For infrastructure projects with shallow overburden a comprehensive geotechnical monitoring program and its implementation in the daily operation is essential for a successful and safe completion of the works. A continuous control of both the tunnel and the surface according to the observational method within a strict geotechnical safety management is one of the most challenging tasks for such projects. The paper gives a short overview about the geotechnical design and monitoring at the large OeBB railway project Lainzer Tunnel lot LT 31 in Vienna/Austria. Two case histories shall illustrate the implementation of the geotechnical safety management.
Core of the OeBB Lainzer Tunnel project with 12.8 km is lot LT31, having a length of 3.6 km, where residential areas and major traffic infrastructure are situated along the tunnel route (see Figure 1).
The tunnel was constructed as a double-track tube with an excavation cross-section of about 130 m² using NATM. Due to the hydrogeological conditions dewatering and groundwater relaxations in advance to the excavation were necessary. Excavation started from the shafts at "Klimtgasse" and "Lainzerstraße" in both directions. 2/3 of the tunnel alignment follows a major railway line ("Verbindungsbahn") under operation. The overburden ranges from approx. 6 m (southern part) to 26 m in the soft ground sections and to approx. 55 m (western part) in the bedrock region. Due to the difficult geotechnical conditions and the potential direct impact of the project activities on the public, a Geotechnical Safety Management Plan (GSMP) including a comprehensive monitoring concept was established and strictly followed (Moritz et al. 2011).