THE HOLLAND TUNNEL GRAY AND HAGEN 595 



This material had to be entirely removed after each shove before the 

 erection of tlic cast-iron lining could proceed and slowed down proor- 

 ress. In addition it was desired to retain this material in the tunnel 

 directly behind the shield so as to increase the weight of tlie tunnel 

 and reduce the tendency to rise. 



To meet this situation a dilTcrent method of tunneling was adopted. 

 The work was stopped and a steel bulkhead semicircular in shape and 

 fitting into the lower part of the tunnel Avas built to trail about 10 

 feet behind the shield, and four iM)ckets of the shield immediately 

 above the springing line were equipped with hydraulically operated 

 doors. When the shield advanced, these doors were opened varying 

 amounts, depending upon conditions, to aUow the material to flow 

 through the shield into chutes which cropped the silt back of the 

 trailing bulkhead. This method of tunneling permitted both the 

 shield and the tunnel to be kept on grade. 



River-shaft caissons were built, launched, floated into position, and 

 sunk, as on the New York side. 



On October 22, 1924, shield driving was suspended in the north 

 tunnel from the New York side and a bottom heading or junction 

 drift was started to meet a corresponding drift from the New Jersey 

 heading. On October 29, the rock barrier remaining between these 

 headings was blasted away. After this all tunneling operations were 

 conducted from the New York side, as the junction was much nearer 

 the New York shaft. The south tunnel headings were joined on 

 December 7, 1924. Work on the New York side was suspended and 

 the New Jersey shield driven to meet the New York shield. 



In July, 1924, the placing of the concrete lining forming the road- 

 way and air ducts was started on the New York side in the north and 

 south tunnels between the land and river shafts. The concrete invert 

 was first placed in both tunnels from the land shafts to the river 

 shafts. The remaining concrete was then poured in nine operations. 

 Five types of collapsible steel forms in CO-foot sections, afterward 

 increased to 75 feet, supported and moved by carriages resting on 

 previously placed concrete, were used. 



The approach tunnels from the land shafts to the open approaches 

 at Dominick and Hudson Streets, New York City, and at Provost 

 Street, Jersey City, were built by the cut and cover method as usually 

 employed in subway construction. 



A visitor to the Holland Tunnel in 1921 has written the following 

 graphic and interesting storj' of the shield method of construction. 

 The invitation to inspect the tunnel read, " Wear old clothes and 

 bring your galoshes." 



Such was the admonition of our host on a warm September evening in 1924. 

 But knowing our host, we conijilied without ado other than a casual lifting of 

 the eyebrows. Ten o'clock that evening found four of us being piloted toward 

 Canal Street and the administration building of the Vehicular Tunnel. 



