Trench Footing with Perimeter Drain

[TMS1978]

Hi guys, I'm a general contractor and I could use some help with a detail involving a trench footing with a perimeter drain on a project I'm working on currently. Admittedly, I have not built many structures on a crawlspace, however, when pouring trench footings in the past, I've been told that it is never a good idea to excavate the virgin/compacted soils on the sides of the trench footing as it could sacrifice the structural integrity of the footing. Essentially, the virgin/compacted soils on each side of the trench is what helps to stabilize the footing, thus excavating the soils to install the perimeter drain and gravel is never a good idea. I would love to hear the group's thoughts on this. Subject detail is attached for reference.

 

[dik]

...IMHO, a bad detail. The insulation should be on the outside of the building envelope and the drain tile should be below the insulation, in free draining material, complete with a geofabric encapsulation.

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So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik