Civil Engineering Reference
In-Depth Information
Figure 8.12
View into the unplugged existing Piccadilly Line Eastbound Turnout
tunnel
No gaskets had been used to prevent water from infiltrating through the
joints. The London Clay at T5 in general is considered to be practically
impermeable, however water did somehow find its way down to the tunnels
and through the joints. As a result plenty of stalactites were growing on the
lining and rusting of the iron segments was also visible (see Figure 8.13a,
left-hand side and Figure 8.13b for the detail).
The distance between the existing Piccadilly tunnels and the SCL Stub
tunnels was very small (Figure 8.9, Figure 8.14). The remaining ground
pillar between the tunnels varied from 0.4 m at the box to approximately
3 m at the end.
The integrity of the existing structures during the SCL work had to be
ensured, therefore monitoring of the existing Piccadilly Line tunnels was
essential. Of particular interest was the performance of the existing Piccadilly
Line Eastbound Tunnel during the excavation of the SCL Eastbound Stub
Tunnel, which was the first of the stub tunnels to be constructed.
The existing Piccadilly Line Eastbound was approximately 20 m long
(before it merged with the existing Piccadilly Line Westbound, Figures 8.9
and 8.13a), of which the first 8 m, measured from the box, were plugged
with foam concrete to enhance the stability during the excavation of the
adjacent SCL Eastbound Stub. In the remaining unplugged part four moni-
toring arrays were installed. Access was possible through the neighbouring
Piccadilly Line Westbound Tunnel.
