IV 



TUNNELS AND THEIR MAKING 



TUNNELS provide the engineer with one 

 of his most fascinating problems. Boring 

 through a hill or mountain is quite an 

 adventure because one can never be quite 

 sure what will be found ahead of the cutting 

 plant. Over and over again an underground 

 and quite unsuspected spring has been 

 encountered; indeed, it would be accurate 

 to call it a river. A preliminary survey and 

 a trial shaft may show that the job is going 

 to be an easy one, but too often it has been 

 the case that the shaft missed a strata of 

 the hardest rock imaginable, rock which 

 will dull the sharpest cutting machinery, 

 and which will probably need a powerful 

 explosive to get a way through it. 



Perhaps of all things feared by the 

 engineer engaged upon tunnelling is the 



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