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

Stephen B. Thomas wrote: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...!

Steven, can you draw the diamond pattern you’re describing. I need to do this at my house because of a landslide and trying to figure out the cheapest option to stabilize the area. Your method sounds like it should work. Although I’m thinking of driving fence posts instead of using sticks. Thanks

There is a reason landslides occur, it involves water and soil that can slide under particular circumstances.

From https://www.usgs.gov/faqs/what-a-landslide-and-what-causes-one#:~:text=Landslides%20can%20be%20initiated%20in,any%20combination%20of%20these%20factors.
'CAN HUMANS CAUSE LANDSLIDES
Yes, in some cases human activities can be a contributing factor in causing landslides.
Many human-caused landslides can be avoided or mitigated.
They are commonly a result of building roads and structures without adequate grading of slopes, poorly planned alteration of drainage patterns, and disturbing old landslides.
Detailed on-site investigation is required to determine the importance of human...'

Nicholas Adam wrote:Steven, can you draw the diamond pattern you’re describing. I need to do this at my house because of a landslide and trying to figure out the cheapest option to stabilize the area. Your method sounds like it should work. Although I’m thinking of driving fence posts instead of using sticks. Thanks

Here's a summary of what we did. And sure, I think fence posts, T-bars, and other stuff like that ought to do the same for Step 1.

When I mentioned "diamond pattern," it's like a parallelogram diamond shape, like you'd see on a deck of classic playing cards. But hopefully these diagrams - when imagined from a bird's eye view - will help.

John C Daley wrote: A 6 feet deep trench is a trap looking for a body unless you do it correctly.

Our industrial safety board has some very strict rules about this one! The OP doesn't mention "length" and that's part of the equation.

Factors off the top of my head:
1. Wet soil is so much heavier than dry, and "expands" adding pressure as well as weight. This is big in my climate and I'd be looking at where and how the water travels and be trying to redirect it high up in the ecosystem.
2. How vertical do the sides *really* have to be? Every bit of slope towards "less steep" one can get, the better.
3. Everything man makes has a lifespan - so how long will the system last? Thomas' system is short term, but if appropriate trees/shrubs/ground covers are planted, it will make the system self-sustainable to some degree. Even whether a tree is planted from seed vs transplanted could be a critical factor, as from seed it may have an intact tap root that will add lots of stability *if* the chosen species has that characteristic.

I remember watching a Geology video about landslides - the biggest risk factor is signs in the landscape that landslides have happened in the past. Permaculture is all about mimicking nature. In this case, we are trying to make sure we do the reverse!

From https://www.keller.com.au/expertise/techniques/soil-nails
"Soil nail walls are generally constructed from the top down. Typically, soil is excavated in 1m to 2m deep stages.
After each excavation stage, near-horizontal holes are drilled into the exposed face at typically 1m to 2m centres.
Tension-resisting steel bars are inserted into the holes and grouted in place.
A drainage system is installed on the exposed face, followed by the application of reinforced shotcrete wall facing.
Precast face panels can also be used. Bearing plates are then fixed to the heads of the soil nails.
This installation process is repeated until the design wall depth is reached. The finished soil nails then produce a zone of reinforced ground."