Small-scale physical modelling of scour at bridge piers with light-weight sediments

This study entailed physical model testing to support the design of marine facilities associated with a proposed 36 km long causeway, which is under construction in Kuwait Bay. The marine facilities include 1050 bridge piers, to be built in varying conditions in terms of water depth, soil conditions, current and wave conditions. Seabed levels vary from intertidal to approximately -12 m MSL and three different types of seabed material were observed: cap-rock underlain by sand, silty sand and silty clay. Light-weight sediment physical models with scales 1:20 and 1:37 were used to assess scour potential due to waves and currents at the base of the bridge piers and to guide the design of scour protection (rock armouring of the seabed). The PVC light-weight particles used to model the prototype silty sand had a density of approximately 1200 kg/m3 and a median diameter (d50) of 0.25 mm. Quantitative assessments of the seabed evolution were made with advanced photo-scan techniques. The model results provide insight to the evolution of scour over time and equilibrium scour hole dimensions, which were compared to predictions using empirical formulae. The similitude laws that apply for this type of model and observed model effects are also discussed.