MBT Underground Construction Group’s (UGC) track record in underground construction includes the development of new products and state of the art equipment to meet project specific requirements. The lining of the 3.2km long North Downs Tunnel, part of the Channel Tunnel Rail Link, was designed as a double shell structure. A temporary sprayed concrete lining, followed by a reinforced permanent in-situ concrete. The client had not considered the sprayed concrete lining as part of the permanent lining design. In the past sprayed concrete linings have proved to be of variable quality and there were questions about the long term durability and interaction between primary and secondary linings. MBT’s Meyco SA range of alkali-free accelerators , coupled with high performance concrete admixtures enabled the construction of permanent sprayed concrete linings, providing the client with significant cost and programme savings. To achieve the permanent quality lining MBT undertook extensive trials to maximise strength development and durability in line with a modestly increased specification, while minimising unit material cost.
Judging Panel’s Comments: MBT have made striding advancements into shotcrete technology through extensive research and development into concrete admixtures. This research has benefited our industry world wide in both shotcrete quality and safety and the company’s perseverance has enabled huge progress to be made in the use of wet spray shotcrete as a viable temporary and permanent lining.
