. Railroad construction : theory and practice : a textbook for the use of students in colleges and technical schools . - exces-sive blasting) must he refilled with stone well packed in. Occa-sionally it is necessary to fill these spaces with concrete. Ofcourse it is not necessary that the lining be uniform throughoutthe tunnel. 167. Shafts. Shafts are variously made with square, rectan-gular, elliptical, and circular cross-sections. The rectangular. Fig. 90.—Connection with Shaft, Chfrch Hill Tunnel. cross-section, with the longer axis parallel with the tunnel, ismost usually employed. General
. Railroad construction : theory and practice : a textbook for the use of students in colleges and technical schools . - exces-sive blasting) must he refilled with stone well packed in. Occa-sionally it is necessary to fill these spaces with concrete. Ofcourse it is not necessary that the lining be uniform throughoutthe tunnel. 167. Shafts. Shafts are variously made with square, rectan-gular, elliptical, and circular cross-sections. The rectangular. Fig. 90.—Connection with Shaft, Chfrch Hill Tunnel. cross-section, with the longer axis parallel with the tunnel, ismost usually employed. Generally the shaft is directly over thecenter of the tunnel, but that always impHes a complicated con-nection between the Hnings of the tunnel and shaft, provided 198 KAILROAD CONSTRUCTION. § 168. such linings are necessary. It is easier to sink a shaft near toone side of the tunnel and make an opening through the nearlyvertical side of the tunnel. Such a method was employed in theChurch Hill Tunnel, illustrated in Fig. 90.* Fig. 91 t showsa cross-section for a large main shaft. Many shafts have beenbuilt with the idea of being left open permanent h for ventila-tion and have therefore been elaborately lined with masonry.
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