TECHNICAL | WATERPROOFING/BTSYM WORKSHOP
Right:
Connecting waterproofing system at tunnel access junctions
Similarly, for a cut-and-cover tunnels, the options
consist of: synthetic sheet membrane systems; fully bonded polymeric sheet membrane; liquid applied reactive membrane; waterproofing mortars; bituminous membranes; or, the watertight concrete (white box). It is important to understand the consequences of
the options you chose, she explained – for example, watertight concrete creates a buoyancy effect resulting from water pressure acting on the underground structure as groundwater is unable to drain away. Another important parameter of the design consists
of the durability of the waterproof system. In some ways, a functional waterproof system within the tunnel is what enables the tunnel to meet its long design life requirements as it prevents defects and damages incurring within the tunnel as a result of active water ingress. To demonstrate how Sika meets this requirement,
Sarah explained the testing Sika carried out on the new Alpine Railway Transversal (NEAT) – a strategic ‘flat’ rail corridor passing through the Swiss Alps and comprising two giant rail tunnel projects: the Lötschberg, Gotthard and Ceneri base tunnels.
12 | December 2023
The client, AlpTransit, specified a 100-year design
life with minimal maintenance on the concrete, in accordance with the sealing used in the Gotthard Base Tunnel. Taking into consideration the unique conditions for this tunnel, such as the high mountain cover and the increased ambient temperature, both the individual components and the way the combined system works had to meet the difficult requirements. The developed aging process for the components was extremely tough with all system components being stored for 24 months under various conditions before being tested. On NEAT, a durability research programme was undertaken (2.5-yr & 10-yr, in rock temperatures up to 45°C-50°C). Through targeted developments, Sika was able to meet the challenging requirements of the Gotthard and Ceneri tunnels. In situ tests were also carried out on the application and fixings, and checks carried out on the vertical folds. A further project example the workshop attendees
heard about was waterproofing for a road tunnel, also in Switzerland, that was much shorter – the 600m-long, twin tube, three lane Reussport tunnel. PVC membranes were originally installed in the tunnel
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