Rammed earth Berms

I'm looking at building a 12-18" rammed earth berm for my house. It will be 3.5-4' tall and act as a retaining wall.  I am working solo and have roughly 100-200ft to build eventually.  I purchased a towable air compressor that I'm now not exactly sure is going to run.  My original plan was to build some forms, use local soil (fine sandy loam) and 5-6% concrete to stabilize and compact using a backfill tamper.  The more I think about it, I was wondering if anyone had used a plate compactor for rammed earth?  It would seem fairly easy for me to build the forms around the compactor, compact it to the top and roll it off the forms using some ATV ramps. Having the forms the width of the compactor would mean I would fill, run the compactor back and forth for a few minutes...rinse and repeat.  Has anyone tried this method? Results?  My forms would be 3/4 plywood with 2x6 walers and 4x4 strong backs dug 2' into the ground.   Thanks for any information.  

You say "berm"... that sounds like it will be outside the house to some degree. How will it be protected from getting wet? No matter how tightly it is rammed, if water gets in, and especially if it freezes, the berm will lose integrity.

Plate compactors don't compact dirt that well, they are for gravel/road base.  A jumping jack may work, it is made for clay/dirt, but still might not be dense enough.  They are even less fun than an air tamper to run.

If you simply want a massive wall within your house, that should work.  If you truly want a retaining wall, you need to think it through VERY carefully.

You could/should do a few test blocks.  Make them the same size but use a couple methods to pack them and a couple ratios of cement.

There are other stabilizers out there, including polymers that are supposed to do an awesome job on road bases and have a much lower embodied energy than cement.

Sandy loam is niot a good material to use, it needs to have clay as a binder.
It will cost a lot to use cement as a binder.

Rammed earth needs to be rammed with a 100mm diameter pounding hammer head.

Traditional rammed earth is made from clay-rich soil, water, and natural stabilizers like animal blood or urine and plant fibers that have been packed down.
This technique has been used in the Great Wall of China, in Japanese temples, and the Alhambra palace and fortress.

Sorry for the confusion...it's an exterior garden type wall...I've seen many rammed earth walls...this will be a retaining wall.  It's purpose is to hold back the hill. I would need to stabilize it somehow. I was thinking 5-10% Portland.   I do have some clay, but don't think it's enough to stabilize long term.  It appears though that a plate compactor is more for vibrating irregular grains into voids where rammed earth needs more force to compress for cohesion.

Have you seen outdoor rammed earth walls in your climate that have lasted? Just concerned that you might waste a lot of work on something that might disintegrate.