Reducing Moisture in "Red Dirt"

[splurt]

Hey fellas,

I am in the process of building 3 engineered boulder retaining walls, problem is I can not reach a 95% compaction rating with my fill, engineers keep telling me the soil is too moist. I have tryed various methods of compaction & keep coming up short around 87%.
My question to you is "What are some of the methods to dry out the soil so I can reach compaction"
The fill is local, western upstate SC. "Red Dirt" very much like clay, as it came out of the ground you could easily ball it into about any shape you like.
Any thoughts on this??

Thanks,
Round

 

[GeoPaveTraffic]

The most fool proof method is to spread the soil in a thin layer to dry in the sun and disc it periodically. Once the soil gets within 5 or percent of the optimum moisture content it should compact fairly easily.

Now if you don't want to wait or don't have the space or whatever the reason you don't want to do it the "natural" way there are other options. Those options depend on the nature of the soil other locally available materials and local practice. My suggestion is to ask the soils engineer for the project what they recommend.

 

[darthsoilsguy2]

hmmm.. retaining wall and clayey sand

check your material spec to make sure your kosher. many retaining walls will have soil parameters specified and whether its fair or not .... the blame lands hardest on the contractor when out-of-spec materials are used (even though retaining wall engineers blanket those designs with language about the geotech engineer for the site having all the responsibility). it may not be the case.... and feel free to repost with the soil parameters listed from the design basis.
most importantly you'll want to pay attention to something called the "Phi angle". if a high phi angle is specified, it doesn't matter how compact it gets... it won't make spec.

 

[darthsoilsguy2]

i don't see any good drying weather coming this week in SC..

protect your subgrades, keep everything draining away, and don't stockpile loose soil.


drying soil can be a real pain when it rains every third day like it's been doing in the carolina region for the last while.

 

[splurt]

Thanks Guys,

it is sounding more and more like patience is going to be key here, it is true the rain keeps coming and coming to the point that this project has been seriously delayed, in my frustration I am seeking alterntives to letting the sun dry out the material, as there has been very little sunshine.

thanks again
Roundtable

 

[GeoPaveTraffic]

I understand the lack of sunshine. I'm in the St. Louis area and we have had 8+ inches of rain this month. Been raining every 3rd day.

Good luck.

 

[WHEngineer]

I know you feel your engineers may not be giving much guidance, but this is a problem that we deal with our clients on a regular basis. In wet periods, the solution is often a matter of time or money - time to wait for a drying period, or money to haul in drier soils from a borrow area (if available). Depending on the local soils, lime or cement stabilization may be possible, however, these methods are additional costs and may change the assumed soil parameters used in the retaining wall design. Good luck with the weather. We are experiencing similar problems here in Georgia!

 

[oldestguy]

Who is responsible for the design? Too many times pounding the heck out of the backfill will cause so much pressure on a retaining wall that it moves out. In this case, if you pound the heck out of it and move your boulders out, who is responsible?

What is the "percent compaction" of the stuff in the borrow area? Why is that not a suitable degree of compaction for your job? Will not this fill revert to that density some day?

 

[splurt]

We are building up a sloped face that will one day house a swimming pool, to meet up with the natural grade we will be building two 9' terraces on which a patio and pool will set and beyond that will be a concrete foundation and evevtually an approximately 8000 sqft home. We plan to use geogrid at a 3 to 1 ratio every two feet, with compaction being done every 4 to six inches and test compaction throughout the entire process, problem is with all this rain we have not been able to above 87% compaction, which is far from the 95% our engineers have asked for.
I am assuming when you say "borrow area" you are referring to the land the soil came from ?? This I have not tested is this a step I am missing here??

Thanks Again,

 

[WHEngineer]

The borrow area is simply the source of the soils you are using. Has your geotechnical engineer discussed the proctor curve for the soils (ASTM D698 for standard compactive effort)? That should give you an idea of the possible moisture ranges for the soil to be able to reach 95% compaction. If you are significantly over that moisture range, you may not be able to compact the soils regardless of effort. Also, was global stability analyzed during the wall design? That can be critical, especially if the original slope is not well benched.

 

[darthsoilsguy2]

Splurt,

Now that you've told us you're using geogrid, we know you're building a reinforced wall. There is a good chance that the soil you have doesn't meet specification regardless of how wet/dry it gets or how compact/loose it gets. ultimately it comes down to how much sand there is to grip the geogrid in the soil mix. check my 2nd post.

Now is a good time to look at your contract/specifications to see who pays for import soils if on-site soils don't meet the defined soil parameters in the retaining wall design. you may be able to justify getting paid a change order for importing dry fill materials. Either way, you should review your contract/specifications for a good position to make up costs since you'll probably end up importing anyway.

find out the from the on-site testing the Proctor Maximum Dry Density, Optimum Moisture Content, and repost.

 

[aeoliantexan]

Self-cementing fly ash, if locally available, can be very effective to dry the soil at less cost than lime or cement. Kiln dust is another alternative. Either one can add some cementation to the soil.

 

[msucog]

wow! redflags just went up now that there's more details!

if you haven't already done so, i'd re-read the contract and construction documents to see who's going to be responsible for the testing, design and overall construction should something not-so-good happen in the future. the wall designer should be the one to approve/reject the materials being used based on the test results provided by the testing firm...it's just as for concrete and a structural engineer approving/rejecting a questionable placement. quite often, once all the details of responsibility are laid out on the table, it changes the direction that the project goes for situations similar to yours...i see it happen on every single project these kinds of walls are used in my area.

i also suggest having a meeting with the owner, architect, engineer, geotech, wall designer, testing firm, and anyone else on the project. go ahead and get all the details of the project on record with everyone present and try to move forward from there.

i won't get on my soapbox in this thread yet...but feel free to ask any questions if you'd like input based on my experience.

 

[fattdad]

Have you reconfirmed the Proctor?

f-d

¡papá gordo ain’t no madre flaca!

 

[oldestguy]

Now some other important info provided the group. Placing a swimming pole above this system of walls requires an experienced geotech engineer to do that global stability evaluation mentiioned above.

Pools frequently have a deck that has plenty of water on it. The site may need some special drainage in the ground to prevent that water from causing a situation that then has that pool and all the things around it sliding down the hill.

I'd be especially careful about the "borrow" material hauled in. It sounds like this is high in clay content and that may be quite weak when saturated by those wet conditions to be expected as the pool is used. This situation is a whole lot more complicated than how to get a high degree of compaction in the fill.

In using the term "borrow", that is an old expression and for some reason the borrower never returns the stuff borrowed, like my neighbor.

That recommendation to get all the parties together at the start is a very good one and, even now, it may not be too late to avoid a failure down the road. How's your errors and omission insurance? Paid up?

 

[barriergeocon1]

I'm probably jumping in here a bit late, I just joined this forum. I am very impressed by the replies you have received thus far and concur with them all. But here's my nickel's worth.

Red dirt and its application to reinforced earth structures is a problem faced all throughout the southeast US, it is red because of the iron oxide clay, we have. This clay can have low to high plasticity and how plastic it is, is the issue.

Your soils probably contain clay and as such, many in this forum have indicated concerns as to the prospect of problematic strength characteristics common in clays under reinforced eart applications. With proper drying techniques (I would be concerned about any grading contractor that does not know how to manage his materials and control his moisture content) you should be able to reach your target mnoisture-compaction range to achieve your target percentage compaction. However, clays typically have low strength characteristics for unit weight and angle of internal friction, which commonly leads to some serious creep making your wall butt ugly; with buldging, loss of batter, unsightly cracks and open seams, especially in outside radius and worse case is failure...(OK, is plural for radius radiuses, radius or radii???)

Seriously, You need to look at all the design factors, for internal, external and global stability and see how reduced unit weight and angle of internal friction affect your structure. On a brighter note, we have designed and built a bunch of MSE/geogrid reinforced structures with clayey soils (within certain plasticity limit criterion, of course) and they have performed well....you just have to be careful!!!

 

[bb29510]

when ever you cant get compaction;
1) too wet
2) not compacted.
a)modifly compaction methods
1)bigger equipment, heavy roller, vibrator roller,proofroll
2)different method, vibrator,jumping jack, lifts

1) too wet
a) dry material
1) sun, heat, wind, time
2) replace borrow with dry but same borrow
3) replace borrow with different but suitable borrow
4) modifly borrow, cement, sand, flyash etc

3) method of testing
a)vertifly proctor
b) nuke
sandcone
drive tube