Shaft resistance of pre-bored precast piles in Shanghai clay

Abstract

Pre-bored precast piles with an enlarged base (PPEB piles) have been increasingly used in China over the past 5 years. However, the distributions of the shaft and toe resistance of the pile are still unclear. In order to reveal the ultimate bearing capacity and load transfer mechanism of PPEB piles in clay, three full-scale ultimate static loading tests were carried out in Shanghai. The test piles were instrumented with vibrating wire strain gauges to enable accurate measurement of the local shaft resistance along the pile shaft during the loading tests. The tests results revealed that about 75% of the pile bearing capacity was provided by shaft resistance when the ultimate load was applied and the majority of the shaft resistance was mobilised along the lower part of the test piles. After load testing, the soils around the test piles were excavated to evaluate the reliability and constructability of PPEB piles. The applicability of conventional methods (α-method and β-method) in estimating shaft resistance was assessed. In comparison with instrumented bored piles, the local shaft resistance of the PPEB piles in the lower stiff clays was significantly higher.