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?
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?
