Due to the very difficult geological conditions and the partly low overburden the TBM drives of the ?Tunnelkette Perschling? have been a challenge for the persons involved in the project. This paper is a report on the experiences and conclusions gained from two of the three driven tunnels. It deals with the unexpected major occurrences and the related solutions as well as with the adjustment of the concept for backfilling the annular gap in order to achieve sufficient stabilization of the segmental tunnel lining under all conditions encountered.