Engineering Wonders of the World
Volume I

THE RIVER TUNNELS under the sea-wall. The stone filling offered a free outlet to the air, causing an enormous uprush that raised a huge bubbling fountain at the water surface. That this made the face excavation extremely dangerous may be appreciated ; at the same time it was neces- sary for the men to cut through the wooden foundation piles of the sea-wall. Clay in sacks (to prevent it from being blown away) was dumped into the river over the work in large quantities to control the outrush. Mr. Charles M. Jacobs was the company’s engineer for these tunnels, assisted by Mr. James Forgie. The contractors were the O’Rourke Engineering Construction Company. The East River tunnels of this same enter- prise met with entirely different conditions— rock, quicksand and boulders, a great depth of water, and a rock reef in the The Four middle, the underwater con- Pennsylvania t,inua/tøon of Blackwell’s Is- East River Tubes. land. The four tunnels, 4,000 feet long between banks, and 23 feet in diameter, start from the New York shore as two pairs of tubes some 300 feet apart, but converge towards the Long Island shore. The engineer of these tunnels was Mr. Alfred Noble, assisted by Mr. C. L. Harrison, and the firm of S. Pearson and Son built the work. Great steel caissons (Fig. 17), 74 feet by 40 feet in plan and 90 to 100 feet high, were sunk on the banks down to rock, and firmly bedded there on concrete. In these the shields were erected, and the riverward ad- vance started. Thereafter, except for short distances at each shore in full rock, the advance was a continuous battle with quick- sand, and even of this there was often but a very shallow thickness between shield and river. Two caissons were sunk on each shore, one serving for two tunnels. The New York caissons were sunk without compressed air, OF NEW YORK CITY. 117 but those on the Long Island bank had to be roofed over and put down by pneumatic process, just as a bridge-pier caisson is sunk. Fig. 18.—A BULKHEAD AT THE ENTRANCE TO A COMPRESSED-AIR SECTION, WITH SEPARATE AIR- LOCKS FOR MEN AND DIRT-CARS, AND AN UPPER EMERGENCY LOCK. (PENNSYLVANIA HUDSON RIVER TUNNELS.) The shields seen in the view (Fig. 16) are of a type unique in New York practice, being highly complex. Instead of having but a single cross-wall they have two, and the space between can be utilized as an air-lock, so that a pressure may be maintained in front of the shield differing from the pressure of air in the tunnel. It was thought that this device might prove of great value under unusually severe circumstances ; but it was not used, presumably because the conditions did not require it. One other feature was unusual—the shield carried two “ segment erectors ” on its rear face. These are pivoted hydraulic jacks used to put the heavy cast-iron lining segments in place (one Segment is at work in Fig. 16). Gener- ally only one erector is used. In large tunnels, where the shield is strong and roomy, the erector is fastened to the back of the shield. In smaller tunnels it is more often carried by an independent timber platform adapted to roll along behind the shield; this was done in the Hudson tunnels, the Battery and the Steinway Tunnels. The Pennsyl- vania Hudson River shields had a single erector attached to the shield, its pivot being on the centre line.