Investigation Of Crack Propagation In Asphalt Pavement Under Moving Traffic And Thermal Coupled Loads

Asphalt pavement is one of the main highway structures.It is influenced by natural environment,also subjects to repeated action of various moving traffic loads.The moving traffic loads include vertical load,horizontal load and friction during vehicle starting and braking.In addition,the temperature gradient is formed along the depth of pavement structure and temperature changes when the external environment changes.Stabilized base with inorganic binders is a kind of common structure in asphalt pavement in our country.This structure has its advantages.But the stabilized base with inorganic binders has the shortcoming that the dry shrinkage crack is produced easily.In the asphalt pavement with cracks in base,the concentrated stress is generated at crack tip under the moving traffic and thermal coupled loads,and the reflective crack is produced easily.At present,there are mainly analytical method,finite element method and experimental method to investigate the law of reflective crack propagation in pavement.Due to the scale of asphalt pavement structure and the characteristics of multilayer with complex materials,it is difficult to study reflective crack propagation under moving traffic and thermal coupled loads by experimental method.The analytical method based on fracture mechanics and damage mechanics is difficult to get analytical solution.The extended finite element method(XFEM)which is a kind of finite element,can not only solve the problems of complex structures and boundary conditions,but also analyze the law of crack growing freely.In this dissertation,XFEM method is used to analyze the law of reflection crack propagation of asphalt pavement under moving traffic and thermal coupled loads.The main contents of the current research are as follows:(1)Fatigue preformance and crack propagating process of asphalt mixture were analyzed by four point bending fatigue test and semi-circle bending test.Fatigue parameters and cracking parameters were obtained to provide as the inputes to numerical simulation.The simulation results show that the fatigue test and crack propagating test are in good agreement with the simulation results.The three-point bending test model of asphalt concrete beam was established by XFEM method.And the propagating law of composite crack was studied.The comparison between the results and experimental results showed that the crack propagating path,yield load and yield displacement fitted very well.It indicated that XFEM method can simulate crack propagation of asphalt concrete effectively.(2)Dynamic response of asphalt pavement with cracks under different moving traffic loads was analyzed.The asphalt pavements with crack and without crack were established.The dynamic response of asphalt pavement under two-axles moving traffic loads was studied.The dynamic response of the asphalt pavement with discontinuity between layers was investigated based on cohesive element method.The response of asphalt pavement structure with crack under heavy load and overload was studied by applying various axial loads of high and low tire pressures.The mechanical response of asphalt pavement under various moving conditions such as uniform velocity,normal acceleration,general braking and emergency braking was analyzed by introducing horizontal force coefficient of vehicle.The results indicated that the initial crack tip of asphalt pavement has the greatest tensile stress under general braking condition.(3)Propagation law of reflective crack in asphalt pavement was investigated under primary cooling and cyclic temperature load.The temperature field model of asphalt pavement was established based on the results of external airflow,solar radiation and variation of external temperature.And the distribution of temperature field in pavement is obtained.By using XFEM fatigue damage evolution equation and mechanics model of asphalt pavement,the response of pavement structure,crack growing rate,crack width and crack growing path of reflected crack in asphalt pavement under primary cooling and cyclic temperature load were analyzed.At the same time,the influences of initial crack length and initial crack Angle on reflective crack propagation were investigated.The results showed that the longer the initial crack was,the faster the crack growing rate would be,and the larger the initial crack Angle was,the slower the crack growing rate would be.(4)Propagating law of reflective crack in asphalt pavement under moving traffic and thermal coupled loads was researched.The model of moving traffic-temperature-pavement system including vertical and horizontal load of traffic was established.The propagating law of reflective crack and dynamic response in pavement structure were analyzed.The influences of the thickness of asphalt overlay and discontinuity between layers on reflective crack propagation were studied.Moreover,the influence of heavy load and overload on propagating law of reflective crack was investigated.Results indicated that heavy load and overload could accelerate the reflective crack propagation and enhance width of reflective crack.