Pragmatic Concrete

by Don Friedman on May 16, 2017

That strange-looking pier above requires some back-story explanation. The New York subways were originally built as three systems – the privately-owned IRT and BMT, and the city-owned IND – which were organizationally integrated in the 1940s. The IRT and BMT were competing with each other but were also joined at the hip by an expansion plan called the Dual Contracts. The Dual Contracts specified a number of locations where free transfers between the two companies had to exist; other locations* where it would have been logical to have a free transfer, but were not required to have one, do not have transfers to this day.

The free transfers were not always well designed to expedite movement. For example, the passageway that connects the N/Q/R (BMT) to the 4/5/6 (IRT) at Union Square was built rather narrow and proved to be a real bottleneck for people trying to transfer. In 1998, the transit authority renovated the station and doubled the width of this passage; as part of an art project, portions of the old wall were left in place to show the history of the station.

The picture above is the back of one of those old sections of wall. The dark freckles are the coarse aggregate in the concrete that makes up the structure of that wall. Old concrete tends to have aggregate that isn’t as carefully graded (sorted for size) as modern concrete: some of those stones are bigger than would be allowed now.

But wait, there’s more! Here’s the back of another section of wall:

The right side has the same aggregate pattern, but what’s going on off to the left? Those big stones are the remnants of an old rubble wall that got incorporated into the subway construction – either the IRT work in the early 1900s or, more likely, the BMT work in the 1910s. Concrete can subsume other materials, which is exactly what appears to have been done here, probably to avoid having to alter some existing non-subway construction.

* For example, in East New York where the 3 and L lines cross and have adjacent but unconnected stations.

Previous post:

Next post: