I need some advice on how to repair a dry rock wall that has been in place for over 50 years that the previous owners of my home installed to stabilize the slope that takes up half of my back yard.

Many of you may know that California has been going through a severe drought. We did not get our usual precipitation in November, December or January. So that means the slope was very dry. In February, we got ... officially ... 10 inches of rain out of two storms, soaking everything, including the slope very, very well because it was not a hard rain with lots of run off.

Yesterday, when I went up the stairs to go to the top of the slope, I noticed that many of the rocks at the base had fallen off of the slope and I think I need to rebuild the wall. I can't afford to hire someone, so I am going to have to do it. I haven't got a clue as to how to make it strong and stable. I don't think I should ignore it and hope everything will stay put even though I think the junipers play a big role in stabilizing the slope.

In the photos below you will see a fence in front of the slope. There is about two feet of soil at the base of the fence and then the rock wall is almost vertical for another two feet. Then the rocking follows the slope.

These photos were taken in January and I can't take photos of the damage because it is raining again. We are supposed to have rain almost every day for the next ten days.

Sorry, if I am adding too many photos.

This is the area where I first noticed the rocks had fallen away from the slope ... note the rocks behind the woodshed are also falling.








I've noticed "rock slides" in several places behind the fence. These are photos that show more of the slope.






These photos show how the slope was rocked further up above the wall.





To add more rocks to the wall would be an awesome task as they would have to be hauled up from the street level which is down another flight of stairs.

Any advice would be greatly appreciated.

Smiles,
Lyn

First things first you want to plant a cover crop, you do not want any bare earth. Another things you could do is plant trees and find one's that fit your area. You could also move rocks into the slope and onto it and it will slow the degradation of the soil as well. You want to stop the erosion and you want something to hold the dirt in place.

It's difficult to tell from the photos, but it appears to be that the stones were laid on top of the soil and not constructed as an actual wall. Unless the wall is hiding behind the fence. How long ago was the fence installed? Have you removed sections of fence to inspect what is behind it?

I have some experience building walls; there is a lot about a stone wall that you cannot see. The most important parts are in the base design, the angles required for the wall to be self-supporting (to rest), the larger stones placed at intervals to support all of the smaller stones, the all important backfill material.

This does not seem like an easy fix. Something as large as what is in the photos, plus the fact that it is on a grade, seems more likely to require a professional.

>> There is about two feet of soil at the base of the fence and then the rock wall is almost vertical for another two feet.

I agree that it's hard to tell from these photos exactly what the base looks like right behind the fence on the sloping side, and that the angle of the wall is key, and that professional advice would be a Good Thing, if advice can be had much less expensively than having them do it.

>> many of the rocks at the base had fallen off of the slope

If they were "just sitting on top of the soil", no problem, they were not holding up the slope. At most they were preventing erosion, which might also be done with tough-rooted perennials (juniper bushes sound great for that: once I had to dig juniper roots out of clay and rocks!)

If the rocks that fell out left holes behind, with other rocks above those holes, then they WERE supporting something and prompt action sounds necessary (but it IS hard to tell). Just pushing them back into place doesn't sound like much, but if you can hammer them in firmly, that MIGHT be all you need. (But more photos might help, and an expert ON SITE who will inspect it for free or in return for dinner or a pie would give 100 times better advice than I can.)

My only useful idea is like what Greene said: build an [u]angle[/b] into the wall to help you. If it really was vertical and not mortared together, it might not have been supporting anything much, just slowing erosion.

If you can carry a few more stones up to the wall, and put it back together at an ANGLE at the base, using up some of the two level feet you have to play with, THEN it should be able to resist subsidence better than before. Like the pyramids: they lasted longer with sloping walls than they would have with vertical walls.

For example, position your biggest stones 12-18" closer to the fence than they were. Backfill the part where the rocks were so as to form an angle. Build the new and big rocks into the angle, and merge that with the existing wall.

I assumed that backfill should be the heaviest clay I can find for a concrete-like base, but maybe "well-draining is better.

I had a chance to go and take a closer look this afternoon between periods of rain.

It looks like the rock slide was from rocks used to face the slope and were not used for support. The support work is hidden by the fence. There is a flat path-like area between the fence and the rocks facing the slope where there were no junipers planted.

So, the task is to reface the slope not to repair a wall as I first thought.

The house was built in the mid-sixties, so it's probable that the slope was shored up when they made the cut for the house pad.

The slope is primarily rock with a thin crust of soil. I agree @lovegreen that I need to plant something between the rocks to avoid soil erosion. I'll probably use sedum or some other kind of alpine plant for that purpose. Thanks for the idea.

@greene and @RickCorey ... I live in an old gold mining town in the mountains and professionals that do this kind of work are hard to find. I did some checking around before I headed out for an appointment.

Last week I did some checking to see if I could purchase some smaller rocks needed for another project and found that I can only buy them by the ton up here. I am certain I don't need a whole ton of rocks for either project.

Sounds like I need to keep trying to find someone to come and take a look.

Thanks for taking the time to answer my question.

Smiles,
Lyn

This may be of some help, although I'm sure you've done your own online search:

http://www.laspilitas.com/gard...

Seems since your dry-rock slope has been in place for some years, with the junipers now a much greater presence, perhaps just adding more layers of plants may contain the problem. Or I'm just looking for the quick fix... Best of luck.

Deb ...

What a great site. Thank you for the link.

I know I need to cut the junipers back for fire safety and that is on this year's list of projects.

I think the reason this rock slide occurred was because the slope was very, very dry and then very, very wet.

I think planting native sedums and crevice plants between the rocks when I reface the slope will, in the long run, make the rocks more secure.

Yeah, I do need a quick fix. I have too many projects for one woman and they are all maintenance projects, not the fun stuff of planting.

....

Smiles,
Lyn

>> The slope is primarily rock with a thin crust of soil.
Great link, Deb! I never knew grass was bad for a slope (and I still don't know WHY).

>> The slope is primarily rock with a thin crust of soil.

Ahhh! Then you probably are already safe.

At most, if you have time and energy to spare (what gardener ever does?) you might split the current wall into two shorter walls with a 1 foot wide terrace between them. And "lean them back" as you re-stack the rocks.

I had to give up on a manufactured home with a GREAT view because the many wooden ties that WERE holding up a huge slope in many small terraces, were all rotting away to sawdust.

That same slope, though, had a great irrigation system on a timer. A few very small hoses going up the slope, with spaghetti tubing going to each (expensive-looking) bush.

I'm sure it would be better to use locally-adapted species, but that slope LOOKED great. However, in a few years or decades I think it was going to sweep the house with it as it slid downhill.

Ahhh! Then you probably are safe. I had to give up on a manufactured home with a GREAT view because the wooden ties that WERE holding up a huge slop were rotting away to sawdust.

Rick ...

>>>>>Ahhh! Then you probably are already safe.

At most, if you have time and energy to spare (what gardener ever does?) you might split the current wall into two shorter walls with a 1 foot wide terrace between them. And "lean them back" as you re-stack the rocks.

We'll see how it goes. When I was painting the woodshed, I had to practically re-build the rock wall behind it to keep it from falling down on me. I did something similar to what you have suggested. It was the only way the rocks would stay put ! Of course, I had never had to fix anything like that before ...

Smiles,
Lyn

>> It was the only way the rocks would stay put !

That was my thought. lean them, or pour concrete around them. I wonder what backfill would be best?

@RickCorey, Rick ...

I don't think concrete is the answer because I don't want to change the drainage. When it stops raining, I'll go out and take another look. I do think erosion control has to be a part of the solution. I just haven't figured that part out yet.

I don't think I'll need to do any backfilling, because as I said before, I think these rocks were just kind of a facing to the slope in that area. I think I need to make a wider base and then follow the slope up with the rocks, but I do think I need to wedge in some smaller rocks along with some alpine plants to hold the rocks in place to avoid another rock slide.

I have to tell you, I am getting tired of hauling rocks up from the street level ...

Smiles,
Lyn

>> ... these rocks were just kind of a facing to the slope
>> I think I need to make a wider base and ...
>> ... wedge in some smaller rocks along with some alpine plants

It sounds like you know exactly what's needed. Great!

This is the best place I know for perennial alpine wildflowers:
http://www.alplains.com/

Rick ...

Thank you for the link. I like the fact that he reports where he collected the seeds and the elevation they were found. A geologist friend had told me that often people plant "alpine" plants that thrive at higher elevations and in other alpine areas that are never vigorous or healthy at my elevation simply because the plants don't get enough chill hours here that are found in the areas where they are native plants. That will help me as I seek the "right plants" to use on the slope.

I am also going to copy the technique Mrs. J used on another slope on my property to hold the stones in place while the plants matured. She used chicken wire to anchor the stones in place until the plants grew through the stones and wire.

I might even just use the creeping or prostrate juniper she planted on a different part of the slope because I know it has a deeper root system than the sedums I first thought about using. I know that plant works in this climate and in my soil.

I am seeking functionality more than I am looking for new plants for this fix.

I never water the junipers during the dry season and they are thriving. I don't want to be watering this part of the slope, so it's something to think about.

Smiles,
Lyn