Moisture-density curve for clean sand 1

[regonto]

Standard Proctor test for clean medium to coarse grained sand always creates a problem with bleeding and dry density going up, even after crossing ZAV line. Is there any method to determine optimum moisture content and maximum dry density using curve that goes only up?

 

[fattdad]

Nothing crosses the zero air-voids curve.

The sand curve will often have its maximum dry density on the ZAV.

If it's too clean, you may be better specifying relative density rather than relative compaction.

Hope this helps.

f-d

¡papá gordo ain’t no madre flaca!

 

[iandig]

Rather than use the proctor test for sands, have you considered the methods developed specifically for granular soils, such as the maximum and minimum density of granular soils. If you can source a copy of BS 1377-4: 1990, Section 4 of this standard covers a number of tests to achieve this. Mehtod 4.2 is specifically the determination of maximum density of sands. The method accounts for the fact that single sized materials don't act the same way as either well graded soils or cohesive material. Unfortunately these methods are not used as often as they should, and there are many engineers out there who do not include this within their earthworks specifications

 

[garrettk]

If you are doing a Proctor test, don't be surprised if instead of a traditional "curve" you end up with a somewhat flat line that bounces +/- 5 lbs up and down as you move up in moisture. I've seen that numerous times.

 

[jfljoe]

I know how much of a pain this can be for interpretation. The nearly asymptotic behavior of the line as particle lubrication continues with no more retention of water is frustrating. I often see a mini peak of the curve to the left of this and would consider it more likely the peak of field conditions, barring a free-draining layer underneath the free-draining sand. If not, good luck trying to convince the contractor to hydrate to a crazy-high MC!

In Lars Forssblad's Vibratory Soil and Rock Fill Compaction, he discusses an assumed maximum dry density of a free-draining sand as the same dry-density you would get from compacting an oven-dried sand. After some testing of my own, I have found this to be characteristic of many sands with less than 2% fines, but shaky above that.

Hope this can be a useful reference...

 

[regonto]

I think my question wasn't clear enough. I need your opinion on how to deal with "bleeding" through the gap between mold and base plate. Because of this "bleeding" pore water replaced by soil particles reducing moisture content and increasing density. That is why the curve goes up. Some labs would collect the water, weigh it and subtract from wet soil weight.
But that is not always enough. Another way of dealing with "bleeding" is to go back 3%( why not 1% or 2%? ) from the point
of crossing with ZAV and consider this point on the curve as maximum dry density at optimum moisture content.
This "bleeding" happens, more or less, in every lab when some clean sand or sand and gravel tested, especially when using modified effort.
The problem is not new, and there is no suggestion from the authors of D698 and D1557.
Any suggestion would be highly appreciated.

 

[dgillette]

If there is bleeding, the material is just not suitable for D698, which is usually limited to materials with >15 or >10 percent fines.

Like fattdad and iandig said, it may be time to go to vibratory testing and the relative density (although you can control compaction in the field using just the percentage of the vibrated lab max density, rather than relative, once you figure out what it needs to be to give RD>70% or whatever).

 

[Stoph]

While I agree with DGillette completely, some agencies still require standard proctor on these poorly graded sands and gravels when used as fill or backfill.

To deal with the bleeding between the bottom of the mold and the base plate, I use a little vacuum grease around the base of the mold (which I already have on hand for use on the triaxial chamber), then I tighten the wingnuts with pliers (carefully because the "wings" will snap off).

 

[fattdad]

Let it bleed. Whatever water excapes the mold will not contribute to the compaction moisture content determination when you assemble the proctor curve anyhow.

f-d

¡papá gordo ain’t no madre flaca!

 

[Stoph]

I would agree with the "let it bleed" option if the water were clear, but this bleed water is typically not which means that the few fines that you do have in these materials are washing out with each successive test point. So the material changes, which is a change in specific gravity, which changes the ZAV line. This is why the density "appears" to cross the line as Regonto originally stated. Another solution would be to start with a fresh sample for each point, but who does that;-)