MEl'llANU'AL INSTALLATIONS FOR TUNNEL WOKK 125 



one shaft, the wide heading and single-bench method being 

 employed, with the center-cut system of blasting which was 

 here used for the first time. The tunnel was begun in 1854, 

 and continued by hand until 1866, when the mechanical plant 

 was installed. Most of the particular machines employed have 

 now become obsolete, but as they were the first machines used 

 for rock tunneling in America they deserve mention. The 

 drills used were Burleigh percussion drills, operated by com- 

 pressed air. Six of these drills were mounted on a single car- 

 riage, and two carriages were used at each front. The air to 

 operate these drills was supplied by air compressors operated 

 by water-power at the portals and steam-power at the shaft. 

 The air compressors consisted of four horizontal single-acting 

 air cylinders with poppet valves and water injection. The 

 compressors were designed by Mr. Thomas Deane the chief 

 engineer of the tunnel. 



Palistuli-x Tunnel. The Palisades tunnel was constructed to 

 carry a double-track railway line through the ridge of rocks 

 bordering the west bank of the Hudson River and known as 

 the Palisades. It was located about opposite 116th St. in New 

 York city. The material penetrated was a hard trap rock very 

 full of seams in places, which caused large fragments to fall 

 from the roof. The excavation was made by a single wide 

 heading and bench, employing the center-cut method of blast- 

 ing with eight center holes and 16 side holes for the 7 x 18 ft 

 heading. Ingersoll-Sergeant 2^ in. drills were used, four in 

 each heading and six on each bench, and 30 ft per 10 hours 

 was considered good work for one drill. 



The power-plant was situated at the west jmrtal of the 

 tunnel, and the power was transmitted by electricity and com- 

 pressed air to the middle shaft and east portal workings. The 

 plant consisted of eight 100 H. P. boilers, furnishing steam to 

 four Rand duplex 18 x 22 in. air compressors, and an engine 

 running a 30 arc light dynamo. The compressed air was car- 

 ried over the ridge by pijies varying from 10 ins. to 5 ins. in 



