Abstract
The Semmering Base Tunnel in Austria is currently one of the largest tunnel construction sites in Central Europe. Two tunnel tubes, each 27.3 km long, are being built from the portal and three intermediate construction sites. Each access point poses specific challenges, and structural monitoring is a crucial element to ensure both economic and safe construction. In this paper, the authors describe one of the most comprehensive distributed fibre-optic sensing installations on a tunnel construction site worldwide. At the Semmering Base Tunnel, fibre-optic sensing is used at every construction location to monitor tunnel linings, shafts, reinforced earth structures and pipelines. The authors also discuss the challenges posed by the installations and the results of long-term monitoring programmes. The installed monitoring systems will, furthermore, be used throughout the expected 150-year operational lifetime of the tunnel. Unlike conventional sensors, fibre-optic sensors do not comprise electric or moveable components at the measurement location. A longer lifetime can, therefore, be expected for fibre-optic sensors, which makes them promising candidates for condition-based maintenance of civil infrastructure.
Highlights
The Semmering Base Tunnel (SBT) is currently one of the main infrastructure projects in Austria
At the north portal and the Göstritz and Grautschenhof intermediate access points, conventional tunnelling based on the New Austrian Tunnelling Method (NATM) (OeGG, 2010) is being applied
3.1 Monitoring of a shotcrete tunnel lining The idea underlying NATM is that the tunnel cross-sections are cut out sequentially – that is, first the top heading followed by the bench and invert
Summary
The Semmering Base Tunnel (SBT) is currently one of the main infrastructure projects in Austria. All trains must cross the mountain ridge on the 165-year-old Semmering railway, comprising several short tunnels, viaducts, large height gradients and small curvature radii. Due to this historic track layout, the train speed is low and only short freight trains with two engines can pass the mountain. The tunnel is being driven from the portal at Gloggnitz and from three intermediate construction access points in Göstritz, Fröschnitzgraben and Grautschenhof (Figure 1). At the north portal and the Göstritz and Grautschenhof intermediate access points, conventional tunnelling based on the New Austrian Tunnelling Method (NATM) (OeGG, 2010) is being applied. As well as conventional geotechnical sensors, distributed fibre-optic sensing (DFOS) is being used at every construction site to increase worker safety, enable more efficient construction and assess the structural integrity of the tunnel during construction and over its expected 150-year operational lifetime
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