Stability of Steel Oil Storage Tanks

Abstract

Oil storage tanks built on weak and compressible foundations have suffered catastrophic failures due to foundation instability. These experiences are reviewed and used to establish simple procedures for evaluating factors of safety against base shear failure and edge shear failure. Methods for averaging foundation shear strength values for these two modes of failure are described, which make it possible to apply simple bearing capacity formulas to conditions where the shear strength of the foundation varies with depth, and where the foundation contains or is overlain by layers of sand or gravel. Recommendations concerning minimum values of factor of safety against undrained foundation failure are provided. In cases where the first loading of the foundation is very slow, or where drainage is accelerated by sand drains, wick drains, or natural sand lenses, appreciable drainage and strength gain occurs during water load tests. Methods of rehabilitating tanks after failure of the foundation are reviewed.