Centrifuge Modeling for Uplift of Buried Structures by Liquefaction: A New Measure for Uplift

Abstract

大地震時に液状化による埋設構造物の浮き上がりが生じた事例は数多く報告されている．2004年新潟県中越地震では，長岡市，小千谷市などで1, 400箇所以上のマンホールの浮き上がりが発生し，緊急車両の通行が阻害されるなど，市民生活に大きな影響を与えた．マンホールの浮上防止対策についても，埋戻し土の締固め，固化改良，砕石による埋戻し，間隙水圧をマンホール内に逃がす方法(小西ら，2008)などが考案されている．しかし，既存のマンホールに対する浮上防止対策については，有効かつ経済的な方法がいまだ模索されている．本研究では，遠心模型実験を用い，既存および新設のマンホールに対して間隙水圧をマンホール内に逃がす方法の有効性を評価した．その結果，浮き上り量は対策なしよりマンホール長さの12%まで低減された．

Many types of damage of buried structures occur due to liquefaction during an earthquake, such as flotation, settlement, bending and buckling of buried pipes. Among those, this paper focuses only on uplift of sewerage manholes. Uplift behavior of buried structures with and without a measure for uplift is investigated in model tests which are dynamically tested in a centrifuge modeling. In this study, effectiveness of the new measure for uplift which is to dissipate the excess pore water pressure is investigated to mitigate uplift displacement of the manhole during earthquakes (Konishi et al. 2008). The measure consisted of two configurations which are a filtering net and pipe. The tests showed that the mechanism of the uplift behavior and the effects of the measure for the uplift, but the uplift amount may be still too large (8% of the length of the manhole) when it is applied in practice.