THE DYNAMIC EFFECT OF PORE-WATER-PRESSUREVARIATION ON THE FOUNDATIONS IN MAN-MADEDEPOSITS

摘要

In this study the dynamic behavior of foundations located in the reclaimed lands near coastal areawas investigated. It was found that during the 1999 Chi-Chi earthquake (magnitude of Richter'sscale reaches 7.3) a series of wharves of caisson type located in the harbor area were sufferedsevere damage. According to the investigation, the area of the harbor having seriousfoundation-damages is mostly the reclaimed land. The investigation also found the associatedstructural damage, landsite settlement and sand-boils induced from the possible liquefaction ofthe soil. Most of all are the seriously displaced caisson quay-walls, the infrastructures for thewharves. The distorted caissons ranged more than 1 km long and 1.5 meters away from theoriginal alignment. In the reclaimed landsite among many sand-boil holes some larger ones aremore than 4 meters deep. Comparing to 1995 Kobe earthquake the damages in the harbor areaseemed unreasonably drastic. Therefore, it is interested to know except for the influence of basicproperties of the soil what really causes those serious damages in this area.For the wharf damaged due to infrastructure failure, factors considered may include theenlargement of ground motion during transmission of the seismic waves, the liquefactionphenomenon and pore-water pressure variation, the interaction effect between the structure andthe soil and other influences of reclaimed land in the area. Due to the complexities of all kinds offactors, this study focused on the dynamic behavior of the foundation subjected to seismic waveswhile the soil-structure interaction is ignored. In the analysis, the transmission of the seismicwaves mostly the P-wave and S-wave from underground source through a multi-layer of soil ofgenerally the kind of man-made subjected to variation of pore-water pressure is taken intoaccounts. Based on the experimental data from cyclic loading tests on the liquefaction andsettlement including the variation of pore pressure ratio and axial strain percentage related to theloading cycles and volumetric strain percentage to the pore pressure ratio, the analytical modelfor the foundation located in the reclaimed soil subjected to the pore-water pressure variation isestablished.