Research of observational method on the groundwater in the tunnel approach crossing

Groundwater issues related to mountain tunnels are discussed from the aspects of construction and environment. The former is related to groundwater control for safe construction, such as prevention of cutting face collapse due to large amount of inflow. The latter is related to impact of construction work on the natural environment including the groundwater system as well as surface water, which has been a key issue in recent years. This paper describes observational method executed in Inariyama Tunnel intended to carry out construction with higher reliability, including groundwater control. The methods of analysis and assessment employed are reported as well. Since the tunnel crosses an existing water-way tunnel at a separation of 27 in, the control of the impact of groundwater changes on the waterway tunnel was considered to be a crucial issue. The observational method for groundwater adopted in the project is a method for carrying out streamlined and reliable construction with high safety and cost efficiency. This is realized not only by a preliminary survey and numerical analysis for estimation but also by confirmation of the validity of construction methods by measurement and numerical analysis at each stage of excavation to grasp the impact on the waterway tunnel while feeding back the information to subsequent work.