Observational Method for Tunnel Construction in Difficult Conditions Considering Environmental Impact to Groundwater

摘要

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 reliability, including groundwater control. Since Inariyama tunnel (10m diameter) crosses under an existing aqueduct tunnel at a distance of 27m, 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.