Research On Full-scale Pavement Accelerated Loading Testing System

With the increasing of highway transportation volume and large tonnage vehicles, especially the high-grade highway channelization run, quite number of highway faced to the early damage of pavement structure after a few years such as rutting, cracking, wave and potholes. Even under heavy traffic conditions, serious structural damage will be occurred3-5years around, which not only affects the performance and life time of the road surface, but also causes huge economic losses. In order to study the reasonable structure and failure mechanism of the road surface, reduce construction and maintenance costs, optimize road performance, dynamics analysis and kinematics analysis for the loading vehicle virtual prototype are researched. The effects of pavement roughness, velocity, tire pressure and axle load on vehicle dynamic load are studied in different loading pattern. Finally, a full-scale pavement accelerated loading testing system is designed and developed, which can simulate the driving conditions of the vehicles on road and through controlled application of wheel loading to a layered pavement structure to accelerate road damage.At first according to the dynamics analysis and kinematics analysis for the loading vehicle virtual prototype, the variant curves of the velocity, acceleration, displacement and mechanical can be obtained in uniaxial loading and biaxial loading. The analysis results show that the running condition of the virtual prototype accord with operation requirement of the full-scale pavement accelerated loading testing system. The velocity and acceleration of the loading vehicle are all changed during the simulation of the virtual prototype, and what’s more, a delay time is needed in order to get stable loading. In uniaxial loading pattern, the transient time is about1.05s, while in biaxial loading pattern is about0.6s, which can provide a theoretical basis for full-scale pavement accelerated loading testing system design.The affects of pavement roughness, velocity, tire pressure and axle load on vehicle dynamic load are researched according to the uniaxial and biaxial loading model. The function is established among the vehicle dynamic load and the affect factors. In the static loading pattern, the vehicle dynamic load increases in proportion with the axle load, but increases almost unchanged with the tire pressure. In the dynamic loading pattern, the vehicle dynamic load increases in exponential relationship with the axle load and velocity, increases in logarithmic relationship with the wavelength, but increases almost unchanged with the tire pressure. The efficiency in biaxial loading pattern is approximately1.5times of the uniaxial loading pattern when the full-scale pavement accelerated loading testing system is used.Unique design method for wheel-rail contact angle curve is proposed to design the loading wheel tread. The contact points are well distributed and the profile has a small abrasion during the operation of the full-scale pavement accelerated loading testing system.The self-development full-scale pavement accelerated loading testing system adopts lot of patent technology such as double-axis eight-wheel, ellipse curve and linear guide, non-contact traverse. The system has been run870,506times single axis (axle load180KN) load and198,563times biaxial (axle load360KN) load tests in Shandong Jiaotong University Accelerated Loading Testing Center, which shows that the system has a good operability, maintainability and higher reliability.Finally, through paving flexible base full-scale straight test road which embedded asphalt strain gauge at the bottom of asphalt layer, structural simulation experiment was conducted using full-scale pavement accelerated loading testing system. Based on the experiment result, the experience relationship model is constructed of the dynamic response for pavement structures with the axle load and velocity. The dynamic response rule is also analyzed in the uniaxial and biaxial pattern. As the loading vehicle running, there is not only tensile strain but also compressive strain at the bottom of the asphalt layer. The compressive strain is occurred as the loading vehicle arrival or departure, and the value of the compressive strain is bigger in arrival. As the loading vehicle passes, the tensile strain is occurred. At the test temperature, the maximum compressive strain, the maximum tensile strain and strain amplitude are all in exponential relationship with the axle load. Velocity affects the strain response at the bottom of surface layer significantly, but it has little influence on the vertical compressive stress, and affects the stress pulse duration only, and the stress pulse duration and strain response at the bottom of surface layer reduce with the increase of velocity. The destroy degree of pavement is more serious in low velocity and heavy load, but tire pressure has little influence on the strain at the bottom of surface layer and the vertical compressive stress at the top of subgrade.