Overlength pile foundation is successfully used in more and more civil engineering

but the study on its behaviour is still very little. Based on an example of a large-scale overlength pile group foundation engineering

the behaviours of overlength single pile and pile group foundation are investigated using nonlinear three-dimensional finite element method (3D FEM). A hexahedron isoparametric element with 8 nodes is employed in the finite element model of pile

foundation slab and soil. A special thin element with a very little thickness is used to simulate possible nonlinear deformations between soil and pile. Linear elastic-model and nonlinear Duncan-Chang elastic model are used to simulate the constitutive relation of concrete of pile and foundation slab

and soil mass respectively. The course of building foundation slab is simulated by adding elements in calculating

and that of hardening concrete of foundation slab is simulated using the method of increasing its modulus. Calculating results indicate that the behaviour of overlength single pile is frictional

and its failure is the result from the failure of soil around pile firstly. In group pile foundation

many clear differences in behaviours of piles can be found among the piles located in different positions under the foundation slab

especially between the piles near the edge of foundation and ones in the centre of the foundation. The behaviour of side pile near the edge of foundation slab is almost same with that of single pile

but apparent difference from that of centre pile. Reduction factor of pile group can be obtained from both current technical code for building pile foundation and calculating results of 3D FEM. The large difference in the reduction factors of pile group from the two methods indicates that it is necessary to investigate further the behaviour of overlength pile group foundation

because the current technical code isn’t enough for the designation and construction of overlength pile group foundation

especially for larger-scale overlength pile group foundation.