Engineering Wonders of the World
Volume I

THE ROTHERHITHE TUNNEL. 57 On the north side of the river the tunnel passes round a curve, as may be Lining seen on ^ie pjan (page 51). This the • Tunnel necessitated specially prepared iron lining, each ring of which was made taper, being slightly narrower on the inside of the curve. After the tunnel had been driven right through and the lining made per- fectly water- tight, it was lined with concrete. The sides of the subway under the road were then formed and the arch built, after which the roadway and the various drains, pipes, etc., were laid on the top. The last oper- ation was to cover all the exposed face of the con- crete with white glazed tiles, of which FRONT VIEW OF SHIELD. S is a “ safety curtain.” Compressed Air used for Driving the Tunnel. about 1,250,000 were required. The tunnel is lighted by means of incandes- cent electric lamps, arranged in three parallel rows. In addition to its use in sinking the shafts, as already described, compressed air was employed for driving the whole of the tunnel. In both cases the object aimed at was the exclusion of water from the workings. We have already seen that in the case of sinking the shafts the compressed air was confined by an air-tight deck or floor, and only the space below this floor, about 12 feet high, was thus un- der pressure. During the tunnel driv- ing the com- pressed air was at first retained by a similar tem- porary air- tight floor fixed high up in the shaft from which the tunnel- ling started, so that the whole of the interior of the shaft under this floor was full of com- pressed air, and also the tunnel itself as it pro- gressed. Af- ter a consid- erable length of tunnel had been completed, a vertical air-tight bulkhead was built in the tunnel and the air retained in front of it, the space behind it and that in the shaft being then opened to the atmos- phere. The bulkhead, constructed of steel plates and girders, was fitted with air-locks for the passage of men and materials.