How to test compaction on sites improved with Class C fly ash?

[grabens]

I am working on a site in the panhandle of Florida. The site soils are clayey sands with about 30 percent passing the No. 200 sieve. We have been getting large amounts of daily rain. The soils have become too saturated to compact. The project is on a strict time line and the weather outlook is not favorable. I am contemplating recommending using Class C Fly Ash to dry out the soils. THe site soils do not seem to be clayey enough to use Lime based upon the research I have done. The questions i have are:

How do you test compaction in the field? Standard nuclear guage testing?

Do you need to run a proctor sample mixed with fly ash?

How much fly ash would need to be added just to dry out the soils to get closer to the optimum moisture content?

Can you work with fly ash with daily afternoon rain storms? Or do you need an extended period of dry weather to use this material?

These materials (lime, fly ash, etc.) are not commonly used in Florida since most of the soils are clean sands to slightly silty sands. Any help would be greatly appreciated.

Thanks,

Guy

 

[fattdad]

are you working for the contractor or the owner?

f-d

¡papá gordo ain’t no madre flaca!

 

[grabens]

I am working for the owner by contract. However, both the owner and contractor are working together to meet a 3rd party's contractual deadline.

 

[Ron]

Yes, you must do a proctor with the proposed fly ash proportion in the mix.

Density testing can be done with any of the typical methods; however, you should note that fly ash can actually hydrate in a manner similar to cement, so make sure the density testing is done right after the mixing and compaction process, not the next day....you might get failing results the next day because of chemical issues.

As for how much fly ash, you'll have to do a few trial batches with different percentages. Further, you can't work toward an "optimum moisture" because as the percentage of fly ash is changed, so will the optimum moisture.

Why are you using fly ash? I'm familar with the panhandle soils of Florida and you should be considering sand first over other materials. Sand mixtures are easier to predict and easier to control. Since you have not given the context of you issue, it is difficult to say which would be better, but generally sand is easier to deal with.

 

[grabens]

The soils on site are clayey sand with about 30 to 35 percent fines passing the No 200 sieve. The Modified proctor values of 129 pcf at 12% moisture. The top 12 inches of the pad need to be compacted to 98% modified proctor MDD. We just just got 23 inches of rainfall in the last 48 hours in Pensacola. We have a 100 percent chance of rain tomorrow too with 60% chance the remainder of the week. The pad needs to be completed and handed over by this Thursday (6/14). The site is currently underwater due to the rainfall and the clayey soils on site. I am concerned about placing clean sandy soils for the upper 12 inches due to the potential for a perched water table trapped in the upper 12 inches of clean fill. No good answers really here.

Importing slightly clayey soils (-200 about 10 to 15%) will be about $80k. After this weekend's rain, these too will be dificult to work with. I am trying to find a way to dry out the on-site soils with these constraints.

 

[Ron]

grabens...sometimes you just have to live with nature. In your case, wait until the site is dry or provide some supplementary drying measures, such as aerating the soil and re-compacting. If the site is "under water", you have little choice but to wait. Deadlines such as you are facing are not controlling if the natural conditions cannot be reasonably dealt with. Tell someone in charge, the project will be delayed because of this.

 

[fattdad]

I agree with Ron's perspective.

f-d

¡papá gordo ain’t no madre flaca!

 

[jgailla]

I also agree with Ron.
This is extraordinary weather, even for Florida. Northeast Florida got pounded recently as well.
If I'm not mistaken, Pensacola has experienced upwards of a 100-year, 24-hour rainfall event once and a 25-year, 24-hour rainfall event once in the past week, along with heavy rains every other day.