Influence Of Structure And Material On Premature Failure Of Pavements

Premature failure has been a great concern for highway engineers due to prevalent presence and frequent occurrence in China' s newly-built national highway networks which severely damage the public image of highway agencies as well as greatly compromise the cost-effectiveness of highway investment. With the implementation of West Development Strategy and continuous expansion of freeways,pavement premature failure becomes more and more important. Research efforts about premature failure have been reported over years with the rapid construction of China' s freeway network. Due to the variation in traffic,environment,axle configuration,subgrade condition,pavement structure,construction quality,supervision rule,acceptance specification,and maintenance policy from agency to agency,from place to place,premature failure may be. caused by different factors. Governing factors resulting in premature failure and rehabilitation strategies that follow may change significantly from projects to projects. As a result,site-specific study of premature failure of pavement structures is an integrated part to generate rigorous data in the optimization of transportation management system.This thesis presents an orchestrated research program on premature failure of highway pavement structures in the 2nd phase of Guangbei Section of National Highway 108 (Beijing to Kunming). Factors influencing pavement performance were explored with emphasis in pavement structures and asphalt mix materials. Extraction tests were conducted on asphalt concrete specimens sampled from field roads. Asphalt concrete and aggregate gradation were compared to design and acceptance specifications. Structural analysis was performed using commercial finite element analysis (FEM) software,ANSYS for various configuration of loads,structural layer combinations,and working environments. In order to simulate the deformation behavior of granular materials (subgrade soils and subbase materials),an elasto-plastic constitutive model,the Drucker-Prager (DP) model,was used in the analysis. Based on field investigation of traffic volume and axle loads,analysis about the influence of overloaded tracks on pavement performance was studied to quantify the actual amount that heavy axle contributes to pavement damage. Structural analysis using ANSYS was also performed to extract the influence of geometric design of subgrades on the responses of pavement structures,especially in cut-fill transitional section over longitudinal profiles and in cross sections. The determination ofpavement materials as a result of traffic accumulation,environmental influence,and/or poor construction quality was investigated through the analysis of critical responses.Major conclusions drawn from this study can be beneficial to the design,maintenance,and rehabilitation of pavements for mountainous roads. Research results indicate that aggregate gradation extracted from field samples are out of gradation bounds specified in the design file,which can be one of the contributing factors in the development of pavement distress,especially premature failure. Structural analyses suggest that overload trucks present a big concern for pavement performance,and might become the governing factor in the formation of premature failure. Overloaded trucks causes based layer to failure and promote in turn the nucleation,propagation and development of refraction cracks in surface layers. Structural analyses also concludes the influence of tire pressure on pavement responses,especially for overloaded axles. As a result tire pressure as well as axle load has to be strictly limited in accordance with design specification and heavy fines need to be charged with the truck companies to compensate the extra pavement costs of highway agencies. Recommendation of integrated design of subgrade-pavement systems is proposed for further research.