Effect of soil improvement on ground subsidence due to liquefaction

Abstract

Liquefaction occurred at many sites along Osaka Bay during the 1995 Hyogoken-Nambu earthquake (the Great Hanshin-Awaji earthquake disaster) and caused extensive damage to buildings, bridges, quay walls, etc. The authors conducted detailed site surveys at the liquefied sites and found a remarkable phenomenon. Some zones in two big artificial islands, Port Island and Rokko Island, in Kobe City, did not liquefy even though the zones surrounding the islands liquefied. Damage to buildings and ground subsidence in these zones were also less severe than the damage and subsidence in the surrounding zones. Based on a study of the soil conditions in these islands, it was found that the non-liquefied zones had been improved by several methods, including sand compaction piles, rod (vibro) compaction, sand drains and preloading, before buildings had been constructed on them. These ground improvement methods were effective in mitigating liquefaction even though the ground shaking was as extreme as more than 400 gals of maximum surface acceleration.