Drilled Shaft on Soft Clay

[DenseSand]

I am having a very deep subsoil profile consisting mainly of soft clay with cohesion of about 250 psf increasing with depth to about 750 to 1000 psf. My question is, If the tip is left resting at this clay, should the difference in weight between excavated material and the concrete be considered to obtain the allowable capacity?

 

[DenseSand]

Or settlement may be computed by only using the Reese and Oneill correlation?

 

[Mccoy]

Densesand, it depends on local regulations.
Technically speaking, it makes sense to consider the difference in weight obtained by substituting concrete to soil. Under some regulations though, like it happens in my area, the actions must be determined conservatively by considering the full weight of concrete.

http://www.mccoy.it

 

[DenseSand]

Thanks McCoy. At the end, it's a communication monopole what we are dealing with. Required wind loads in my jurisdiction govern required shaft length in design. Working load plus weight of shaft is about 0.4 the ultimate skin friction. Therefore end bearing will not be mobilized at all and pressures under the tip would not be a concern.

Thanks for your help