| Summary: | 博士 === 國立臺灣大學 === 土木工程學研究所 === 105 === Series of shaking table tests on a model pile within a saturated sand specimen using a large bi-axial laminar shear box were conducted at the National Center for Research on Earthquake Engineering (NCREE), to study the soil-pile interaction in a liquefiable ground during earthquake. The shaking table tests included a single pile within the level ground and inclined ground with a slope angle of 2。. The pile tip was fixed at the bottom of the shear box to simulate the condition of a pile foundation embedded in a firm stratum. The pile top was mounted with steel disks to simulate the superstructure. In addition, strain gauges and mini-accelerometers were placed on the pile surface to observe the behavior of the pile under shaking. The near- and far-field soil responses, including pore water pressure changes, accelerations, and settlements were also measured. According to analyses of the dynamic responses of the soil-pile system, it was found that the behavior of the model pile and soil-pile interaction under shaking was affected by the dynamic characteristics of the piles and the surrounding soil, the mass of the superstructure and the frequency content of earthquake shakings. In addition, the kinematic and inertial loadings on the model pile due to lateral spreading during shaking can be evaluated independently with the input motion imposed in the direction perpendicular to the slope direction.
These experimental data were analyzed to identify the time-dependent predominant frequency of soil-pile system during generation and dissipation of excess pore water pressure under the shaking by performing time-frequency analyses and system identification. The relation between the predominant frequency of soil-pile system and the coefficient of horizontal subgrade reaction can be obtained by the proposed mathematical model of soil-pile system. Hence, the relation between the normalized coefficient of horizontal subgrade reaction and the pore pressure ratio was established based on the experimental data and the proposed mathematical model of soil-pile system. It can be seen that the stiffness of the soil almost vanished during the period of liquefaction and the stiffness of the soil would increase with the dissipation of pore water pressure. The trend of the stiffness reduction is found close to the reduction of soil parameter proposed by Architectural Institute of Japan (AIJ, 1998).
|
|---|
