Case studies on variability in soils and driven pile performance

In a pile foundation design, it is presumed that the pile performance variability could be related to the variability in the design soil parameters. The variability of these parameters is determined by considering the natural soil variability and the measurement errors, as well as the transformation uncertainty. The transformation uncertainty would theoretically increase the variability in the design parameters and therefore in the expected pile performance. The uncertainty of the calculation models would increase the expected foundation performance variability as well. To examine whether the variability increase is factual, the variability in actual pile performance is evaluated in relation to the variability in field test results. This paper focuses on the variability in driven pile performance, and three case studies in Jakarta are examined. The driven pile performance deduced from axial compressive pile load tests is evaluated, and the variability of pile settlement at different load levels is examined. The soil variability is deduced from the N-SPT values and the cone penetration resistance in the upper part of soil profiles. In general, the COV of soil profile is relatively comparable to the COV of pile settlement at different load levels. This trend is different from the results of the theoretical approach. The possible approaches to bridge this difference are subsequently discussed.