The Hammersmith Connection Tunnel forms part of the £4.2billion pound Thames Tideway scheme. The tunnel will intercept sewer flows from the Hammersmith Pumping Station, where on average 2 million m3 of untreated sewage is discharged into the River Thames each year.
The design of the tunnel includes a sprayed concrete primary lining and cast in place secondary lining. The waterproofing philosophy adopted by the designer omitted the need for a traditional waterproof membrane between the primary and secondary linings. Instead a crystallisation agent was specified and incorporated in the primary lining, with the aim of improving the permeability of the section and watertighness of the sprayed concrete joints.
The ability of this crystallization agent to limit water ingress was verified through a programme of pre-construction testing. This testing proved that an admixture dosage of 5kg/m3 was sufficient to satisfy the design. During the construction of the tunnel a number of key innovations were implemented by the project team. These included the use of a fully hydrostatic PLC driven formwork system to cast the tunnel secondary lining. The presentation with discuss this innovation plus others, whilst providing a detailed overview of both design and construction aspects of the works.
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