An Investigation on Horizontal Resistance of Piles and Sheet Piles during Earthquakes.

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Dynamic centrifuge tests were carried out using a laminar box in which model pile groups were embedded in a soil layr so as to study the dynamic response of piles and soil mass and their dynamic interaction. We used four different soils (low plasticity soil : Ip=2, Intermediate soil : Ip=10, Clay : Ip=30 and Toyoura Sand) to make soil layrs. A random wave simulating the El Centro record was applied to the soil mass. Comclusions derived from these are as follows.1) In case of soils with extremely low plasticity, it was observed that the rigidity of ground was reduced during the early stage of earthquakes and as a result, the amplitude of the acceleration of model pile structures was much smaller.2) The ratio of the observed acceleration spectrum of a model pile structure to the input acceleration spectrum is larger for the higher plasticity soil layr.3)In case of lower plasticity soil layr, less bending moment was observed in model piles during earthquakes but more permanent displacement was measured.Dynamic centrifuge model tests with sheet piles were also conducted applying sinusoidal wave as input motion to the model ground. The observed strains in sheet piles were smaller and observed horizontal irrecoverable displacement of sheet piles were larger for the ground with less resistance for liquefaction.