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nutbutter (Civil/Environmental) (OP)
6 Dec 06 10:07
I'm designing a construction road and I'd like tie-in to the existing grade at a slope steeper than 3:1.  This road is on an industrial site and the side slopes won't need to be mowed.  I was wondering if going to a 2:1 slope would present any problems beyond not being mowable.  Would a 2:1 slope offer less stability for the road?  The road will be subject to heavy truck traffic for about a year.

There were borings taken along the centerline of the alignment and they revealed primarily soft to very stiff lean clay (CL) or silt (ML) with occasional lenses of fat clay (CH).

What do you think about going to a 2:1 slope?  I don't want to add any geogrid or reinforcement mats obviously.  I don't know how vegetation would do on this kind of slope either.  There probably needs to be some form of vegetation to prevent erosion.  I don't know.

Peace,
Stoddardvilla
Helpful Member!  GeoPaveTraffic (Geotechnical)
6 Dec 06 13:28
Yes you the slope would need to be protected from erosion.  Either vegetation or riprap can be used.

What does the geotechnical engineer say about slopes?  How tall is the slope, both the part you are constructing and the parts above/below where you are working?  Why do you think a 3:1 slope will work?

In short we need more information, much more to offer any opinion that would mean anything.
francesca (Civil/Environmental)
6 Dec 06 14:49
Is a terraced slope with some short retaining walls too expensive?

I would not go steeper than 3:1 without supreme confidence in the earthwork contractor and the blessing of a geotech engineer.
gbam (Civil/Environmental)
6 Dec 06 15:02
First, Where are you located?  Is the location in an arid region?  Here in Arizona it is not uncommon to see 2:1 fill slopes, especially in high fill conditions like bridge approaches.
nutbutter (Civil/Environmental) (OP)
6 Dec 06 16:30
What does the geotechnical engineer say about slopes?
I haven't had the opportunity to discuss this with any geotechs yet.

How tall is the slope, both the part you are constructing and the parts above/below where you are working?
The slope will only be about 2-3' tall from the crown of the road to where it ties into existing grade.  In some fill areas, the road will tie into an existing 3:1 slope along the edge of a ditch.  The distance from tie-in to the bottom of ditch is probably again about 2-3' or so.

Why do you think a 3:1 slope will work?
Are you asking why I think 3:1 would be structurally sound?  I guess I don't have a technical answer other than the fact that it is standard and I've never encountered an instance where it won't work.  However, I want to go steeper to keep the flowline in the existing ditch.

Peace,
Stoddardvilla
nutbutter (Civil/Environmental) (OP)
6 Dec 06 16:32
Yes, retaining walls are too expensive.  This is for a temporary construction road.  This project is smack in the middle of the US along the Missouri River.

Stoddardvilla
GeoPaveTraffic (Geotechnical)
6 Dec 06 20:17
For a 2 to 3 foot tall slope, in clays, vertical will be stable for a long time.  Make the slope any height you want.
blueoak (Civil/Environmental)
7 Dec 06 11:02
If it can't hold it it will flatten, but for only a 2 to 3 foot road if you have construction equipment just fix it.
You will probably have more trouble from rutting and rain.

As for erosion, look at a temporary fabric like jute or something, unless you are using road base which you could probably just push on the side and have good luck.  Even in the midwest it is hard to get your grass up in time.

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