How deep will my spud legs sink?

[FAK]

I have been asked to approximate how deep the spud legs of a barge are likely to sink when moored in various offshore locations. I only have a few borehole records in nearby areas that give vague soil descriptions and SPT blow counts. What would be the best way to tackle this problem? I only need an approximate solution.

 

[Focht3]

You are dealing with a treacherous problem. As I understand things, most of the failures of offshore structures are due to plunging failures of jack-ups.

It's a bearing capacity problem; you need to use the strength data to estimate the ultimate bearing capacity. When the ultimate bearing capacity is 1.5 to 2 times the estimated footing pressure, you have a reasonable estimate. The depth to this pressure is the approximate leg penetration.



Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[VAD]

Hello Fak:

It depends on how the barge is to be utilized. We used spud barges to drill wide river crossings and the approach did not require any calculations of bearing capacity using SPT etc. For jackup barges for oil well drilling this may be a different issue as pointed out by Focht3. In such a case you may need to do some profiling of the river bed to obtain a suitable answer. The sensitivity of the structure is important as well.