TIMBERING OB STRUTTING TUNNRLB 



TABLE I. 



51 



Showing Sizes of Various Timbers Used in Strutting Tunnels Driven 

 Through Different Materials. 



IRON STRUTTING. 



In 180:2 Mr. Ilziha employed old iron railway rails for 

 strutting the Naensen tunnel, and his example was successfully 

 followed in several tunnels built later where timl>er was scarce 



