Phi angle in Mudmat Design

[kat6787]

I am currently working on my first mud mat design for a subsea manifold. I've been following API RP 2A-LRFD to determine bearing capacity and sliding stability. I ran into a problem when trying to determine the depth correction factor, dc. The equation has tan(phi) in the denominator, but for an undrained analysis I was assuming phi=0.

I noticed the other correction factors have two equations, one for phi>0 and one for phi=0. I was curious as to why the depth factor doesn't allow for phi=0, and how to account for the depth factor if phi=0.

Thanks in advance.

Cheers,
Kat

 

[Gimbli]

I am not pretty sure if I understand your problem, but it looks you are talking about Nc. If so, Nc is about 5.7 for phi=0.

 

[Gimbli]

And you should know that you may have certain bearing capacity but you need to check for settlements also.

 

[kat6787]

I was looking at the depth correction factor in the appendix of API RP 2A, where dc = dg - [(1-dq)/(Nc*tan(phi))]. Because I was using an undrained scenario phi=0, which was causing division by zero.

I spoke with somebody here in my office and found a way around it using some trig function substitution.

As for settlement, I calculated the horizontal and vertical displacements using the uh and uv equations in the main text of API RP 2A. Are there other settlement calculations I need to check?

Thanks for the help.

Cheers,
Kat