Oversize Particles in Fill

[rkbengineer]

I have a project going in where the contractor is placing onsite fill material for a permanent quarry haul road. Unfortunately the contract and specifications do not limit the particle size (usually taken as about 3"). The material is generally very good, but has quite a few cobbles in it. Their sizes range from 3" up to 12" and are visually estimated at 25% to 30% of the total sample. The material gradation was only performed on the material passing the 3" sieve and shows 32% to 44% retained on the 3/4".

I am trying to use the ASTM documents referenced in the specs to enforce a maximum particle size of 3" to 4". ASTM D2922 and D1557 both refer to D4718 for oversize particle correction. D4718 puts the ...upper limit of oversize particles at 30% of the plus 3/4" material.

My question is whether there is an upper limit on particle size in addition to the percentage. I need something that I can use contractually to enforce this. This will be clarified in the next phase of work. Any help will be greatly appreciated.

 

[VAD]

It seems that you are concerned about compactionof the fill. The georgia Department of Transportation has on line some specs that deal with oversize particles outside the range that is in the ASTM specs. There is nothing really wrong with using sizes up to 12 inch. It is tough to limit particle size if it is not in the specifications. Good assortment of sizes makes agood roadbed.

 

[rkbengineer]

True, but not if you have the larger 8", 10" and 12" cobbles in a 12" lift. The compaction roller can bridge from one rock to the other and leave the soil in between uncompacted. There is also the concern that the nuclear densities are providing skewed results from larger rocks just below the surface.

The fact that the max particle size is not in the spec is beyond my control. I still need some guidance on how to utilize the ASTM's that are referenced to enforce this.

 

[LCruiser]

First off, who's going to use this "permanent quarry road"? Next 30% isn't that much, unless there is truly a problem with compaction of smaller lifts. The roller can shove larger rocks into the previous lift, right? That said, are you sure there's nothing limiting larger pieces to 1/2 the thickness of the lift? Any reference documents? The biggest thing is to make sure you in fact have a problem. I'm not sure you do.

 

[VAD]

In the meantime as you debate, the contractor is presumably constructing the road. If you are so concerned about the max particle size then you should halt the construction operations.

If you are confident and like confrontation then go for it. You would probably have to decide who is going to pay for the Contractor's downtime. If you are certain that you can get him to accept the cost then more power to you. If you like to battle with claims and are gungho go for it.

The above is the fight mentality which believe it or not has to be part of the qualification of any resident or inspector in the real world.

The other approach is to discuss the issue with the Contractor, explaining your concerns, listening to his and try to come up with an approach that would be to the benefit of the product and to both parties.

In some instances we are faced with using other methods to evaluate compaction given a particular situation. While it is always nice to have numbers to show, visual observations such as observing the grade movement under the scrapers or loaded trucks along with some selective testpits can provide confidence as to the state of compaction and state of packing.

As Lcruiser asks who/what is going to use the quarry road
Is this road going to be paved etc are some of the issues that could allow you to make decisions. Have you explained the situation to your Client or Owner. If they are behind you then put the on pressure on the Contractor. Let them know that they may have to pay some extras.

I am not sure how ASTM can help you in this situation.

 

[GeoPaveTraffic]

VAD has given you some good advice. I would just add that ASTM specifications are NOT construction spectifications and you should not try to use them to make for a poorly written construction specification.

If you feel very strongly that the "oversize" material should not be used, talk to the owner or your client and see if they want the extra expense of changing the construction requirements at this point. Because the contractor will be entitled to extra compensation if you change the requirements once a contract has been aggreed upon.

 

[emmgjld]

Our area has large amounts of River Cobbles and this is how I have dealt with this problem in my own recommendations and specifications:

The imported structural Fill (Hveem-Carmany R>50 , swell not critical) is to be Granular, Medium to Coarse Grained, Very low plastic (PI<4), Non Freedraining, Compactable and within the following Gradation:
Maximum size, by screening 8"
Passing the #4 screen 20% - 85%
Passing the #40 screen 10% - 60%
Passing the #200 screen 3% - 15%

The maximum aggregates size may be exceeded if the contractor can provide evidence of proper compaction of the matrix material while avoiding excessive particle size segregation of the fill material or avoiding excessive overworking of the subgrade soils.


I should note that the cobble size is oftentimes up to 12"
and we have had very few problems with properly constructed fills with the larger cobbles in the 28 years I have been working here. I need to emphasize the 'Compactable' criteria, as this has proven to be the Giant Killer. This item and 'probing' during the performance of the density testing is important and the testers/engineers must be firm and CONSISTANT.

In addition, I include this note on our density test reports.

Nuclear Density Testing of ‘pit run' or other coarse grained soils may require correction of Unit Weight And Water Content, ASTM D-4718. If soils contain oversize particles in excess of the limits of ASTM D-4718 Nuclear Density Testing is performed for acceptance control and is combined with visual and penetration methods.

 

[DRC1]

Large pices do make the compaction more difficult and left near the surface, will create "hard spots" ion the pavemnt wich can lead to cracking. I would talk to the contractor. True the material meets the specs, but will it give the owner what he wants? Most contractors will pull out some of the really large particles. If it is a quarry road, and esp. if it is unpaved, I think you will be okay. I would give the contractor a spec for the top 12", even if it is a change in contract, for compacted gravel no cobbles.