How to stabilize a 50 degree slope of rocks and fill?

[JasperFrank]

Background. We are building a fire break in the form a lined pond that is down hill from our house. The pond area was originally a site that was dug out for a pond. But over the span of 20 years I never had the time to finish the pond, so for years I was dumping rocks and dirt from the property to build this pond area up to the level of the yard by the side of the house that faces a forested area. I'm semi-retired now and the pond idea is being revisited after we quite easily completed an access road on top of the down slope side bank of the pond area. We've spent the better part of a month removing the rocks and dirt down to the original base of the pond area. However this has created the problem of all the fill and rocks I added to the slope beween the house and the side of the pond depression. This down grade is a very lose mix of rocks and dirt and is now at approximately 45 to 52 degree slope. I have some ideas on how to stablize the hill, but don't want to give those ideas out just yet. I would prefer to hear anyone else's original ideas and then see if it comes close to what I was thinking about doing..... I'm sure someone has had to solve a problem like this one in the past.

 

[3Ts]

Some questions first:
- How tall is the slope? I'm guessing it's around 6' tall
- What do you intend to do with the pond? i.e. what is it's purpose - water storage for fire fighting, fish pond, catch basin for run-off? I see some pipes that look like one is a water supply and another is a drain.

If it's not too tall, I'd use a short retaining wall about 3' tall, that would catch any loose rock/dirt/fill and reduce the angle. You could use the existing rock to build it. If it's taller, you can put in a second short retaining wall, but there are foundation issues you'd have to check on for the upper wall.

 

[oosik]

One idea - a retaining wall, as 3Ts suggests. Another idea - as the Highway Dept does. Heavy nylon mesh covering the entire slope. Then hydroseed. Hydroseeding will grow grass on anything the green goo can stick to.

 

[4570Man]

I’d either add more rock and dirt to decrease the slope or build a retaining wall.

 

[3Ts]

This down grade is a very lose mix of rocks and dirt and is now at approximately 45 to 52 degree slope.

This is going to limit your options. I'd also thought about gunnite on the hill side, but with a loose hill side i'm not sure. Maybe if you have weep holes at the bottom? You will need to keep water out from behind whatever you do.

 

[crashz]

A couple different options:

- You could dig back the slope and rebuild the entire slope going back 10 feet or so using a geotextile every two feet. You could lay a 24ft length down (out along the cut away from the house), fill two feet, compact in 1 ft lifts, and roll the excess back over, making a mattress of soil. Place a little soil in between mattresses. Overlap fabric along the length of the hillside. Compact everything, but always use compaction equipment on the level. You can then add a bedding soil on the slope that you remake with shorter and shorter mattresses. Place the rock on the outer surface of the slope on the bedding (to avoid ripping the geotextile). While building mattresses, I would add some drain pipes on even intervals to relieve any water that may collect in the soil.

- Grouting the rock in place will give a solid surface and with some drainage behind the stone, should be relatively stable, but not long term. The grout will crack, water will leak out and eventually you'll have loose areas.

- Another DOT thing is Gabion baskets or Gabion mats. You could contour the hillside the way you want, make a key at the bottom and fill these huge wire baskets with rock (labor intense), the mat is usually placed by an excavator, but you could place them first, then fill with rocks. The baskets are wired shut and a little geotextile on the end allows for covering with loam and seed. They look nice, but are not pedestrian friendly.

 

[Industrial Toys]

You have enough stones handy to use Gabions.

 

[Egon]

Easiest is to add material to the slope till it’s at its natural angle or less. (Angle of Repose)

 

[JasperFrank]

Excellent, excellent suggestions here. I never even though about the Gabion's. My hair-brain idea was to buy some used chain link fence, nail it in to the slope and drape the hill with a shallow fill of dirt over it. You've given me a lot to think about. Thank YOU!

 

[redman135]

15 - 20 ton digger with a vibrating plate compactor to do entire slope and top as well as you said it id all loose fil.