AbstractThe 32.9 km long Koralm tunnel (Austria) is the core piece of the Koralm railway and will be one of the longest railway tunnels worldwide after completion. At the longest construction section ”KAT2“ two approx. 17 km long parallel single‐track tunnels were driven by two double‐shield tunnel boring machines with a diameter of about 10 m. Accompanying the tunnelling of the two tubes, the continuous Tunnel Seismic While Drilling (TSWD) method was used shortly after the start of mechanical excavation in January 2013 until the final position was reached in February 2018. The aim was to consistently explore the rock mass up to 100 m in front of the tunnel face to detect faults and water‐bearing zones which were relevant for tunnel construction. Another purpose of the measurements was to reduce the number of exploration drillings ahead of the tunnel face. After an initial test phase of about 5000 m, where exploration drillings were continuously carried out parallel with TSWD, an advanced and optimized exploration concept was evaluated and performed for permanent operation. This paper summarizes the findings gained from the TSWD measurements at this tunnel site.