I picked up some land and the access road has unstable ground above it. It has come down and blocked the road a few times in the past.I took a dozen alders off the shelf above and cut back the toe. 30 loads later (close to 400yds) it was looking good. This took my slope from 60ish to 40 something. I had a great shoulder and ditch....for about an hour. I'm thinking of soldier pile at 10' and excavating section by section (60 feet) adding timbers as I go. There is enough 4-5 foot rock on site for ballast at the toe but I think it may blow out. I just have a 135 out there so I can't place anything larger easily. In the photo the upper section held and the clay layer is apparent. The layer moving appears to be reject from an old pit up above that has the grove of alders knitting it together. Any suggestions? If I am just a complete idiot feel free to let me know that as well.
Step one: soil scientist. I'm sure one could educate you well and save you time/money. Soils are different and will need the proper approach for a solution that works. They know what I don't. I would hate to make a big investment without proper planning. Years ago I cut a path into some steep ground. My customer talked about soil securement but I doubt he ever did anything about it. I did some research on these products https://ii-supplies.com/products/earth-anchors/manta-ray-or-sting-ray-anchors at the time. Maybe the StingRay anchors and the correct type of matting might be a permanent cure for what ails your land? But, find a SS first and see what course of action they might recommend first. Then, if the StingRays are cost effective, maybe see if that would work. Nothing worse than watching hours of work be wiped away in a second long unwanted movement of material.
Thanks! Sound advice. I am waiting to hear back from an engineer from the timber company with an easment to their rock pit above the slide. It would be in their best interest to preserve the upper road so we'll see what they come up with. I appreciate your input!
I started my working days as a geologist, working on landslides and such. You need to find the slip plane, (bottom of slide) first. Then anything you construct to hold this hillside back, must penetrate well through that slip plane area into solid ground. A fix could be as simple as some steel pipe/beam piers, set in holes by drilling or driving, and concreted in. These would then hold back the slide by use of timbers stacked behind them like a wall and holdbacks as needed. Whatever you do here, a geologist/soils engineer needs to be involved to do it properly.
MM beat me to it. Basically the in place soil is over it's angle of repose (to steep) and you either have to design a hold back system or reduce the angle - IE cut the entire slope down. The current angle is too steep and that material will continue to slump until it's below the soils specific angle of repose. What that angle is and what it would take to retain the slope is beyond my pay grade as I lack those capital letters after my name.
Scoop from the high side, dump on the low side. Sooner or later the slope will be gentle enough.
Since the slope is fill rather than natural the task is much more difficult and less well defined.
If the OP has the extra property on the down hill side, the equipment and time he'll find the right angle.
Thanks for all the input! While the property extends below there is a county road and right of way that prevents shifting the slip layer down there. I had to truck it across the road. The I beams and timbers (soldier pile) is still looking like my best bet but again, waiting on an engineer. I'll have to get a drill rig up there for a well sooner or later so I will try some 4' rock as ballast at the toe tomorrow with minimal material removal. I am curious if I would be better of removing the trees all the way up as they are moving with the slide. Here is the top of the current movement, though there is clear evidence of past shifting above.
8" wide flange beams, 9' in ground @ 6 foot spacing. 6 beams to go and tons more timbers. Engineer was a no show so yeah, I'm winging it. Used a hoe pack to vibe in the I-beams. We'll see if they all fold over when it moves again.
I'm for sure interested in what a soil engineer comes up with on this. So many places the hill/mountain areas are overburden on top of structure, whether by eons of nature or by result of man, making the slip plane. Enough material at the toe provides a bulwark to prevent things from going sideways. And often enough, when man makes a cut in that undisturbed settlement to make a road, whether it's an interstate highway or a driveway, **** goes south, or, downhill. A sometimes contributing factor to this is underground water between the overburden and the slip plane. That water both causes hydraulic pressure on the overburden as well as lubricates the contact of the overburden with the slip plane. Take away the bulwark at the toe keeping it all in place and now it's being shoved downhill on a greased skid. I spent 7 years traveling all over the USA operating a drill rig to install horizontal drains just for that purpose, drain water that exacerbates the problem of overburden sliding off a slip plane.
I am in complete agreement. We had almost 4" of rain in 48hrs. The area moved again and the wall section held. Lots of water exiting the drilled lower beam of the wall. Flow subsided after another 48hrs. Drilled a well above the area yesterday. 30 feet to bedrock, sandstone layer at 180 for 60+ feet, back into good rock and finally hit a 60gpm aquifer at 340'