Piles & Overburden

[LearnerN]

I've been reading the PE reference manual about piles. It says "For piles supporting a compressive load, the pile weight is balanced by the overburden and is not considered." What does this mean exactly?

 

[BigH]

The ultimate bearing capacity of a pile (Qp) is equal to Qs (shaft resistance) plus Qb (base resistance) less the weight of the pile (Wp). With respect to your question, rather than use my own words, to quote Tomlinson: "Usually Wp is small in relation to Qp [ultimate bearing capacity of the pile] and it is often neglected because it is not much greater than the weight of the displaced soil. However, it must be taken into account for marine piling where a considerable proportion of the pile length extends above the sea-bed."