DISCUSSION ON ULTIMATE LATERAL RESISTANCE OF PILE IN CLAYEY GROUND DURING EARTHQUAKE

Pile foundation has been designed against the lateral load acting on the superstructure which is induced by the seismic coefficient method. After the Great Hanshin Earthquake, the response displacement method has been employed to assess the reaction force acting on pile. However, this method overestimates the interaction force from the viewpoint of practical design. Various specifications recommend to use the bilinear model on reaction force by considering that the ground goes through the pile. This paper evaluates the ultimate resistance of ground against lateral movement of pile by both model test and rigid plastic finite element analysis. The validity of obtained results is examined through the comparison of both results. The followings are obtained in this study. (1) Ultimate lateral resistance of pile was obtained as 12~13c for clayey ground where c is an undrained shear strength of clay. It was examined by model tests and numerical analyses. The failure area of ground reached to 2.5~3D from the pile center, where D denotes the diameter of pile foundation. (2) Effect of friction cut between pile and ground was investigated. Ultimate lateral resistance of pile was obtained as 9c which is almost same with Brom's formula. Besides, the effect of strength reduction in surrounding ground due to pile installation was parametrically investigated. (3) Ultimate lateral resistance of group piles was obtained as 11c in case of the pile center spacing of 3D. It matched with that of single pile in case of 5D. (4) The current specifications were shown to provide the smaller estimation on ultimate lateral resistance of pile in case of depth that is deeper than effective length on pile (1/ beta ), where the ground deforms through the pile by earthquake vibration. It reveals the specifications may prescribe the dangerous side evaluation in design.