of such communication. All lines from the south 

 terminated along the west shore of the river and the 

 immense traffic — cars, freight and passengers — was 

 carried across to Manhattan Island by ferry and 

 barge with staggering inconvenience and at enormous 

 cost. A bridge would have been, and still is, almost 

 out of the question due not only to the width of the 

 crossing, but to the flatness of both banks. To provide 

 sufficient navigational clearance (without a draw- 

 span), impracticably long approaches would have 

 been necessary to obtain a permissibly gentle grade. 



Haskin formed a tunneling company and began 

 work with the sinking of a shaft in Hoboken on the 

 Xew Jersey side. In a month it was halted because 

 of an injunction by, curiously, the D L & W Railroad, 

 who feared for their vast investment in terminal and 

 marine facilities. Not until November of 1879 was 

 the injunction lifted and work again commenced. 

 The shaft was completed and an air lock located in 

 one wall from which the tunnel proper was to be 

 carried forward. It was Haskin's plan to use no 

 shield, relying solely on the pressure of compressed 

 air to maintain the work faces and prevent the entry 

 of water. The air was admitted in late December, 

 and the first large-scale pneumatic tunneling opera- 

 tion launched. A single 26-foot, double-track bore 

 was at first undertaken, but a work face of such 

 diameter proved unmanageable and two oval tubes 

 18 feet high by 16 feet wide were substituted, each 

 to carry a single track. Work went forward with 

 reasonable facility, considering the lack of precedent. 

 A temporary entrance was formed of sheet-iron rings 

 from the air lock down to the tunnel grade, at which 

 point the permanent work of the north tube was 

 started. Immediately behind the excavation at the 

 face, a lining of thin wrought-iron plates was built up, 

 lu provide form for the 2-foot, permanent brick lining 

 that followed. The three stages are shown in the 

 model iii about their proper relationship of progress. 

 Tlie work is shown passing beneath an old timber- 

 crib bulkhead, used for stabilizing the shoreline. 



The silt of the riverbed was about the consistency of 

 puttj and under good conditions formed a secure 

 barrier between the excavation and the river above. 

 It was easily excavated, and for removal was mixed 

 wiili water and blown out through a pipe into the 

 shaft by the higher pressure in the tunnel. About 

 hall was left in the bore for removal later. The basic 

 scheme was workable, but in operation an extreme 

 precision was required in regulating the air pressure 



in the work area. 5 It was soon found that there 

 existed an 11-psi difference between the pressure of 

 water on the top and the bottom of the working face, 

 due to the 22-foot height of the unlined opening. 

 Thus, it was impossible to maintain perfect pneumatic 

 balance of the external pressure over the entire face. 

 It was necessary to strike an average with the result 

 that some water entered at the bottom of the face 

 where the water pressure was greatest, and some air 

 leaked out at the top where the water pressure was 

 below the air pressure. Constant attention was es- 

 sential: several men did nothing but watch the be- 

 havior of the leaks and adjusted the pressure as the 

 ground density changed with advance. Air was sup- 

 plied by several steam-driven compressors at the 

 surface. 



The air lock permitted passage back and forth of men 

 and supplies between the atmosphere and the work 

 area, without disturbing the pressure differential. 

 This principle is demonstrated by an animated model 

 set into the main model, to the left of the shaft (fig. 

 39). The variation of pressure within the lock cham- 

 ber to match the atmosphere or the pressurized area, 

 depending on the direction of passage, is clearly 

 shown by simplified valves and gauges, and by the 

 use of light in varying color density. In the Haskin 

 tunnel, 5 to 10 minutes were taken to pass the miners 

 through the lock so as to avoid too abrupt a physio- 

 logical change. 



Despite caution, a blowout occurred in July 1880 

 due to air leakage not at the face, but around the 

 temporary entrance. One door of the air lock jammed 

 and twenty men drowned, resulting in an inquiry 

 which brought forth much of the distrust with which 

 Haskin was regarded by the engineering profession. 

 His ability and qualifications were subjected to the 

 bitterest attack in and by the technical press. There 

 is some indication that, although the project began 

 with a staff of competent engineers, they were 



■'■ Ideally, the pressure of air within the work area "I .i pneu- 

 matically driven tunnel should just balance the hydrostatic 

 head of the water without, which is a function of its total height 

 above the opening. If the air pressure is not high enough, 

 water will, i>l course, enter, and if very low, there is danger of 

 complete collapse of the unsupported ground areas. If too 

 high, the air pressure will overcome that due to the water and 

 the air will force its way out through the ground, through in- 

 creasingly larger openings, until it all rushes out suddenly in a 

 "blowout." The pressurized atmosphere gone, the water then 

 is able to pour in through the same opening, flooding the 

 workings. 



234 



BULLETIN 240: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



