I need both the voice of experience and engineering brains here. I'm going to have to put a loong driveway up a hill which has about a 22 degree slope. When I say driveway, I mean a very primitive farm road type of trail, very simple, and I have no intention of it ever being used by heavy equipment...a very occasional loaded 4wd pickup would be the biggest vehicle, and the rest of the time it would be minor ATV, bike, or foot traffic only, and there won't be any hay trucks, well drilling rigs, or septic tank pumpers so please don't argue with me about this. The nearest fire station is 125 miles away so emergency vehicle access isn't a consideration. The hill has about 7" to 1' of topsoil, beneath that is rock. I don't want to dig perpendicular to the slope, especially in the two closely parallel lines of a switchback for fear of slope failure. There's a highway at the bottom of the hill and as you can imagine a landslide would be unspeakably horrible. Something on top of the existing soil that would allow water to pass through, yet slow soil loss, and let the road's surface still be reasonably good, is my goal here. Maybe two layers of wooden pallets? So what I'm shooting for is something that won't worsen erosion, preferably even something that would slow erosion, and something that wouldn't become a massive drainage problem, and a big built up dam-like road is not an option financially. I'm hoping to get these benefits by intelligent shape design and maintenance of existing vegetation along the path rather than expensive materials. I realize that a road shooting straight up a hill is bad for several reasons, the main thing being drainage. As far as switchbacks go, it sounds like they do well at erosion and drainage control only if they are industrial strength, since otherwise they have massive side pressure from the slope. The other option, and as far as I can see the best one, is a road shaped like a "C", or in other words just ONE large, extended switchback rather than a series of them. Or how about a straight but diagonal road up the slope? I'd really like some advice on this. Thank you.
As for a roadbed we used 1 1/2" river rock. This is the stuff a lot of people use for landscaping. It grows naturally around here so is inexpensive. It looks nice in the woods and packs down great. Then the grass can just grow up through it and hold it all together. We only put a couple of inches down over forest dirt. Then drove on it and put more where needed. We have had concrete trucks, well drilling rigs, lumber trucks,etc on it at all times of year with no problems. As for the uphill road I think I would tend to go with a diagonal uphill. Any time you have a curve in the road it causes your differential to work which will lead to a loss of traction if it is slick.
A couple questions come to mind...... What sort of climate/conditions do you have? Snow? Lots of rain? Also, what do you mean by "Loong"? My drive is not quite 2,000 feet. Some people I know consider that short and others consider it long. It's still within the range of putting down gravel. It's a straight shot up a hill (there's one small jog in it) that's got a fairly steep grade. I can tell you that it gets fun when it is packed down snow/ice. Keep moving up it and keep traction. I've seen a company that sells these concrete forms (kind of like a honeycomb) that give traction and allow grass to grow in between. I'm sure they aren't cheap though. Mike
We have a construction background. You'd probably better check with a civil engineer. In California you cannot cut a driveway into anything beyond 15 degrees -- obviously at 22 degrees you'll have to go diagonal. Since you've got a highway below and potential for legal issues in the event of mudslides, etc I'd strongly urge you do have stamped engineering plans just in case anything happens. Unengineered driveways that cause problems could lead to the state/county billing you for the clean-up. BW
Based on the information given, I'd put crushed rock (instead of river rock) on the driveway - its edges tend to dig in and stick better on strong slopes. Also, I'd put down a three inch size at 1 rock layer thick. It will imbed in the soil and carry the weight without moving around like smaller rock. Its slightly more bumpy than gravel. If you don't like the slight bumpyness then add a rather thin spread of base (limestone fines) or even agricultural lime to smooth out the ride. If not limestone, then similar approach with other rock. Just my opinion.
