Engineering Wonders of the World
Volume I

120 ENGINEERING WONDERS OF THE WORLD. Fig. 22.—EXPLORING WITH BORING MACHINE. (PENNSYLVANIA RAILWAY TUNNEL.) (Photo, Pennsylvania Railroad Company.) rear of one of the shields, with its erector, the commenced. The compressed air started rushing up through the soil, scouring out a passage to the river. In such a blow, of course, the outward passage of air is accompanied by an inward rush of soil; and if the “ run ” is extensive, the whole front of the shield may be filled up, burying the unfortunate workmen who happen to be there. The time to stop a “ blow ” is at the start. A lump of mud, or a bag, or a bundle of hay stuffed promptly into the weak spot may check it. The workmen know the danger so well that, if nothing is handy for stuffing into the hole, they unhesi- tatingly shove their arms or their bodies against the weak spot to pack the soil and check the rush. Sometimes they .fail : the rush is too strong and sucks the man in, earth caves around him and entombs him. That is precisely what happened here. But the rush was so strong that it sucked the man in, and took him along with it up through the whole thickness of earth overlying tunnel, and shot him up into the river bolting-platform, etc. water. A moment later he bobbed up on the As may be surmised, the conditions of the work were similar to those of the other East River tunnels, and the methods were the same. Clay dumping was resorted to in a considerable degree, to strengthen and seal the river bottom. Escape of air, which had been notable in all the other tunnels, was here also extensive, as the photograph (Fig. 21) indicates. A most astonishing incident, altogether unique in pneumatic work, occurred in this tunnel. It was nothing less than the bodily An Astonishing Incident. ejection of a workman from the front of the shield up through the soil, and up to the surface of the river. And the man lived to tell of it! While working at the face, in the fine quicksand, a blow-out surface, and a passing boat rescued him unhurt. So extraordinary is this accident that we may quite safely say that the like will never happen again. By far the most interesting phase of the Battery Tunnel work is not the tunnelling itself but its sequel. A word has already been said as to the difficulty of guiding the shields accur- ately. There is often further difficulty in preventing sub- sequent settlement, especially A Delicate Operation. in fine quick- sand, which tends to flow in through the un- caulked joints of the lining, leaving a space below into which the tube sags down. This latter action actually took place in the Battery tubes to a very considerable extent, and when the two shields met and the tunnel was