DIY soil nails (like for slope stabilization)

Does anyone have experience with stabilizing earth using soil nails?

They are used to stabilize hillsides, embankments, can often be seen next to roads. It's basically a rod with a metal plate at the end that's drilled into the soil/rock with cement to hold it in place and provide a grabbing force on the surrounding soil.

I'm thinking of using these to stabilize a 6 foot deep x 6 foot wide trench. Possibly with a thin layer of ferrocement on the sides of the trench.

Hi there, I've come up with soil nails once in the past, and it was very effective. The Engineer also combined soil nails with ferroconcrete.  But you’ll need to do several tests to make sure the surrounding soil is suitable for anchoring the nails.

We did something like this earlier this year, though it was with completely natural materials. It's an attempt to "remediate" a mudslide location at Basecamp, Wheaton Labs.

To sum it up:
- Hammer a bunch of thick sticks (1" or 3cm diameter) into the earth, about 3 feet deep, with at least 1 foot still sticking out of the earth. Arrange them into a "diamond" pattern.
- Take the rest of your sticks and throw them on top of these spikes, creating a kind of lattice or matrix of sticks.
- Throw your soil back on top. Mix in all sorts of other organic materials. We used lots of pruned tree branches and other branches that we found on the ground.
- Add your soil back on top, ideally mostly- or completely-covering your spikes.
- Plant a bunch of taproot and/or spread-root plants on there, so they hold the topsoil.

Does this work? We'll find out. The good news is that it was made with entirely natural materials and our only cost was time.

Have to run now, but if you want a diagram/photo or two describing this process, just ask. Best of success to you and your project...!

You may be thinking of Ground anchors that are used in major  earthworks to hold various structures, slopes or embankments stable.
Its a real Engineering science, known as Geotechnical Engineering and is more sophisticated that what I see above.
A 6 feet deep trench is a trap looking for a body unless you do it correctly.
Somewhere I have a great video detailing different systems, I will look for it.

A webinar on the use of geo engineering to repair infrastructure
landslide issues will open you eyes to the issue of hold soil in stable situations.
Landslide issues