Applicability of the SPT-based methods for estimating toe bearing capacity of driven PHC piles in the thick deltaic deposits

Abstract

Standard Penetration Test (SPT)-based design methods for pile foundations have been extensively used in Korean practice. However, their applicability for local application has seldom been examined, particularly for the thick deposits, such as in the Nakdong River deltaic area. This paper examines the applicability of three common SPT-based methods to deep sandy deposits in the delta. Routine SPT data, in which the test was completed for each of the N = 50 blows at less than 30 cm penetration in the last two increments of 15 cm, were adopted. A special SPT was conducted to examine the general relationship between penetration and blow counts in dense sands. Based on the special SPT and another well-documented case study, a simple linear extrapolation was developed to estimate data equivalent to N > 50. PDA (Pile Driving Analyzer) tests were also carried out to evaluate energy efficiency of the donut hammer used for the routine SPT. Energy correction factor (C E ) was determined as 0.9. Using the corrected N-values, the estimated SPT-based toe resistances were compared with data obtained from PDA tests, field load tests on piles, and a CPT (Cone Penetration Test)-based method. Results indicate that the SPT-based methods generally manifest a rather low reliability. The recommended Meyerhof’s method is deemed applicable for the preliminary design.