How can I solidify excessively wet soils? 10

[ever7grene]

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?

 

[KRSServices]

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

http://www.krs-services.com

 

[BigH]

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.

 

[KRSServices]

Thanks BigH,

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

KRS Services

http://www.krs-services.com

 

[gbowen]

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

 

[Focht3]

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?"

 

[Maury]

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.

 

[dicksewerrat]

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.

 

[ever7grene]

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?

 

[Focht3]

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?"

 

[Reeltime2]

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.

 

[pba]

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'.

 

[iandig]

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.

 

[Rockjoint]

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.

 

[GeraldN]

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.

 

[SirAl]

Great post iandig!

 

[agsgeophysics]

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.

 

[radwaste]

Try kiln dust or fly ash.

 

[exploengineer]

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

Frank Lucca M.I.Exp.E.

http://www.terradinamica.com

 

[cvg]

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