Amalgamation of tunnel secondary lining and first stage concrete at Whitechapel crossover

The Whitechapel Crossover will provide two switches for the transfer of railway traffic between the eastbound and westbound Crossrail tracks. In tunnelling terms, the works making up the Crossover form a westward extension of the sprayed concrete lined (SCL) tunnels of Whitechapel Station. The location within Crossrail is shown in Figure 1 below:

The SCL tunnels include (Figure 2):

The tunnels are identified on the drawing excerpt below:

The tunnels were traditionally excavated and a primary SCL layer was applied. This paper considers the subsequent construction of the secondary linings of the tunnels in the Whitechapel Crossover.

The original design of the tunnels foresaw the application of a continuous sprayed and/or sheet waterproofing membrane together with a thin non-steel fibre regulating/protection layer over the inside face of the primary lining, then the application of a secondary lining consisting of a cast in situ reinforced concrete (RC) invert slab, cast in situ RC side walls and an SCL arch, in most cases reinforced with steel fibres only, but in some cases (e.g. junctions, headwalls) including steel bar reinforcement. At this stage, the tunnel structure would have been complete and the tunnels ready for the internal track bed build-up and fit-out.