Figure 4. — Hoosac ["unnel. Bottom of the 

 central shaft showing elevatoi car and rock 

 skip: pumps ai far right. In the center, the 

 iop bent li is being drilled by a single 1 olumn- 

 mounted Burleigh drill. Mill mo lei 

 si ale. Smithsonian photi 1 19260 N 



has been extracted since at least 1000 B.C. Similar 

 workings existed in the Tirol as early as about 1600 

 B.C. Two means of breaking away the rock are 

 shown: to the left is the most primitive of all met he ids. 

 the hammer and chisel, which require no Further 

 description. At the right side, the two Figures are 

 shown utilizing the first rock-breaking method in 

 which a Force beyond that of human muscles was 

 employed, the ane-old 'Tire-setting" method. The 

 rock was thoroughly heated by a tierce lire built 

 against ii- Face and then suddenly cooled by dashing 

 water against it. Thethermal shock disintegrated the 

 rock or ore into bits easily removable by hand. 



The practice of this method below ground, of 

 course, produced a fearfully vitiated atmosphere. It 

 is difficult to imagine whether the smoke, the steam, 

 or the toxic fumes from the roasting ore was the more 

 distressing to the miners. Even when performed by 

 labor considered more or less expendable, the method 



could be employed only where there was ventilation 

 ol Mime sort: natural chimneys and convection cur- 

 rents were the clnd sources of air circulation. Despite 

 the drawb.uk- ol the fire system, its simplicity and 

 efficacy weighed so heavily in its favor that us history 

 ul use is unbroken almost to the present day. Fire 

 setting was nt greatest importance during the years of 

 intensive mining in Europe before the advent ol 

 explosive blasting, but its use in many remote areas 

 hardly slackened until the early 20th century because 

 of its low cost when compared to powder. For this 

 same reason, it did have limited application in actual 



tunnel work until about 1 



Direct handwork with pick, chisel and hammer, and 

 fire setting were the principal means of rock removal 

 for centuries. Although various wedging systems 

 were also in favor in some situations, their impor- 

 tance was so slight that they were not shown in the 

 model. 



PAPER 41: TUNNEL ENGINEERING— A MUSEUM TREATMENT 



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