Study of Loading Rate Effects on Characteristics of Negative Skin Friction for Pile Groups   Gang-Qiang Kong School of Civil and Hydraulic Engineering, Dalian University of Technology, Dalian, China Email: gqkong1@163.com Qing Yang School of Civil and Hydraulic Engineering and the State Key Lab. of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China Mao-Tian Luan School of Civil and Hydraulic Engineering and the State Key Lab. of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China
			ABSTRACT

Using FLAC3D, a three-dimensional 3×3 pile group and a single pile were analyzed numerically. Loading rate was controlled by compiling FISH sentences, by which can analysis the characteristics of negative skin friction of pile groups influenced by loading rate. Firstly, it was proved that using this paper’s numerical model to study the negative skin friction of pile foundation is correctness by the comparison with the numerical model built on literature. Then, the drag-load and down-drag of pile groups and single pile which influenced by loading rate were studied; the influencing factors, such as step loading or direct loading, pile head load, the sequence of applying pile head load and surface load were discussed. Finally, it was proved by comparison with the results of model test results that numerical analysis method is reliable for engineering calculation. The results showed that, the drag-load and down-drag of pile become smaller with the slowing of loading rate, and tend to a stable value gradually at last; The negative skin friction of pile groups influenced by the load sequence, the negative skin friction obtained by surface load applying after pile head load larger than surface load applying before pile head load, while simultaneous applying surface load and pile head load is in the middle.

Keywords: pile foundation; negative skin friction; drag-load; neutral plane; loading rate; numerical analysis

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