combined footing with piles

[august2010]

i have to design a combined footing which can take care of 30,000 lbs uplift for a carport. its not difficult to design it in case when i have moment and uplift/downward force acting on the foundation.

but in this case i need to put piles in the foundation. piles will take care of the downward force from the superstructure and foundation will take care of uplift force and moment.

I have attached the drawing for your reference.

i need to know if i should consider the continuous loading from the soil on the foundation bottom when i will design it for compression or should i assume that the foundation is not taking any load even if the pile and concrete acts as one unit.

also should i consider settlement for the foundation and pile. or just the pile?

i can not decide what is going to be the load transfer between pile/concrete foundation in compression.

 

[SlideRuleEra]

IMHO, it is best to totally ignore any support that the soil may provide (for gravity loads) - design the foundation for 100% support from the piling. If there were any soil settlement (there almost always is some), the piling loads will exceed your expectations.

Assuming that you are considering driven piling, you probably want to maximize soil friction to resist uplift. The traditional choice for maximum skin friction would be displacement piling, such as treated wood, or prestressed concrete. Get a Geotech's advice on the soil's properties.

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