Some insights from modeling groundwater levels in open boreholes in crystalline rock in tunneling projects

Book chapter, 2025

This study focuses on the importance of explicitly representing hydraulic head measurements in open boreholes in crystalline rock in numerical models. Open boreholes in crystalline rock can lead to hydraulic short-circuiting of the groundwater flow system, leading to potential misinterpretation of hydrogeological risks in tunneling projects. Such projects often rely on numerical groundwater models to assess risks, such as groundwater intrusion into tunnels and ground deformations. An example of this is studied here. A case study was conducted using MODFLOW-NWT with the Multi Node well package (MNW2) in Haga, Gothenburg, the site of a planned commuter train station, comparing simulations with and without explicit open boreholes. The findings reveal that deformation zones with higher transmissivities and connectivity that intersect open boreholes can significantly redistribute the hydraulic head, potentially affecting the estimation of pore pressure changes in overlying subsidence-sensitive clay. In addition, the study concludes that groundwater flow leakage near tunnels leads to increased short circuiting in wells and higher gradients around the tunnel.