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 13 m depth in some boreholes. This necessitated ground improvement to meet the high bearing capacity requirement of 250 kPa and 300 kPa under marine gas oil tank, fuel oil tank and other structures and to achieve settlement criteria of a maximum uniform settlement of 50 mm and 100 mm during operation and hydrotest respectively. As the soil profile varied across the tanks, stone columns of 0.9 m dia. with a grid spacing of 2-3 m 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.

Climate change is expected to continue over this century and beyond with important impact on currently stable soil embankments. Soil response to precipitation pattern variation, due to climate change is directly related to pore water pressure and stress state changes. To accurately assess the behavior of embankments under changing climate, a deformation assessment using coupled hydro-mechanical analysis, with an appropriate elasto-plastic constitutive law may be required. However, priority in current engineering assessments is to identify the factor of safety against local, shallow or global failures, whereas deformation assessments are of a minor concern. In this research, the effect of climate change on the stability of embankments was quantified by estimating a field of Local Factor of Safety (LFS) using a coupled in-situ stress finite element analysis and variably unsaturated flow analysis. In this method, the effect of moisture content variation on the effective stress was taken into account using suction stress state. For a case study, the effects of climate change on the stability of a typical highway embankment consisting of sandy or silty soils in Niagara Falls, Ontario was considered. The study results demonstrate that the proposed simplified assessment approach is capable of identifying global and local failure zones without the use of advanced elasto-plastic simulations.