Chicago : Engineering and Contracting Pub. Co. · leaf 667
1 25 11 28 3D 1 29 -Bridge-Block starting the drives a breach block should beplaced between the lagging and the newdrive, as is shown in illustrations. This pre-vents the drive from being forced down infront by the weight of material upon it. Italso keeps the butt end of the drive from fly-ing up… … ] 29 FngDConfg Fig. 5 Fig. 6. Fig. 7. terial resemble gravel in lack of firmnesseven where no water is present. It is impos-sible to mine it the ordinary way. Material such as broken rocks, dirt, gravel,etc., commonly known as wash, is generally,or often, met with in opening a tunnel orshaft. At…
Buildings
Internet Archive · University of Illinois Urbana-Champaign · Public Domain Mark 1.0. Free to use for anything.
