Compressed Air Work And Diving 1909

EAST RIVER TUNNELS. 89 each well, and plug holes were left on each side, onc on the land side, and one on the river side. These plug holes were slightly larger in diameter than the shields, and until these were built the plug holes were closecl by a single skin well braced ancl strutted. Two tunnels starteel from each shaft, ancl there were therefore two shafts on each side the river. These shafts were a little distance apart, so that the tunnels formeel two pairs. This arrangement brought the two of each pair rather close together, ancl so for safety it was founel necessary, after the shields had been starteel together, to shiit clown two of the tunnels, one in each pair, sufficiently long to allow the other two to get ahead. The workinQ- chamber was 9 ft. in height, and had a single skin stiffeneel by open brackets. It had a strong water-tight and air-tight roof, ancl the wells above were filled with water as required, which was pumped in or out as the tide rose or feli, so as to give the necessary weight at high ticle when the upward air pressure woulcl be highest, ancl to take the weight off the packings supporting the caisson at low water when the pressure would be lowest. There was a combinecl shaft for men and material in the centre of each well. The shafts had parallel sides with semicircular encls, one of which was clivided off by plates to form the man shaft. The air-locks were in general appearance very similar to the Davis air-lock (see Fig. 11), but the bottom cloor of the bueket chamber was closecl by a shaft passing through the sides of the lock, ancl worked from the outside by a balancecl lever. The bueket chamber was closecl at the top by two slicling doors worked by two compressed air cylinders. These locks were liirecl by the contractors, as the import duty did not make it