Bunds around liquid storage tanks are generally designed so that they will retain more liquid than is contained in the tanks within them. A slow leak will therefore be contained. However, a sudden catastrophic tank failure will result in a surge of liquid, some of which may overtop the bund. Analysis of hazards allowing for this possibility therefore requires an estimate of how much liquid will overtop the bund. There is also the possibility that a bund may fail owing to the hydrodynamical forces exerted on it, but that is not considered at this stage.
The overtopping is predicted by HSL's model SPLOT (SPreading Liquid Over Terrain), which embodies a mathematical model based on Shallow Water Theory in a computer program which solves the equations in a robust manner. The Shallow Water Theory is supplemented by a model for the interaction of the liquid with a vertical bund. HSE also use two other models for predicting bund overtopping, namely OVERTOP and LSMS.
In order to test the efficacy of these models, HSE commissioned experiments from a team at Liverpool John Moores University (LJMU) which are described in full by Atherton (2005). Most of the trials used a cylindrical tank surrounded by a concentric circular bund wall, though others were done with rectangular and square bunds.
Earlier data (also with a concentric bund) exist where the bund is a bank sloping away from the tank at 60° and 30° and, again, SPLOT may be used to predict the overtopping in the case of sudden liquid releases.
The objective of this work was to validate SPLOT, LSMS and OVERTOP against experimental bund overtopping data, in order to gain confidence in the model and/or highlight any possible shortcomings.
This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.
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