Bearing Capacity of Suction Foundations

A suction bucket foundation is a closed-top steel tube that is lowered to the seafloor, allowed to penetrate the bottom sediments under its own weight first, and then pushed to full depth with suction force produced by pumping water out of the interior. In recent years, suction bucket foundations have been used increasingly for gravity platform,jackets, jack-upsetc. They also have the potential of being used for several other purposes, such as offshore wind turbines, sub-sea systems and seabed protection structures. The first advantage of suction bucket foundation is the convenient method of installation and repeatedly use. The second advantage is that it may mobilize a significant amount of passive suction during uplift under some conditions.

A series of centrifugal experiments, numerical modeling and theoretical analysis on the dynamic responses of suction bucket foundation under ice-induced or wave-induced load were carried out. The following results were obtained:

  1. Two sets of dynamic load devices, one can output loads with frequency of 0-200Hz and amplitude of 0-20kg, and the other can output frequency of 0-10Hz and amplitude of 0-600kg, for centrifugal experiments under high (150g) acceleration are designed and made.
  2.  Effects of factors (bucket size, load frequency, load amplitude, soil’s properties etc.) on the dynamic responses of suction bucket foundation were investigated. Development of softening and liquefaction of the soil layer surrounding the bucket foundation under vertical or lateral dynamic load was observed and measured. Development of excess pore pressure and the thickness of completely liquefied sand layer were investigated.
  3.  A perturbation method to analyze the dynamic responses of suction bucket foundations under dynamic load was presented.
  4.  A new method to model the percolation in centrifugal experiments is presented.
  5. Controlling parameters and their value range in practice were obtained.
(a) Electro-magnetic type(200Hz, 20kg) (b) Electro-hydraulic type (20Hz, 600kg)
Fig.1 Static/ dynamic loading devices for centrifugal experiment
(a)  Circular fractures under dynamic loading (b) Settlement of suction caisson with time
(c) Maximum pore pressure along depth (d) Changes of pore pressure with time
Fig. 2 Results of centrifugal experiments for suction caisson