Discussion of 'Load and Resistance Factor Design of Drilled Shafts in Sand' by D. Basu and Rodrigo Salgado

摘要

The authors relate their approach to LFRD of drilled shafts in sand with three definitions: pile capacity determined in a static loading test, limit unit shaft resistance, and limit pile base resistance, alternatively expressed as ultimate toe resistance. First, the authors define the pile capacity determined in a static loading test as the load that induces a pile head movement equal to 10% of the pile diameter. The definition has its origin in a mistaken quotation of a now 70-year-old statement by Karl von Terzaghi (1942). Terzaghi wrote "the failure load is not reached unless the penetration of the pile is at least equal to 10% of the diameter at the tip (toe) of the pile." For the full quotation and context, see Likins et al. (2012). Note that Terzaghi did not define the capacity as the load generating a movement equal to 10% of the pile head diameter; he emphatically stated that, whatever definition of capacity or ultimate resistance used, it must not be applied until the pile toe has moved at least a distance corresponding to 10% of the pile toe diameter. (The pile head will then have moved an additional distance equal to the pile compression.)