I loved to dig as a boy in Vermont, but I gave up in frost. It's an
interesting problem. The best solution may depend on the type of soil,
its temperature, and how much ice it contains. In Korea, soldiers
sometimes used explosives, sometimes fires, and sometimes an assortment
of hand tools.
Thawing will stop when the surrounding ground draws heat away as fast as
you apply it. I think very cold ground and ashes might even stop
thawing from a fire.
Others have recommended light bulbs. That sounds simple and pretty
safe. Most of the heat from a bulb is radiant, so lining the box with
aluminum foil would reflect more heat to the soil. I'd use several
hundred-watt bulbs with porcelain sockets and wire with high-temperature
insulation. A little ventilation may be necessary to keep the
electrical stuff from overheating.
A professional solution is a trailer-mounted boiler with hoses to
circulate water between the boiler and the hole. One could use a stove,
two pots of water, and a big syringe or pump to draw water from the hole
for reheating. An infrared thermometer would make it easy to monitor
the temperature of the water in the hole.
If you're going to rent equipment, just use a drilling rig.
or a ditch-witch. There's no point in using finesse
when raw power will do.
But still, we're talking three postholes/footings,
not the Comstock.
Around here people dig holes through the ice with an augur for fishing.
Those who don't have an augur use a hatchet. Before playing with
fire, I'd just buy or rent an augur.
Option 1. Electric jackhammer rental. It works on concrete. Should work
on frozen dirt.
Option 2. Pickaxe and power posthole auger.
Option 3. Rock bar, San Angelo bar, etc. 72" long, 1" diameter steel.
chisel or pointed end.
I drive them with a 50# T-post driver made from drill stem.
Option 4. Steam cleaner (watch out for the hot mud)
Option 5. Tractor with auger driven from a 3-point frame on the back
When I was in Girl Scouts, we used to do pothole cooking. Dig hole,
build wood fire, wait till it had good hot coals. Then we put in
packages of food wrapped in foil, covered that with wet leaves and then
dirt. Kept it buried a coupld of hours and then feasted.
You could do something similar with charcoal, it seems. Get some good
hot coals going, cover with wet leaves or straw, wait a couple of hours.
Doesn't seem the ground can be frozen very far down yet, and this
method would keep most of the heat on the hole.
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