Improved Relationships for the Pile Base Response in Sandy Soils

Abstract

Design codes vary in their recommendations for the end-bearing response for bored piles founded in sand, both for the ultimate design value and the response at small settlements. The ultimate end-bearing resistance may be expressed either in terms of bearing factors Nq relative to the in situ vertical effective stress, with the Nq value varying with the friction angle of the sand, or as a factor applied to in situ test data, such as the standard penetration test blow count or the tip resistance qc. Numerical studies have led to proposed ratios of design end-bearing pressure to qc at specific settlement ratios, such as 5% and 10% of the pile diameter. The work presented here used numerical analysis to evaluate the full pile base response from initial stiffness to ultimate end-bearing resistance at a settlement ratio of 10% of the pile diameter. The resulting base responses are suitable for implementation in beam column analyses and have been validated by comparison with published design guidelines and with data from a full-scale instrumented pile load test.