Woolworth: Caissons

The book A History of the Singer Construction that I was mining last week is not unique. The position of skyscrapers in the early twentieth century – interesting expressions of the high-tech of the day, accessible to view by any passers-by – meant that they were popular subjects for magazines and newspapers, and that publicity via book and pamphlet was a realistic option for related businesses. As I said last week, it makes sense to compare those skyscrapers to more recent popular technology, and ask yourself how many articles and books there have been over the last ten years on the topic of the iPhone. The picture above is the frontispiece of Master Builders of the World’s Greatest Structure, a commemorative book about the Woolworth Building. In 1913, there was a reasonably consistent cornice line in lower Manhattan at around 25 stories, as seen from the Hudson; the buildings that project above it are, left to right, Woolworth, City Investing, Singer, and Bankers Trust.

Master Builders has fewer illustrations than the Singer book, and they’re generally less interesting, but the text has some great nuggets. On the topic of the sub-surface investigation at the site we have “The many borings made by the engineers disclosed loam, gravel stone, shoal water, quicksand and solid rock, and at the great depth of 130 feet below the curb was commenced the problem of building the piers and monoliths which should be impervious to shifting sand and form a solid construction equal to the enormous load.” The answer to that soils mess was the same as at Singer (which was all of five blocks away): pneumatic caissons down to rock.

If the picture looks familiar, it’s in part because all pneumatic caissons look somewhat similar, but its also because they were built, like the caissons at Singer, by the Foundation Company. The foundation work began in 1910, four years after Singer, so it’s not surprising it’s so similar. Woolworth is substantially larger than Singer: 792 feet high versus 612, and the base that fills most of the lot is 30 stories versus 14 at Singer. This is a much heavier building subject to a lot more wind load. The result was the use of 66 caissons, ten to twenty feet in diameter, sunk about 110 feet. (The difference between 110 feet of caisson and bedrock being 130 below grade is simple: the caisson tops are below the lowest excavated cellar.) There is a lot of concrete buried below the visible structure.

In short, similar problems at two building sites near to one another in time and space were addressed with the same solution. That’s not all that surprising, as foundations for tall buildings had been in development since the 1890s. This was not experimental technology, this was the best of available and known techniques.

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