Reliable fire-safety for the Cassanawald Tunnel
The Cassanawald Tunnel forms part of the northern approach ramp of the A13 motorway close to the San Bernardino Tunnel, and serves as an avalanche shield for the road. It features two-lane contraflow traffic for its length of 870 m, and is located in the Canton of Grisons.
The following modifications were implemented in mid-2010 in order to provide reliable protection against fire damage for this tunnel:
• Demolition of the salt-decayed wall structure to a residual height of 2.60 m, and its restoration with new polypropylene-fibre-reinforced structural concrete. This fibre-reinforcement system is known to reduce or even eliminate spalling of the concrete in case of fire.
• Installation of a special fire-safety mortar (the BASF „Meyco Fireshield 130“ system) on the tunnel roof; a high-pressure water jet (2000 bar) was first used to roughen and clean the original concrete, in order to ensure total adhesion of the fireproof mortar to the substrate, the adhesion requirement for this refractory safety mortar being not less than 1MPa; the necessary substrate roughness was determined by means of on-the-spot inspection and continuously verified using a laser profilometer.
The safety mortar was then sprayed on to the tunnel roof (layer thickness: approx. 40 mm) by a spraying robot using the wet-spraying method at a daily application rate of up to 30 m³. The tunnel was closed in one direction to permit performance of this work, and rails laid in the traffic-free lane to carry flatcars, which were used as mobile platforms for installation of the fireproof spray mortar (total application: 12,000 m²).
The fire-safety system installed here, supplied by BASF Construction Chemicals Europe AG, of Zurich, fulfils the strict requirements of the RWS fire-load curve (e.g. assured fire resistance after 10 minutes at 1200 °C and even after one hour at 1350 °C). The work was performed by Bauunternehmung Marti AG, of Lucerne. ⇥G.B.
