# Building a retaining mesh on a 100' hillside?



## cwolves (Jun 1, 2010)

Let me preface this by saying this is not my area of expertise, I'm just trying to help a client. I'm looking at a house that has a ~100' wall hovering behind it. The house has been on the market for over a year and has apparently had issues with rocks falling on to the house / into the bedroom windows at the back of the house.

I'm looking for a bit of expertise from anyone that's had experience building a hillside retaining mesh so I may be able to accurately quote this, or accurately pass the job off.

A retaining wall is out due to the proximity of the hillside to the house and the sheer height of it.

From what I gather, the process of building a reliable retaining mesh includes:
- anchoring rebar into the hillside
- attaching a mesh to it

So my questions are as follows (again, NOT my expertise):
- How far, and at what direction do you anchor into the rock? If more than a couple feet (I'm estimating 15' anchors), how do you drill that far?
- If the anchors are non-vertical, how do you anchor rebar into stone?
- I'm looking at having to cover 3,000 vertical sqft of rock with mesh. What material is used? High strength plastic? Steel mesh?

Thanks for any insight as to where to start to tackle this problem.


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## cexcavation (Apr 17, 2008)

Your question might be better posed as how fast should I run from this job and how far!!!!:laughing:

On a serious note, if you have rocks falling on the house, you likely have an unstable hillside. Granted, critters walking around, wind, water, etc. can cause some movement, but ultimately a screen mesh is not going to "hold" a hillside. The mesh will stay on top of the hill as it engulfs the house when it lets go. 

I see houses built like the one you describe, and it amazes me that a group of people got together and agreed that it would be a good idea to place one of their most prized posessions at the base of a compromised slope.

Even with geological studies, engineering, and lots of cash, there is no guarantee on what that hill is going to do. 

Just my opinion:thumbsup:


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## cwolves (Jun 1, 2010)

Thanks for the response. I'd normally agree with you, but this case is a little different. Again, this is not my expertise, but I have been climbing rock for 15 years and this actually seems quite stable. It's a very solid limestone mix at approx. a 7 deg slope heading away from the house. There is a lot of vegetation on top of the cliff, and a fair bit on the side. I believe that the rocks are coming mostly from root systems pushing them out.

I talked to the neighbor for a short while. His property is about 20' further from the same cliff than the property I'm talking about here and he has a retaining wall. He's lived at the property for 20 years and there has never been a rock slide, but there is a "constant" stream of rocks ranging from pebbles to ~20lb boulders coming from the cliff. He said that the retaining wall has worked for most things but that occasionally a rock will bounce over it. In the 10 years since he'd put up the wall, I'd estimate that there is about 30 cubic feet of loose material behind it, roughly consistant with what is behind/under the house in question.

I'm of the opinion that a mesh that has the intention of funneling stones below the house would do very well due to the stability of the hill, I've just no clue where to even start on such a project or who to contact. I may call a few civil engineers, but am hoping for some feedback from anyone that has undertaken a similar project.


Even if I do end up running from this project, I'd like to be able to point my client in the right direction so that if they do end up undertaking this project they'll be on the right track. They've been a great client over the years.


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## EES (Jan 4, 2010)

cwolves said:


> Even if I do end up running from this project, I'd like to be able to point my client in the right direction so that if they do end up undertaking this project they'll be on the right track. They've been a great client over the years.


Sounds like good customer service, and I think that you start by making them realize that an engineer should be called and that you can more accurately price the project, or give them a referral, based on the engineers professional opinion. If something does go awry, you've made the appropriate effort within your power and expertise to insure that the correct approach and execution was taken in order to provide the best/safest solution. And you should be able to sleep a little better.


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## Rooney (May 5, 2010)

I've never built anything of that sort but I've seen crews using chain link fence rolled out on the slope to protect roads from falling/bouncing rocks. I looked around on google but I couldn't post any pictures because these forums wont site let me yet. It should be easy enough to get wide enough fence to drape the troubled areas. You would have to check with an engineer on how you should secure it properly or someone who has done it before.


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## Kgmz (Feb 9, 2007)

You need a expert at this with the right tools and a engineer.

How are you going to drill and set rock bolts, soil nails, etc. 50, 60, 70 feet up. A properly engineered system for this may require that this rock face be covered all the way to its 100 foot height. Thats going to be a lot of drilling and rock bolts, etc. And the rock bolts may have to be set very deep, 4 feet or deeper. Remember these bolts will also be helping the face stay together by compressing the face, and thats why so deep.

I would bet it will cost more than the house and land is worth. So it might be cheaper to tear the house down and build a new one farther away.

And what you are looking for is called rockfall protection, may help when trying to search companies, etc.


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## tgeb (Feb 9, 2006)

Since you don't bother to mention what continent you are located on, it might be difficult to give you accurate information. 

But there is a guy on here regularly that has done this type of work, maybe he will stop by, and since he is also a mind reader...... he could probably help you out.


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## Kgmz (Feb 9, 2007)

Some more info for you.

The Washington State 
*DESIGN GUIDELINES FOR **WIRE MESH/CABLE NET SLOPE PROTECTION*​ 
http://www.wsdot.wa.gov/biz/mats/geotech/WA-RD612.2WireMesh.pdf


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## Taylor8 (Feb 17, 2010)

> I talked to the neighbor for a short while. His property is about 20' further from the same cliff than the property I'm talking about here and he has a retaining wall. He's lived at the property for 20 years and there has never been a rock slide, but there is a "constant" stream of rocks ranging from pebbles to ~20lb boulders coming from the cliff. He said that the retaining wall has worked for most things but that occasionally a rock will bounce over it. In the 10 years since he'd put up the wall, I'd estimate that there is about 30 cubic feet of loose material behind it, roughly consistant with what is behind/under the house in question.


Rather than attempting something as specialized as rock fall protection, why not build a retaining wall?


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## Boadey (Dec 18, 2008)

tgeb said:


> Since you don't bother to mention what continent you are located on, it might be difficult to give you accurate information.
> 
> But there is a guy on here regularly that has done this type of work, maybe he will stop by, and since he is also a mind reader...... he could probably help you out.


 
:laughing:


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## ch0mpie (Nov 30, 2005)

There are not many companies doing this type of work, and depending on the hieght of the slope custom equipment is required. If you look through my previous posts you can see some examples. PM me if you want to discuss.


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