Canadian engineer . ual of a little bit ofeverything^ including boulders, sunken timbers, &c., whichwe afterwards found to be correct. The filled in portion extended from the street leveldown to from 8% to 18 feet below the curb, while the bor-ings indicated that the river mud or silt extended from 14ft. 8 in. to 33 ft. 6 in., or a variation of nearly 17 feet. Itis not conceivable that the river silt was originally so muchout of level, so the inference is that the sand, &c., sank intothe silt, displacing it in places and forcing the adjoiningportions to a higher level. This is the regular Huds
Canadian engineer . ual of a little bit ofeverything^ including boulders, sunken timbers, &c., whichwe afterwards found to be correct. The filled in portion extended from the street leveldown to from 8% to 18 feet below the curb, while the bor-ings indicated that the river mud or silt extended from 14ft. 8 in. to 33 ft. 6 in., or a variation of nearly 17 feet. Itis not conceivable that the river silt was originally so muchout of level, so the inference is that the sand, &c., sank intothe silt, displacing it in places and forcing the adjoiningportions to a higher level. This is the regular Hudson River silt, and is a verymuch more treacherous material than the so-called NewYork quicksand which overlies the hardipan in the wholelower portion of Manhattan Island. Under these circumstances the writer was very stronglyof the opinion that the only really reliable foundation forthis building would be pneumatic caissons, and the way thecaissons acted while being sunk confirmed this opinion Fig. 2.—Showing Two Four-Masted Steel Derricks. SteelForms used for Building up Cylinders—Collapsible SteelShafts Inside of Steel Forms. Wooden Cofferdams, Usedwhere Concrete Stopped Below Ground. Pile of CastIron Blocks Marked B used for Weighting DownCaissons. Each Block Weighs 1% to 2% Tons. In addition to the very treacherous nature of the soilthat repeatedly held a caisson up and let it drop to thedeck without warning, there is the fact that a subway willprobably be built up Eleventh Avenue some day, whichwould tend to lower the water below the tops of any wooden 312 THE CANADIAN ENGINEER Volume 22. piles. The writer, having previously underpinned a build-ing- which had been built on piles 30 feet long, which, whencut off and capped, were entirely under standing water, butafter the construction of a railroad tunnel were found to befree from water from top to bottom. It is well known, ofcourse, that wooden piles have lasted for centuries in goodcondition when drive
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