228 TUNNELING 



and to use caissons in the construction. Prof. Winkler pro- 

 posed to build caissons from 30 ft. to 45 ft. long, with a width 

 depending upon the lateral dimensions adopted for the tunnel 

 masonry. The caisson was to be made of metal plates and 

 angle iron with riveted connections on all sides except those 

 running vertically transverse to the tunnel axis, whose connec- 

 tions were to be bolted. The roof of the caisson was to be 

 made of T-irons resting upon templates placed on the edge 

 of the longitudinal sides of the caisson, and strutted in the 

 middle by the crown of an iron arch having its springers upon 

 brackets inserted on the vertical angle irons forming the frame 

 of the caisson. Between the T-irons of the roof small brick 

 vaults were to be built, and a very thick stratum of concrete 

 laid on their extrados so as to obtain a level surface. In the 

 middle of the roof an opening was to be left ; this was for the 

 shaft having the air-locks to allow the passage of men, mate- 

 rials, and compressed air. 



Across the river two parallel rows of piles were to be 

 driven into the river bed, to fix the place where the caisson was 

 to be sunk. Then the first caisson near the shore was to be 

 lowered in the ordinary way, and a second caisson was to be 

 immediately sunk very close to the first one. When both cais- 

 sons had reached the plane of the tunnel floor, the sides which 

 were in contact were to be unbolted and removed, and the 

 small space between made water-tight by filling them with yarn 

 and tar. The chambers of the two caissons were to be opened 

 into a single large one communicating above by means of two 

 shafts. At the same time that the masonry was being built in 

 the two first caissons, from the inverted arch up, a third cais- 

 son was to be sunk ; and when by excavation it had reached 

 the plane of the projected tunnel floor, the partitions were 

 to be removed so that the three caissons were in communica- 

 tion, forming a large single caisson. To limit the compressed 

 air to the working-place, walls were to be built across the tun- 

 nel near the advanced part completely lined. The first wall 



