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How can I solidify excessively wet soils?
10

How can I solidify excessively wet soils?

How can I solidify excessively wet soils?

(OP)
We have an earthwork dilemma at a 13 acre site in NJ that is jeapordizing both the cost and schedule of a school addition. The onsite soil, slated for cut to fill, is unsuitable as controlled compacted fill for use under roads, parking lots, etc because it is too wet and will not reach 95% compaction densities. Is there anything that can be done that will allow us to use this soil besides importing clean dry fill, which will be costly, or spreading the wet soil in 1' lifts and waiting for it to dry, which is taking too long and delaying the project?

RE: How can I solidify excessively wet soils?

What is causing the soils to be so wet?  Is this a low area or are there springs or high groundwater involved?

if they are just wet, drying is cheaper than importing.  The soils can be excavated and spread over a predetermined area.  Provided there is plenty of hot sun, the material can then be disked to futher promote quick drying.  I've done this on several projects and it works quite well.

KRS Services
www.krs-services.com

RE: How can I solidify excessively wet soils?

ever7grene:  First, identify your soil type.  If it is a clayey soil, then KRS is right about cutting, breaking it up, drying, etc.  This can be done but can also be time consuming depending on the volume.  Perhaps, as I once had in NJ, it was a sandy soil with perched water over a marl.  In this case, some ditching at suitable locations, then we used a sheepsfoot roller to continually aerate the soil.  Same basic principal - using the sun and time to dry out the soil.

RE: How can I solidify excessively wet soils?

Thanks BigH,

Yes, I should have clarified that my post related to clayey soils.

KRS Services
www.krs-services.com

RE: How can I solidify excessively wet soils?

2
Have you considered using some type of additive?  For instance, Lime drying is relatively inexpensive and can speed up the process tremendously.

RE: How can I solidify excessively wet soils?

2
Cement kiln flue dust is also quite effective - and cheap.

But lime, Portland cement and flue dust all will require mechanical mixing - which is no easy feat on a very wet soil...and site.



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.  See FAQ158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

RE: How can I solidify excessively wet soils?

I've used lime stabilization a few times with excellent results.  When compared to bringing in other material or moving the existing soil to another site to dry, it's not expensive at all.  

RE: How can I solidify excessively wet soils?

To mix the soils, use a tractor and disc. There must be a farmer around you that needs some extra cash to pay for his fuel needs. spread the soils over a couple of acres and let him have at it. Disc four times a day for about a week. That should give you 3-5 dry days.

RE: How can I solidify excessively wet soils?

(OP)
Thanks for the posts guys.  The soil IS clayey, and the excessive wetness has been caused by the tremendous amount of precipitation we've had here in the glorious Garden State over the past several months.  My problem is that since it is a school project, we have to be done by September, so there is no time to wait for the spread lifts to dry, especially if it keeps raining. We've tried that to no avail, due to wet Spring months. How exactly does the lime stabilization work, or can tarps be used when it rains, to speed drying?

RE: How can I solidify excessively wet soils?

Lime chemically modifies the clay so that it is less reactive to water, and uses water in the process.  The chemical reaction also generates heat.  The soils become friable - that is, they break up readily even when wet.  Lime works best in "heavy" clays.

Portland cement is a less expensive alternative, but is much less effective.  After all, Portland cement is only 30% lime - and 70% clay (pozzolans)!  It will work well in low plasticity clays and very silty soils, though.

Fly ash/flue dust work best in sandy silts/silty sands and some clayey sands.

Tarps might be useful in preventing additional rainfall penetration - but be sure that the rain doesn't drain into your "dry" patch!



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.  See FAQ158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

RE: How can I solidify excessively wet soils?

Be careful using lime.  I use it to dewater saturated remediation waste on a regular basis, but... on certain days (cloudy and high RH), you can get a significant ash-like fallout from the operation that will cover and stain automobile finishes as far as 1/2 mile away.  The cars need to be washed, wiped with vinegar or similar acidic wash, then waxed.  Very costly.

RE: How can I solidify excessively wet soils?

Thank you Reeltime2. I've only used lime once but met with blank expressions from the contractor when I questioned the safety of the white cloud billowing across the site!

Are there any particular risks to the machine operators etc?I understand the material used is effectively pure 'quicklime'.

RE: How can I solidify excessively wet soils?

5
Just to add in some additional information to the way in which the lime works with clay, it also changes the structure of the clay which in turn effects the plastic limit. The plastic limit is simply the moisture content at which the clay becomes wet enough to act plasticly, by adding lime, this increases the moisture content at which this happens.The result of this is the point at which the clay becomes too soft and wet to be handled increases, so not only do you remove some water(heat of hydration) you increase how wet the soil can be to be used. Therefore there are several distinctive process  which all 'improve' the soil. Also if you keep adding lime, the clay minerals start to break down and the silica and alluminum in the clay combine with the water and calcium (from the lime) to form cementitious materials [calcium alluminate hydrate and calcium silica hydrate]. It sounds like what you only need to achieve is an improvement in the soil by reducing the moisture, but there are also beneficial side effects which can improve the soil above and beyond the same soil if was only dried.
I have written a presentation in microsoft powerpoint on how this all works, and will send you a copy if you are interested, but I will probably have to generate this as a .pdf due to its size, sorry but the animation wont work. (contact me at ian@geotechnical.co.uk)
As to the effect of the lime clouds, this is a VERY serious issue, yes it is normally quicklime that is used, as this is the most reactive, and you should assess all the risks involved with this. Suitable protective clothing, such as masks, goggles and gloves should all be available.
Approaching people from agriculture to help is a very sensible solution, in the UK we have found that there is some cross-over between the two sectors, and often they have plant and equipment which although designed for farming, works very well on construction sites.
There is also specialist plant availble which rotovates, mixes and blends the lime within a hopper to prevent problems with lime dust, and this also includes much smaller plant suitable for single track roads. Whether or not this currently available to you, unfortunatley I cannot comment, wrong side of the world sorry.
If you wont to have a look at some of the kit available, companies in the UK who specialise in this are people like Powerbetter, Con-form, Beaches, Geo-firma, Stabilised Pavments, O'keefe Soil remidiation etc... all have their own web-sites.

RE: How can I solidify excessively wet soils?

Perhaps you can consider the use of heated pads or mats (not sure of proper term)... I saw them used once to help dry out wet clayey soils, in conjunction with lime treatment as discussed above.  The coils within the blankets were heated by circulating, heated ethylene glycol, if I remember correctly.  Could be of posible use for you, but not sure.

RE: How can I solidify excessively wet soils?

I am having the same problem with wet clay in Florida.  We have 100,000 cy of dredged material and the rainy season has started. We are barely passing the density tests but the ground continues to yield.  We are discing all day but can not stay ahead of the rain.  No one around here has ever heard of using lime.  Does anyone know where it can be purchased in bulk amounts in the Tampa Bay area and how much do you spread?  We have mixers and spreader trucks available.

RE: How can I solidify excessively wet soils?

Great post iandig!

RE: How can I solidify excessively wet soils?

Hi,
I've run across this issue in the environmental field - a large amount of imported clean fill was too fine-grained.  Rather than hold up the project to dispute the specs on our fill and wait for new deliveries, cement was added for stabilization.

Added a small amount of cement will work wonders.

RE: How can I solidify excessively wet soils?

Try kiln dust or fly ash.

RE: How can I solidify excessively wet soils?

We have done soil compaction and densification using explosives.  Its quick and cost effective.

Frank Lucca M.I.Exp.E.
www.terradinamica.com

RE: How can I solidify excessively wet soils?

would explosives / dynamic compaction work with wet clay soils?  seems unlikely

RE: How can I solidify excessively wet soils?

It works real well in wet soils.  I've done it in soils with clay and it worked.  I would imagine it would be dependent on the clay percentaqe.

Frank Lucca M.I.Exp.E.
www.terradinamica.com

RE: How can I solidify excessively wet soils?

Hmmm,

I'm with cvg on this one.  Where would the water go?

Most of my clients would take a pretty dim view of even trying it.  And with all of the military bases in my area (5 within 30 minutes' drive) the use of explosives is discouraged.



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.  See FAQ158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

RE: How can I solidify excessively wet soils?

The water bubbles up out of the drill holes.  Its an amazing thing to see.  I didn't believe it until I saw it work.

The company with the most experiance in this is Vet's Explosives in Torrington, Connecticut.

Frank Lucca M.I.Exp.E.
www.terradinamica.com

RE: How can I solidify excessively wet soils?

Well, seeing is believing.  Guess I'll reserve final judgement for now -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.  See FAQ158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

RE: How can I solidify excessively wet soils?

I would create an weather protected impoundment with a pitched surface ( 2% to 5%) and store the fill for a couple of weeks to let water run off.  The fill can be spread out or piled however you may want to give it some thought on the best storage procedure.
I dont think the authority will let you add a drying medium and have the material be used as a clean fill.

RE: How can I solidify excessively wet soils?

In the Midwest, (I am located in Columbus, OH) additives such as kiln dust, fly ash, lime and portland cement are used very commonly to dry or stabilize soil.  The additive is selected based upon the soil type and the required stability.  The process of drying versus stabilizing is also dependent upon the desired outcome.  For example, lime works extremely well with soils with a high clay content and cement is preferred for soils with lower clay contents.  It gets complicated because there are many types of lime with different levels of hydration.  Fly ash and kiln dust are byproducts of other processes and tend to be significantly cheaper than lime or portland cement but are less effective at stabilizing soils.

One of the big issues we are dealing with is the concept of drying vs. stabilizing.  Drying is adequate for materials that need to be dried but do not need additional strength for bridging over soft soils.  Stabilization on the other hand will result in strengths much stronger than the original soils and can often form a layer that will "bridge" over softer soils.  

The issue here has been if drying is used it is not very complicated but if stabilization is proposed than the unconfined strength of the modified soil is measured and in the future credit may be given for this additional strength towards the pavement design.

Back to the original post, if drying is all that is needed it can be very inexpensive and can produce very quick results with the right additives and equipment.  I have seen 3000 feet roadway stabilized in a period of a couple of days.  One of the limitations is the equipment available.  We have specialized companies here with large mixers(similar to the ones that mill asphalt)but they are still only capable of about 18" of mixing.  The next question is how deep can the compactor effectively compact?  We have found anything beyond 12" to be questionable.  In cases where 12" of drying/stabilization was not sufficient we have done it in multiple 12" lifts.

This information may be more than anyone here wants to read.  But I have worked with soil modification exstensively for the last 5 years and if anyone has questions I would be happy to try to answer.

RE: How can I solidify excessively wet soils?

Just a quick addition to the theme of this thread. In southern France, Italy, Spain and a lot of other southern European Countries (maybe States is a better word now?) they are so used to using lime to stabilise soils, that they apply it to dry dusty soils. The use of lime here is not to dry the soil, it is already in a desscicated state, but to control the soil during very dry and very wet periods. As the lime needs moisture to work properly, they have developed a technique whereby the lime is added in liquid form from spray bars after pre-mixing with water immediatley before application. They call the liquid 'milk of lime' (lime milk), and it has proved very succesful. There is a massive industry in Europe with the use of lime for road and building construction with earthworks, and it is the standard way in which a lot of Countries build.

RE: How can I solidify excessively wet soils?

This also happens here in the "States" as well.  We have found that the use of lime sluury is limited for dry soils unless it is mixed with the soil/dust, however, because the calcium hydroxide that doesn't bind with clay minerals tends to combine with other chemicals/materials.  You just don't get the "bang for the buck" that is otherwise expected -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.  See FAQ158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

RE: How can I solidify excessively wet soils?

If the time table is critical enough you could consider renting a portable asphalt plant to pass the wet soil through for drying and stockpiling or replacement.  Perhaps a combination of heated drying with reduced lime addition would produce a desireable material.  There would be considerable handling cost involved therefore, a cost/benefit analysis would have to be performed to evaluate the practicality for your project.

Good Luck!             

RE: How can I solidify excessively wet soils?

I feel for you.  I am presently working on a project in Southeastern Virginia.  The structural fill we have been provided with is an SM (barely, on the line with an ML)and with all the rain this summer it has not dried out at all.  We are achieving good compaction but when the material is prood rolled it is not stable at all.  I looked into Lime Stabilization.  There is a company in Maryland that specializes in this.  I'll try to locate their name/number.  I saw a caution in another post regarding the white cloud and painting of cars.  I have been warned about this and as our project is in close proximity to many vehicles we are not going this route.  The engineer has advised us to cut an additional 12" of material off the roads and replace with compacted stone base.  We'll see how that goes.  We gave up on the disking method.  Too much rain and if the material is left in furrows when it rains you end up with a bigger problem.  

Since it is now October, what was your final fix?

RE: How can I solidify excessively wet soils?

We're dealing with wet conditions at a site in Washington that is mostly due to the rain.  

This is going to sound pretty obvious, but we noticed that the fill we had on site was still in the ground-  it was  only when we left stockpiles exposed to wet weather that we saw problems with compaction.  

With a fair amount of finageling with the General, we saw big improvement using many rolls of visqueen and as many bags of sand and some timely off-days when the rain became excessive.  I believe we increaced our time out there by at least a month and a half.  The contractor had a special method of weighting the liners using twine for windier areas at the site.  

This method in the end still left us with a few wet stockpiles, but for the most part was testing in the neighborhood of 7%, where previously I had readings upwards of 20%.  I was surprised to be the only one excited on site!  (I think the rest of them were sick of me :).    

Anyway, for what it's worth, we're going through the same thing in the Evergreen State as well.


ds

PS.  We also tried compaction of exposed stockpiles, but in the end liners proved far and away the best method for wet weather.  

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