Effects of Soil Movement on Pile Group in Term of Negative Skin Friction NSF - using FEM

The development of additional compressive force (dragload) in a pile and excessive pile settlement (downdrag) could cause difficulty in construction and maintenance of the structure supported. Using piles in group is a simple and common approach to reduce NSF on piles. In this paper a full 3D FEM model, using ABAQUS, is established to study the behavior of Pile group with NSF. The results were compared against a centrifuge test data and two different analytical approaches. Based on FEM results, salient characteristics of capped pile foundation behavior subjected to NSF are as follow: 1. Reduction of effective stress regime of soil within a pile group, which reveals the fundamental mechanism of NSF group effects; 2. unbalanced stress inside and outside a pile group leads to substantial additional bending moments which develop along the corner and side piles within a pile group; 3. Reduction of dragload and increasing NSF group reduction factor (GRF) from corner pile to inner pile; 4.development of tension and compression force on pile head of corner and inner pile, respectively; 5. Moderated distribution of NSF among piles at different positions in a group

Keywords:

Soil movement , Negative skin friction (NSF) , Dragload , FEM , Pile group , group effect , Analytical approaches