pavement structure" of cement concrete pavement + asphalt concrete(including stress absorption layer)was adopted,and the key technology research of design and construction was carried out.The structure adopts many methods to ensure the long-term service performance of the pavement,including the use of reinforced subgrade,high flexural concrete,large thickness and small size cement panels,and the setting of stress absorption layers.However,after about15 years of service and operation,the whole line of Wei Xu expressway has been damaged by reflection cracks and structural fractures,requiring comprehensive pavement maintenance.Based on the maintenance project of Wei Xu expressway,the term "long-life composite asphalt pavement structure" is still used in this paper.Through on-site full-scale composite pavement mechanical response test,combined with finite element simulation analysis,this paper focuses on the detection and identification standard of slab bottom void,crack reflection law and asphalt layer crack fatigue life prediction of the structure,and finally forms the concrete slab stress prediction method,slab bottom void detection and identification,and asphalt surface crack fatigue life prediction method.The paper mainly includes the following aspects:(1)On the basis of summarizing the theoretical simulation of traditional composite road and rigid road,the large-scale finite element software ABAQUS is applied to establish the free plate model on Winkler foundation,analyze and discuss the influence of many modeling parameters on the calculation results of the model,put forward the recommended value range of these parameters,and establish a three-dimensional finite element analysis model of cement pavement considering the coupling effect of slab bottom void and joint load transfer,It lays a theoretical foundation for the simulation in the following chapters.(2)Based on the established single plate finite element model and double plate finite element model,several parameters that have a great impact on the stress of cement panel are selected,the influence mechanism of each parameter on the stress of cement panel is analyzed in detail,and the change law of the position of the maximum stress of the panel in the process of stress change is focused on.By analyzing and regressing the simulation results under various working conditions,the calculation formula of absolute void pavement structure panel stress considering void size,panel thickness and load is established.The calculation verification shows that the error of the formula is less than 3% and has high accuracy.(3)Based on the finite element model of cement pavement,combined with the field measured data of FWD deflection basin,the finite element model of composite pavement deflection analysis is established.The influence of each index on pavement deflection is analyzed through simulation,and the variation law of pavement deflection response is obtained.Relying on the physical project of Weixu expressway,the on-site detection of slab bottom void is carried out,the deflection values of 880 points are collected,and the applicability of five current detection methods is compared and analyzed.Based on the response law obtained by simulation and field detection data,an evaluation method of slab bottom void based on FWD single point deflection value is proposed.The proposed composite pavement void evaluation method is suitable for composite pavement with asphalt layer thickness of no more than 10 cm,and void detection should be carried out in non summer,which can greatly reduce FWD workload under the condition of ensuring high detection accuracy,guide the detection and maintenance of Expressway long-life pavement,and improve the corresponding technical specifications.(4)Combined with the detection and maintenance project of Weixu expressway,the strain sensor is embedded at the bottom of the asphalt layer,the tensile strain at the bottom of the asphalt layer is detected in real time,and the mechanical response of the asphalt layer with FWD and freight car as the load source is studied.Then,according to the measurement results,the appropriate mechanical parameters are selected to establish the vehicle load finite element model and temperature load finite element model of the composite pavement,and the influence law of many indexes on the mechanical response of the pavement is discussed.Based on the theory of fracture mechanics,two stress intensity factors of asphalt layer are calculated on the established finite element models of vehicle load and temperature load,and the prediction model of cracking fatigue life of asphalt layer of composite pavement is established based on the calculation results.The crack fatigue life prediction model of composite pavement asphalt layer proposed in this paper has been verified by the actual standard axle load times of multiple Expressway composite pavement,and the prediction effect is good,which can be used to guide the design and construction of composite pavement.The stress response law of composite pavement analyzed in this paper can help us understand that the proposed composite pavement void evaluation method can greatly reduce the void detection workload,and the established crack fatigue life prediction model of composite pavement asphalt layer can better predict the service life of composite pavement.The research of this paper provides theoretical basis and technical guidance for the design,construction and testing of long-life composite pavement. |
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