How durable are roads on sidehills/steep slopes?

[airbiscuit]

It's not an issue that I have, but I am curious. I enjoy reading the threads about people making roads on slopes and sidehills. I see in my own small hills how damaging erosion can be, and the need to be vigilant. A small problem can get a bunch worse real fast if left unattended.

So my questions about roads on sidehills/switchbacke. steep slopes are?

What methods do you use to minimize erosion (inward facing ditches, water bars, french drains, etc.)?
..... What happens if those systems fail or are overpowered by an intense storm?

Are there any ground stability problems with sidehill roads/switchbacks?
...... Is there potential for a portion to slough off if the ground becomes over saturated?

I know there are lots of these roads out there, but is it possible to have ant that are maintenance free, or conversely, no matter how well it's built, there's always potential for damage/failure?

 

[Jstpssng]

Any road is going to require maintenance, it doesn't matter how well it's designed and built. Old Mother Nature can't stand a static environment.
Even if the road bed doesn't blow out completely, the fines eventually wash out of the gravel and it will need to be resurfaced. Look at how much work, time, and money the various DOT's spend redoing roads every year. All that asphalt really does is create a barrier so that the gravel doesn't wash away as easily; but do you have frost heaves in Wisconsin even on your best roads?

 

[Egon]

It all depends. Some last longer than others.

[video]https://www.ancient-code.com/40000-km-long-ancient-inca-road-system-extraordinary-feat-ancient-engineering/[/video]

 

[airbiscuit]

We are already seeing some frost heaves. My own 1//2 mile road doesn't have big hills, but any erosion or standing water can quickly become a problem. I was just thinking those problems are amplified in steep slopes and wonder about serious failures.

 

[MossRoad]

A lot of it depends on the angle of repose.

from here:
A review on the angle of repose of granular materials - ScienceDirect



If you cut across a material that is already at or near the angle of repose, it's gonna collapse. If the slope is less than the angle of repose, it's possible to cut across it and still have the material above the cut be less than the angle of repose.

Water soaking into a material can change its angle of repose (think dryer concrete VS watery concrete) and it'll then give way.

Water running across a material can wash it away as well, which also changes the degree of the angle of repose.

You can build structures to anchor into a steep slope and then backfill them to make a level path on top of the structure. You'll still have to contend with water, frost, etc.... all that stuff.

When I was a kid, we lived at the top of a 90' escarpment going down to a lake that was greater than the angle of a repose of the soil. However, it was heavily wooded and the trees and shrubs anchored the soil. My dad built steps out of broken chunks of sidewalk concrete, usually in 12-18" slabs that he stacked up on piers dug into the hillside. Many switchbacks, piers, retaining walls, etc... but every so often, one of those large trees would tip off the bank, take it's roots out with it, and then the soil would collapse down the hill. More retaining walls and repairs to the steps on an almost annual basis. In a nutshell, it was not a good place for that type of staircase. He'd have been better off sinking deep pilings into the slope and building wooden steps.