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<p>The Semmering Base Tunnel (SBT), a&#xa0;railway tunnel under construction with a&#xa0;total length of 27.3 km in the eastern end of the Austrian Alps, comprises many geotechnical challenges including the crossing of major fault zones. The largest zone is the more than 1 km long Grassberg-Schlagl fault system at lot SBT&#xa0;1.1, which consists of a&#xa0;wide range of heavily sheared lithologies. A&#xa0;major part of the fault zone has undergone a&#xa0;secondary cementation by sulphatic minerals, which caused a&#xa0;significant improvement of rock mass properties. However, the core zone of the fault system consists mainly of faulted schists and phyllites without competent rock bodies and consolidation. Thus, the rock mass properties are very poor, similar to fine grained soil even aggravated by the remnant schistosity of the cataclasite.</p><p>Due to the challenging geological conditions and proposed radial displacements of several decimetres, it was evident from the outset that a&#xa0;ductile support system with yielding elements was necessary in this fault zone. To enhance structural resistance in cases of ongoing displacement, an additional shotcrete lining was added. The original design approach successfully established a&#xa0;stable interaction between the support system and the rock mass in 75% of the fault zone. With the transition to the core zone, the total displacement of the rock mass increased up to 2 m. An ongoing modification of the excavation and support concept was necessary to deal with an initial displacement up to 20 cm. Amongst other measures a&#xa0;much more ductile support was developed. Additionally, a&#xa0;pilot tunnel was constructed ahead of the main excavation to provide stress relief.</p>

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Geotechnical Challenges at Crossing a Major Fault Zone at the Semmering Base Tunnel

  • 期刊论文

  • 发表日期：

    2025年9月5日

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  • Mario Hein,
  • Andreas Kelder,
  • Robert Holzer,
  • Gerhard Gobiet

摘要

The Semmering Base Tunnel (SBT), a railway tunnel under construction with a total length of 27.3 km in the eastern end of the Austrian Alps, comprises many geotechnical challenges including the crossing of major fault zones. The largest zone is the more than 1 km long Grassberg-Schlagl fault system at lot SBT 1.1, which consists of a wide range of heavily sheared lithologies. A major part of the fault zone has undergone a secondary cementation by sulphatic minerals, which caused a significant improvement of rock mass properties. However, the core zone of the fault system consists mainly of faulted schists and phyllites without competent rock bodies and consolidation. Thus, the rock mass properties are very poor, similar to fine grained soil even aggravated by the remnant schistosity of the cataclasite.

Due to the challenging geological conditions and proposed radial displacements of several decimetres, it was evident from the outset that a ductile support system with yielding elements was necessary in this fault zone. To enhance structural resistance in cases of ongoing displacement, an additional shotcrete lining was added. The original design approach successfully established a stable interaction between the support system and the rock mass in 75% of the fault zone. With the transition to the core zone, the total displacement of the rock mass increased up to 2 m. An ongoing modification of the excavation and support concept was necessary to deal with an initial displacement up to 20 cm. Amongst other measures a much more ductile support was developed. Additionally, a pilot tunnel was constructed ahead of the main excavation to provide stress relief.