Understanding inner friction mechanism of open-ended piles-An experimental study

Abstract

An open-ended pile can produce a bearing capacity similar to a closed-ended pile depending on inner frictional resistance, Qin, which depends on the degree of soil plugging. The degree of soil plugging may depend on many factors including pile outer diameter (D), tip thickness (t), sleeve height (l) and relative density (Dr). In this research, we studied the effects of t, D and l on bearing capacity using laboratory scale model piles. The tests were conducted on a medium dense sandy ground using model piles with different values of D, t and l. The results showed that bearing capacity increases with t, which can be attributed to increase in annular area. They also showed that soil plug height, h is dependent of l for larger diameter piles. The results of incremental filling ratio (IFR) showed that penetration of straight piles (i.e., no sleeve) is closer to unplugged state than the piles with a sleeve. While Qin is independent of l for smaller diameter piles (D=30 mm), it is dependent of l for larger diameter piles (D=50 mm). The results of Qin suggested that as large as 50% of Qt (Qt is total resistance) is contributed by Qin even with a small l (e.g., 10 mm) for smaller diameter piles, while Qin in larger diameter piles increases with l and requires 2D of l to produce a large as 50% of Qt by Qin.