Free-draining - What does this mean?

[BigH]

Okay, friends. Specification calls for common fill (no sizes larger than 150 mm and no more than 40% finer than the #200 sieve). Other materials specified are base course and gravel wearing course. Later, another section of the specs calls for "free-draining" fill to be used behind retaining walls. Mmmmm. What is "free-draining?" (A technical specification) Contractor shows up with common fill and "says" it is free-draining. Is well graded crushed stone compacted to 98% MDD Modified free draining? I can see the contractor bringing in crap and says, "Well, this meets common fill and its free draining." - and it is not.

Let's see what we come up with . . . .

 

[BigHarvey]

Cedergren is defining "free draining" in page 272 of "seepage, drainage and flow nets 2nd ed" but it is not quantifying this property.
Common sense would call for a simple water test : pour water on the compacted fill, if it's free draining, it should disappear in the fill immediately !If not it's not "free draining" !

 

[Ron]

Not sure of a true definition, but the geotechs I learned from considered it to be in the permeability range of 10^-3.

 

[SlideRuleEra]

BigH - The American Concrete Pavement Association has a paper that gives suitable values of "free draining" for their purposes: 50 to 150 ft/day and mentions older requirements of 500 to 3000 ft/day. See this paper:

http://www.pavement.com/Downloads/TS/EB204P/TS204.4P.pdf

Also, the US Federal Highway Administration website indicates that California has has a controversial value for free draining soil. See this link:

http://knowledge.fhwa.dot.gov/cops/...b=DISCUSSION#EFC44A60442DC872852570A60020A26D

A nice, simple definition of "free draining soil" was stated by, of all people, the California Avocado Society (in 1943), it reads:

Under free drainage conditions a soil is capable of holding against gravity a certain amount of water. This is normally referred to as field capacity. If water in addition to this amount is added, water will pass through and beyond the depth of soil under consideration.

See this paper:

http://www.avocadosource.com/CAS_Yearbooks/CAS_28_1943/CAS_1943_PG_38-39.pdf

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[fattdad]

If the soil has a moisture-density relationship, it's not free-draining.

That's the definition that I came up with this morning.

(I would not think 1x10^-3 as free draining. More like 1.0 cm/sec or so.)

f-d

¡papá gordo ain’t no madre flaca!

 

[Ron]

f-d...most of our clean fine sands in this area (Ga/Fla coastal plains) generally will not significantly impede water flow above the groundwater level, and they are usually in the 10^-3cm/sec range. Obviously they have little storage capacity, but water flows through them readily.

 

[dgillette]

In a different climate, we have considered free-draining to imply that it would drain under gravity, leaving behind a low degree of saturation, so that freezing water could expand into air voids, rather than pushing and damaging the retaining walls. Obviously, this rules out anything with much in the way of fines.

This is similar to the avocado definition, but we weren't able to grow avocados on these projects in UT and WY at elev >7000 ft.

 

[oldestguy]

Aw come on. Out there in the sticks the common solution is using what ever water is on hand. That means urine.

By the time your zipper is closed and the stuff is gone, you know it is free draining.

 

[Ron]

Agree, OG....pi$$ on it

 

[BigH]

I always wanted to do the permeability tests with Stroh's Beer!

Contractor actually came in with a nice well graded material that would be fine for a subbase - but 15% passing #200; would pack well but we don't need water build-up. Now he's wanting to use 20-40 mm; I'd prefer 10-20.

 

[fattdad]

Yes BigH, I'd want about zero percent fines if the material is to be "free draining." My instinct would be to use AASHTO #57, which is basically the No. 8 to 1 in. I refer to this as an "open-graded" aggregate, as opposed to a dense-graded aggregate, which typically has some fines and not free-draining.

f-d

¡papá gordo ain’t no madre flaca!

 

[fattdad]

Just found in the VDOT Road and Bridge Specifications:

"Once geotextile for embankment stabilization is placed, the initial lift of material to be placed atop shall be free draining and shall be end dumped onto the geotextile and spread to thickness as shown on the plans. Free draining material shall be any material having 15 percent or less of which will pass the #200 sieve. If the geotextile becomes punctured or torn, the Contractor shall repair the area with geotextile lapped at least 3 feet all around the damaged area."

Not that I'd agree with VDOT, but that's what they consider "free draining."

¡papá gordo ain’t no madre flaca!

 

[dgillette]

I wouldn't agree either, fattdad. 15% clayey fines would blow that definition right out of the water. Avocados or Strohs!

 

[Ron]

Stroh's...

 

[BigH]

From one beer over to another . . . . Stroh's Beer; from one beer lover to another STROH's ! (have to have the jingle correct).

Terzaghi, Peck and Mesri has a pretty good section on soil permeability. I passed on the contractor's request for 15% fines.

 

[BigHarvey]

Sand blankets for vertical drains can be considered as free draining ( otherwise you would delay consolidation ) and it's commonly accepted 5% passing #200 sieve.

I'm afraid you'll have to use Bintang for the permeability test ( I suppose 25 years later it's still OK ! )

 

[BigH]

Yeah - Bintang is still here as well as Anchor beer. Normally I pay the extra dime and buy Heinekin (spelling?)

The reason for the question was also to point out the less than stellar specifications that are written - especially by non-soils types. They think nothing of putting in "earth fill", common fill, sometimes "fill". These all lead to potential disputes. Best to over indulge and list the details desired for each and every fill in each and every usage.

 

[GeoPaveTraffic]

I don't think you can make a determination about "free draining" without knowing the context. Generally, I consider something free draining if it can drain the water as quickly as the water can reasonably be expected to reach the material. For practical purposes, I take that to be 2 orders of magnitude greater permeability than the material providing the water.

If you have enough water, you make any material pond water.

 

[BigH]

agree GPT - but this is for fill behind retaining walls and we don't expect rivers from precipitation or water moving through the jointed periodotite. They are going to use a mix of 10-20 and 20-40 to get a free draining material.

Design engineers must define in their specifications what they really want - not just put some esoteric words on paper; especially when such "not seeing the same thing of the same words" when in the middle of construction. Backfilling of this wall could, by being delayed while "discussing" what is free draining and what is not could delay several thousand metres3 of concrete being placed because one can't get the crane out far enough to reach the next placement.