Kansas Clay/Foundation Backfill 1

[cgroth]

I live in Kansas, and the clay soil is a problem for backfill. I can not afford to backfill with rock, is there a cheaper method. I was told once that I can backfill with the clay to about 3 feet from the top and then mix fly ash with the remaining clay and then backfill. Or possible fill the rest with flowable fill from a concrete plant (sand, flyash, cement). Of course there will be about 6" of good soil on top of this. Any thoughts would be greatly appreciated. Also because of my job I cannot answer ?'s daily (maybe weekly). Thanks!! Craig P.S. Those not familiar with this clay, I'll give an update. Our hot weather causes the soil to dry out and crack. When we get a good rain the clay expands back to where it was before. The problem is the soil doesn't expand right away, and the cracks fill in with other debis, thus becoming a wedge. When the clay expands back to where it was before, instead of filling in the cracks, it pushes on the basement walls.

 

[oldestguy]

It appears you are stuck between a rock and a hard place. There are other materials that are not affected like your clay is, such as sand. I suppose that is scarce, but it may be worth it considering the damage potential.

Do you think the soil outside of the backfill will not affect your wall? Maybe not as bad, but it may.

A cushion of some sort may be placed against the wall, such as the pink extruded foam insulaton. It may not be sufficient in the long run, but may do the job. Makes the basement more livable also, but may allow freezing in the backfill and expansion from that factor. I have done this for two houses I built and no problem in Wisconsin. On my jobs it also is under the basement slab.

Another thing that can be considered is no-compaction of any backfill next to the wall. To avoid the typical backfill settlement later, some degree of compaction outside say a 2 foot distance from the wall should be done. I regularly call for this loose zone to permit active pressure to develop.

Lastly don't plant any fast growing trees nearby. More mischief potential there than from weather.

 

[MiketheEngineer]

It sounds as if you are plaqued with "Plastic" clays.

Do ANYTHING to avoid them. They will destroy your foundation over time. I live in St. Louis and we have some of the same problems.

Do something and good luck!!

 

[civilperson]

Soil is cheap, a truck load of granular is about $125. Replace all the clay within two feet of the walls with select material or treat the clay soil with hydrated lime.

 

[Mickney]

Ahhh, the "shrink-swell" CLAYs. We have areas of these soils in the metro-Charlotte, NC area. Nasty stuff that resembles Play-Do. A major contributing factor to the movement of these CLAYs is introduction of moisture. If you can reduce the amount of moisture that these CLAY soils are exposed to, you should limit their propensity to move. If you backfill with a permeable or open graded sand soil above the CLAY, you could actually create a conduit for moisture to the CLAY soils. Lime is a great way to "chemically stabilize" the CLAY soils. Could get expensive. Also, you may wish to extend your downspouts 10 to 15 feet beyond the walls and limit vegetation immediately around the structure to those with a low water demand.