Specification Focus: Roads & Landscaping

The Clyde Tunnel in Glasgow, described as "one of the most ugly and unloved parts of the city" offering "no uplifiting qualities whatsoever" by HoldYourBreath, a local campaign for its improvement, has finally undergone renovation.

It is unlikely, however, that the occupants of the 65,000 vehicles that pass through the tunnel each day will have their experience enhanced by the presence of sound and sculpture, as requested by the campaign. Instead main contractor Byzak, a tunnelling specialist working for Glasgow City Council, settled on a solution that met both the strict levels of fire protection, durability and the logistical demands of the project.

The twin bore tunnel, measuring 762m in length, links north and south Glasgow. It was opened in 1963 at a total cost of £10m, just £2m short of the cost for its improvement. Having been constructed to cope with 13,000 vehicles per day at its opening, the unanticipated high volumes of traffic since have accelerated the wear in the tunnel, resulting in repeated closure for repairs.

In order to halt this cycle, a complete renovation has now taken place. This included the installation of a new secondary lining to bring the tunnel in line with European safety standards - set out by the RWS (Rijkwaterstaat) fire curve - introduced after the St Gotthard and Mont Blanc tunnel fires. Promat, a passive fire protection specialist, teamed-up with Ancon, Ceramicote, Polyvision and Osborne Associates to provide Byzak with a solution designed to meet modern fire safety requirements.

"Many years ago, there was a contract to strip the secondary lining from the tunnel," explains Andy Dickson of Byzak. "So we had to devise a system that would attach to the primary lining and protect the tunnel."

The contractor also had to deal with Glasgow City Council's request that the work was to be carried out only at night, to allow traffic to flow as normally as possible during the day. "The demands for the project were huge, with the added complication that we wanted to only carry out work at night," explains Marco Bardelli, structures manager at Glasgow City Council. "This meant that any system had to be relatively easy to install, without the need for permanent scaffolding."

After considering the required abrasion resistance and durability requirements, Byzak specified a total of 40,000m2 of Promat Promatect T boards. These were used within two bespoke systems to protect the concrete structure and the cast iron rings of the tunnel bore.

The contractor attached fabricated brackets to the existing bolts on the cast iron tunnel lining, followed by circumfluent steelwork. A stainless steel layer was then added as a dripshield - to divert water to drainage - on top of which the Promatect boards were installed.

Fire resistance

The non-combustible mineral bound boards offer Class 1 fire resistance and have a smooth matt upper surface, which is off-white in appearance. As required of any tunnel protecting layer, they will not collapse in the event of a fire.

In tests conducted at the Runehamer tunnel in Denmark, Promatect T boards were subjected to temperatures in excess of 1,365°C in conditions that would be expected in the event of a cargo truck fire. In these extremes, the maximum temperatures recorded on the cold side of the 1x25mm and 2x15mm boards were only 210°C and 179°C respectively.

With fire resistance assured, the boards had to look the part. For the Clyde tunnel project they were pre-finished with ceramic coves, allowing for ease of pressure washing, while also being more reflective than the naked fire boards. "Any reflective coating had to be able to withstand the effects of vehicle exhausts and dirt almost from the moment the panels were installed, because we were opening the tunnel back up to traffic each morning there was no real curing or drying time available," continues Bardelli. "The pre-finished option presented to us was ideal."