I just got a manually powered hydraulic log splitter (the Sun Joe LJ10M) and was amazed at how the hydraulics let me use my puny human muscles to generate 10 tons of splitting force, no fossil fuel required.
This got me wondering what other kinds of tools could be powered in this way. For instance, I need to dig some trenches in stony soil, and was assuming that this would require a backhoe, which is expensive (even to rent), loud, smelly, and requires you to deal with diesel fuel, etc.
But I started to wonder if there could be some kind of shovel/digging contraption that uses hydraulics to dig a trench with 10 tons of force, but using only human power.
I know of no ditch digging miracles. Others may, but I have yet to see a tech gizmo transform dirt work.
And most every endeavor in all of life involves real and unavoidable trade offs. The splitter you have trades slow speed for less required skill and strength, compared with a skilled ax-man, or less capacity, noise and stink, compared with an engine driven splitter. Although that may feel like a non-issue for you in your present circumstance (and that's great), in other circumstances it can become critical. There's No Such Thing As A Free Lunch, as one of the hallowed iconic characters from the '70s famously opined. No getting something for nothing.
I worked many jobs laying pipe in trenches. I only ever saw the hole done two ways - muscle and heavy machinery. But muscle can move mountains and it can go almost anywhere. It takes time but it's much, much faster than you would expect, given good dirt workers. It's a real skill. And the money goes (more or less) straight to a human being as opposed to an energy company. Machines need space and large jobs to look good.
Human beings often turn out to be the best tool. But dealing with a human is some different from turning a key and pressing a pedal. Still, the results can be amazing. Worth checking to see how skilled muscle pencils out against a machine. In many situations, it wins, hands down. Muscle can also come with a brain attached and that brain can save you money or even save your ass. If you find the right workers, and I confess, that can be a matter of purest luck.
I am afraid that I cannot help you on this other than to possibly scale down your project (seems unlikely) or consider a true power tool.
For my part, in this particular context, “manual” and “power tool” are pretty much contradictory.
If you really need to dig a ditch and don’t have the combination of time, strength and endurance (I tried this when I was younger and stronger—I gave it up), I would recommend at least thinking about renting a power tool to do the task. You can probably rent a mini excavator to do the job efficiently.
I would add that if you lack experience with the equipment, hire to have the work done unless you are trying to get an education on the equipment. An experienced operator can do more in a couple of hours than I can in a couple of days with a rental.
"Good decisions come from experience. Experience comes from bad decisions." ... Mark Twain
There is a trench digger that uses air to blast a trench into the ground. Great for rocky soils... but towing the giant air compressor into your worksite to power it might disqualify from your criteria.