Figure 18.—Soft-ground tunneling. The model of a 16th century mine in the Museum of History and Technology was constructed from illustrations in such works as G. E. von Löhneyss' Bericht vom Bergwerck, 1690, as well as the better known ones from De re Metallica.
Figure 19.—The successive stages in the enlargement of a mid-19th century railroad tunnel, using the Austrian system of timbering.
MHT model.