Oversize Particles in Borrow Material

[martin888888]

We have a maximum 3' fill area that we area calling out maximum 12" lifts and that the material shall 100% pass a 4" sieve. The fill material will come from a granular onsite pit.

Since we are calling out in our spec 100% passing a 4" sieve I am assuming they would be required to pass all material through a Rock Screen in order to meet this criteria? Would oversize particles generally be allowed?

Since the 4" spec is called out would there be any rock correction neccessary in the proctor?

 

[Ron]

If you have particles greater than 3/4" in size, there will be a correction needed when the Proctor is done.

I hope that your specification also has further direction on the grain size distribution on particles passing the 4" scalping screen. What happens if all of the material passes a 4" sieve but is retained on a 1" sieve? That type of material would not be good for fill as raveling of finer particles would occur.

Preferably, your specification would state something to the effect of all material shall pass a 4" sieve and shall be consistently graded from that size to dust.

 

[martin888888]

Yes, there is much more to the spec then that, it was jsut the basics of it to get my point across.

As far as the correction part of my question, even though the proctor test material will match what is used in the field (since its being screened) there is still a correction factor involved?

 

[cvg]

means and methods for producing borrow material meeting the specs are up to the contractor. they may choose to screen if there are a lot of cobbles in the borrow pit. You may ask them to dig in another part of the pit and find finer material. If there are only a few large rocks, you might accept the material. It all depends on what the end purpose of the fill is and how many cobbles you have.

 

[martin888888]

Right, as long as they meet the spec and get compaction it is up to them. So it sounds like a correction is needed in the proctor at all time material is greater then 3/4"

 

[JTRdirt]

The sample you have collected for the proctor will have material from dust to 4" in diameter - but when performing the proctor test, all material larger than 3/4" is screened out (The test is only run on material finer than 3/4").

After the test is completed, a correction factor is applied based on the percentage of oversized (larger than 3/4") material. If I remember correctly, the oversize correction only applies if there is greater than 5% oversize and less than 30% oversize.

 

[martin888888]

The sample they take will be from the pit and not necessarily after the contractor screening, so material can be larger then the 4" (in your "dust to 4" comment)

 

[cvg]

I suppose to be completely accurate you should screen your raw pit sample to remove the larger than 4" rocks first. Then screen out everything larger than 3/4 and use that quantity to do the rock correction.

 

[Dozerman56]

It kind of depends on the rest of what your specification says. If you tell the contractor to use the on site borrow source, have you ascertained whether the material meets the specification? If not, have you clearly stated that any processing necessary to meet the specification will be at the contractor's expense? If the material is substantially in conformance with the specification, is it good engineering economy for the owner to plan on spending another $1.50 - $3.00 per CY to pay the contractor to screen out an occasional 6-8" rock?

 

[cvg]

it hardly matters whether it was specifically called out, if the spec requires 4 inch minus material from the pit, so be it. Contractor should have planned on bringing in a grizzly. End of story.

Now, if you want to partner / value engineer with the contractor and you decide that a few 6 inch rocks are OK and resulting in great cost savings which will then be split between the contractor and the owner - than it is a win-win situation.