There is one specific form of temporary construction that people not in the field never think of, but, when informed of its existence, immediately understand: support of excavation. People understand, without prompting, the need for protective fencing, for shoring, for temporary utilities on site, and so on. But “support of excavation” sounds weird: how do you support a hole in the ground? That phrase refers to supporting the edges of the hole so that they don’t cave in as the hole is dug. In a city, SoE (to give it the name used all the time in our office) includes supporting loads from the neighboring buildings on the soil at the edges of an excavation, which is no small thing. Do it badly, and the neighboring buildings can move, break, or even collapse.
The picture above shows the heavy-timber braces used to support the edges of the foundation excavation at the 15 Broad Street site, in late 1926. That incredible grid of timber made sure that Broad Street (and the BMT subway below it), Exchange Place, the J. P. Morgan building, and two other buildings all stayed in place as the pit was dug. Here’s an oblique view that makes the complexity of the timber more clear:
Here’s a view of how the timber braces one of the adjacent buildings:
And here’s the vertical (gravity) support for the timber, with the top of a caisson on the lower right, behind the caption text.:
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