Seepage Induced Soil Failure and its Mitigation During Suction Caisson Installation in Silt

Suction caisson is an advantaged foundation option for offshore wind turbines in sandy and clayey soils. In this work, a series of model tests were conducted to investigate the installation behavior of a suction caisson in silty soils. The test results showed that the total soil resistance to the caisson increased steadily with penetration depth in the beginning of the suction-assisted penetration (SP) process, but rose slowly or remained constant after reaching a certain depth with excessive soil heave. This failure mechanism, which was quite different from that identified in sandy or clayey soils, was caused by the seepage induced silt soil failure in the caisson, such as erosion, liquefaction or piping, with reducing internal side friction and tip resistance. To suppress this type of failure, a special filtration method was introduced to help caisson penetration. The test results showed that such filtration technique had the advantage of reducing the height of soil heave and prevent seepage induced soil failure in the silt, but also suppress the under pressure effects on reducing the soil resistance. Numerical simulations were also performed to aid in understanding the observed test results and mitigation mechanisms.