Development of swing method with sequential data assimilation (SDA-SWING) and its application to groundwater problems in real tunnel construction

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. Herein, the original SWING system was modified by the Ensemble Kalman Filter (EnKF) in order to automatically optimize the hydraulic parameters. The newly developed SWING method, SDA-SWING (Sequential Data Assimilation-SWING), was applied to two different tunnel construction sites in Japan and its applicability was discussed by comparison with the results obtained from the original SWING method. The effects of initial hydraulic conductivity and the frequency of data acquisition on the predicted results were also investigated using the SDA-SWING method. The SDA-SWING method can automatically optimize the hydraulic parameters using EnKF algorism without the need for highly skilled personnel and thus leads to a significant reduction in working times. The estimation of groundwater inflow by the SDA-SWING method generally agrees well with results obtained by the original SWING method and also with observations at the tunnel site.

► The Ensemble Kalman Filter (EnKF) was introduced to the original SWING system.
► The hydraulic conductivity was optimized automatically by EnKF.
► The newly developed SWING method was applied to the real tunnel construction.
► The groundwater inflow to the tunnel during excavation was predicted.