With use of membranes being a well-established technology among the waterproofing solutions in the development and operation of underground space, developments in the field continue along with R&D investment and changes in market conditions, and opportunities.
Norwegian manufacturer Protan produces a wide range of membranes and has a dedicated unit serving the international tunnelling sector. Among Protan’s products for use in underground structures and environments are its InfraPlan PVC membranes and TPO membranes, certified to German, Swiss, Austrian and Norwegian guidelines to suit mined and cut and cover tunnels.
Trends in waterproofing membranes for tunnels, Protan tells T&T, include membrane sheets becoming wider, and more focus coming on both resource conservation and waste reduction.
The membranes for tunnels and underground works are manufactured using flat-die coextrusion technology to thicknesses such as 3.2mm down to 2.0mm (P32+ to P20 type).
Thinner membranes can be made, down to 1.5mm, which also have geotextile reinforcement such as polyethylene terephthalate (PET – an unsaturated polymer) and polypropylene (PP – a saturated polymer) fleece laminated to the backside, helping improve adhesion to concrete.
Arrangement with the membranes in tunnels can include partial waterproofing, the most common of which is the umbrella or drainage system, used for underground space with dripping water conditions. They are used in projects like road and rail tunnels.
In Norway, the road tunnels require a Type III reinforced membrane for dripping water conditions. The InfraPlan reinforced membrane is mounted on an anchor grid, a slight distance from shotcreted walls, providing a void for drainage space. The traffic-side of the membrane is covered with concrete panels or shotcrete, for which a geotextile reinforced membrane, such as with PP, is used.
The InfraPlan+ classes of membranes, such as P22+ and P32+ (2.2mm and 3.2mm thick, respectively) were specifically developed for the German and Austrian markets.
Protan says that among developments in membrane technology to match future trends are ways to reduce shotcrete rebound, new welding for wider sheets that also benefit from the simpler Norwegian ‘hanging’ system. Remaining a full system supplier is also important, it adds.
The geotextile membranes help to reduce shotcrete rebound.
A new welding system, called InfraWeld, has been developed that enables wider membrane sheets to be installed, says Protan. The system is based on fast induction welding and avoids the need for physical penetration of sheets to achieve an effective fix for the product.
The induction heating helps to bond the membranes to plates laying underneath and fitted to hidden anchors.
Speed of installation and continued integrity of the membrane are key qualities of the technique in dripping environments.
The system also uses a connecting bar for internal reinforcement that can be screwed to be watertight.
The new system works with PVC and FPO/TPO tunnel membranes.
