The prefabricated pile

driven in soft clay

can squeeze the soil laterally in a certain scope around the pile

and the void ratio is reduced significantly;consequently

the shear bearing capacity is raised.But the soil parameter

which is used to estimate the capacity of pile

is reduced according to the soil state before the pile was driven.Then

a certain difference appears when the pile is working.The calculation result usually is partial to conservative.This paper analyzes the squeezing mechanism of the pile using the theory of cylindrical cavities expansion.And a formula

which is used to estimate the increment of shear bearing capacity of soil around the pile when excess pore water pressure from pile driving distributes completely

is presented based on the unique relation between the shear bearing capacity and the density of the soil.This formula can be used to estimate the final ultimate-bearing capacity of the pile.The calculated results by the proposed formula are in good agreement with those of the site measurement.