The effect of soil density on offshore wind turbine monopile foundation performance

Centrifuge model tests were performed to evaluate the response of offshore wind turbine monopile foundations, in both loose and dense sand deposits, subjected to lateral loading at serviceability limit state (SLS). Model monopile experiments were performed at 100 gravities (100g) of a prototype pile of di-ameter 5 m embedded to a depth of 30 m (L/D = 6). Evolution of pile deflection, lateral force and pile bending moments were monitored. Comparison of the observed deflected shape and pile bending moments against p – y methods of analysis predictions (API, 2011; DNV, 2014) indicate that design codes may underestimate the two parameters by up to 20 % at SLS. An initial series of 10 cycles at SLS were also carried out on the two sand densities. Results indicate an amount of ‘locked-in’ bending moment upon unload; a phenomenon which is more evident for the loose sand deposit.