Load-bearing characteristics of concrete-filled steel tubular combined piles (CFSTCPs) in sand-rock composite ground

Abstract

Novel concrete-filled steel tubular combined piles (CFSTCPs) have been widely used in offshore wind power projects in Fujian, China. The bearing capacity of their foundations has become a particular concern in the offshore wind power industry. However, experiments to understand the bearing performance of CFSTCPs in sand-rock composite ground remain few. In this study, a series of model experiments were conducted to investigate the load-bearing characteristics of CFSTCPs in sand-rock composite ground, and evaluate the effects of the rock-socketed length and uniaxial compressive strength (UCS) of the bedrock. Moreover, the accuracy and regularity of the test results were verified through numerical testing. The results showed that the load-settlement curve of the CFSTCP exhibited the failure pattern of “continuous and gradual, without obvious inflection point.” When the ultimate load was reached, interface sliding occurred between the steel pipe and sand. The pile tip penetrated the bedrock, resulting in penetration failure. The dimensionless relationship between the bearing ratio of the pile-tip resistance, rock-socketed length, and bedrock UCS was obtained to determine the critical rock-socketed length. Finally, an empirical method for calculating the ultimate bearing capacity of CFSTCPs was proposed. These findings promote the design of CFSTCPs for offshore wind turbine foundations.