Quickest way to check road base material follwoing rain event

[nagatalluri]

Guys

Good Morning. We are working on access roads for a wind project in Oklahoma. The contractor is using a different material than the one specified in spec. Following a rain event, the road surface looks muddy and slush. Is there a quickest way to check road base material like pocket penetrometer for soil to assess the quality of the road base material?

Your suggestions are highly appreciated

Thanks
NT

 

[oldestguy]

Apparently you are concerned about meeting a spec for gradation. You provably did not spec shear strength or similar usage criteria. Then, a quick test of gradation is micro wave drying of sample, and a dry sieving to roughly check, but a wet sieving and quick drying may be required to be sure. Driving on it probably not good idea, since you probably did not spec a usage requirement.

 

[cvg]

you really need to verify more than just gradation
[ul]
[li]was the road crowned[/li]
[li]was the gravel compacted[/li]
[li]how was drainage handled, any culverts or ditches[/li]
[li]was subgrade scarified and compacted[/li]
[/ul]

 

[nagatalluri]

Oldestguy

Thanks for the input, the road is to be used as an access road for a wind project for turbine deliveries and site construction during the construction of the wind project. During construction the traffic will be heavy with the concrete trucks moving and other wind turbine carrying trucks and construction traffic. later it is to be used only for access.

Based on your experience is there a quick way (like we measure the shear strength of clay using pocket penetrometer), is there a quick check that we can make for the aggregate material.

Thanks
NT

 

[oldestguy]

Considering you may be stuck using what they supply, you need to know that the thickness is suitable for the loads. I frequently have decided that based, not on a theory, but on a field test of a typical, or marginally as good as the average area. What we do is prepare a typical area with a tapered varying thickness of the base material. Place it and compact it. the we take a fully loaded dump truck and drive it on the test area, sometimes back and forth, observing deflection under the effect of the heavier axles. Also look at ruts developed and generally OK a rut not more than one inch deep. Then we take the thickness of the area that "passes" and that is used for the whole job (generally used for commercial parking lots in these cases.)

In your case, you may have some weaker subgrade places where a greater thickness may be needed. I'd also be prepared to add base where I see the traffic is deflecting too much and there may be bad rutting.

You may even decide to undercut obviously bad areas and replace that thickness with base, adding above that the "design' thickness base.

If there is going to be a lot of repetitive heavy traffic, you may decide to go a little thicker than the "test" area "design". Repeated loads on some areas (usually silty soils, saturated) will cause a build up of pore pressures, leaving a much weaker subgrade result. Wait until the next day and all is OK, until repeated loads come again.

In some cases the added "repair" base material is a much coarser breaker-run quarry rock to soak up the softer base material.

Before doing the test, see if you can just add a layer of that coarser material to see if that thickness can be used to salvage what yu now have, instead of more of the same (failed base type).

One one job I was on the coarser stuff was reject bricks from a brick yard. However, that got stuck between the duals of the trucks.

Be sure the base roadway is sufficiently wide that shear failures off to the side don't occur.

 

[BigH]

Firstly, why is the contractor using a different material than that which is in the specifications? If so, he is non-compliant. HE should be the one to prove, if you have an idea of accepting his materials, that the road base is suitable and acting accordingly.

Oldestguy has good discussion on what you can do - forgetting the contractual arrangements. Without knowing your subgrade, the basecourse material and the like it is not possible to really offer more than general commentary. You could do a benkelman beam test - which is a deflection test - to determine the road base's behaviour under loading and then "top up" with extra granular - but the driving of heavy trucks looking for rutting might be more expedient.

Did you think of adding a geogrid? this might be possible if the road is not behaving good under its current thickness (and this leads back to why the contractor is using non-compliant material). I would consider adding if you will top up with granular.

Is the road going to be used permanently?

 

[oldestguy]

Big H has a good idea for a permanent road, but not temporary. you don't just put it down and cover. You design it. Depending on what the geogrid or fabric has for strength and depending on the base course shear strength is, an under design will result in fabric or grid failing. There one might also use a field test and then be conservative as to cover thickness.

 

[BigH]

OG - many temporary platforms for oil rigs and that are designed with geogrids (not fabric) . . . of course, all has to have the correct thickness of granular, too.

 

[nagatalluri]

Guys,

I really appreciate your feedback on this issue. This gives me some insight. Another question I had is that the contractor is proposing to use 4" road base material (based on the anticipated traffic volume) and the rut depth considered is 3" as per AASHTO design methodology. Do you think considering 3" rut depth makes sense. What is the practical rut depth considered for soils in Oklahoma Panhandle ? or in general.

if 3" rut depth is normal, what happens to the road with a base material of 4", there is only 1" material left after rut.

Thanks
NT

 

[dicksewerrat]

Get a different contractor. His bid must have been .4 of the next one. You will have a permanent road and the windmill parts are heavy. May have to redesign the road.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com