Thames Tideway | Innovative propping for Chelsea shaft excavation The Thames Tideway megaproject has used a complex propping solution. However grand the scale of a project, successful delivery always comes down to fine details. In West London, at one of 24 sites serving the London’s 25km Thames Tideway Tunnel project, a complex excavation job required special attention from engineers. Tideway Tunnel will run from Acton in the west of London to Abbey Mills in the east. It will mostly run underneath the tidal section of the river Thames and will collect, store and convey to treatment works downstream almost all of the raw sewage and rainwater that currently overflows into the river.