Tunneling: A Practical Treatise.

by Charles Prelini

Section A-B.

Fig. 88.—Sequence of Excavation in the American Method.

Fig. 89.—Strutting the Heading in the American Method.

Section C-D.

Fig. 90.—Temporary Timbering of the Roof in the American Method.

Section E-F.

Fig. 91.—Showing Crown Bars Supported by Segmental Arches.