Shaking Model Tests on Behavior of Group Piles Undergoing Lateral Flow of Liquefied Subsoil

Abstract eng:
This study addresses shaking model tests which concerns group pile models subjected to lateral flow of liquefied soil. The main objective of this research was on the magnitude of lateral load exerted by the soil flow, with emphasis on the distribution of the load to individual piles. Model tests employed three kinds of group pile which consisted of 33, 66, and 1111 piles. They revealed the following important points. Firstly, the displacement of the ground surface around a pile decreases within a few times of the pile radius. Hence, due to the overlapping of the range of pile influence between two adjacent piles, the entire lateral load decreases as the pile spacing becomes smaller. What is important is that the magnitude of the lateral load on individual piles in the front row (the upstream side of the group pile) as well as on the most downstream side (rear row) takes the maximum value. In contrast, the piles inside the group pile undergo less magnitude of lateral load. Then, a practical distribution of lateral loads on individual piles is proposed. Consequently, it becomes possible to protect existing group pile from lateral pile by installing additional rows of piles in front and back. Next, the variation of the lateral load with the relative displacement and the velocity between piles and soil was studied. Both small and large pile group model tests showed better correlation between the load and the velocity than the displacement. This implies the viscous nature of liquefied sand. This experimental finding strongly supports the analytical method in which the seismic performance of liquefied soil and mitigative measures are assessed by the idealization of liquefied sand as viscous liquid.

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