[dice]

I was thinking about the problem with the gravel falling
in when the bucket on the loader or backhoe hits water.
It seems like you could dig a fairly wide hole with gradually
sloping sides to get around that problem. Maybe start 10' out
all around for the outside of circumference of the hole, dig
down a couple of feet in the center, than clear out a gradual
slope out to the sides of the hole. Dig down a couple of
more feet in the center, and then dig out around the sides,
maintaining that gradual slope, so that the lip at the outside
edges drops at the same rate as the center of the hole.

When the center gets down as deep as it needs to be, you
don't have much in the way of sides around it to cave in.
If any of the lip caves in, out at the edges, it is 10' from
the hole, so no damage done. Just increase the slope as
you go from there, not digging the outside lip any deeper.

I remember a kid from high school that was out helping
hand-dig a well in one of the local river valleys decades
ago. The water tables are shallow there, so they did not
estimate that the hole would need to be very deep, 25 feet
maybe, and the soil was clay subsoil and silt with a lot of sand
in it, easy to dig in. They had a hole about 6' around and 20'
deep, and it caved in on him. Not wide enough.