Study On Mechanical Properties And Design Method Of Highway Asphalt Pavement With Combined Base

Most asphalt highways in China are of semi-rigid base. Due to poor crack resistance of semi-rigid base, there are radioactive cracks on newly-built asphalt pavement, and thus service life of asphalt pavement is greatly reduced. In order to make up the shortcoming of semi-rigid base, the following method is adopted when damaged pavement is repaired:firstly, milling-planing for cracked semi-rigid base is conducted and large stone asphalt mixture is filled in as the upper base; secondly, the remained semi-rigid base which is in good condition is used as the lower base, and finally a combined base appears. Experiments on pavements show that this method is quite effective, and the combined base can not only be applied to pavement repairing but also be used in pavement building.Design code of asphalt pavement in China is tailored for semi-rigid base, so it is not rigorous to design asphalt pavement structure with combined base based on the existing design methods. As a result, design methods of asphalt pavement with combined base are in need. The thesis makes research on the following points.1. Study on anti-cracking performance of large stone asphalt mixture based asphalt pavement. Using finite element software to make models and conducting comparative analyses of crack resistance of bases between semi-rigid based asphalt pavement and large stone asphalt mixture based asphalt pavement, stress and stress intensity factor of the two bases under the same load are calculated, and it shows that large stone asphalt mixture based asphalt pavement structure is better in crack resistance.2. Study on the stress and strain distribution of the asphalt pavement under vehicle load. Finite element model is established to calculate tensile stress, tensile strain and shear stress under standard axle load, heavy load and overload. And taking the influence of change in subbase modulus on stress distribution of asphalt layer into consideration, stress characteristics of asphalt pavement with combined base are summarized.3. Study on design method of asphalt pavement structure with combined base. Integrating research results of both Chinese and foreign scholars with finite element modeling analyses and field tests, design method fit for asphalt pavement with combined base is proposed. This method takes the bottom tensile strain of asphalt layer and large stone asphalt mixture base as control index, and takes shear checking of asphalt layer as checking index. Based on this method, reasonable thickness of combined base under different moduli and vehicle load is recommended.The research result of combined base can not only be applied to renovation project of asphalt highway, but also be used in building new asphalt pavement. It enriches asphalt pavement structure and provides references for engineering designers.