Q$5)$

A foundation design involves a group of insitu bored concrete piles, each $500$ mm diameter, formed in saturated clay soil as recorded in the accompanying borehole $\backslash (\backslash$log $\backslash )($See Figure Q$5).$ Each pile is to extend from ground surface to a depth of $16$ m $.$

a$)$ Estimate the vertical working load that may be applied to the head of each pile, assuming that the top $4$ m of loose fill will settle after the piles have been cast.

Assume that the skin friction coefficient for a concrete bored pile is $\backslash (\backslash$alpha$=0\mathrm{.}45\backslash )$ and that Skepton's bearing capacity coefficient for a deep circular foundation is $\backslash ($ N$\_\{$c$\}=9\backslash )$

Take a value of F$.$O$.$S $\backslash (=3\backslash )$ overall

b$)$ What are the main causes for negative skin friction?

c$)$ What methods can be used in general for reducing negative skin friction?

Bore hole log