影響予測解析による離隔約5mで並行するⅠ期線トンネルへの影響低減対策:東海北陸自動車道　上野第一トンネル

摘要

The 2nd phase of the Uwano No.l Tunnel project were to construct a new tunnel adjacent to the 1st phase tunnel in service at the smallest distance of approx.5m.In order to control the impacts on the lining of the 1st phase tunnel,two-and three-dimensional excavation analysis was conducted to plan excavation and auxiliary methods and monitoring.Two main monitoring cross-section were set in the zone where two tunnels get closer.Selection of suitable auxilially methods was conducted based on the analysis input conditions of which were reviewed through comparing monitoring and analysis results,and excavation was carefully progressed through monitoring and management with control standard.In addition,based on the results of monitoring and analysis,it was possible to control stress on the existing tunnel lining to within the allowable values by setting installation ranges for forepiling and casting invert concrete earlier.%上野第一トンネルのⅡ期線工事は，供用中のⅠ期線との離隔が最小約5mとなる近接施工の工事である.Ⅰ期線覆工への影響を抑制するために，3次元および2次元掘削解析を行い，掘削方法，補助工法，計測計画などの検討を行った.近接施工区間には，2つの主計測断面を設け，解析結果と計測結果を検証して解析の人力条件を見直すことで適切な補助工法を選定するとともに，管理基準を設けて計測管理を行いながら慎重に掘削を進めた.また，計測結果と解析結果をもとに，長尺鋼管先受け工の打設範囲を設定し，早期閉合を実施することで，Ⅰ期線覆工に発生する応力を許容値以下に抑えることができた.