Research On Long-term Deformation Characteristics Of Super-long Bridge Pile Foundation In Deep-soft Soil Layers Of Passenger Dedicated Line

In order to ensure high speed, security and comfort in operation of the passenger dedicated line, which laying ballastless track, the post-construction settlement is restricted strictly. The length of large span bridges is86.62%in Hangzhou-Ningbo passenger dedicated line, along with which has a wide distribution of deep-soft soil(flow plastic). The geological condition is so complicated that the bridge foundation settlement controlling become an urgent problem. In this paper, based on the project item of pile foundation in Hangzhou-Ningbo passenger dedicated line, combined with the methods of theoretical analysis, field tests and numerical simulation, the long-term deformation characteristics of long pile foundation in deep-soft soil area were researched. Following are some main issues and achievements:(1) Bridge foundation settlement monitoring schemes of typical worksite were laid out, and components field burying methods were summarized. Field test results showed that the deformation test methods were effective, and the components and equipments for testing were reliable.(2) The strain and compression of pile body, compression of soil between piles and under piles were monitored for a long time through field test. During construction process of pile caps, pier and bridge superstructure, the laws of deformation with time and load development were revealed. Combined with monitoring results of the bridge pier subsidence, the effect of subsidence controlling by ultra-long bored cast-in-situ piles was evaluated.(3) Using deep massive foundation method and equivalent layer settlement accumulation method, the final settlement of pile group and the thickness of compressed layer were calculated.(4) Typical piers’s piles foundation were simulated with finite difference software FLAC3D, by which the stress fields and displacement fields of foundation, the axial force transmission and foundation deformation of pile group, the load-sharing ratios of piles to subsoil were given. Combined with the calculation results, pile group effect was analysed.(5) Based on the growth curve (Logistic, Gompertz and Verhulst curve),variable weight combination forecasting method was discussed. Using FORTRAN programming language, prediction program VCFMS was developed. Then settlement data of subgrade and pier measured in the field was used for verification and application.