| dc.description.abstract | During the Kobe Earthquake of magnitude 7.2 occurring in 1995, intense liquefaction resulted into the lateral spreading of caisson type quay walls in two artificial islands (Port & Rokko Islands). This type of failure is quite similar to that of Piers #1 to #4A in Taichung Harbor during the 921 Chi-Chi Earthquake in 1999. Accordingly, numerical study of these two failure cases in Kobe and Taichung is very beneficial to help identify the failure mechanism, stability, liquefied zone and ground deformation of backfill behind caisson type quay walls during severe earthquake.
The FLAC 3.2 is the main analysis tool in this study, including a dynamic analysis module. Prior to numerical analysis, the basic data of the above two cases (composed of quay wall cross-section design diagram, in-situ and laboratory test results, groundwater level, earthquake records, and damage document) are compiled. The general procedures of numerical modeling for each case include generating geometric mesh for the port site, assigning material parameters, setting up boundary conditions, adding interface elements and turning on gravity, applying lateral water pressure, leveling groundwater table, checking mechanical equilibrium, using Finn mode, setting dynamic damping and dynamic boundary conditions, exerting earthquake loading, and monitoring the variation in displacement and pore water pressure. The analysis results of both two cases are compared with field observations, and those of shaking table tests and numerical analyses performed by other researchers.
The numerical simulation results of this study show that the failure mechanism of both two cases in Kobe and Taichung is due to liquefaction of backfill (a hydraulic sand fill) during earthquake, the same as that found in literature. The increasing excess pore water pressure in the backfill produces large lateral pulse acting on the caisson, leading to its lateral spreading, rotation and settlement. The excess pore water pressure stimulated in the backfill is higher than that beneath the caisson. The effective stress of soil just behind the caisson does not reach zero during shaking, but the further inside portion of the backfill is liquefied. Learning from this study can provide an insight to understand the interaction between quay wall and backfill during strong ground motion, as well as a future guideline to design a caisson quay wall and soil system sensitive to liquefaction damage. | en_US |