Engineering Wonders of the World
Volume I

THE TUBE RAILWAYS OF LONDON. 309 Placing a Segment. the space is so limited that it is not possible to design a segment-erecting machine suffi- ciently compact not to interfere with other operations at the face. The lining is sent to the working face on small trolleys, three segments as a rule being stacked together at one time, convex side downwards. On arrival at the face, at the words “ Say when ” from the leader, four men lift a segment from the trolley with iron bars inserted through the end holes in the curved flanges, carry it some four paces, and deposit it on the stage forming the work- ing floor of the shield. It is then turned concave side downwards, is raised by six men and put over on to, say, the left side of the floor, from which it im- mediately slides down the side of the shield by its own weight to the lowest part of the invert. The floor planks are then removed, to give access to the bottom. A labourer at once descends into the bottom of the shield and starts bolting up this segment to the last ring. The right-hand invert segment having been similarly dealt with, the floor planks are restored to their normal position, and the two side segments are put into place and bolted up. A temporary timber stage is then formed across the tunnel, and the two roof segments are lifted into position. Finally, the key-piece is driven in from below, and the ring is complete. The whole operation of ejecting a ring complete takes twenty minutes when all goes well. The men, working by piecework as a rule, lose no time. Each man of the gang has his allotted duty. Some fetch, others tighten up bolts, while the bulk of the gang is en- gaged in the more arduous task of getting the segments into their final positions. In order to hasten the work to the utmost during the erection of the ring, a couple of men are told off to pick down the clay in the face and restart the excavation of a new “ length.” When the erection of the ring is finished, two miners go into the heading again and proceed with its further construction. The grouting up of the ring to which the SECTIONAL DIAGRAM OF A “ GROUTING ” APPARATUS, SHOWING HOW THE GROUT IS FORCED BETWEEN THE TUNNEL LINING AND THE GROUND; new ring has been bolted is then proceeded with, the operation taking about twenty minutes to complete. The grout itself sets very hard in a Grouting short time, and so gives sub- _.a Ring. stantial support to the ground by completely filling up the annular space left between the iron lining and the ground. METHODS OF GETTING RTD OF WATER FROM COMPLETED TUNNELS. It is always necessary, in those portions of a Tube railway which have been constructed in water-bearing strata, to provide for the permanent removal of water which leaks into the tunnels despite the great care exercised in making the joints and bolt-holes water- tight. The usual practice is to provide a small length of tunnel at a slightly lower level than, and at the lowest part of, the works, and to install therein duplicate electrically driven