PanzRule posted the information below on the ConstructionKnowledge Forum last week and I thought it was too good not to share further. I used lime on a fast-track factory project a few years ago with excellent results. We finished the project on time, which couldn’t have happened without the lime soil mixing.The experience shared by PansRule below should be read by everyone who has to work to control construction schedules and wet/frozen soils.
Post subject: Soil Modification/Stabilization by Panzrule
I have been working on a site project that began in early October of 2009. If you can remember this winter here in Pennsylvania, we had a record winter in terms of snowfall. In conjunction with the snowfall we had what I would consider a cold winter. Now this is coming from a guy who spent the last 11 years working in an office who now was the acting site project superintendent, project manager and occassional equipment operator. So needless to say my opinion may be slightly skewed due to the time spent in the office becoming soft.
Because of the wet & frozen soil conditions throughout the winter and the owner’s need to maintain the project schedule soil modification was used. To be totally honest, I was skeptical of the process. I had never seen this process used and by the prices that I recieved for purchasing the material, I was petrified!
We applied a blend of hydrated lime and lime kiln dust. The amount of this product varied depending on the moisture content of the soil. The product is added by percentage of weight of the soil (soil proctor value) and how much moisture you are trying to reduce. Depending on the soils, for every 1% of hydrated lime added to the soil will reduce the moisture by 1-3%. If by spec you are only allowed to be 2% over optimum for moisture and the virgin ground being cut is 10% over in January, you probably won’t be able to make it without some type of modification to the soils.
On previous projects in the past if schedule had to be kept in these situations either stone was place in lieu of fill or stone was mixed with fill. This works fine except if the site balances for every yard of stone imported you will have an equal yardage of fill to haul away. As it turns out here locally the cost to modify a cubic yard of soil on this site was about half the cost of purchasing stone. Let alone what it may have cost to export that same volume of earth.
I was amazed how this product melted 20″ of frost and was compactable in about 2 hours. There were also soils that I would classify as pus. You know the kind that almost level themselves when dumped. Treat that stuff with about 5% hydrated lime and now you have something to work with.
Needless to say I am no longer skeptical about the product or the process. It made a believer out of me. I would love to try using a type 2 or 3 portland cement and mix with soils. From what I am told you have about a 3 hour working time before it becomes rock hard. In some cases I am told that if excavation is required after soil is treated with portland you may have to sawcut the treated soils so you are able to dig through it. I am also told that if the subgrade is treated using portland beneath paved areas, the sectional thickness of stone and asphalt could be reduced. This would be beneficial if the cost of asphalt continues to rise and would help reduce the use of our natural resources.
So if you have a few thousand yards of wet fill to place and natural air drying is not an option give soil modification a shot. Once you get past the sticker shock you won’t be dissappointed.