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In open-ended piles, inner friction is developed between inner pile shaf and the inner soil. Inner frictional resistance depends largely on the degree of soil plugging, which is influenced by many factors including pile diameter, relative density and end conditions of piles. In this paper, effects of inner sleeves on inner frictional resistance are discussed. The experiments were conducted on a medium-dense sandy ground using laboratory-scale piles. It was observed that the piles penetrated under partially-plugged or unplugged state. The results suggest that inner fiictional resistance, Qin increases with sleeve height, l linearly and requires 2D (D is pile outer diameter) of l to produce a large as 50% of Qt by Qin (Qt is total resistance). The results also indicate that bearing capacity increases with wall thickness at the pile tip, which can be attributed to the increase in annular area. The results also indicate that soil plug height is independent of sleeve height. The results also reveal that the penetration of straight piles is closer to unplugged state than the sleeved piles. The results of incremental filling ratio and plug length ratio also indicate that the degree of soil plugging is affected by the sleeve height.