With Wall Plates.
Without Wall Plates.
Old Timber Sections.
Minimum Section.
Average Section.
Permanent Work.
Fig. 163.—Relining Timber Lined Tunnel, Great Northern Ry.
The original timbering consisted of sets spaced 4 ft. apart c. to c., with 12 × 12 in. posts supporting wall plates, and a five-segment arch of 12 × 12 in. timbers joined by 11⁄2-in. dowels. The arch was covered with 4-in. lagging, and the space between this and the roof was filled with cordwood. Except where the width had been reduced by timbering placed inside the original timbering to increase the strength, the clear width was 16 ft., and the clear height 20 ft. above the top of the rail. [Fig. 163] shows the timbering and also the form of masonry lining adopted. The side walls are of concrete and the arch of brick. This new masonry, of course, required the removal of all the original timbering. The manner of doing this work is as follows: A 7-ft. section, A B, [Fig. 164], was first prepared by removing one post and supporting the arch by struts, S S. After clearing away any backing, and excavating for the foundation of the side wall, two temporary posts, F F, were set up, and fastened by hook bolts. [Fig. 146], L, and a lagging was built to form a mold for the concrete. Several of these 7-ft. sections were prepared at a time, each two being separated by a 5-ft. section of timbering.