English: Identifier: shieldcompressed00hewerich

Title: Shield and compressed air tunneling Year: 1922 (1920s) Authors: Hewett, Bertram Henry Majendie Johannesson, Sigvald, joint author Subjects: Tunneling Publisher: New York [etc.] McGraw-Hill book Co. Contributing Library: Prelinger Library Digitizing Sponsor: Internet Archive

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Text Appearing Before Image: of the primary lining is to furnish an immediatesupport of the ground. This lining must be able to satisfy therequirements as to strength, ease of erection and reasonablewatertightness, Imt does not need to be permanent without fur-ther preparation. A metal or a wood lining answers theserequirements. 3. Secondary Lining.—If it is thought that the permanenceof the primary lining is not assured, an inner lining, usually ofconcrete, is provided. The function of this lining is either toform the permanent lining or to protect the primary lining so thatthis will remain permanent. In some cases the secondary liningis provided to give a smooth and pleasing interior finish. 4. Lining Materials.—The lining may be made of almost anyof the usual materials of construction. Cast iron has mostfrequently been used but wood, steel and concrete are also usedas lining materials. A description of linings of various materialswill be given in the following pages. 94 LININGS FOR SHIELD DRIVEN TUNNELS 95

Text Appearing After Image: 96 SHIELD TUNNELING B. CAST IRON LINING 5. General Description.—In its usual form cast iron lining is acylindrical structure with a circular cross-section Iniilt up of aseries of rings, and each ring is made of a number of sections. Figure 27 shows a cast iron lining erected. Each segmenthas a web or skin conforming to the curvature of the tunnel andprovided with flanges along its four edges. When erected theskin forms an enveloping cylinder which is stiffened by the cir-cumferential flanges. The segments and rings are connectedby means of bolts through the flanges.

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