Improved Relationships for the Pile Base Response in Sandy Soils

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 N-q relative to the in situ vertical effective stress, with the N-q 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 q(c). Numerical studies have led to proposed ratios of design end-bearing pressure to q(c) 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. DOI: 10.1061/JGGEFK.GTENG-11035. (c) 2023 American Society of Civil Engineers.

Automated summary

Design codes have different recommendations for the end-bearing response of bored piles founded in sand, both in terms of ultimate design value and response at small settlements. The ultimate end-bearing resistance can be expressed in terms of bearing factors N-q relative to the in situ vertical effective stress or as a factor applied to in situ test data. Numerical studies have proposed design end-bearing pressure to q(c) ratios at specific settlement ratios, such as 5% and 10% of the pile diameter. This study used numerical analysis to evaluate the full pile base response and validate it against published design guidelines and data from a full-scale instrumented pile load test.