On 20 Jun, 14:49, "Paul Scott" wrote:
Is it what they call the 'launch chamber' for the tunnel boring machine? I
believe the TBM has to initially jack itself forward towards the tunnel
face, once its sufficiently far into the tunnel for the lining to be
installed, it then moves forward against the lining IYSWIM.

Its too far away from the tunnel entrance for that. My guess is its
just to keep dirt and noise out of the station as much as possible and
to make it look a bit neater. Compared to the price of the extension
as a whole the price of a 20 foot concrete wall is peanuts.

B2003