We have a small project of about 3000 sf, a new building on a site where a structure had been for years. I said to myself, “If a building has been there for 3 decades, the subgrade should be good enough to support a new building.” I was wrong.
After we had performed the demolition and started the grading, it occurred to me that we may need to put a few borings in the ground. I’m glad we did. We found sand and slag on top of fatty clays. We may have been all right still, but I did not wish to take the risk. We removed this existing material and backfilled it with good structural fill as a safeguard.
This was a good reminder for me: Do not forget the basics, no matter how busy or sure you might be. “An ounce of prevention is worth a pound of cure,” as the saying goes.