Bruce, according to what I found with google, “axial loading” and “axial compression” have to do with a load or compression being parallel to the long axis of a structure rather than with the load distribution profile in soil beneath foundations.
However you’re right about the “angle of repose”.
Here’s a successful attempt to dig out a crawlspace to create a basement. It does interrupt the cone of compression at 45 degrees but has been effective enough so that there was no evidence of failure after many years.
