I had a company with power auger bore to 7 foot depth and put steel bars in the concrete footings before having the concrete poured for the base of my greenhouse. It was to be a magnum opus with all mod cons for my orchid culture.
It all worked for a few years and then one end sank a couple of inches, throwing the ventilation machinery out of line and cracking a couple sections of glass.
I had to give away my plants.
Not I have a large storage shed filled with old pots and other gardening leftovers.