Shaking Table Tests on A Scale-Model Pile Group in Liquefiable Ground

Abstract

To investigate the seismic response of a pile group during soil liquefaction shaking table tests on a 1/25 scale model of a 2×2 pile group were conducted which were pilot tests of a test project of a scale-model offshore wind turbine with jacket foundation The pile group model comprising four slender aluminum piles with their pile heads connected by a rigid frame was designed with similitude considerations focusing on soil-pile interaction The input motions were 2 Hz sinusoids with various acceleration amplitude The excess pore water pressure generation indicated that the upper half of the ground specimen reached initial liquefaction under the 50-gal amplitude excitation while in the 75-gal amplitude test almost entire ground was liquefied After liquefaction the soil and the movable-frame accelerations that represented the ground response considerably reduced while both the movable frames and the piles exhibited high frequency jitters other than 2-Hz sinusoid and meantime remarkable phase difference between the responses of the pile group and the ground was observed Axial strains along the pile implied its double-curvature bending behavior and the accordingly calculated moment declined significantly after liquefaction These observations demonstrated the interaction between soil and piles during liquefaction In addition 1-D shear beam idealization was further introduced to deduce the stress-strain relationship of soil based on seismic ground response Thus the variation of mechanical properties of saturated sand with respect to the development of shear strain and excess pore water pressure were examined The repeated liquefaction was also investigated using two of the excitation tests using the same input motion

Date of Award	2020
Original language	English
Supervisor	Yung-Yen Ko (Supervisor)