Improvement of karstified rock through the example of the Irlahüll Tunnel on the new railway line Nuremberg – Ingolstadt

Abstract

In the Irlahüll Tunnel section to Ingolstadt, the high-speed rail route Nuremberg-Ingolstadt-Munich passes through limestone and dolomite with pronounced karst character. Various karst structures were encountered during the driving of the Irlahüll Tunnel. These were classified into four karst types. In order to activate the load-bearing effect of the ring of rock around the tunnel, karst structures had to be stabilised. The required thickness of the treatment was determined by structural calculations. Four specialised civil engineering contractors carried the work out.The challenge was to appropriately stabilise slightly-to strongly-jointed rock, heterogeneously interspersed with karstification structures. The treatment ranged from filling cavities to grouting loose material and rock. The karst structures were stabilised according to karst type, with materials ranging from cement suspension to concrete. The karstified rock mass was systematically drilled, each individual borehole was geologically evaluated and, where required, further investigated by inserting a camera. The quantity, strength and pressure of the grout used were evaluated continuously by the team of experts for the site supervision and appropriate further steps were decided. The success of the stabilisation was demonstrated through quality control drillings and control grouting. The improvement of the rock mass was achieved to the required degree.