Deformation characteristic of piles foundation pit engineering of urban rail transit in Beijing

According to the difference of excavation depth and the formation conditions, 80 case histories of foundation pit engineering of urban rail transit in Beijing are analyzed. The deformation laws of piles excavation induced by foundation pit engineering are studied in Beijing sand & gravel zone and clay soil zone. The results show that: (1) The horizontal displacements of retaining piles at top and body are in two directions, that is, towards and out of the foundation pit and the measured displacements are approximately in normal distribution. (2) The maximum pile deformation is the pile body deformation. The maximum pile deformation is about 0.05%H~0.12%H towards the foundation pit and about 0.02%H~0. 07%H out of the foundation pit. (3) The insertion ratio, the ratio of length to width and the system stiffness have certain influence on the maximum pile deformation. (4) The maximum value of horizontal displacement of piles towards the foundation pit mainly appears at 0.26H~0.45H, and the maximum value of horizontal displacement of piles out of the foundation pit mainly appears at 0.18H~0.20H. The results can be used to predict the lateral deformation of similar projects in Beijing and other areas and to guide the design and constructions. It also has great significance for preventing accidents foundation pits.