Liquefaction Assessment and Lateral Spreading in Nantou, Taiwan

On September 21, 1999, Taiwan was struck by an earthquake, called Chi-Chi earthquake, one of the largest in 100 years. The epicenter was located 12.5 km west of the Sun Moon Lake (Northern Latitude 23.85°) Eastern Longitude 120.78°), with focal depth of 8 km, and magnitude of Mw=7.6 (USGS). This earthquake caused heavy casualties and severe property damages around central Taiwan. It was found that this earthquake resulted in sand boiling, differential settlement on the ground and lateral spreading around part of the Maolou River bank in Nantou City. Field investigation, geological exploration and in situ tests, which include 14 borings with standard penetration tests and 8 cone penetration test soundings, were conducted to demonstrate the soil profiles and to perform soil liquefaction potential assessment. The ground failure due to spreading liquefaction near Maolou River bank was also described. The result revealed that soils about 5-8 meters below the ground surface contains fine to medium silty sand or sandy silt which is the same strata as the highest liquefaction potential based on SPT-N and CPT-qc liquefaction simplified procedures. It is also shown that the critical depth also has the physical properties similar to the boiled sand taken from the sand volcanoes