Change of DesignThe west section was originally planned to be constructed using a sprayed concrete primary liner and a cast in situ secondary liner with a waterproof membrane placed in between the two layers.The addition of Xypex Admix C-Series meant that following the trials, the stake holders were satisfied enough to remove the membrane in the Hammersmith connection tunnel. The benefits of Xypex Admix C-Series was in addition used throughout the whole of the west section.