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Re: Gravel Road - wearing course

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Hello Marc,

I was once told a general rule for roads from and old transportation
engineer.  It's like the one for real estate.  It goes like this: Drainage,
Drainage, Drainage.  The Class 2 material has clay in it which makes
it bind but doesn't allow it to drain, right?  What happens to this Class
2 material when it's saturated and you put a heavy load over it?  Will
it pump?  I could see this being a good material with drainage layers
to protect it.

As a second point, I wouldn't want to use a gravel road for something
that steep.  Around here the fire marshall will not allow anything over
10% to go unpaved.  Trying to get a fire truck up an 18% grade covered
in gravel and with the possibility of the base pumping while trying to
climb that hill does not for a quick extingushing of a fire make.

The DG will likely provide a good compaction and allow for better
drainage than the Class 2 material.  I would maybe try to talk the
client into a roller-compacted concrete for the road.  That will
provide the load capacity and wouldn't have to cost as much as
pavement.  He could put that on as a wearing surface over the DG
or the Class 2 material.

Good luck,
Lloyd Pack, P.E.

On 15 Jun 2011 at 6:06, Marc Mitchell wrote:

> Folks,
> We're building a 1/2 mile gravel road (client does not want asphaltic
> concrete) up a relatively steep incline (10~18%).  We have a local
> quarry that supplies a 3/4" downgraded crushed rock that I've used in
> the past and liked - it's got a good clay component and compacts well
> - it meets Caltrans Class 2 gradation requirements and this is the
> material I consider to be best suited for the application.
> The contractor disagrees completely about using a Class 2 base and
> wants to use either a local pit run shale material which is
> considerably cheaper or, as a better option (in their opinion), a
> decomposed granite.  The contractor tells me the Class 2 would be the
> worst performing option in the long term.  They're an experienced
> engineering contractor and I trust their judgement, but in this case I
> cannot convince myself as to why DG would outperform a 3/4" minus
> crushed rock for a gravel road - but I also do not have first hand
> experience with using DG for a gravel road.  The area gets about 30"
> rainfall per year and the road is traveled by slow moving vehicles.
> Do any of you have any experience and/or opinions regarding the best
> aggregates and gradations for a steep gravel road?
> Regards,
> Marc Mitchell, P.E. 

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