You know when you drive under or over a freeway bridge that it’s a massive structure …
There are the two abutments (the upright supporting structures at each end that carry the load of the bridge span), there are usually center columns or piers, and, of course, the girders and the bridge deck (the part you actually drive across).
The girders and the deck make up the bridge’s superstructure. But what you don’t see is that buried beneath the bridge is part of the equally impressive substructure formed by rows of caissons – massive steel-and-concrete pillars that support and lock in place the abutments.
Head over to the ADOT Blog for more on these huge underground structures – including how many tens of thousands of pounds of concrete it takes to fill just one caisson!