Tunnel Waterproofing – A New Level Of Protection
The greatest risk to the long-term integrity of reinforced concrete structures is water ingress. Water in the fabric of the structure can cause corrosion of the steel reinforcement and long term major damage. This is nothing new, and various forms of waterproofing techniques have long been used, with varying degrees of success, to protect civil engineering structures.
If it becomes a requirement to undertake remedial works to the waterproofing because it proves to have an inadequate life span or does not perform as well as had been expected, the potential disruption and ease of carrying out this work will vary greatly depending on the type of structure. Tunnels are the extreme case!
You Only Get One Chance
Usually a tunnel is built as the only possible link at a certain point, which means that tunnels cannot be readily or easily taken out of service for repairs without causing major disruption, for both road and rail infrastructure this is a major concern. They are the highest value assets on a transport network and have the longest design life so protecting their long-term integrity should be at the top of the list in the design criteria.
The importance of this is highlighted further by the complexities and costs of performing remedial work if the waterproofing fails. For example an immersed tube tunnel which has been waterproofed externally cannot practically have effective, large scale repairs carried out to its waterproofing once it has been submerged. Cut and Cover tunnels present the same issue, as it is impractical to “uncover” them at a later stage.
In bored tunnels of the New Austrian Tunnelling Method (NATM) or Sprayed Concrete Lined (SCL) design the issue becomes more acute because the waterproofing membrane is installed between the primary and secondary concrete linings, which means that there is no opportunity for maintenance to the waterproofing. Therefore the integrity of the waterproofing membrane is vital; it must not suffer from long-term degradation, even over the 100+ year design life of the tunnel. Choice of waterproofing is therefore critical from the outset.
Sprayed Waterproofing – The 21st Century Approach
Over the last 30 years throughout the construction industry there has been a significant shift away from sheet systems to the use of sprayed membranes for waterproofing. This is predominantly because the welded seams between the sheets are weak points and so are susceptible to failure. Although welding and joining technology has advanced, complex geometry and detailing necessitates the requirement for potentially thousands of seams in a sheet-waterproofing scheme, thus dramatically increasing the risk of leaking. Once this occurs, migration of the water around the structure between the membrane and the concrete means that leaks can show themselves anywhere, often remote from the actual leak point and hence leaks are very difficult to pinpoint and rectify.
The use of spray applied liquid membranes reduces the number of seams to zero and thus substantially reduce the risk of leaks. Seamless waterproofing technology has benefited countless structures.
Bringing Experience To Bear
Stirling Lloyd have specialised in the design, manufacture and application of high performance waterproofing membranes for almost 40 years. Iconic structures including major bridges and some of the worlds highest value civil engineering assets are protected with the unique waterproofing technology developed by Stirling Lloyd utilising Methyl Methacrylate (MMA) resins. These include the Manhattan Bridge in New York, the underground stations of the Mass Transit Railway in Hong Kong, nuclear waste disposal facilities in France and the Bosphorus I & II bridges in Turkey.
The Effective Solution To Confined Space Waterproofing – Integritank HF
Stirling Lloyd has supplied seamless sprayed membranes for tunnel waterproofing since 1989. This includes the external lining of immersed tube tunnels, such as the Western Harbour Crossing in Hong Kong, and cut and cover tunnels, as well as inside tunnels to waterproof suspended concrete road decks, such as the Blackwall Tunnel in London and the Queens Midtown Tunnel in New York.
However their recent focus, utilising all the experience and know how of sprayed waterproofing membranes in all other types of tunnel construction, has been on providing a solution to the internal waterproofing of tunnels, to develop a new product specifically for the SCL / NATM construction method. Although various methods of waterproofing have been used for a number of decades, few have provided complete confidence in the protection of the structure for its design life because the conditions encountered in building a tunnel by NATM or SCL methods pose particular challenges that need to be addressed.
Working closely with major tunnel builder Morgan Est in the UK, Stirling Lloyd have developed a new spray applied waterproofing membrane, Integritank® HF, was officially launched at the Rapid Excavation and Tunnelling Conference (RETC) in Las Vegas in June this year.
The membrane is based on the advanced Methacrylate technology behind Stirling Lloyds extensively used waterproofing systems, which has been adapted specifically for use in confined spaces and for application between primary and secondary concrete linings.
The spray applied, two-coat system ensures a seamless finish and eliminates the chance of leaking through any seams. The membrane is fully bonded to both primary and secondary concrete linings and therefore water cannot circulate around the structure between the waterproofing and the concrete layers. After application to the primary concrete, uniquely in tunnelling the Integritank HF membrane can be electrically integrity tested to prove that 100% effective waterproofing has been achieved prior to the secondary lining being installed. The robust and intimately bonded membrane enables the use of sprayed concrete to form the secondary lining as well as the primary lining without complex reinforcing schemes, thus speeding up tunnel construction and reducing the overall cost of the structure. The high output rate and rapid cure of the membrane accelerated the waterproofing process while the application to overhead areas of the tunnel also poses no challenge for the system due to the thixotropic nature of the material.
The Integritank HF membrane has already been used successfully on a number of projects in the UK, providing an effective and fast method of waterproofing, simplifying the use of sprayed concrete secondary linings and providing complete confidence in the effectiveness of the waterproofing; something that is not usually attained during the construction of a NATM or SCL design.
Protecting The Asset
On high profile and high value tunnel projects it is unacceptable and now unnecessary to install the secondary concrete lining and find a leak at a later stage resulting in disruptive and costly remedial work, if indeed the work can be carried out at all. Sheet membranes present a risk of leaking through seams and water circulation, particularly in tunnels of complex shape. Consequently for designers that require the highest level of waterproofing integrity with the minimal amount of risks, Integritank HF provides a unique and innovative solution to the problem of high performance waterproofing in SCL / NATM tunnel construction, giving complete protection of the asset.
For further information, contact Stirling Lloyd on +44 (0)1565 633 111 or email marketing@stirlinglloyd.com
For more information please contact:
Roxanna Anderson on +44 (0)1565 633111 or roxanna.anderson@stirlinglloyd.com
Stirling Lloyd Polychem Ltd
Union Bank
King Street
Knutsford
Cheshire
WA16 6EF
www.stirlinglloyd.com
www.highwaymaintenanceproducts.co.uk
