Observational Method for Tunnel Construction in Difficult Conditions Considering Environmental Impact to Groundwater
Takaharu NISHIOKA, Kenji TAKAHASHI, Toru YASUDA, Yuzo OHNISHI and Hiroyasu OHTSU
Abstract:Excavation of tunnel in Japan recently faces a lot of difficult conditions such that very complex geology, interaction with adjacent structures and groundwater problems in relation to environmental impact. This paper describes a new observational method executed in Inariyama Tunnel (Kyoto) intended to carry out construction with higher reliabilityCincluding groundwater control. Since Inariyama tunnel (10 m diameter) crosses under an existing aqueduct tunnel at a distance of 27 m, control of the mechanical and groundwater impact on the active aqueduct tunnel was considered to be a crucial issue. Very careful excavation was done with accurate measurements of deformation to eliminate instability of both tunnels. The observational method for groundwater is performed not only by a preliminary survey and numerical analysis for prediction, but also by flow rate into the tunnel and water pressure distribution measurement with 3 dimensional groundwater finite element analysis at each stage of excavation. Measured and calculated results are compared to grasp the subsequent work. Construction was successful with this proposed method. Key Words:Tunnel excavation in difficult condition, Observational method, Groundwater, Environmental impact, 3-D finite element analysis