Research On Differential Settlement And Prevention Technology Of Pavement Under Viaduct

With the development of infrastructure in China,viaduct has become an important part of urban traffic system.During the operation of viaduct,differential settlement of pavement under viaduct exists universally which have caused serious diseases in transition section between road and cap.These diseases reduce the service life of the road and impact on traffic safety.Therefore the research on differential settlement mechanism and prevention technology of pavement under viaduct can effectively control differential settlement and reduce pavement diseases,which is of great theoretical and practical significance for ensuring road traffic safety.Relying on the scientific research project of Wuhan Urban Construction Committee,“Study on the differential settlement mechanism and prevention technology of pavement under the viaduct”(NO.2015-44),the differential settlement of pavement under viaduct is taken as the research object in this dissertation.The formation mechanism and influencing factors of differential settlement of pavement are analyzed to explore the comprehensive prevention and control technology in combination with field investigation and test,theoretical analysis,numerical simulation and engineering application.The main research contents and conclusions include:(1)Based on the field investigation,statistics and analysis of the characteristics and types of diseases,the differential settlement of pavement under viaduct is quite serious at the soft soil areas and mostly occurs in transition sections of caps.A vehicle-road system model under the viaduct was established to study the additional load caused by differential settlement of the pavement.The results show that the differential settlement aggravates the vibration of the vehicle;the additional load generated on the pavement accumulates the permanent deformation of the road surface,and the maximum additional load is caused by slab faulting of the pavement.(2)The formation mechanism of differential settlement of pavement under viaduct were analyzed as follow: the soft soil foundation deformation,the relative stiffness of the transition section of the cap,the long-term effects of the vehicle load on the viaduct and under the bridge,and accidental factors.The difference of stiffness between the cap and the subgrade is the main causation of vehicle bump.The key to alleviate the differential settlement of the pavement is to make the relative stiffness of the transition section of the cap evenly change.(3)The numerical simulation model on pavement settlement under the viaduct was established to analyze the influencing factors and its sensitivity.The results show that with the increase of deformation modulus of soft soil foundation,the differential settlement of pavement decreases,the foundation reinforcement treatment should be carried out to increase the foundation stiffness in design.With the buried depth of cap increases,the differential settlement of road surface decreases,the buried depth of the pile cap should be greater than 3m in design of viaduct pile foundation.With the decrease of the relative stiffness between backfill soil and soft soil foundation,the differential settlement of pavement decreases,both of stiffness should match in design and construction.Based on the sensitivity analysis of the influence factors in orthogonal test,the relative stiffness of the transition section in the cap and the deformation characteristics of the soft soil foundation are the key factors for the differential settlement of the pavement.(4)Based on the rigid-flexible transition principle,the treatment effect and applicable conditions of the rigid reinforcement and the flexible reinforcement treatment technology of the geocell were studied combined with engineering practice.The results show that the rigid reinforcement technology has better treatment effect when the differential settlement of the pavement is within 60 mm,which is suitable for old road transformation.The flexible reinforcement technology of the geocells can uniformly change the differential settlement of pavements within the reinforcement range and reduce the change rate of road slope,which is suitable for settlement control of new roads.Baesd on the optimization design for the flexible reinforcement of geocells,the flexible structural layer should be arranged with inverted trapezoids and evenly dispersed 3 to 5 layers,and the thickness of the top layer should not be less than 0.5m.In engineering practice,both of the reinforcement methods reduce the differential settlement of pavement and have achieved a significant effect on avoiding the vehicle bump finally.