The last photo from yesterday’s discussion of caissons at the construction of 15 Broad Street showed the beginning of the next stage of work. On September 21, 1926, the construction photograph captured the installation of sheet piling along the east edge of the site, adjacent to 43 Exchange Place:
This was the beginning of the next phase of work, the excavation of the new cellar, which is deeper than the old cellar hole left over from the Mills Building. Nine days later, a “bird’s eye view,” most likely from the roof of 43 Exchange:
Most of the old masonry walls from the cellar of Mills had been removed. It’s not clear if there had been any general excavation yet. The cylinders visible are caisson shells, either already installed (if vertical) or ready for use (if laying horizontally). The piles of timber – on top of the Broad Street sidewalk shed at the top of the photo and on site at the lower right – were for the next stage of work.
Here’s the south edge of the site a little later:
The general level of work – where the mud is – is a floor below the sidewalk. The vertical timbers at the edge of the site on the right are inboard of a foundation wall (I’m not sure if it was new concrete, as was seen in one of the photos yesterday, or an old masonry wall) at their lower halves, and posts supporting the sidewalk shed roof at their upper halves. The transition from foundation wall to wood construction fence is visible.
By October 22, the general scope of excavation had become clear:
That’s a temporary wood-framed ramp to allow trucks to drive in above the work (and above street level) to deliver materials and, likely, to receive excavated earth. Timber framing to support derricks is visible in the center, against the side wall of 43 Exchange, and on the far left foreground. The piles of timber were, by November 15, turned into a beautifully cartesian set of bracing for the perimeter foundation walls. Today, we’d call that support of excavation.
This series will return next week, after a few days of other topics.
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