Shotcrete-Technology ´06


Fire-resistant sprayed concrete for Sedrun’s shaft II

Dipl.-Ing. ETH Urs Streuli, ARGE Transco-Sedrun, Switzerland 

In the construction of the Gotthard Base Tunnel, shaft II in the Sedrun section was originally designed as an 800 metre deep ventilation shaft. In order to resolve transport problems, its diameter was extended from 4 to 7 metres, and it was provided with a lining of fire-resistant sprayed concrete and a shaft conveyor system installed. For fire protection purposes fire-resistant wet mix sprayed concrete was applied to the shaft walls, having been carried by way of pipes up to 800 metres in depth, with the help of a sprayed concrete machine and placed by a spraying robot. Arge Transco [Transco Joint Venture] had three different fire protection systems tested. Two of these systems consisted of sprayed concrete with abraded granular materials from the excavation of the Sedrun tunnel section. The fire-resistant sprayed concrete was applied to Sedrun’s shaft II over a total area of around 18,000 square metres, to a minimum thickness of 75 mm. Results of fire tests (at 900 °C over a period of four hours) were as follows:
• No spalling (not even when subsequently subjected to high pressure ventilation)
• No sign of deterioration (sandy decomposition) on the surface
• Temperature below 350 °C at the concrete structure contact surfaces.