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Seafloor soil mechanics for jack-up leg pads

Seafloor soil mechanics for jack-up leg pads

Seafloor soil mechanics for jack-up leg pads

(OP)
   I am a naval architect by trade, so please be patient.
   I need to understand the seafloor soil mechanics supporting the base pads (typically 15 ft x 30 ft) of liftboat jack-up legs in Gulf of Mexico service.
   I am wrestling with API RP 2A and DNV Class Notes 30.4.  However, these seem to require site-specific soil data, which is never available.  The liftboats simply pre-load with water ballast (to simulate wind/wave loads) and jack up alongside client rigs (anywhere in GoM) until the pads penetrate to an equilibrium depth (typically 3 to 20 ft).  I need to determine the allowable water depth/cargo loading envelope based on leg strength, which depends on base pad/seafloor fixity, etc.
   Base pad loads (vert reaction & moments) are calculable, and I have found representative undrained Su values, but I need to determine rotational soil stiffness (spring constant) under the pads.  Is there any correlation between Su and G?  Alternatively, can I safely deduce values for Su and G based on satisfactory pre-load and penetration?

RE: Seafloor soil mechanics for jack-up leg pads

You might be better off following the SNAME guidelines for jack-up rig emplacement.

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