Ground Improvement by Stone Columns - A Case Study

ABSTRACT: Stone columns have been widely used as a cost-effective, fast and environmentally friendly ground improvement method. Stone columns improve the load-bearing capacity, reduce settlement and mitigate liquefaction of soft subsoil under structures like liquid storage tanks, earthen embankments, raft foundations etc. This paper first presents the basics of the stone column technique and discusses the design considerations, applications, advantages and limitations of this method. Then a case study of stone column installation under oil tank foundations and auxiliary buildings for a bunker terminal project in the Middle East is elaborately explained. Geotechnical investigation data of the project site revealed subsurface conditions comprising of very loose to loose and medium silty sand with low SPT N values for the top 13m depth in some boreholes. This necessitated ground improvement to meet the high bearing capacity requirement of 250kPa and 300kPa under marine gas oil tank, fuel oil tank and other structures and to achieve settlement criteria of a maximum uniform settlement of 50mm and 100mm during operation and hydrotest, respectively. As the soil profile varied across the tanks, stone columns of 0.9m in diameter with a grid spacing of 2-3m square and varying treatment, depths have been used. The design procedure, construction method and verification or confirmatory tests adopted for the successful delivery of the project is also covered in this study. Keywords: Ground improvement, Stone columns, bearing capacity, oil tank.