Soil Properties Evaluation Of New And Old Foundations And Differential Settlement Of Expressway Extension Based On CPTU Data

With the economic and social development,the original expressway with 4-lane dual carriageway can no longer meet the increasing traffic demand,resulting in an urgent task that is expanding road capacity.Due to its complicated geological conditions,highways in soft soil areas have great difficulties in splicing new and old subgrades.It is difficult to ensure that the differential settlement between new and old subgrades is controlled within a safe range.Therefore,it is of practical significance to study the differential settlement between the new and old subgrades and the treatment of soft foundations.Relying on the expansion engineering of the Beijing-Shanghai Expressway between Huaian and Jiangdu,and cooperating with China Design Group,the CPTU in-situ testing technology was conducted on the engineering.CPTU parameters are provided for comparative evaluation of soil engineering characteristics.Combined with finite element numerical simulation,the settlement and deformation characteristics of the new and old roadbeds are analyzed and studied.In addition,the existing settlement calculation empirical formula is improved,and a calculation formula more suitable for the differential settlement of the new and old roadbed expansion in the soft soil area of Jiangsu is proposed.The specific research contents of this article are summarized as follows:In the first chapter,the research on the characteristics,influencing factors and calculation methods of soft soil foundation settlement in China and abroad are summarized,and the differences between the expansion roadbed and the general roadbed are abalysed.At the same time,the contents of CPTU parameter prediction engineering characteristics are also reviewed.In view of the above research status,the urgent problems in related fields and the research framework of this paper are proposed.In Chapter 2,the engineering characteristics of new and old subgrade soil based on CPTU test are compared and evaluated,and basic physical and mechanical test parameters are acquired in laboratory test.An improved method for predicting soft soil engineering parameters using CPTU test parameters is proposed,including the compression modulus and undrained shear strength,consolidation coefficient and permeability coefficient.Besides,comparation of the difference of the engineering properties of the new and old subgrade soils and study of the correlation between each parameter and the treatment effect of the soft foundation under the existing subgrade is used to understand the rules of spatiotemporal evolution of existing roadbed under longterm load.In the Chapter 3,using the software called ABAQUS to study the various influencing factors of new and old roadbed settlement deformation,including soft soil layer thickness,filling height,loading rate vehicle load,and soft foundation treatment measures,etc.,the new and old roadbed settlement Deformation characteristics and rules are acquired.According to different treatment methods,the influencing factors were discussed.Specifically,the influence of the weight of foamed lightweight soil and the elastic modulus of pile composite foundation on vertical settlement and lateral displacement was understood by finite element calculation.And the reinforcement effects of various treatment methods were evaluated preliminarily.In the Chapter 4,based on the tangent modulus method proposed by Yang Guanghua,as well as the relationship between the initial tangent modulus obtained by the side pressure test curve and the resistance of the cone tip,the calculation of total settlement,post-construction settlement and differential settlement of the foundation soil after expansion formula are carried out.According to the calculation results of this method,combined with engineering examples,specific calculation and analysis are carried out on each section,and the treatment methods of soft foundation and design parameters are reasonably selected through comparison and optimization.The actual measured settlement data was used to verify the accuracy of CPTU parameters and the feasibility of the improved method,and the soft foundation treatment effect was evaluated.