Quantitative hydraulic analysis of pre-drillings and inflows to the Gotthard Base Tunnel (Sedrun Lot, Switzerland)

The hydraulic conductivities from pre-drilling analysis are used for inflow prediction for the excavated tunnel. Compared to the small-scale (50 m) variations of hydraulic conductivity as derived from pre-drilling analysis the sampled volumes of long term tunnel inflows are at least one order of magnitude larger (> 500 m). This leads to very uniform steady state inflow rates of 500-1000 m long monitoring sections for cumulative tunnel inflows. These inflows range between 3 and 5 l/s·km and compare very well with the predicted tunnel inflows from geometric mean hydraulic conductivity as derived from pre-drilling analysis.