Study On Freezing-Thawing Resistance Of Expanded CFG Pile-Soil Compite Foundation With High-Speed Railway Section In Seasonal Frozen Region

In recent years,high-speed railway has widely developed because of its speed and transportation ability.Meanwhile,with the implementation of ‘One Belt,One Road' and the continuous innovation about high-speed railway technology,many high-speed railway projects will be built in seasonal frozen area and will also bring many key technical problems restricting the constriction and development of high-speed railway.The study on subgrade's stability is the core of the high-speed railway research in seasonal frozen area.According to the data of Harbin to Dalian high-speed railway project and the influence of different climate,hydrological condition,the numerical model of expanded CFG pile foundation is established and the relevant verification is carried out.In this paper,the ability of expanded CFG pile-soil composite foundation is calculated and analyzed on anti-freezing-thawing performance and bearing capacity of high-speed railway subgrade under different working conditions.The numerical results show that the expanded CFG pile foundation has a significant effect in controlling the freezing-thawing deformation of the high-speed railway subgrade.The working performance of expanded CFG pile-soil composite foundation is also studied in detail,which provides relevant theoretical guidance and design reference for the construction of the high-speed railway subgrade in seasonal frozen area.This paper mainly focuses the following research and obtains the relevant results:1)The temperature field under the isothermal environment is calculated,as well the influence of different pile parameters on freezing-thawing resistance of expanded CFG pile-soil composite foundation.It is found that the effect of expanded CFG pile-soil composite foundation is proportional to pile length,pile diameter and expanded head diameter,but inversely proportional to pile spacing and expanded head's position.Expanded CFG pile could reduce the freezing-thawing deformation of the original highspeed railway subgrade by about 80%.2)The displacement of the subgrade and the pile stress of the expanded CFG pilesoil composite foundation is studied under the usual,even extreme freezing-thawing environment.The results show the anti-freezing-thawing ability of expanded CFG pilesoil composite foundation is more remarkable when the yin and yang slope effect and the frozen conditions get stronger than usual.Compared with the CFG pile-soil composite foundation,the freezing-thawing deformation of high-speed railway subgrade will be reduced by about 50% under strong frozen condition.Expanded CFG pile could restrain the extreme uneven freezing-thawing damage effectively.3)The bearing traits and changing laws of the expanded CFG pile-soil composite foundation with different pile parameters are researched under the action of static load and the melting phenomenon during the seasonal melting stage.Furthermore,according to the calculating results,this paper presents the best pile type parameters of expanded CFG pile-soil composite foundation in seasonal frozen area.