A little History

The pioneering success of the flexible PVC membrane came as a result of the application in a Subway Station in Vienna - Austria in 1969.

The success of this project encouraged tunnel specialists in Austria and beyond the country's border to take notice of and consider the new system. Numerous successful sealing works were reported in the 70's with the flexible membrane used in underground constructions.

In 1984, PVC membranes were introduced to the United States on the Washington Metropolitan Area Transit Authority (WMATA) B-10a project, a part of the Red Line section. For the first time it was demonstrated to the North American underground construction market that dry tunnels can be designed and built an economically justifiable cost to the owner.

The PVC membrane tunnel waterproofing system has since been incorporated into various other tunnel projects throughout the United States, including twelve other WMATA Projects. The Owner who has specified and/or accepted value engineered PVC membrane waterproofing systems has received dry tunnels which will save them substantial amounts in future repair and maintenance costs.

Why PVC Sheeting

The main reason to use PVC sheeting is its good flexibility and the high stretchability of over 300%. Good resistance to low temperatures, to aggressive water, aging, as well being easily welded and repaired, and having good mechanical and high tear strength are additional advantages.
The major advantages of the PVC membrane are, the very efficient and fast application process and weldability characteristics and it can be laid and welded on moist/wet areas; on the other hand it also allows insulation of uneven substrates, which is a considerable advantage over other sheet membranes.

Why flexible membrane waterproofing
(Road and Subway Tunnels)

It shall prevent the following negative effects:

• effloresce and blisters in paint
• ingress of percolate water
• dropping water inside the tunnel
• bloom of chalk or cement at walls inside
• wet construction joints
• wet surfaces
• icicles, ice on roadway
• elevation of runway due to frost
• ingress of water at cracks, construction joints, dillatation joints, honeycombs
• destruction of inner concrete lining by frost and aggressive water
• destruction of reinforcement by aggressive water
• corrosion of fixations, destruction of cables and hoses of various installation (lightning, telecommunication, traffic-control, etc.)

Summary

Every tunnel builder is familiar with the difficulties and risks in obtaining a watertight tunnel lining. The requirements of the construction authorities in this respect are extremely rigorous. The idea of a rigid sealing has not proven to be satisfactory, since crack formation due to the cooling of the concrete, as well as to later rock settlements, cannot be avoided.

We have seen that flexible sealing membranes in underground construction have been used for over 25 years and play a leading role when absolute tightness of the insulation is desired.