The design of the sprayed concrete tunnel linings for Crossrail typically adopted the use of spray-applied waterproofing membrane between two layers of permanent sprayed concrete. However structures on the west side of London were constructed through sandy clays, and therefore the risk of higher water ingress in the lower level tunnels drove the design towards conventional PVC sheet membranes. At Farringdon Station, BFK JV adopted the use of TamSeal 800 spray membranes for the higher level escalator and ventilation shafts as they were driven in the London Clay formation.
In sections with highly variable cross-sections, complex geometries and construction sequences the use of TamSeal 800 spray applied waterproofing membrane was considered the most suitable solution by the JV team. At Farringdon Station two ventilation tunnels and two escalator shafts were selected as suitable for this construction method. For the shafts the ‘tanked‘ and ‘double-bonded’ spray applied membrane offered by TamSeal 800 prevents the important risk of water traveling down the shaft along the membrane and filling up the space behind the sheet membranes installed in the platform tunnels. Therefore using a fully bonded TamSeal 800 waterproof membrane solution prevented a “reservoir” being established in the lower tunnels and the risk of constant water ingress issues, should the sheet membranes in the lower tunnels be breached.
The bond strength for the connection between the spray and sheet membrane systems had to be tested to prove the suitability of the material and the robustness of the connection details. Technical tests were conducted at the Normet test facilities in Coventry to assess the bond strength of TamSeal 800 onto concrete, sheet membrane and connection tape as well as the hardness development.
Training and information for applicators, engineers as well as for client and consultant inspection teams was required as the spray membrane technology and method of application is fairly new in the UK tunnelling market.
TamSeal 800 was applied in two separate 2 mm thick coats (first coat orange, second coat white) to ensure the correct thickness of 4 mm was achieved consistently, and to ensure 100% coverage the contrasting coat colours approach was used. Given the geometry and slopes of the escalator and vent shafts, hand spraying from lifting baskets using an electric Normet Piccola pump set-up achieved the required performance. In preparation for the TamSeal 800 application any water leaks were treated with TamPur 150 to allow successful membrane application and curing.
Farringdon Station is a good example for choosing a combination of spray applied and sheet membrane and successfully combining the strong properties of both systems. TamSeal 800 proved flexible for complex tunnel geometry but also for ease in forming the watertight connection to the previous sections by just over-spraying a 30 cm wide strip. Simple repair methods can be applied if the membrane is damaged during construction. The long term advantage of the sprayed membrane solution is the double-bond between primary and secondary concrete linings and preventing the development of water paths between the surface and the lower tunnels.
The success of TamPur 125 for stopping water ingress has also opened doors for other Normet injection products. The Gold Line is now highly interested in TamPur 150 for segmental crack repairs. Trials have been successfully completed through Tempo, Normet’s recommended applicator both in the UK and in Doha. They are now expecting to secure work next year for repairing cracks along 7 km of running track.
After hearing positive feedback from the Gold Line project, the Red Line North ordered TamPur 100 for a leak on its project. The product has worked perfectly, and the customer is delighted with the performance. This has once again proved that our polyurethane range can yield effective results.