ABSTRACT OF PROCEEDINGS. XXIX, 



being carried out in the old-fashioned system, that is, by 

 compressed air drills and explosives and concrete lining, 

 but if the tunnels were excavated by machinery we should 

 have a perfect tube in the sandstone of the exact diameter 

 required, and supposing the rock to be free from fissures, 

 which at that depth might reasonably be expected, the 

 concrete lining could be eliminated, and a saving of one 

 and a quarter million pounds for the concrete lining alone 

 could be made without taking into account all the extra 

 excavation saved." Mr. Oardew proceeded to describe a 

 tunnel boring machine that was used in the Bondi Sewer 

 Tunnel which cut a perfectly true tube of smooth internal 

 surface, and this machine he said was intended for use in 

 the Channel Tunnel. "Owing to the incompetence of the 

 men who worked it, there were continued stoppages, first 

 one thing went wrong then another, and finally owing to 

 the delay incurred, the contractor ordered it off the job, 

 and the tunnel was excavated in the ordinary way." 



Now this had been the experience everywhere in the 

 history of tunnelling, so far as I have been able to ascer- 

 tain. A similar machine was tried in the Nepean tunnel, 

 with almost exactly similar results. In the very excellent 

 description of the great work in connection with the New 

 York water supply by Mr. Prelini, in Volume xcvii., 

 Engineering, the pressure tunnels were excavated in the 

 ordinary way, and surely if mechanical science has devised 

 a machine which would effect so great a saving as Mr. 

 Oardew estimates, it would have been used, or at least 

 tried, in one of the most recent tunnels of considerable 

 length, viz., the Long Bay Outfall Sewer ; but such was 

 not the case, the work being carried out in the old-fashioned 

 way, viz., by compressed air drilling and the use of 

 explosives. 



Until a satisfactory machine has been invented to cut a 

 perfect tube through the sandstone rock, I think it will be 



Ll— December 5, 1917. 



