Study On Post-Construction Settlement Of Road Under Traffic Load

Road settlement can be divided into construction settlement and post-construction settlement. The construction settlement can be solved by filling soil. But it is difficult to mend the leak that caused by the post-construction settlement after the road is open. It will reduce the operational ability and increase maintenance cost of road. Both pore pressure dissipation and traffic load result in the post-construction settlement of road. Accurate prediction of post-construction settlement under traffic load is of great importance for controlling and reducing post-construction settlement by taking reasonable control measures in the design and construction. To solve this problem, the main studies of this thesis are as follows:First, a impulsive function of finite difference approximation expressions is used to describe the axle load, vehicle speed of traffic load in this paper. This function can simulate the vertical dynamic stress characteristics induced by uniform moving load moving on uniform elastic half-space surface or real traffic load moving on road, and it is verified by theory and field test.Secondly, by triaxial compressipon test, the relationship between axial strain and deviatoric stress is increasing or decreasing, and the relationship between Es/E50ref and q/qf are unlinear. Two equations were suggested to describe not only unlinear stiffness degradation but also strain softening and strain hardening in this paper. The correlation coefficient is 0.97 compared the new model with the measured stress-strain curve.Thirdly, The visco-elastic artificial boundary was built in Plaxis in this paper. It can simulate the dynamic stress fluctuations to the far-field in the vibration and eliminate the stress wave reflection in the fixed boundary by setting viscous absorbing boundary at the truncation boundary of finite element model. The spring unit setted on the viscous absorbing boundary simultaneously solves the drift of the finite element model in low frequency.The finite element model with the visco-elastic artificial boundary can accurately simulate the dynamic properties of road induced by traffic load, and it only needs a much smaller model size than that with fixed boundary.Fourthly, based on the cyclic triaxial experiments and the analysis of one factor, the relationships of accumulated plastic strain with load times and accumulated pore pressure with load times were fitted with power function. These factors included traffic load factors such as the amplitude of dynamic deciator stress and the rate of vibration, road factors such as void ratio, grain diameter, water content, resilience modulus and initial stress conditions such as initial static deviator stress, confining pressure.Finally, a numerical model to study the dynamic response in road induced by traffic load was built based on Plaxis FEM software in this paper. This model used an impulsive function to describe traffic load, the modified Hardening soil model to simulate the constitutive relation of soil and the visco-elastic artificial boundary to be combined with FEM. Using this numerical model, initial static deviator stress, confining pressure, the amplitude of dynamic deciator stress was calculated. The pass depth of traffic load was also calculated. The 6-15m of the pass depth was obtained acrroding to the standards defined by 0.001 percent the maxmen vertical dynamic strain. Then, accumulated plastic strain and accumulated pore pressure were calculated considering all of factors such as road factors, traffic load factors and initial experimental conditions. This numerical model was used to predict the post-construction settlement of Gu-cui road in Hangzhou. The 0.046m of the post-construction settlement after opening 300 days is according with the result of the field monitoring.