Research On Behavior Of Combined Composite Foundation To Track's Test Of Beijing Section On Beijing-Tianjin Intercity Railway

Beijing-Tianjin inter-city rail traffic was the first passenger line opened in China in which the technology of ballastless track and CFG-pile composite foundation were applied. The post-construction settlement should be controled within 25mm. Basing on the gap of CFG-pile composite foundation applied in high railway,settlement characters of composite foundation was studied between Beijing test section, which relied on the subject—study on subgrade settlement control measures and deformation observation technology in passenger line.Then, the effect of CFG-pile composite foundation appiled in Beijing section was evaluated,by comparing pile-soil stress and settlement differences in different location;at the same time,the factors which affect settlement characters and pile-soil stress were researched and a reasonable design parameters were made.The factors they are the length,pile pitch,modulus and thickness of cushion.Based on the above study,some conslusions are below:1,Most of the load was beared by pile,but during the process of preloading.Some load was transferred from pile to soil; ultra-pore water pressure caused was little in the region;the settlement was the largest during the preloading and it was little after the load removed.2,The settlement characters of CFG-pile composite foundation caused by subgrade load were inverted bell-shaped;the surface settlement was the largest at the roadbed centerline;with the distance from the roadbed center increaseing,settlement reduced gradually;there was little ground uplift close to the border region.3,To a certain length,the relationship berween settlement and pile-length is inverse ratio; the longer length, the greater pile-soil stress ratio and the role of pile;the larger distence between pile.the large settlement and pile-soilstress;With cushion modulus increased,the settlement reduced slightly;but the pile-soil stress ratio increase,the impact of cushion thickness on the settlement is not significant,but the pile -soil stress ratio is noticeably affected by the cushion thickness.