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Re: Gravel Road - wearing course

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Thanks for the response Lloyd.  I wouldn't expect  ~6% fines in class 2 would pump much based on its own gradation, but maybe with a poor subgrade.  Your point about the fire protection is well taken, and we have the same requirement where I live - but happens to be moot in this specific case.

Here is an interesting read published by a DOT: 
http://water.epa.gov/polwaste/nps/upload/2003_07_24_NPS_gravelroads_gravelroads.pdf

The reference above suggests using more fines and a higher plasticity index for a gravel road surface than for a base material such as class 2 - this requirement is specifically for binding the aggregates together.

Anyway, we're going with the DG - I've had two engineering contractors tell me that class 2 will often unravel the larger particles from the fines when used as a road surface.

Regards,
Marc

On Jun 15, 2011, at 8:34 AM, Lloyd Pack wrote:

> 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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