Based on Geddes stress solution

calculating 3-D stress of arbitrary point in group piles according to superposition principle

and based on Duncen-Chang constitutive model

to calculate settlement of arbitrary point in group piles according modified layered summation. then

establishing set of equations according to basic point method[1] and coordinative relationship of loading and deformation of group piles foundation

to obtain the loading-settlement relationship of group piles. To compare with general method based on Geddes stress solution

three parts have been improved

they are as followings: (1)adopting Geddes 3-D stress solution

its effect on settlement of group piles can be calculated;(2)the constitutive model(Duncen-Chang model) is used to study the settlement of pile

the nonlinear character of soil can be considered.;(3)using modify layered summation

the layer character and lateral deformation of soil can be computed. Therefore

the method that proposed in this paper is more perfect in theory

amount calculation is moderate and apply to engineering practice.