Evaluation of Liquefaction Potential and Post-Liquefaction Settlement of Tzuoswei River Alluvial Plain in Western Taiwan

Taiwan is located in the conjunction area between Eurasia Plate and Philippine Sea Plate. As a result, the geology condition of the island is complex and the earthquake activity is frequent. On September 21, 1999, a severe earthquake (ML = 7.3) hit Chi-chi Town and resulted in significant damages and casualties in the mid-west plain of Taiwan. The alluvial deposits of Tzuoswei River, the largest river system of the island, had also experienced serious liquefaction damages during the shaking. The aim of the study was to as-sess the potential of liquefaction and the associated post-liquefaction settlement of the area. A total of about 1200 effective boreholes were collected. Three types of liquefaction analysis procedures were adopted, including Seed, Tokimatsu & Yoshimi, and the new version of Japanese Roadway Authority methods. A weighing technique suggested by Iwasaki was then used to evaluate the overall liquefaction potential. In addition, post-liquefaction settlements were estimated based on the procedures proposed by Ishihara. Con-tours of liquefaction potential and post-liquefaction settlement were also generated for the entire study area. Finally, results of the analyses were compared with the regional topography, geology, environmental factors, as well as the locations of critical projects in this area