What exactly is a cassion?

Factual Questions
1

I overheard someone mention that they had to use cassions to support a home which was being built on poor soil. Typically, I have heard of either piers or pilings used for this (pier being the generic term for a vertical support and a piling being a one-piece support that is driven into place.) I have never heard anyone refer to a cassion in residential construction, and the only time that I have heard of cassions being used is in building bridges over water. I had the impression that the term referred to the formwork, typically made of driven plates, for a pier set in water, but it seems that I was wrong.

So, what exactly is a cassion, and what are the defining features?

2

IANA Civil Engineer, but here are a couple of definitions to get you started.

I’m mainly posting to let you know that you’ll get a lot further in your searches if you spell it “caisson”. (No snark intended, just trying to be helpful.)

3

:smack: Thanks.
…and essentially it is the formwork.

I suspect that the home that I mentioned in the OP was built on land with a high water table. The cassions may have been needed to keep water out when pouring the foundation.

(Would any mods care to fix the spelling in the title?)

4

Checking a few more web pages, it seems that caisson is used in other parts of the country to describe a reinforced concrete pier going down to bedrock, or at least to bearing soil. Around here, we just call them piers.

5

Interesting note…

Originally, the bends, what scuba divers get was called cassions disease. When drilling deep cassions in a river for a bridge, high pressure air was pumped into the cassion to force water out. The people working in the cassions would get the bends/cassions disease from breathing the high pressure air, and not properly decompressing as they exit the cassion.

6

caisson

7

I know you’re referring to homes, but if you pick up David McCullough’s The Great Bridge you’ll learn more about caissons than you ever cared to know. And it’s readable, too!

link

8

Caissons also refer to chests that carried artillery, and later to wagons that carried this artillery as in the song “The caissons going rolling along …”