Study On The Formation Mechanisms Of Top-Down Cracking And Methods Of Structure Optimization On Flexible Pavement In Xinjiang

With the rapid socio-economic development in Xinjiang in recent years,there have been major changes in the volume of traffic and traffic composition compared to the past.On the high-grade highways and national highways,the semi-rigid base asphalt pavement has experienced significant early damage and required extensive repairs,which has seriously hindered the development of Xinjiang.A large number of studies show that the flexible base asphalt pavement has excellent structural mechanical properties as well as good road performance,and can solve the common problems such as reflective cracks on semi-rigid base asphalt pavement.There are two problems to be solved when constructing the flexible base asphalt pavement structure in Xinjiang.One is the common Top-Down cracks on the flexible base asphalt pavement,and the other is the structure and design method of the flexible base asphalt pavement.Therefore,according to the special climate and traffic environment in Xinjiang with great temperature difference,the mechanism of Top-Down cracks formation and propagation in the flexible base asphalt pavement structure was studied.At the same time,its structural design as well as optimization method of the flexible base asphalt pavement based on Xinjiang's large temperature difference climate environment were investigated,which has important theoretical and practical significance for the application and promotion of flexible grass-roots asphalt pavements in regions with large temperature differences.This paper analyzes the traffic and climate environment in Xinjiang,and studies the effect of different pavement structures,different axle loads and different vehicle speeds on the Top-Down cracking of the flexible base asphalt pavement under normal temperature conditions by using ANSYS finite element software.Based on the theory of fracture mechanics,a three-dimensional fracture model was established.Besides,the variation law of stress intensity factor(SIF)was analyzed under different fracture location,fracture size,fracture ratio,different structural design parameters,and different axial load parameters,which confirmed the factors for crack propagation control.Based on the large temperature difference climate in Xinjiang,the temperature field and temperature stress field of flexible base asphalt pavement were studied under the extreme heat conditions in southern Xinjiang and extreme cold in northern Xinjiang.Subsequently,a simulation model of flexible base asphalt pavement was established under temperature-load coupling field,and the change of structural mechanical response of flexible base asphalt pavement was studied,from which the Top-Down cracking initiation mechanism of flexible base asphalt pavement was revealed.This study investigated the structure design indicators of flexible base asphalt pavement at home and abroad,combining the characteristics of climate zoning in Xinjiang,suggested the structure design indicators based on the Xinjiang different climate zoning.Study also optimized the structure design indicators of flexible base asphalt pavement,including layer thickness and modulus.At the same time,the structure design indicators were continued optimized to establish the simulation model of temperature-load coupling field,combining with partition in Xinjiang the most unfavorable climate,confirmed optimized flexible base asphalt pavement structure.Then study based on AHP analytic hierarchy process,analyzed the comprehensive mechanics performance of the flexible base asphalt pavement structure under the condition of normal and the most hostile environment in Xinjiang.Eventually,this study recommend the suitable flexible base asphalt pavement structure for different climate zones in Xinjiang province.