LIQUEFACTION SIMULATION FOR THE OSAKA GULF COAST USING THE LIQCA PROGRAM

Abstract

A Nankai megathrust earthquake is expected to occur in the Kansai area within the next 30–40 years. According to the worst-case estimations by The Headquarters for Earthquake Research Promotion [1], the earthquake will cause economic losses of approximately 220 trillion yen, and 134,000 buildings will be damaged by liquefaction. To estimate future damage to the Osaka gulf coast, we conduct liquefaction simulations based on the LIQCA program developed by the research group at Kyoto University. The liquefiable layers are composed of relatively loose sand and the underground water level is high. The input earthquake motion is the L2 spectrum Ⅰ earthquake-resistant standard spectrum, according to the Design Standards for Railway Structures and Commentary [2]. We consider not only the increase of excess pore water pressure, but also its dissipation. The calculated effective stresses in the sand layers approached 0, after which the sand layers liquefied and unevenness occurred at the ground surface. We evaluated the damage due to liquefaction by calculating vertical displacements and unevenness of the ground surface. Countermeasures are proposed for the shallow sand layers to reduce future liquefaction damage.