One of the main goals of the ground investigation for the Koralm Tunnel project was the detailed investigation of the Lavanttal fault systemwhich lies in the contact between the Koralm crystalline and the neogenic formations of the Lavanttal. The above-ground investigation programme (mapping, core drilling, geophysics) was able to deliver the first estimation of the geological, hydrogeological and geotechnical rock conditions of the fault zone many hundreds of metres thick ( fig. 1). The Paierdorf investigation tunnel, which has now been constructed, clarified the thickness and the internal structure of the fault zone as well as the hydraulic and mechanical rock properties along the tunnel. Equally important was the practical experience gained by tunnelling through the fault zone. The knowledge gained from the Paierdorf investigation tunnel will be used in further design work for the mechanical driving of this very heterogeneous region of rock.1 Knowledge of engineering geology gained from the investigation tunnel
Main fault zoneThe prognosis Immediately to the East of the neogenic-crystalline boundary, a main fault zone of the Lavanttal fault system was forecast, with a thickness of several hundreds of metres. In this region, a sequence of softly plastic, finegrained and coarse-grained cataclasites was expected, alternating with less faulted, competent blocks of rock. The thickness of the cataclasites was supposed to be a few metres to many tens of metres. Steeply dipping faults were expected to be dominant, dipping towards and also against the advance direction.The groundwater table in this area is up to 270 m above the crown of the tunnel. In the main fault zone dry to damp conditions for tunnelling were expected with locally trapped water pockets. In the jointed competent rock and in the boundaries of steep faults trickling water ingress was expected. Isolated water or mud inflows with up to some tens of l/s were also considered possible.
The conditions encountered
This paper discusses the design and construction of a fault zone of the OeBB Koralmtunnel lot KAT3. Due to the experience gained during the advance of the parallel‐situated southbound tunnel and the aim to minimize the geotechnical hazard for the subsequent excavation of the northbound TBM bore, an extensive redesign regarding the excavation‐concept and ‐method was performed. Five different alternative solutions have been subject to a risk analysis to optimize the required measures and to minimize the cost‐effective risks and hazards to an acceptable level. The set of measures, which was evaluated and juxtaposed, contained solutions for strengthening the rock mass with grouting from the TBM and from aside the bore, conventional tunnelling and backfill with a top heading or full‐face excavation. Finally, the fault zone has been excavated with a conventional top heading drive from a nearby‐situated cross‐passage. Subsequently this tunnel stretch has been excavated by TBM without any construction delay. The paper focuses on highlighting the importance of a consequent application of the observational method and thereof derived measures in the context of a geotechnical safety management plan for controlling the residual risks.
The Paierdorf ventilation facility is a part and a preparatory contract for the Koralm Tunnel KAT 3 contract, and is situated approximately 3.7 km from the western portal. It consists of a vertical 120 m deep shaft, an 88 m long expanded section of the south tunnel, access tunnel/TBM entry cavern, an approximately 100 m section in the north tunnel and a ventilation tunnel having a length of around 93 m. The shaft, the access tunnel and the top heading of the south tunnel had already been constructed during the extended exploratory programme of the Koralm Tunnel. The TBM entry cavern, the segment of the north tunnel as well as the section in the south tunnel and the ventilation tunnel were then added in 2012. The ventilation tunnel crosses over the south tunnel with a minimal separation of 2.8 m and connects to the vertical shaft. This geometrical arrangement results in complex geometry of the underground structure and complex geotechnical interaction between the parts. This paper concentrates on the prediction of system behaviour in the design phase with 2D and 3D numerical calculations and the comparison of predicted with observed behaviour during construction.
The Koralm Tunnel, a twin-tube single-track railway tunnel with an overall length of almost 33 km and a maximum overburden of about 1,200 m, closes the most significant gap of the future highcapacity railway line from Graz to Klagenfurt, Austria. Located close to the tunnel centre, an emergency stop will provide the facilities for future travellers to be evacuated in case of an emergency. The paper discusses the challenges of the design and incorporates the current state of the ongoing construction works of the emergency stop. In addition, the structure and content of the geotechnical safety management plan, as well as the applied monitoring program are presented in detail, emphasizing the analysis of the observed system behaviour in connection with the encountered geological conditions.
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