Research On The Mechanism Of Rut And Its Control Measures In The Asphalt Pavement With Long-steep Longitudinal Slope

Rutting has been one of major early diseases in asphalt pavement. With freeway extending to mountain areas, the road designers inevitably encounter the problem of "long" and "steep" slopes in designing highways. However, rut in steep and long slope sections is more serious, which affects traffic safety greatly. Therefore, studying the formation mechanism and control measures of rut in long and steep slope sections of asphalt pavement is not only necessary, but also urgent.From driving state of vehicles in steep and long slope sections, the maximum ideal slope, maximum slope of unlimited length and restriction of maximum slope length were proposed under different altitude conditions. Through field investigations and laboratory tests for rut in uphill sections of typical steep and long slope, the influence factors of rut distribution laws were analyzed and interpreted in uphill sections of steep and long slope for asphalt pavement. The reason why the heavy vehicles run slowly was that the slopes were steep and long. In addition, the formation mechanism of rut in long and steep slopes was studied taking multi-axis heavy load and slow traffic as researched objects by studying the influence factors of rut.The static load creep test was carried out under different temperatures and stresses, and the equivalence of stress, temperature and time on the creep of asphalt mixture was analyzed. The mathematical expression of the joint displacement factor The temperature shift factor under constant stress, stress shift factor under constant temperature and connected shift factor under temperature and stress of asphalt mixture were deduced by the stress-temperature-time equivalence principle nonlinear viscoelastic body, and experimental data based on asphalt mixtures of AC-20 were used to verify it.According to the traffic characteristics of heavy load and slow speed in steep and long slope sections, numerical simulation of rut in asphalt pavement was carried out. And the influences of axle load, speed and number of cumulative axle load on the surface rut, permanent deformation in each layer of asphalt pavement, shear stress in pavement and equivalent creep strain were analyzed. The regression equation between surface rut and axle load, speed and number of cumulative axle load was established. However, rut in each layer of asphalt pavement was closely related to shear stress in pavement and distribution of equivalent creep strain, and the proportion of permanent deformation in each layer was consistent with the conclusions of field investigation.Mechanical responses of asphalt pavement were studied by simulating the process of climbing slopes with moving load under multi-axis heavy load and alienation of tires parameters in summer to the traffic characteristics of heavy load and overload. The results indicated that the front axle load of suspending axle vehicles was evenly applied to middle axle and rear axle which increased the influences on pavement significantly, and the influences included that the maximum vertical displacement, the peak of shear stress and the peak of conpressive stress increased significantly. As temperature increased, the mechanical indexes of pavement caused by the changes of tire pressure increased by nearly 10%. The distribution of maximum shear stress moved from wheel gap to wheel center on surface and moved from intermediate surface layer and lower surface layer under wheel center to surface along depth direction.Through studying high-temperature properties of asphalt mastic, filling effect of fine aggregates and skeleton effect of coarse aggregates, the optimal design method of asphalt mixtures for rut resistance was presented in steep and long slope sections. The type of modifier was selected using comprehensive evaluation method of fuzzy math and then the optimal modifier and hard asphalt were used in material composition design of asphalt pavement in steep and long slope sections. And the results from laboratory test showed that the modulus of asphalt mixtures increased, creep performance was improved and surface rut was reduced significantly after using modifier and hard asphalt.Finally, combining the analysis on formation mechanism of rut in long and steep slope, the treatment system of rut was proposed in long and steep slope from active control measures, optimal design of pavement structure and materials, heavy load and slow speed and traffic control at high-temperature.