SINCE SPRAYED MEMBRANES WERE launched in 1996 there have been some good successes and a number of disasters,” explains Ross Dimmock, managing director for Normet UK, manufacturers of the TamSeal 800 spray applied waterproof tunnel lining system. “The problem areas came from extremely wet tunnels where it wasn’t appropriate to use these liners or where the tunnels were left to freeze before it was coated with concrete and where people hadn’t done quality control checks prior to putting the secondary lining in place,” he says. In short such “disasters” are avoidable and lessons are being learned from problems of the past.
Today he says that the market for these systems has improved although it remains a very small proportion of the waterproofing sector where sheet membranes still dominate. Complex geometries or cross passages on TBM bores are particular hot spots. “There is a small window where this is very useful and that is what we try to do,” says Dimmock pointing to recently completed projects at Farringdon Station and Fisher Street on London’s Crossrail where the TamSeal 800 product was used by the BAM Ferrovial Kier contracting joint venture to waterproof the crossover cavern, two ventilation tunnels and escalator shafts.
“The double-bonded spray applied membrane solution prevents the danger of water travelling down the shaft along the membrane and filling up the space behind the sheet membrane in the platform tunnels and loading and pressurizing the sheet membrane and secondary lining,” explains Dimmock pointing out that PVC sheet membranes were used for the more uniform underground spaces. “A lot of people don’t realise that if you have these bonded spray applied membranes they can’t let water move and that was the key criteria for this project – to stop the water travelling down from the overlying water laden gravels through to the clays.”
Just as importantly these bonded membranes can favourably change the structural characteristics of the tunnel lining. “If you can effectively connect the primary and secondary lining then you have what we call composite action and a researcher at Southampton University, Jiang Su, has recently modelled that behaviour to give the industry clues as to how to make the linings more efficient,” says Dimmock, noting that the forthcoming contracts in London are set to include this benefit in their design, where water pressure can be considered to act at the back of the primary linings, rather than inefficiently at the membrane interface. This wasn’t possible on Crossrail.
“I was employed with Mott McDonald on development designs for Crossrail but we didn’t have the knowledge or products in the market at that time but I’d say now, six to seven years on, we have the opportunity to and London Underground is very bold to allow the designers to consider it, and the linings there are more efficient, which is good. The client’s design standards also prevented us from considering water pressure acting anywhere else other than the membrane interface, be it spray applied or sheet membrane.”
The TamSeal 800 system uses co polymer dispersion based on ethylene vinyl acetate (EVA) technology, as does BASF’s Masterseal 345, which is also used for tunnels and underground spaces. “EVA based membranes are robust and can be used on shotcrete and damp areas and you are not worried about condensation. We have done a lot of occupational health studies and it is quite safe,” says Dimmock noting that recent advances in their formula are helping accelerate the curing process. “We have got a built in curing system in the product so it is not just wholly reliant on evaporation and drying like in the old days. If it is humid that used to cause problems or it would just dry on the surface and now we want the curing right the way through the product so it has a built in chemical curing system that works when you spray it. It is activated straight away.”
Application is recommended as a two-stage approach with the first bright orange layer applied and left for an hour or two before the white top coat. Total thickness is between 3mm and 5mm depending on the substrate surface, and the degree of crack bridging required. No primer is required.
“The two layer approach covers all defects and is commonly used in other industries to ensure coverage. We saw that in waterproofing tests, not all of our membranes passed when we applied just one layer but when we applied two, we never had a problem.”
Thanks to the new formula Dimmock says that the membrane can be sprayed and walked over after 24 hours and ultimate cure time is around seven days. Manual or robotic application is possible but the relatively high cost of robots means that most contractors stick to manual spraying with cherry pickers and lifting platforms to achieve the required height. Dimmock says application rates are similar in either case and 100m2 per hour is the typical rate.
Another high profile project to successfully use sprayed membranes was the Hindhead Tunnel in Surrey, UK, where sprayed concrete lined tunnels and spray applied waterproofing was used for 1.8km of twin bore tunnel. Here BASF’s Masterseal 345 was used and once again lessons have been learned for future applications. “We learned a lot about how we go about the concrete and the substrate and getting the boundary conditions for the membranes right and that is where the improvements have been,” says Karl Gunnar Holter, technical manager for underground construction at BASF. He says that these are important steps forward and that getting the boundary conditions right includes managing the evenness of the regulating layer, fibres in the regulating layer, crack width control, as well as interfaces with other structures that come later.
He says application speed for the Masterseal 345 system is between 50 and 80m2 per hour and curing time is two to five days. Like the Tam Seal 800 system no primer is required and it gives the same potential benefit of composite action between the primary and secondary sprayed concrete linings.
