Settlement Controlling Effect in Pile Raft Composite Foundation on Collapsible Loess in High Speed Railway

Based on the experimental study at home and abroad,the centrifuge model test is used to imitate pile raft composite foundation in different pile spacing to research and analyze the settlement controlling ability of pile raft composite foundation on collapsible loess ground in high speed railway.The research results show that collapsible loess ground which can not meet the request on settlement after construction in track structure in high speed railway need be reinforced.The settlement after construction,differential settlement,pile-soil load share ratio and the negative skin friction of pile get larger with the extending of pile spacing from two to six times of the pile diameter.The foundation settlement,settlement after construction,and the negative skin friction of pile get larger with the extending of pile spacing from two to six times of the pile diameter.Neutral point of the relative displacement between pile and soil drop with extending of pile spacing and rise to a stable level in post-construction stage.Value of the relative displacement between pile and cushion drop to a stable level in post-construction stage with extending of pile spacing.Differential settlement occurs mainly in construction stage.The differential settlement controlling effect of pile raft composite foundation is better in post-construction stage.