Compressed Air Work And Diving 1909

GROUTING. 75 When a tunnel is being driven in rock, a voicl will be left all rouncl the cast-iron lining. This will have to be fillecl up with cement or hydraulic lime grout, which also serves to protect cast iron from the disintegration to which it is often so liable. Quick-setting lime grout is cilso used for tunnels in ballast or in any loose strata. For grouting purposes a plugged hole is left in each segment and when grouting this plug is taken out and a flexible tube screwed in which is connectecl to the grouting or “ baugee ” pan. Equal parts of cement and sand are put into the grouting pan with the right proportion of water and thoroughly mixed by means of a spiiiclle with blades passing through it. The door, which opens inwards, is then pulled upwards and air turned into the pan at a pressure of 100 Ibs. to the square inch. This forces the grout through the tube and plug hole into the space outside the iron lining. If grouting is carriecl up too close behind the shield, it may cement up the tail of the shield and put too much work on the ranis. If this is the case the PToutinp- o must be kept well behind the shield, or else lime grout used, which, while setting quickly, cloes not set so hard. When, however, the tunnelling is under house pro- perty or wharf walls where a subsidence would be serious, the grouting must follow up immediately behind the shield. All rouncl the cutting eclofe must then be well stopped up with clay and the jacks fitted with segmental plates in order to close up the space between the skin of the tail and the cast-iron lining. This space must be well clayecl up. Where there are no grouting plates, segmental boards wrapped rouncl with okl cement bags are used. A tunnel is liable to get flat by reason of the weight