Wide Storage Tanks on Piled Foundations

Abstract

Foundation designs benefit from correlation to well-documented case histories. However, for the design of wide tanks storing liquids, in particular those requiring piled foundations, only few well-documented case histories exist. The authors have found five papers reporting settlement of wide tanks or large groups and have reanalyzed the records. The reanalyzes show that a large piled foundation can be modeled as a flexible raft placed at the pile toe level with the foundation load distributed according to Boussinesq stress distribution, and, for large piled foundations, that the capacity of an individual pile is not relevant to the foundation performance. The findings are used to address the analysis of a hypothetical large piled foundation for an 84 m diameter LNG tank at a site with a 60 m thick soil profile, consisting of clay, sand, and clay deposited over competent dense gravel. The differential settlement between the perimeter and interior piles and the effect of drag force and downdrag are discussed. The limitation of drag force as affected by the pile spacing and the weight of the soil in between the interior piles is addressed.