Lateral Soil Resistance of Each Pile in Pile Group By Shaking Table Tests and Its Simulation Analysis.

Abstract eng:
Pile foundation response during earthquakes is strongly affected by nonlinear soil-pile foundation interaction. The damages to pile foundations during the Hyogo-ken Nanbu earthquake of 1995 and the Tohoku-Chiho Taiheiyo-Oki Earthquake of 2011 were obviously attributed to nonlinear interaction of soil-pile foundation-superstructure. The dynamic nonlinear behavior of soil around each pile affects the lateral load distribution and displacement of each pile. Therefore, shaking table tests were conducted to clarify the dynamic nonlinear behavior of soil around piles, next earthquake response analyses were conducted to simulate the effect of the nonlinear soil-pile interaction system on the performance of the superstructure supported by pile group. In the shaking table tests, 5x5-pile group foundation model was set up in Toyoura sand deposits. The sand deposits were prepared by air pluviation method in the laminar box. The model piles were acryl cylinder with 12mm in diameter and 400mm long. 25 piles were arranged in squares and pile spacing was 2.0 times pile diameter. The superstructure was modeled as a rigid body. The input waves were seismic waves in notification with random phase of Japan and the Hyogoken Nanbu earthquake. 3 input acceleration levels were used to investigate nonlinear effects of soil by input motion level. Tests with or without the mass of superstructure were conducted to investigate lateral load distribution of each pile. The validity of 3D FEM analyses was presented by comparing the calculated analysis results with the shaking table test results, and the nonlinear behavior of the pile group foundation-soil- superstructure was discussed. The concluding remarks of these shaking tests and analytical studies are as follows. (1) Lateral subgrade reaction around piles depends on the location of each pile in pile group. That of the corner pile is remarkably larger than that of the middle pile. (2) The hysteresis curve of soil spring at the corner pile is asymmetric loop, while that at the middle pile is symmetric loop. (3) The bending moment at pile head depends on the location of each pile in pile group. That of the corner pile head is remarkably larger than that of the middle pile head. As the input acceleration level increase, bending moment at each pile head becomes to be almost equalized. (4) It was confirmed that nonlinear 3D FEM model represents well response of the superstructure supported by pile group.

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