Vertical bearing capacity of super-long bored piles in soft soil area

Through the analysis of the results of super-long bored testing piles in soft soil area in Shanghai, the properties of the ultimate bearing capacity, the deformation characters of the pile tip and pile body, the change laws of side friction and tip resistance are investigated. The followings are proposed: (1) the construction of super-long bored pile should take the way of artificial drilling fluid to guarantee the quality of bored hole; (2) under the vertical pressure, the self-compression of super-long bored pile is 94% of the total settlement, and the self-compression coefficient is less than 0.5; (3) under the uplift force, the self-deformation of super-long bored pile is 95% of the total deformation, and the self-deformation coefficient is between 0.5 and 1.0; (4) the side friction of shallow layer soil keeps constant under the increasing loads, but that of deep layer soil increases to constant value; (5) the curve of tip resistance-displacement is linear varied when the tip displacement is less than 2 mm, which is rapidly changes when the tip displacement is more than 2 mm. This research is useful for the design and construction of the super-long bored piles in soft soil area. Also, it has important significance for further studies on load transfer laws of foundation piles.