地下水圧測定結果を反映した支保パターンによるトンネル施工: 新名神高速道路 箕面トンネル西工事

摘要

The Minoh Tunnel West Works are to excavate approximately 3 km on the west side of Mino Tunnel (approx. 5 km in length) located between Ibaraki Interchange and Minoh Interchange on the Shin-Meishin Expressway. The majority of geological condition were Paleozoic era sandstone and alternating beds of predominant sandstone and shale and quartz-porphyry and rhyolite partly intrude them. Because runoff of ground accompanied by water inflow occurred at the excavation site 370 m from the western portal, ground improvement works as a countermeasure were conducted using polyurethane grouting with the two liquid. Furthermore, as the groundwater level did not decrease even after drainage boring, excavation was conducted while tunnel support patterns were changed corresponding to measurement of water pressure.%箕面トンネル西工事は，新名神高速道路の茨木IC～箕面IC間に位置する萁面トンネル(延長約5km)の西側約3kmを掘削する工事である.地質は，古生代の砂岩または砂岩優勢砂岩•頁岩互層が大部分を占め，一部石英斑岩や流紋岩が貫入する.西坑口から370mの掘削地点で湧水を伴う土砂流失が発生したことから，2液性ウレタン系注人材により地山改良対策を行った.さらに，その後の水抜きボーリングによっても地下水位が低下しなかったことから，地下水圧を測定しながら水圧に応じた支保パターンを設定して掘削を行った.