Internal skin friction for a CHS pile in soft clay.

[calky117]

I'm doing a concept design at the moment and trying to calculate the required pile penetration for either 900CHS or 1200CHS steel piles into very soft clay. We've taken zero end bearing into account and only relying on skin friction. For an open-ended steel CHS pile is it reasonable to assume that as the pile is driven the soil column inside the pile (unplugged?) will provide skin friction for the majority of the penetration depth.

At present I have used a factor of 0.75 to reduce the internal friction compared to external friction.

 

[BigHarvey]

I would be surprised that any code would allow you to take into account any internal friction.

 

[hokie66]

Internal skin friction? Don't be silly. The plug would probably provide a degree of end bearing, but not skin friction.

 

[calky117]

hokie66 what about for an unplugged pile not plugged? The link below suggests that partial internal friction may be considered, seems plausible for piles with large diameter:

http://www.pile.com/pdi/faq/?q=Q1049&prod=

I was skeptical but my manager insisted I use internal friction with a 0.75 reduction, note this is for marine conditions with extremely soft soil. Comments are appreciated.

 

[BigHarvey]

Murphy would have said : if you need it unplugged, it will be plugged and if you need it plugged it will be unplugged. The only acceptable way to optimize your design is to construct a test pile and load it.

 

[hokie66]

The plug I spoke of is the soil within the pile. Once you start driving, material will be extruded into the pile. How far it advances within the pile is dependent on the material, but unless it is very soupy, it won't go all the way up.

Your manager knows not of what he speaks. Good luck.

 

[aeoliantexan]

Reason says, the plug acts like a bottom plate and can only mobilize end bearing. The total internal skin friction cannot exceed the end bearing at that depth.

 

[fattdad]

given a free body diagram of the pile, I'd only account for the skin friction on the outside of the pile. Any further rationalization for shear resistance inside the pile would be folly.

f-d

¡papá gordo ain’t no madre flaca!