| Summary: | 碩士 === 國立中央大學 === 土木工程研究所 === 99 === The backfill liquefaction behind the caisson type quay wall and the inertial force of the wall may cause the horizontal seaward displacement during earthquakes. The lateral deformations and large surface settlements on the service area caused the severe damage of port facilities and led to large economical lost. A series of centrifuge model tests was conducted to simulate the dynamic response of caisson type quay wall, focusing on the investigation of the characteristic of vibration modes of quay wall and the dynamic soil-wall interaction. There are two types of vibration modes, i.e., the translation mode and the rotation mode.
In this research, a centrifugal scale-down model was specifically designed and tested at 80 g. The 40% dimension of No.3 quay wall in Taichung harbor was treated as the prototype. The test sand bed was prepared by pluviating quartz sand into the new designed rigid box. Several accelerometers, pore water pressure transducers, and earth pressure cells were instrumented in the quay wall model and backfill. LVDTs were also mounted at the surface of the backfill and on the quay wall, in order to record the displacement histories of the surface settlement and of the quay wall during shaking. Besides, the horizontal colored sand and ground displacement meter were put inside the test model to observe the ground deformation after shaking.
The test results draw the following conclusions: (a)The translation mode dominantly affects the variation of pore water pressure in the shallow layer of soil behind the quay wall, and the excess pore water pressure decreased as the increase of seaward movement of quay wall. (b)The rotation mode dominated the fluctuation of pore water pressure readings beneath the quay wall foundation, and caused drainage from backfill into sea region. Because of the positive and negative pore water pressures alternatively change results in the pumping and suction effects which makes the large surface settlement happened in backfill area.(c) The phase difference between those two vibration modes influences the location of rotation center of quay wall. Quay wall is moving toward land direction and rotating toward sea when it shows out of phase relation between translation mode and rotation mode. Meanwhile, the position of rotation center will be changed toward backfill.(d)The predominant frequency of two vibration modes can be predicted by the formula which was proposed by Wolf (1998), and the calculated values consist with the experimental results.
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