Study On The Settlement Characteristics Of The Widening Pile Slab Subgrade Structure Of Expressway In Soft Soil Area

The application of pile slab subgrade structure in expressway widening construction is a new way of expressway widening in recent years.The pile slab subgrade structure has the advantages of high strength,large rigidity and less land occupation.In this paper,the settlement calculation theory and pile side friction analysis are carried out for the structure of widened pile slab Subgrade in soft soil area.The parameter optimization of the numerical calculation model of pile slab subgrade structure is carried out according to the orthogonal test method,and the optimized numerical calculation model is established by using FALC^3Dfinite-difference software.The theoretical calculation and numerical model are carried out for the numerical calculation model The comparison and analysis of the settlement value measured on site and the overall settlement value of the model.（1）Based on the study of pile slab soil composite pile slab subgrade structure system,the settlement characteristics of pile slab subgrade structure are obtained.The settlement is divided into two parts:the pile-soil composite settlement section influenced by the properties of pile and soft soil together and the pile-soil compression settlement section only affected by the compression performance of soft soil itself.The calculation formula of the overall settlement of pile slab subgrade structure is established based on the load of Sato The basic differential equations of transfer model function and load transfer function method are obtained,and the calculation formulas of side friction and axial force of pile shaft are obtained.（2）The design parameters of pile slab subgrade structure are optimized by orthogonal test method,and the difference of pile-soil settlement is analyzed by the optimized numerical calculation model.Four main factors,i.e.pile length,pile diameter,pile spacing and bearing plate thickness,are selected for orthogonal test.The range analysis method is applied to analyze the settlement characteristics,flexural deformation characteristics and stress characteristics of the pile plate structure of the model.The optimized design parameters are pile length of 20m and pile diameter 0.6m.pile spacing 6m,bearing plate thickness 0.26m Based on the optimized design parameters By comparing the settlement curve of pile foundation with that of soft soil on pile side,it is found that the settlement difference between pile foundation and soft soil on pile side decreases with the increase of soil depth.（3）Through the comparison of theoretical calculation and numerical simulation of pile slab subgrade structure,the coincidence between the two is analyzed,and the overall settlement over time is predicted.After the comparative analysis of theoretical calculation and numerical simulation on the whole settlement of pile slab subgrade structure,axial force of pile foundation and friction resistance of pile side,it is found that the difference between theory and simulation gradually decreases with the increase of soil depth,which shows that there is a good coincidence between them;through the comparative analysis of field measured settlement curve and numerical simulation of the whole settlement curve It is found that the growth trend of the two curves is similar with time,which shows that the established numerical model can predict the final settlement value of the widening section of the expressway well.According to the simulated settlement curve,the final settlement of pile slab subgrade structure is about 22mm,which is in line with the settlement control requirements of expressway widening project,which provides a new method for settlement prediction of new pile slab subgrade structure.There are 47 figures,23 tables and 61 references in this paper.