Digging Post Holes-Help?

Hey guys, hit me with your top post hole tips.
Context: I'm planning to build a shelter over something, using the Humanure Hacienda "plans". I need to dig post holes.
Conditions: This is going to be by hand. Is it possible to do it without a human-powered auger? How to?
Cement? What about digging too wide and the edges being mushy?
Rock on the bottom?
Depth and Width?

What that system?

What is your subsoil? Clay? Sand? Random rock and gravel like glacial till? This determines the method.

I'm in sandy soils.  I use a post hole digger to get through the first 4" of turf/roots/topsoil and then use a hand auger to go deeper.  The post hole digger could do the whole job but the auger is a bit easier if I don't hit a rock.

Doug, my soil is clay and rock. It's pretty diggable when wet but hard as a rock dry. Posts are 8', going into the ground 2' deep. That's why I was considering hand digging. Would y'all say that's a good depth? I could definitely get through the ground 2'. Just worried about getting too wide and not having stable enough sides.
The plans for context:
"Dig 4 two-foot holes, drop in 4 4x4 locust or other suitable posts, back fill with soil mixed with concrete. Posts are 5' apart" mine will probably be further
No soil-to-concrete ratio. Thoughts on that as well?

I don’t have much experience to go off of but I did research setting posts for a deer stand. I learned that concrete can trap water and rot out set posts faster than putting them in straight gravel.

Also I bought a small ax just to cut through all the roots in the way of digging. I’ll let you all know how that works out.

It is better in my experience as a fencer to mix a shovel of portland cement withe the soil at each post.
And ram it it , in 3 inch layers until its full to the surface level.
By ramming it I use a 40mm square bit of wood with a smooth hand drip, which protects my fingers rubbing against the post.
Water can rot some posts if you have concrete at the bottom of the hole, that causes a water trap.
So just have bare earth at the bottom, its the side forces you are working against.

So if no concrete, what? Rock the bottom?

John, what's a shel of cement? Also, is it dry cement+dirt and rammed together?

Water can rot some posts if you have concrete at the bottom of the hole, that causes a water trap.

So put the cement around the post, not under?
Thanks for your patient answers, everybody, this is my first project like this

Sorry about the typos as  we say here in Australia.
I am in hospital with a broken leg and the internet access is stock and sticky .
Many mistakes,
Shel = shovel
Bare earth is ok, you are looking at resisting side forces generally and the soil / cement mix sets very hard, almost like concrete.

Thanks John!

I think the method depends in part on how big the posts need to be, and what kind of vertical load they will have.

For fence posts (pointed 3-4" wide), I like to use a digging bar, with its weight driving it down and wiggling side to side to widen the hole enough to accept the post. I can get to 2' deep this way in proper conditions. The ground needs to be moist, as in springtime or extended rainy weather. I have been known to trickle water into the started hole for some hours to improve diggability. My soil is generally hardpan or glacial till below topsoil level.

If you need to support a significant load such that a pointed post will sink measurably over time, then digging a hole and backfilling is needed. I would backfill with as much flat/angular stone (vertically oriented) as you can get to increase the lateral stability of the post, if that matters to you.

I was involved in building a large deck over a swampy water body, and we got long (10' or so) locust poles for piles. A backhoe was able to easily push them as much as 6-8' into the bottom, only stopping because desired top height had been reached, and the resulting deck has not settled in the 6 or 8 years since, essentially supported by friction on the sides of the posts. The same may work for 2' deep driven posts on land supporting just a shed roof.

Have done hundreds of holes with only a shovel, a spud bar, pick and a correctly sized can.  So certainly possible.

Glenn, do you realise that piles driven in until they have a measured amount of resistance are called ' friction piles',
others maybe driven to bedrock 2-300' deep to bedrock.