BASF has provided its MasterSeal 345 waterproofing system for the A3 Hindhead Tunnel. The tunnel was one of the projects in the Government’s programme of major road schemes.
The tunnelling method proposed by Balfour Beatty was the Sprayed Concrete Lining method (SCL). Despite predictions of low ground water ingress and good self-supporting sandstone, the reference design for the tunnel included a drained PVC-membrane waterproofing system behind an in-situ concrete final lining.
However, consultants Mott MacDonald felt an alternative solution could offer significant time savings and flexibility advantages for the contractor and major time and money savings for the client. Mott MacDonald proposed a spray-on waterproofing system with shotcrete as the final permanent lining in the crown. The tunnels would have cast concrete sidewalls to allow a painted reflector surface and easier wash-down maintenance.
It specified BASF’s MasterSeal 345, which is applied in a simple sandwich construction. The waterproofing system’s performance lies in the excellent bonding properties between the membrane and concrete lining on both sides, which mitigates the risk of water ingress by eliminating groundwater paths. MasterSeal 345 closes and isolates any cracks so that stresses resulting from water pressure can be transferred to the outer lining, leaving the inner lining virtually unaffected.
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