Groundwater inflow analysis during tunnel construction using SDA-SWING method

Tunnel excavation in Japan is beset by difficulties related to complicated geology and groundwater. Controlling the groundwater inflow to the tunnel during excavation is a challenging issue for both tunnel construction and for environmental assessment. The SWING (System for Water INformation of Ground) method was developed to enable predictions regarding groundwater inflow to the tunnel and also to allow evaluation of the impact of excavation on the surrounding groundwater environment. The SWING method is based on the closed-form solution of Dupuit quasi-uniform flow and can follow the tunnel excavation process by reconstructing the hydraulic conductivity fields using data obtained at construction sites. In the SDA-SWING (Sequential Data Assimilation-SWING), the hydraulic parameters can be optimized by the Ensemble Kalman Filter (EnKF). In this study, further development of SDA-SWING was made to consider the change of groundwater level measured at the observation wells in the process for back-calculating hydraulic conductivity. The newly developed SDA-SWING method was applied to two different tunnel construction sites in Japan and its applicability was discussed. The estimation of groundwater inflow by the SDA-SWING method generally agrees well with observations at the tunnel site.