Study On Differential Settlement Mechanism And Control Standard Of Widending Subgrade Of Changyu Expressway

The Changyu Expressway was opened to traffic in 2002 and has been in operation for 17 years.It has undergone a major overhaul period.At the same time,it faces the traffic volume that is growing in Japan and needs to be expanded to improve service levels.In the widening project of expressway,the problem of differential settlement between old and new roadbed is faced.After years of consolidation settlement and external load,the deformation has reached basic stability,and the deformation of the new road has not yet reached stability,which will lead to the new and old roadbed.The difference between the settlements.At the same time,after the pavement structure is paved,the post-construction differential settlement between the old and new subgrades begins to increase,which causes the pavement structure to be overstressed and cracked,eventually leading to various diseases caused by cracking,such as looseness,water damage,etc..At the same time,the Changyu Expressway is located in the seasonal frozen zone,and the cyclical changes in atmospheric temperature and humidity will affect the working state of the subgrade.Therefore,based on the climatic characteristics of the seasonal frozen area,the actual engineering of the roadbed is extended for the Changyu Expressway,and corresponding control indicators and methods are proposed to ensure that the pavement structure has sufficient structural performance and functional performance in future service.A big problem facing.In view of this,this paper combines on-site monitoring and numerical simulation to solve the actual situation of the Changyu Expressway widening project,and expands the water-thermal-force coupling,differential settlement mode and the pavement structure mechanics under differential settlement.The research on scientific issues such as response,the main research contents and achievements are as follows:(1)To solve the problem of water and thermal field changes in the roadbed.Firstly,combined with the actual situation of the project,the physical quantity monitoring of temperature,humidity and stress deformation of the widened section was carried out,and the corresponding roadbed performance monitoring station was established to realize the wireless collection of on-site monitoring data.Further,the roadbed was established.The numerical model of hydrothermal coupling analysis is used,and the reliability of the model is verified by field data.Then the variation of the hydrothermal field of the longterm high-speed widening project with time and space is estimated and analyzed.(2)The problem of differential settlement mode for widening the roadbed of Changyu Expressway.Firstly,based on the research results of widening the water-heat coupling of roadbed,the water-heat-force coupling of the roadbed is broadened by considering the deformation caused by subgrade water,thermal field and foundation consolidation settlement.Based on the water-thermal-force coupling numerical model,the effects of construction period length,roadbed filling height,groundwater level depth,step excavation height and number of freeze-thaw cycles on widening post-construction differential settlement are studied.The one-dimensional quadratic polynomial,parabolic form,can be used as the post-employment differential settlement mode of the Yufu Expressway widening roadbed,and the corresponding estimation formula is given.(3)The standard and method of differential settlement control for widening the roadbed of Changyu Expressway.Firstly,considering the splicing of the pavement structure on site and the splicing of the pavement without structure,the mechanical response model of the pavement considering contact and non-consideration is established.Secondly,combined with the differential settlement mode,the mechanical response of the pavement results with or without pavement splicing,base thickness and different differential settlement values is studied.Again,it is proposed that the two pavement structures should be treated differently,and the pavement structure under the splicing condition is the most The unfavorable position is at the bottom of the joint seam,and the most unfavorable position of the integrated pavement structure is at the top of the base layer;further,based on the mechanical properties of the material,for the integrated pavement,the maximum allowable post-construction difference settlement value is 5.44 cm,which is spliced.The maximum differential settlement value of the pavement structure is allowed to take the value of the tensile strength of the joint at the seam location.Finally,for the widened roadbed with a shallower groundwater level,the gravel pile composite foundation method is adopted at the foundation of the new road.The validity of the method for widening the differential settlement control of the roadbed after work is determined,and the pile spacing is 1.75 m.