Chicago : Engineering and Contracting Pub. Co. · leaf 415
re drifts. These holes would not breakmuch hard rock because of the distance be-tween the bottoms of the cutting-in and squar-ing-up holes. It will be noted that Figs. 3 and 4, depictingstandard cuts in soft rock, show two classesof holes, the cutting-in holes, and the squaring-up holes which… … they relieve the ground to hi1 broken b\ thelatter set. It is in the drilling of such a CUlthai the best judgment is required, for relictboles are a changeable feature and slight \.inations in the toughness of the ground andthe si/e of the workings necessitate diffeienth placed relief holes for…
Buildings
Internet Archive · University of Illinois Urbana-Champaign · Public Domain Mark 1.0. Free to use for anything.
![An illustration from The Antiquarian [serial] (1897)](https://img.insideoutlibrary.com/img/200/ia-antiquarianseria01colu-155-59.webp)
![An illustration from [Electric engineering.] (1902)](https://img.insideoutlibrary.com/img/200/ia-electricengineer04inte-422-190.webp)