710 



Popular Science Monthly 



each of the cyUnders next simultaneously 

 turned wheels which opened a three- 

 inch water-valve in the bottom of the 

 center compartment of each cyliner and 

 by carefully observing the rate at which 

 the cylinders became submerged and 

 testing the subsequent load transferred 

 to the derrick, the nineteen tons of 

 water to overcome the buoyancy was 

 admitted, filling the center compart- 

 ment to about one-half its capacity. 

 Then just enough more was let in to hold 

 the section in position when lowered, 

 against the action of the tidal currents 

 in the river. This total excess load 

 never amounted to more than a few 

 tons, which the derricks readily sus- 

 tained. The section was lowered, until 

 one of the diaphragms at or near each 

 end, rested upon temporary timber 

 frames, in the shape of an inverted "11." 

 By means of the location cables attached 

 to the ends and sides, the section could 

 be shifted north or south, east or west 

 until the masts (which projected about 

 ten feet above the water) indicated that 

 the- structure was in proper position. 

 The control over this large steel struc- 

 ture was very complete; the section 

 could be raised or lowered, shifted at 

 will, or could even have been brought to 

 the surface again if conditions had made 

 it necessary. 



How the Sunk Tubes Were Joined 



Each section after the first, had a 

 positive anchorage to the section pre- 

 viously placed; the ends were brought 

 into perfect alinement by means of steel 

 pins mounted on the end of one section, 

 and guided into tapered holes in 

 castings mounted in the same relative 

 position on the other section. As the 

 two sections were drawn together, the 

 pins were started into the tapered holes 

 and served to guide the ends to a 

 positive junction, then a diver bolted 

 them together. The complete operation 

 from the time of opening the valves to 

 admit the water to fill the tubes, to their 

 final anchoring, required but three hours. 



As soon as a section was placed, prep- 

 arations were made to deposit the 

 encasing concrete, the weight of which 

 was necessary to keep the tubes from 

 coming to the surface when their 

 buoyancy would be restored in the un- 



watering, and the strength of which 

 concrete, together with the reinforcing 

 effect and waterproofing qualities of the 

 steelwork, was to provide a safe working- 

 chamber for the completion of the sub- 

 way structure. The section, as far as 

 described, might be considered to be a 

 large box sunk in the bottom of the 

 river, without top or bottom but having 

 sides and ends, and divided by the 

 diaphragms into a series of pockets 

 which could be filled with concrete in 

 any convenient order. 



Pouring Concrete Through Pipes 



The tubes, being surrounded with 

 water, the problem resolved itself into 

 displacing this water with concrete and 

 without the loss of the cement which 

 would occur in dropping the concrete 

 through even a much less depth of 

 water. This was accomplished by what 

 is technically known as the "tremie" 

 method of depositing which involves the 

 use of long pipes which are kept nearly 

 full of concrete and which are raised a 

 little as the concrete is poured in at the 

 top. A nearly continuous flow is main- 

 tained. The concrete gradually dis- 

 places the water but does not mix with it. 

 Each pocket required an average of twelve 

 hours for its completion by this method. 



When all of the pockets had been 

 filled, except those over which the 

 buoyancy cylinders had been placed, 

 these cylinders having performed their 

 functions, were disconnected by forcing 

 the water out of them; they floated to 

 the surface there to be reclaimed for use 

 on the next section. 



With all of the sections in place and 

 encased and with the extreme ends of 

 the series closed by the heavy wooden 

 bulkheads previously mentioned, four 

 small steel shafts or wells attached to 

 the tubes before sinking, were opened 

 and the water pumped out. It was 

 then possible to get inside of these sub- 

 merged passages beneath the river, 

 assemble the concrete forms and place 

 the lining, thus completing the structure. 

 There were no leaks in the tubes except 

 where some of the bolts in the interior 

 walls had not been tightened sufficiently, 

 and by tightening these bolts, the 

 finished work was, figuratively speaking, 

 "dry as a bone." 



