Stability of scour protection due to earthquake-induced liquefaction: Centrifuge modelling: Fid-Bau Portal

Stability of scour protection due to earthquake-induced liquefaction: Centrifuge modelling

Escribano, D.E. / Brennan, A.J.

AbstractA key aspect of permanent offshore structures is protection against scour. This is typically in the form of a blanket of coarse gravel or cobbles surrounding the structure. These coarse particles are selected for their high resistance to being displaced by strong currents and thus protect the underlying finer sand particles from scour. However, in the event of an earthquake, the foundation sand may be susceptible to some degree of liquefaction. This research investigates the effects of seismic-induced liquefaction over a scour blanket, and if sinking is inhibited by some combination of the additional effective stress imposed by the gravel together with the interlocking resistance that develops when coarse particles are subjected to relative displacements.In order to evaluate the stability of scour protection blankets, a programme of physical modelling was carried out, involving the assessment of different configurations of stone layers over a liquefiable material, and a monopile-type foundation. Models were subjected to scaled base shaking equivalent to earthquake loading. A mass-balance of particle sinkage showed that a filter layer was critical for maintaining the integrity of the armour stones. Based on displacement and pore water pressure measurements, it was found that the presence of the scour protection blankets improved the response of the liquefiable sand under seismic loading, and even inhibited the occurrence of liquefaction. This implies that a well-designed scour protection blanket can assist in protecting against earthquake effects also.

Highlights•Centrifuge modelling was carried out to evaluate the stability of scour protection blankets over a liquefiable material.•Scour protection blankets improve the response of a liquefiable sand.•The stability of the scour protection blankets was highly improved by the use of a filter layer.•Design guidelines should consider the presence of scour layers in offshore foundations for areas prone to seismic action.