Engineering Wonders of the World
Volume I

50 ENGINEERING WONDERS OF THE WORLD. mile from the new Rotherhithe Tunnel, and was opened in 1842. The Act of Parliament authorizing the con- struction of the Rotherhithe Tunnel was passed in 1900, but owing to difficulty in obtaining possession of the land required the works were not put in hand until 1904, when a contract was signed for its construction. The tunnel had to be so designed as— I . To provide a roadway wide enough to allow two of the largest vehicles to pass each other, while leaving room for a sufficiently broad footpath Tunnel. on each side- 2. To give easy gradients to suit local traffic. 3. To be of the minimum length consistent with easy gradients—which meant that it would have to run as near the river-bed as possible. 4. To have the ends of its approaches situ- ated in important streets, and so give easy and convenient access. 5. To be sufficiently water-tight to avoid the need for and expense of pumping. These requirements have been met in the following way :— A width of 16 feet between the curbstones being taken as the minimum possible for the roadway, which is the same as that provided in the Blackwall Tunnel, the footways were made 4 feet _ Large 8 inches wide, and this, it was I)’ar"eter ’ the Tunnel, found, gave the cross section shown opposite. The diameter is 3 feet greater than that of the Blackwall Tunnel, and about the same as that of the largest tunnels which have been constructed for some of the stations on the tube railways. The gradient adopted for the approaches is about 1 in 36, which is less severe than that of the southern approach to London Bridge. As the level of the roadway at the river-banks had to be about 75 feet below ground-level, each slope extends some 900 yards from the river. A glance at the accompanying plan (page 51) will show that this brings the ends of the approaches near the important streets known as Lower Road, Rotherhithe, and Com- mercial Road, Stepney. As executed, the total length between the centres of these streets, where the gradients end, is 6,883 feet, or 1| miles nearly. The depth below the river-bed is arranged so that there will be only 4 feet of cover over the tunnel when the river is deepened to the extent to which it is antici- pated that it may be dredged. During construction there was about 8 feet between the top of the tunnel and the water. Water-tightness was ensured by building the tunnel of cast-iron plates with machined joints, which are practically water-tight, and by surrounding all the work in the approaches with a layer of asphalt. Commencing at the southern end, the ap- proach descends to a depth of 24 feet below the ground in a distance of 280 yards, and then crosses over the East London Railway nearly at right angles. A few yards farther on the tunnel is entered, and there follows a length