Steel pipe piles are widely used by various structures, such as bridges, ports, offshore oil and gas platforms and offshore wind turbines, etc. Vibratory hammers working as an efficient and silent tool are increasingly used for bridge construction in city areas, as well as for noise reduction required habitat for wild-life, like Cetacea, dolphins, and sea turtles. However, in-situ test results show that vertical bearing capacity fails to reach the design value for some steel pipe piles driven with vibratory hammers. Further observation and investigation indicate that the force developed at the pile tip is relatively small and heavily dependent on the degree of soil plug in the pipe. To address this, studies have been con-ducted through full-scale field tests on steel pipe piles driven with resonance-free vibratory hammers in Shanghai area, China. This paper focuses on the soil core developed in the steel pipe piles driven in the clayey site interbedded with sandy soil layers. Field observation and penetration tests show that the degree of soil plug is extremely low, which should be considered during the design of steel pipe piles driven with vibratory hammers.