Civil Engineering: Membrane evolution for tunnels

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Tunnelling Journal recently featured an article about the improvements in sheet waterproofing membranes over the last ten years for tunnelling projects. They asked SOPREMA, as a manufacturer of sheet waterproofing, what improvements they have made.

CivilRock® is SOPREMA’s range of products designed to support the requirements of civil engineers for all types of structures including tunnels, underground and basement structures, bridges, car parks and much more.
Within the article, Vanessa Dos Santos, Civils Manager and Paulo Grazioli, Civils International Business Manager discuss the increasing importance of offering a waterproofing solution which can withstand more demanding conditions than ever before as tunnels go deeper and deeper underground, limiting future repair risk and costs.

Read an extract from the article below:

SOPREMA: limiting repair risks and future costs

The trend towards deeper tunnels and underground spaces means that waterproofing must withstand more demanding conditions, says Vanessa Dos Santos, SOPREMA’s Civils Manager for UK and North West Europe. “What has changed in recent years is the need to design specific solutions tailored to each project that take into account the hydrogeological conditions of the site where the project will take place.”

SOPREMA’s last major technical development was its vacuum system, designed so that sheet waterproofing can be tested before a second layer of concrete is applied to the tunnel. It was first used well over a decade ago on the Milan Metro from 2004 where the high water table meant that the integrity of the waterproofing membrane was important.

More recent uses of the vacuum system include the Tunnel Callao in Peru, a 2.4km road and train tunnel that passes under the airport where over 300,000m2 were installed. This year, 2019, 130,000m2 will be applied to stations on the Sydney metro where high water pressure and saline conditions are among the challenges.

While a standard single-layer sheet waterproofing has water bars at construction joints to limit the spread of water should there be leaks, the vacuum system goes a step further. It is made of two layers which are welded together to form compartments of around 100m2. Hoses from each compartment can be attached to a vacuum pump and tested. If any water is found, the same hoses can be used to apply a resin to seal up the flow.

“With a standard system, they inject until the leakage stops, so you never know how much resin they will need to stop the problem,” says Dos Santos. The injection is a very expensive material. The best way to minimise cost is to make sure you minimise the area of repair .”

FLAGON SOPREMA sheet waterproofing membrane has been used in major projects in the UK because of the quality of the build up and the life expectancy of the products (required for a minimum of 120 years). This matches the specification requirements in terms of service life and exceeds the performance of alternatives product in terms of life expectancy. FLAGON SOPREMA membranes were recently used on two London Underground projects: for a long passenger tunnel at the Bank Station Upgrade and on parts of the Northern Line Extension. These were projects that were originally specified as spray-applied system, but they could not reach the desired life expectancy required for this type of project says Dos Santos.

Dos Santos believes that waterproofing is not given enough weighting when tunnels are being designed: “As a manufacturer of waterproofing products and systems, the biggest challenge we face is to educate the market on products and systems that are normally considered marginal in the design of underground works,” she says. SOPREMA is here to help, introducing further training for consultants and designers to improve knowledge and awareness at the design stage.

Paolo Grazioli, international business development manager at SOPREMA, would like to see a bigger focus on the whole-life costs. Waterproofing accounts for a tiny fraction of the overall construction cost yet can add vast amounts to maintenance costs if it is not done properly, he says. “The budget for waterproofing is negligible compared to the total investment in the project – we are talking about 2% to 5%, depending on the products and systems specified – but this small budget protects and preserves over 95% of the investment over time.”

SOPREMA’s products have been used extensively and most recently on the last two London Underground projects – the Northern Line Extension and the Banks Station Capacity Upgrade – in place of originally-specified sprayed membranes, says Dos Santos. But this is not ideal: “Then you have a tunnel that is designed for a different product. The bore is smaller for sprayed membranes. It is better to design it from the beginning with PVC.”

Grazioli would like to see more transparency in the costs and benefits of the various waterproofing systems in the market. He points out that although there have been few new entrants to the sheet waterproofing market for tunnelling, SOPREMA still continue to invest in product development and innovation, offering the very best waterproofing solutions.

In terms of innovation, SOPREMA under the CIVILROCK portfolio is due to launch in the UK market a fully bonded system, with a dual salvage technology patented by SOPREMA to ensure the safest, most robust and secure installation for basements and underground works. The surface finish formula takes advantage of the exothermic synergy creating a superior mechanical bond strength of the membrane to the structural poured concrete. The specially formulated surface softens slightly as the concrete starts to cure, releasing heat. This promotes adherence of the membrane to the concrete, and prevents the ingress or migration of water around the structure. We have already over 3 million m2 in projects across the globe.

We also offer for cut and cover tunnels our AntiRock fully bonded system on a single layer reinforced membrane and that completes our range to support designers and specifiers in every project. Read more in this brochure.

If you would like to find out more about SOPREMA CIVILROCK, please contact us on info@soprema.co.uk.
• You can read the full article here: https://tunnellingjournal.com/archive/tunnelling-journal-march-april-2019/