Compaction 7

[dik]

We have a drainage layer of 1-1/2" clean stone with no more than 2% passing the No.40 sieve. This is part of a drainage system.

How do you specify the compaction for this type of material?

With the lack of fines, is it possible to spec it using the Proctor dry density value?


Dik

 

[GeoPaveTraffic]

As you have guessed, specifying a Proctor density is not the way to go, however, you see it quite often. A better method would be to spec a relative density, likely in the 70 to 75% range. If the drainage layer is not to thick or if the compaction is not critical, I would use a precriptive spec such as 3 passes with a minimum 10ton smooth drum vibratory roller with a max 12-inch thick loose lift thickness.

In reality, clean rock compacts very easily if vibrated and confined.

 

[BigH]

Not sure you want to compact a drainage layer anyway - by "compaction" you are reducing the void ratio which decreases the coefficient of permeability. I've seen/heard of 1-1/2 inch clear crush called "self compacting". Why would you compact - what difference does it make if it is uncompacted other than simply raking it level - how thick is it? what is founded above? All questions to consider.

 

[cvg]

filter drain layers in dams, levees and underneath structural elements should be compacted and relative density of 70% is the method I use to control that. A french drain with nothing structural sitting over the top, than I wouldn't bother.

 

[msucog]

oh no no...please don't allow "self-compacting" to show its ugly face. no such thing exists when dealing with crushed aggregate. you can get serious settlement out of loose stone especially when you're backfilling say a retaining wall. we see more problems with loose aggregate than just about anything else when we do forensic work. and we also have more fights than just about anything else b/c contractors argue they don't need to densify it.

even in a reasonbly densified state, aggregate of this size should still be freely draining. for all practical purposes, i don't usually suggest spec'ing an inplace density for this material. i spec it similar to rock fill..."densify in 8 inch lifts in the presence of our testing personnel until no further densification is visible" (ie. densify until the testing personnel see it stop moving under compaction equipment and probe that it's firm). probe it regularly to check that it's firm and observe that it's stable under the equipment. if you can penetrate the backfill with a probe rod, it's likely not sufficiently densified. if you can work your probe rod to the handle, try rodding up and down in say 6-8 inch strokes. keep doing this and the probe rod will eventually back itself out as the particles rearrange (ie. densify) leaving a rather substantial cone shaped depression which sort of gives a shocking visualization of how loose the material truly is. i maintain that loose 57 stone can settle say something on the order of 1/2-1" per foot height of backfill.

 

[BigH]

msucog - it all depends on thicknesses and purpose. Of course, it is one thing behind a retaining wall or if it is 3 to 4 m thick and you are putting a footing on it - but as trench backfill or a "thin" layer - I don't see a problem. Is the main purpose of this drainage or is it support? These are questions that has to be answered - would suggest that "clear stone" by itself behind retaining walls likely wouldn't be a good idea anyway - especially if adjacent materials would wash into it - so any and all recommendations are "specific" and must look at the whole, eh?

 

[dik]

The material is used for transformer oil containment with vehicular traffic over and is used in conjunction with a product called Sorbweb.

 

[cvg]

open graded rock does not hold up particularly well to traffic loading unless paved over with asphalt or concrete. Either way I would compact it.

 

[BigH]

In this case, I agree with cvg - but if you insist on the single size material, you might want to consider stabilizing the rock with a thin coat of asphalt - Cedergren in his drainage book talks about this - keeps the particles together - gives them binding but keeps the drainage characteristics.

 

[iandig]

There used to be a check test to assess the difference between compacted and un-compacted aggregate for use as a drainage material. If the difference in the field bulk density was too big (10 to 15% from memory) the material was NOT suitable as a drainage layer.
If you do need to undertake compaction, I would suggest you look at either the information which the compaction plant manufacturers produce (Bomag have an extensive library technical on all sorts of plant and suitable materials to compact) or have a look at Table 6/1, Table 6/2 and Table 6/4 from the UK’s Specification for Highway Works. Find a material with a comparable grading in Table 6/2, then look up on Table6/1 the requirements for compaction and then go to Table 6/4 to find suitable plant, depth of layer and number of passes. The ‘Method ‘placement has been designed to provide ‘adequate testing ?(less than 10% air voids for cohesive soils) at conservative moisture contents’ [DMRB; HA 70, Section 4].
As your material is granular, relatively single-sized, I would seriously doubt that a lab compaction will provide a range of moistures to place the material at, but would provide a target density that could be achieved with the material. If you are going to apply compaction to the drainage material, make sure the aggregate is strong enough to prevent particle break down during placement (Los Angeles) and is resistant to weathering (Magnesium sulfate soundness or similar). Also the rock type will be important, no argillaceous rock, chalk or colliery spoil.

 

[dgillette]

With material up to 1.5", the min, max, and in-place densities will all be a pain to determine.

Consider a procedure spec, e.g., 6" loose lifts each compacted by three passes of an Acme Mark 1 walk-behind vibratory-plate compactor, or equivalent, if the placements are small and you don't need a lot of density; for large areas, something along the lines of 12-inch loose lifts with four passes of a 10-ton vibratory smooth-drum roller, with water applied by hose in sufficient quantity to minimize capillarity, if needed.

 

[dik]

Thanks gentlemen:

The 'pit' is approximately 20'x40'x3' deep and will be subject to light and infrequent traffic. I didn't think that any type of Proctor testing is correct and based on the information/confirmation here, I'm using double passes of a Bomag BW65H on 12" lifts. This is a tandem walk behind machine that generates a centrifugal force of about 5000 pounds (22 kN) per drum. Alternatively, I'll accept a double pass with a D3 Cat which should be equivalent.

The equivalent relative density I'm looking for is about 55% (Gradation is tightly controlled with variations of about +/- 3% for the seive sizes selected.

Dik

Dik

 

[bb29510]

It not that you cant compact it, you just cannot test it very easy

 

[fattdad]

Brownbagg, brings up the most practical point. Sure, relative compaction is likley irrevalent and relative density is relavent. Getting a laboratory to give you the min and max density and obtaining the field density to determine the relative density is the real problem.

On the matter of drainage layer, compaction and its affect on permeability, I'd be more concered about the end conditions. If you are stiving to have drainage go vertically into the media, where will it go from there? Is there a perforated pipe system? Are you hopeful that the water will then continue downward to the water table? Is the goal for the water to leave horizontally at the edge? Somewhere in the conceptual design of the drainage system, you need to make sure that there is sufficient capacity to allow the drainage media to function.

Interesting discussion.

f-d

¡papá gordo ain’t no madre flaca!

 

[RamiCivil]

Try to get the max density by vibration method

 

[dik]

I have a proper drainage system beneath to take away any precipitation. The basin will be used to trap oil from a transformer spill if necessary.

Dik

 

[DRC1]

Clean 1 1/2 crushed stone does not require compaction. It is spread, tamped in aproxximately 12-18 inch lifts with a plate compactor or a backhoe bucket. Resulting base is quite stong. 1 1/2 can be difficult to place by hand 3/4 is easier to handle. Also if you use 1/12 for the base, raking in some 3/4 stone on top will give nice finished surface.