Croydon Cable Tunnel, UK
Integritank HF system overcomes harsh on-site weather conditions in Croydon Cable Tunnel
To facilitate high voltage power distribution in the South East of England, Morgan Est needed to build a 3.05m diameter cable tunnel to house the required heavy duty power cables.
They decided to form the tunnel by boring, using the TBM method. This would necessitate the tunnel lining of the front and back shunts, which were to be 3.9m in diameter, being formed by a primary and secondary sprayed concrete lining with an effective waterproofing membrane sandwich between two layers.
The chosen waterproofing system need to be capable of forming a tenacious bond to both layers of sprayed concrete as well as being tough enough to withstand the application, using spray-blasting equipment, of the second concrete lining.
National Grid PLC
Stirling Lloyd Construction Ltd
- Water & Power - Croydon Cable Tunnel
The Application Part 1.
Morgan Est’s search for a waterproofing membrane that could meet this criteria led them to Stirling Lloyd’s Integritank HF, a seamless spray-applied system. Not only did Stirling Lloyd’s membranes have an unparalleled track record of success, but also Integritank HF provides an excellent bond to sprayed concrete and easily withstands the forces exerted by spraying concrete.
Prior to application Integritank HF was tested in a simulated tunnel environment, specially built by Morgan Est. Proving its ability here convinced Morgan Est Integritank HF was the system to use.
Application Part 2.
The use of this system and it’s tolerance of difficult site and weather conditions enabled application in a February when the temperature was varying between 0°C and 4°C - temperatures that would have precluded the application of systems based on other resins. The use of a liquid, sprayed system that followed contours of the tunnel meant no time consuming, costly scaffolding or detailing associated with sheet membranes was necessary.
The application itself consisted of Integritank HF Primer, which further enhanced the membranes bond to the substrate, followed by two coats of Integritank HF. The application of two coats aids quality control, that is supplemented by the membrane being checked every 2m² using wet film techniques - ensuring the correct thickness was applied. As a final quality check, once the application was complete, holiday detection testing was conducted to confirm the integrity of the waterproofing.
Pull off tests confirmed that the bond achieved by Integritank HF exceeded the specified value of 0.3N/mm2. By using the Integritank HF spray-applied system, Morgan Est were able to produce a tunnel with not only effective, long-term protection to the valuable payload contained within, but to produce it in a very cost-effective manner with both decreased build time and cost.