Long drilled shaft

[aun]

A drilled shaft is 80 ft long supporting an abutment (or a bent column).. Need to consider the slenderness effect??
is it correct if I assume the shaft is confined by surrounding soil??

 

[bosy]

Not if the shaft is completed embedded in soil.

 

[ishvaaag]

What you need is determination of the forces to be used in the design, that may or may not include bending action, for example, as a laterally loaded pile.

However, very small forces of restrain along a column are very efficient ro restrain buckling, (this is the principle of bracing of columns, where the required forces in the braces are found to be 1 to 4% of the acting compressive loads) and the surronding soil is more than able enough to deliver such restraint.

Hence, as bosy indicates, buckling as of itself is not properly a consideration for piles entirely assumed in contact with the soil, since the forces are guided down by the lateral restraint of the soil preventing any buckling.

In fact this guiding of loads mechanism causes some defective in-situ concreted piles to perform well, even with partial discontinuities in the pile.