Engineering Wonders of the World
Volume I

52 ENGINEERING WONDERS OF THE WORLD. CUT-ANE COVER WORK. on a roadway above it. The outsides of the side walls are vertical, and have a layer of asphalt applied to them ; while the inside faces are sloped, or “ battered.” Brick para- pet walls enclose the whole of the approaches. The sections of the tunnel between the open approaches on each side of the river and Shafts Nos. 1 and 4 respec- Cut- and-cover tively are constructed Work on the “ cut - and - cover ” principle. This system differs from tunnelling properly so called in that the tunnel is not “ driven ” or bored, but the whole of the ground is first excavated from the surface London Railway. The crossing occurs at Rotherhithe Station, where a bridge of 64-feet span carries the tunnel approach. This special construction was attended with some diffi- culty, as the old retaining walls of the station had to be cut through, and the approach and the bridge constructed and joined up to the old walls without interfering with, the railway traffic in the station. The headway over the railway is very limited, there being only 19 feet from rail-level to road- level, and the railway traffic is very heavy. The old walls were subjected to a heavy pressure of water, which, during the construction of the cross- ing, was relieved by pumping. Near the bridge are provided staircases communicating with the adjoining streets. The actual construction of the open approaches is simple. Two trenches about 12 feet wide were dug to the bottom of the foundations, and the side walls built in them. The earth between the walls (marked A, page 49), called the “ dumpling,” was then re- moved and the invert laid, and later down to the level of the bottom of the tunnel, which is then constructed, and the earth filled in again on the top. Where the tunnel is not too far below the surface, the cut-and- cover is the cheaper method ; but of course any water met with has to be pumped, the use of compressed air not being practicable. Naturally, the land required must be purchased, together with any buildings upon it, but at SITE OF SHAFT NO. 2.