Constructing gravel road on the side of a hill

[Roadwarrior]

I am currently in the process of designing a gravel road to go across and down a hill to allow access to a cottage below. The road will be approx. 150 feet long. The combined road slope will vary between 5:1 (run:rise) and 10:1. The hill being traversed has between a 5 degree slope (middle and bottom) to a 45 degree slope at the top (10 feet from the crest). I plan to escavate the hill at the top to give a maximum slope of 2:1 (run:rise) on the side of the road. The hill base material is clay while the road goes through a forest. The road will be half cut into the hill and half back filled to give a 5 degree slope into the hill. A ditch on the hill side will drain water to one of 3 culverts which will run across the road at 50 foot spacing. I plan to plant the hill with clover and the ditch with tall fescue grass. The ditch will also have rip rap in it at key locations to limit water velocity. The gravel road is intended to be 6 inches of pit run gravel at the bottom and 6 inches of stone dust as a top cover. An alternative is 1" to 2" crushed stone as a bottom layer (triple the price).

Does anyone see any risks with this approach?
Are there any good resources available with regard to gravel road construction?

Any comments or concerns may save me big bucks down the road so any comments are appreciated.

Regards,

Roadwarrior

 

[ishvaaag]

All sounds quite good. Your slopes are low. The clayey base will make that the selection of natural gravel or crushed stone be indifferent; will nail unto the clay base.

Maybe my only suggestion is that tha base itself warn off waters, being quite impermeable you will have soon an almost dry road once the rain has stopped.

 

[grafter]

What geotechnical laboratory testing have you undertaken to confirm the soil parameters and your design? Have you determined the location of the groundwater table? Have you carried out slope stability analysis to verify your design?

These are the risks in your approach!!! You need sound geotechnical advice before embarking on such a scheme. What you have designed appears satisfactory subject to confirmation of good SI & Lab Test data. You should consider a geotextile separation layer between road formation (clay) and gravel to prevent punching and loss of material. Contrary to Ishvaaag's comments you must classify the 'clay' strata. If it is a clay of high plasticity it will wet-up and soften over time on contact with moisture, hence more the reason for a geotextile separation layer.

Regards,

Brendan.

 

[ishvaaag]

Certainly what grafter advises is better. It is always good to have proper geothecnical assessment and this prpject seems without doubt of the size entirely justifying it (big bucks are referred in potential failure). The risk referred by grafter of the clay being too soft is very understandable seeing the low slope the hill has at the base, and so one can not be safe on the rod not sinking in hte base. So my comment was mainly in the sense of that I saw in what said a number of good practices implemented, not in that what said gathers all the requirements of such road might ideally require.

It is obvious in the question that the aim to avoid expenses even on the design side is extant, as in the fact of designing a gravel road, and maybe even some risk of local damage. Even state designed and maintained roads sustain local damage so one may understand some particular owner thinking why he should better do.

Yet in any case good technics is good technics.