Compressed Air Work And Diving 1909
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EL ACK WALL TUNNEL. 81
meter rams woulcl have been sufficient, but for the faet
that at times some of the rams had to be shut off in
order to guide the shield.
The maximum air pressure requireel in the tunnel was
28 Ibs. per square inch, and the maximum head of water
above the level of the crown of the tunnel was 53 ft.
Since 28 Ibs. is equal to the pressure caused by a head of
65 ft. of fresh water, it will be seen that the hydrostatic
and air pressures balanced at a point 12 ft. below the level
of the crown of the tunnel. [ he range of tide was about
20 ft. and the average pressure was rather below 28 Ibs.
in the tunnel, but when putting in the floor of one of the
caissons a pressure as high as 35 Ibs. was required.
The iron lining for the length under the river, and
for some of the land part, was built up of 2 ft. 6 in. wide
rings, 27 ft. outsicle diameter and 25 ft. diameter inside
flanges, 2-in. metal, and there were fourteen segments
o
and key piece to each ring. These rings each weighed
14 tons 16 cwt. The lining usecl for the rest of the
tunnel had 10-in. cleep flanges (?>., 25 ft. 4 in. diameter
inside flanges) and metal and weighed 10 tons
10 cwt per ring.
The resident engineers were Mr Maurice Fitz-
maurice* and Mr David Hay.
The Rotherhithe Tunnel extends from Lower Road,
Rotherhithe, to Commercial Road, Stepney, and passes
under the River Thames. It is situated 2 miles above
the Blackwall Tunnel, and miles below the Tower
Bridge.
I he general method of construction was very similar
to that aelopted at Blackwall, i.e., four shafts were sunk
on the line of the tunnel, two each side the river.
* Now C.M.G. and Chief Engineer to the London County CounciL
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