Due to the effects of foundation embedded depth and characteristic of axisymmetric deformation of sand have not been considered simultaneously on the failure mechanism,the Berezantzev's theory for predicting the bearing capacity of a deep circular foundation in sand have not been able to support data from the in-situ tests completely,especially for lower foundation embedded depth(2 ≤H/b≤ 5).By analyzing the relationships among the movement of soil particles,soil compaction and shear failure of the soil,the failure process of sand ground was systematically researched in theory.The damaged ground could be divided into three zones:a highly compressed zone Ⅰ,a radial shear zone Ⅱ,and a slightly compressed zone Ⅲ.A resistance shearing force exists in an upward direction on the soil annulus above the zone Ⅲ,similar to the conclusion drawn by Berezantzev.The extents of zones Ⅰ,Ⅱ,Ⅲ were determined by considering the combined effects of buried depth,the relative density of sand and the roughness of base on the failure mode of sand ground.A new model of ground failure was developed to calculate the ultimate bearing capacity of sand under the deep circular foundation for the relative buried depth (H/b) between 2 and 5.According to the static equilibrium of the free body in the damaged ground,the ultimate bearing capacity of the deep circular foundation in sand was deduced.Some practical calculations showed that the ultimate bearing capacity factor,Nγq,determined using the present method was less than that using the earlier semi-empiric formulas proposed by Berezantzev,Terzaghi and Durgunoglu in different internal friction angle decreased with the increase of the relative depth.The ultimate bearing capacity of deep circular foundation calculated in this paper was closer to those given in the specifications than those calculated by earlier semi-empiric formulas.
