> to start the ball rolling and pending a diagram or drawing to confirm or disaffirm the one in the discussion entry.

Better post masse isolée as a separate term. Meantime, subject to any ideas from my builder bother-in-law from Croydon: a separate slab.

Une proposition basée sur la référence que j'ai donné ci-dessus dans l'espace de la discussion, pas avec une grande certitude, mais simplement une proposition qui pourrait bien être valable dans ce cas.

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Note added at 3 ώρες (2024-01-24 13:37:31 GMT)
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isoler [qch]⇒ vtr (protéger des températures extérieures) insulate
https://www.wordreference.com/fren/isolé
https://www.youtube.com/watch?v=YjGqXxHl6RQ
https://www.amazon.com/insulated-well-pump-cover/s?k=insulat...
https://www.outbuildingsok.com/insulated-well-houses.html

That's a very good question, Tony, and I thank you for asking it! ;-)

I've not encountered the term, though puits in this context is obviously 'shaft', so I'd say 'shaft foundation' as a starting point. I don't know that puits or shaft foundations can be anything BUT isolés ... I suppose, though, you could have a string of contiguous shafts, just as you can have contiguous piles (secant piling). Recherche faite, yes, there is such a concept as secant shafts (also tangent shafts): https://www.fhwa.dot.gov/engineering/geotech/nhi18024.pdf

"Shaft foundations. These are constructed within deep excavations supported by lining constructed in place and subsequently filled with concrete or other prefabricated load-bearing units."
[Civil Engineer's Reference Book, L.S. Blake]
As opposed to pile foundations which are not (generally) supported (even if they are not simply piles driven or screwed into the ground, being of reduced diameter, support is not generally required).

If we consider shallow foundations, we have (from my notes):
Semelle isolée - Individual footing; isolated or pad footing [Chudley,vol2,p16-18; CW,19.5.93 p25]

So 'individual/isolated shaft foundation' or 'individual/isolated foundation shaft' would get the correct message across.

It's not common, but you will find 'individual shaft foundation' (and 'grouped shaft foundation') here:
https://ir.canterbury.ac.nz/server/api/core/bitstreams/997db...

I get the impression 'shaft' in the above refers to an oversize 'pile' given that the grouped shafts are the foundation beneath what would normally be called a 'pile cap'.

Note the US 'well foundation' (from my notes again):

Pier foundations - puits de fondation - excavation into which concrete foundation is cast; not as deep as pile foundations, and more massive. Aka "well foundation" in US (and India). Often referred to as "puits marocain" (top-down concrete lined excavation subsequently filled with concrete), though this is really a subset, in any case, a "puits marocain" is in my experience always for a bridge pier, so there may be confusion.

Your masse might be an error for massif which, as described here (I can't cut/paste it), is synonymous with puits :
https://www.ge-2e.com/fondations-geologie-geotechnique-etude...
And from my notes:
Massif de fondation - Foundation block [Blake, 17/26, 27/34], pedestal - In one case the 'foundation block' is the pedestal on which machinery is placed, in the other it is a pile/shaft with an enlarged 'elephant foot'.


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Note added at 7 hrs (2024-01-24 17:44:51 GMT)
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Reading the text in the image below (fondations profondes filantes vs puits isolés), I conclude that the isolé is tautological reinforcement, i.e. as first said above 'shafts cannot be anything BUT isolés. So, just 'shafts', 'foundation shafts', and quite possibly simply 'piles' if, as you say, they are a 'small localized foundation for a single column'.