Development of Shaft Friction on Driven Piles in Sand and Clay

Despite widespread research effort in recent years, design methods to estimate the shaft resistance of displacement piles continue to rely heavily upon empirical correlations. In an attempt to achieve a more reliable design approach several researchers have assembled databases of instrumented pile load tests and used these to propose new design methods e.g. American Petroleum Institute (API-2000) for piles in sand and Lehane et al. (2000) for piles in clay. The most significant contribution to our understanding of displacement pile behaviour has resulted from field tests using highly instrumented piles, most notably those conducted with the Imperial College (IC) instrumented test pile (Bond 1989, Lehane 1992 and Chow 1997). These findings have been synthesised in the MTD design approach (Jardine et al. 2005), which has been shown to be more reliable than traditional design approaches at estimating the shaft resistance of driven piles. However, Randolph (2003) highlights the continuing presence of empirical factors in many new design approaches and demonstrates the need to understand the physical mechanisms governing pile capacity.