186 DAVIES— TUNNEL CONSTRUCTION. [February 18. 



removable steel ends of the boxes were taken out and the permanent 

 roof put on to the side walls. 



The difficulties of doing this work under the conditions may be 

 appreciated when it is understood that, in Cortlandt Street alone, 

 the 6th and 9th Avenue Elevated Roads had to be supported, and 

 not only a public sewer in each street had to be maintained, but also 

 a twenty-four inch steam pressure main (under 90 pounds of steam 

 pressure all the time) as well as a bank of electric conduits which 

 carried about seven thousand wires, comprising every telephone and 

 telegraph wire in the down-town section going out of New York 

 City. 



The tunnels under these streets could undoubtedly have been 

 built by the tunnel methods indicated in the earlier part of this 

 paper, possibly at some saving in cost, but any such methods would 

 have involved such risks of damage to buildings and adjacent prop- 

 erties that such a saving would have been far more than offset by 

 damages in case a building was wrecked. By this method the con- 

 struction of these difficult portions of tunnels, where junctions be- 

 tween the different lines were involved, could be carried on with 

 almost absolute safety, and as the results proved, there was prac- 

 tically no injury to any properties adjacent or immediately above 

 the construction itself. 



The work which has recently been carried out in New York 

 City, the construction not only of the tunnels of the Hudson and 

 Manhattan Railroad, but also those of the Pennsylvania Railroad, 

 have developed almost every possible combination of conditions 

 which could by any possibility arise in tunnel construction, and the 

 enormous magnitude of work carried on in the last six or seven 

 years has been done with practically no disasters of any kind. These 

 methods described have brought the modern construction of tunnels 

 down to almost an exact science. The hazards and dangers are 

 infinitely less than in the case of bridge construction, and tunnels 

 are applicable in many cases where bridges are not. 



In addition to this, the different tunnels permit very much greater 

 elasticity in the development of transportation facilities than the 

 bridges do, and traffic can be more economically and better dis- 

 tributed by developing underground routes than by construction of 



