1896.] on the Tunnel under the Thames at Blackwall. 85 



Lower Thames Street, London Wall, Lombard Street and Thread- 

 needle Street, and as there will be no occasion for stopping at shops, 

 houses and street corners it should be ample for two lines of the 

 largest vehicles. Should the traffic, however, increase beyond the 

 capacity of the tunnel, land has been secured for the construction of 

 another and parallel line of tunnel. The road will be paved with 

 asphalt in the level portion under the river and with granite laid in 

 tar and pitch on the inclined approaches. 



The whole work underground will be lighted by three rows of 

 incandescent 32 candle-j)ower electric lamps placed alternately 

 10 feet apart on the common centre line, no gas being admitted to 

 any portion of the tunnel. The cut and cover portions of the work 

 are formed of brickwork varying in thickness from 18 inches to 

 2 feet, this is covered with IJ inches of asphalt and backed with 

 2 feet of Portland cement concrete, giving a thickness at the thinnest 

 part of 3 feet 6 inches. Internally the cut and cover portions 

 will in all respects resemble that of the tunnel proper formed in 

 cast iron. The open approaches above referred to are flanked with 

 inclined retaining walls, faced with white glazed bricks, carrying 

 a high fence wall with stone coping. At each extremity the tunnel 

 will be approached through an arched gatew^ay supporting the lodcre- 

 keeper's house ; there will also be stairway access at the junction 

 of the open approach with the cut and cover, as well as sitairways 

 down one of the shafts on each side of the river. The shaft near 

 the river on the south side being in private property is domed 

 over and a ventilating chimney carried up from it ; the similar shaft 

 near the river on the north side is devoted to administrative and 

 working purposes such as pumping, elevating, lighting, &c. Each 

 shaft is 58 feet outside and 48 feet inside diameter and is formed as 

 it were of two skins of riveted wrought ironwork ; the two skins are 

 braced and held together by wrought-iron struts and ties, the space 

 between them being filled in solid with Portland cement concrete. 

 Near the lower extremity of each shaft its walls are perforated by 

 two openings 29 feet 4 inches in diameter. These openings are for 

 the purpose of forming junctions with the tunnel, and were tempo- 

 rarily closed during the time the shafts were being sunk by means of 

 large wrought-iron plugs. At a distance of 8 feet from the bottom 

 the inner skin is bent outwards to join the outer skin and together 

 form a comparatively sharp cutting edge. All the shafts will be lined, 

 when finished, with white glazed brickwork. The shafts were sunk in 

 the following manner. Having been built up to a considerable 

 height above the surface of the ground in the positions they were to 

 occupy, the earth, clay, sand, &c. were excavated within the circum- 

 ference of the shafts and from below the cutting edge, and as this 

 process of excavation proceeded, the shaft sank into the ground partly 

 by its own weight and in some cases assisted by additional weight 

 placed upon it. When the final level was reached the bottom for a 

 depth of 13 feet was filled in with concrete, in which, and attached to 



