Geddes stress solution is widely applied to settlement calculation of pile foundation. In order to find the solution

pile skin friction is simplified as concentrated force; however the influence of changing diameter and length of pile additional stress in the ground due to skin friction can not be taken into account. The actual calculated results of the short pile with low ratio of length to diameter are quite different from the results of vertical stress factor by Geddes stress solution. Using the numerical integral function of NIntegrate in Mathematica software

a numerical method of calculating the vertical component of Y-shaped pile skin friction acting at any point in the ground is obtained. One loading case of the skin friction is rectangular distribution from top to bottom along the pile body and uniform distribution in circumference; the other one is triangular distribution from top to bottom along the pile body and uniform distribution in circumference of Y-shaped section. The influences of four independent variables R

s

of Y-shaped section on additional stress factor due to skin friction and errors produced by Geddes stress solution are analysed; and the influences of pile length and calculating depth on errors are also analysed. Some significant conclusions are obtained.