What is caissonin construction?

In commercial building work there is usually no difference: caisson, drilled pier, and drilled shaft are regional names for the same drilled, cast-in-place element. Caisson is the common term in Chicago and much of the Midwest, while drilled pier and drilled shaft show up elsewhere. The confusion comes from bridge work, where a pier is the visible substructure column, and from light construction, where a pier can be a shallow pad or masonry support. Confirm against the drawings and the spec section rather than the label alone.

Size, installation method, and load path. A caisson is drilled at large diameter, commonly 30 in to 96 in, cast in place, and usually placed one per column to carry load in end bearing on rock or hardpan. Piles are slender elements, often 12 in to 18 in, driven or augered in groups under a pile cap, and they develop capacity through skin friction, end bearing, or both. The takeoff differs too: caissons price per VLF of drilling plus CY of concrete, while driven piles price per LF installed plus the cap.

Caissons make sense when column loads are heavy and a competent bearing layer sits at a reachable depth, because one big shaft can replace a whole pile group and its cap. They also win on vibration-sensitive urban sites, since drilling avoids the impact and noise of pile driving next to occupied buildings. Driven or augercast piles tend to win where bearing strata are very deep, where friction capacity in soft soils does the work, or where a lighter rig and lower mobilization cost fit the job.