Assessment of bridge performance after oil contamination below foundation piles

Abstract

Oil contamination does not only have a harmful impact on the environment, but it can also modify the engineering properties of soils, which may in turn affect performance of supported structures. The extent of modification of the engineering properties of sands by contamination is a function of the type of the oil, the percentage of contamination and the relative density of the sand. This paper documents results from a case history of oil leakage from a pipeline in the proximity of a bridge foundation supported on bored piles. The goal of the investigation was to assess the integrity of the foundation piles and determine whether remedial works were required to ensure a satisfactory performance of the bridge after contamination. A combination of experimental program and numerical analyses was therefore adopted in order to: (i) determine and quantify the degree of modification of the sandy soil due to the contamination, and (ii) predict the deformation of the bridge deck and forces in the piles after contamination, particularly under lateral loads. The numerical analysis involved 3D finite element modelling of the pile foundation using PLAXIS 3D Foundation software. The investigation has shown that sand contamination has the potential of increasing the deformation of the bridge. A significant increase of up to 48% in the bending moment has been predicted for the piles. Fortunately the pile structural capacity was not exceeded under the investigated conditions.