CPT-Based Investigation for Pile Toe and Shaft Resistances Distribution

The true distribution of both pile shaft and toe resistances along depth, has been an important issue in geotechnical engineering. Twenty four pile load test case records of deep foundation projects, where CPT, Cone Penetration Test, soundings were also advanced close to piles locations, throughout the world have been compiled for investigations and analyses. The geomaterial at these sites are homogenous, including sandy, clayey and silty soils. Four different methods for determining pile bearing capacity comprising the method based on critical depth concept, recommended approaches by CFEM, Canadian Foundation Engineering Manual 2006 (Unified method), American Petroleum Institute (API), and CPT-based methods are presented, compared and discussed. In addition, the influence of factors such as soil friction angle variations, calculated from qc, cone tip resistance, and overburden stress, are taken into account to perform indirect calculations. Direct and indirect CPT-based calculations on the pile capacity are studied to investigate the actual pile toe and shaft resistances distribution along depth. The comparisons reveal that in practice and in observations from full scale tests, shaft and toe resistances follow a nonlinear and gradual trend beyond the certain depth. However, it is not in agreement with conventional linear-constant or relatively linear distribution concept and some recommended codes.

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