How to slow down road / trail slippage

[Doc]

My main road / trail leading to the river was out all last year. Last fall I had a bulldozer in and he fixed it up nice. It has already started slipping again. Same place as last time. It is barely wide enough for my RTV to get by without driving on the slipped area. I have plans to pull a few trailer loads of treated wood to the river to build a bunch of new docs and am concerned about the slip getting worse and causing an accident. This road is cut into the side of a hill.

I'm thinking of driving some 4x4's into the ground on the outside edge of the slip, but looking for other ways I might slow it down. I know you can't stop mother nature but I hope to slow it down enough to keep the road passable for a few years. It lasted 14years until the slip last year.

Currently the outside edge has dropped 6 inches and is about 12 inches wide. I would put the 4x4's outside of the 12 inches and fill in the six inches with some rock. Any other ideas?

 

[California]

Here's a couple of thoughts that you might include in your solution:

Earth slips because its saturated. So consider burying perforated drain pipe along the uphill side of the road, or at least make a ditch on the uphill side that drains to a point that is harmless.

3/4 inch rock along the downhill side of the roadway will get imbedded as you drive over it and can drain better than pure soil. This also might help stabilize the bond between old steep topsoil and new fill that was placed over it by the bulldozer.

In addition to these drainage ideas, I agree you need some kind of anchored retaining wall in spots that could be dangerous.

 

[Doc]

Awesome info CA.
I will try to get some pics of the area in the next day or two and get further thoughts on how to drain it best. You made some very good points.

 

[Doc]

Raining here today but I was able to go down to the area and get some pics. I walked it and viewing it slowly from all angles it does not seem as bad as when trying to drive past it.

Here are some pics to give you all an idea what I am talking about.

First some pics on my way to the slip. Pic two is not the slip, it is the creek, solid rock where I cross there.

 

[Doc]

Some more. The thing that looks a little like a golf green at the end of the road is the river lot (last pic in this post).

 

[Doc]

Also afraid of losing some of the trees on the edge of the hill on the up side of the road. View up hill from the slip. Last pic is of the river from the slip.

 

[20/20]

I would dig back into the high side some, level things off, possibly put a ditch or some sort of drainage in, with an occassional cross over pipe. On the down hill side some locust logs placed in the ground may help, rip rap, or even plant some type of trees/brush. It's hard to exatly see what is going on and how much work you really need, but the pictures do help. You could also put road/driveway cloth down, comes in rolls.

 

[California]

Doc, your place looks gorgeous.

I think you need to talk to a soils engineer for advice. Sometimes a professor (engineering, in this case) will advise for free if its just a phone call. Your soil conditions are probably the same as everybody else fronting the river for miles and there likely are local standard remedies for slumping off.

Just a hunch but I'll bet the fill is shearing and sliding at the lamination where it rests on the original topsoil.

You think you got problems! Did you read about the Kennecott copper mine in Idaho?

 

[Doc]

Thanks 20/20 and CA.
Good thoughts. Right now I'm looking short term. I have had Dept of Ag Forestry folks here and they have provided reports on how to manage the trees for best results. We never talked about trail slippage. Good idea to contact them and ask what they recommend.
For now I think we'll try out muleys suggested solution over on FF. It is much similar to mine, but he suggested driving 5 or 6ft sections of rebar in about 10 inches to a foot apart along the slip. His suggest was 3 rows of support and that differs from my one row of 4x4's (which are much harder too drive anyway.
I want to be able to get the wood down that trail next month and not much time to do anything major tween now and then. After that I will work on a more long term solution.

 

[Doc]

I've opted to try Muley's idea of driving in 5ft stakes of 3/4" rebar in the area in hopes that will pin the dirt to the bottom layer that has been in place for years. Like was pointed out, it is probably the new dirt that was bulldozed into place last fall is settling and the ground under it is most likely staying in place. The stakes of rebar might hold it all in place, plus I'll add some gravel to the area to help with drainage.

I have the rebar and a post driver all set to go. Plus I have some younger backs (SIL's) coming here to help drive the 24 5' rebar stakes. With a little luck the slip should be under control and passable this weekend.

 

[bczoom]

Are you going to keep the top of the rebar exposed or bury it deep? Assuming you're going to keep it off the driving section, I'd leave it exposed then take a 4-6" log or something and have it lay against the rebar on the trail side. The log will help stop erosion.

 

[Doc]

I had planned to do just that when I was going to drive 4x4's in to hold things. The rebar idea will let me drive more of them in, in multilple rows (3 rows of 8). I had not considered that yet, but it does sound like a good idea, and a good reason not to drive the 1st row of rebar all the way in. Maybe I'll leave all of them up a bit. Just hope they don't end up hurting someone IF someone rolled a 4 wheeler right there. Hmmmmmm yet another consideration.

 

[California]

maybe pre-drill the 4x4's then drive the stakes down through a snug fit in these holes?

 

[Doc]

I had not considered that CA. Good idea. I might use landscape timbers instead of 4x4's as they are more rounded, just in case someone fell on them.

 

[20/20]

Personally I think your making a mistake playin around with the rebar. That's why I wrote to use logs. Black locust(75yr wood) is the best, and it may be the cheapest, depending on whats in your area. Next choice would be cedar(30yr wood), if neither of those are aviable then go with treated. Leaving a bunch of rebar sticking up, sooner or later, could easily cause some serious dangers, to equipment and/or people. If the problem is caused by water then you need to figure how to help the water run off without destroying your path.

I'm not sure what a lawyer would do if someone impaled themselves on purposely stuck rebar left sticking out of the ground 2-4-6-8inches. If you do go that route make sure you post what is there. I've never seen a trail done with rebar, not saying there are none, just never seen one.

 

[Doc]

Yep, that is possible 20/20, rebar might be a mistake but for now that is what I'm going to try. I do have locust available but getting them in the ground where I need them would be next to impossible right now the way things are.

As someone mentioned I do not believe it is a slip of the entire hillside, but just settling of dirt that the bulldozer moved last fall. I will soon know if my guess is right or wrong. If wrong I will plan a fix with locust posts or build a bridge over the area.

I also plan to address drainage. I picked up 1 1/2 ton of rock yesterday that will be used at that site to help with drainage, and I'm using some perforated pipe and trenching to direct water away from the area in question. Not optimum but I do think it will work. If it doesn't work I will go with the backup plan.

Thanks for your input.