Modelling Discharge Rates and Ground Settlement Induced by Tunnel Excavation

Interception of aquifers by tunnel excavation results in water inflow and leads to drawdown of the water table which may induce ground settlement. In this work, analytical and numerical models are presented which specifically address these groundwater related processes in tunnel excavation. These developed models are compared and their performance as predictive tools is evaluated. Firstly, the water inflow in deep tunnels is treated. It is shown that introducing a reduction factor accounting for the effect of effective stress on hydrodynamic parameters avoids overestimation. This effect can be considered in numerical models using effective stress-dependent parameters. Then, quantification of ground settlement is addressed by a transient analytical solution. These solutions are then successfully applied to the data obtained during the excavation of the La Praz exploratory tunnel in the Western Alps (France), validating their usefulness as predictive tools.