Basement backfill

[cgroth]

I live in a area full of clay, compromised by weeks of drought followed by the flood of rain. This is hell on the average basement. To keep pressure off the basement wall, it is advised to wet the soil around the walls periodically to keep large cracks from appearing in the soil (clay). This will soon be rental property and I want to keep it as maintence free as possible. Any ideas? I was told by one of my instructors at the college to use engineered soil. Having trouble finding this he told me I could mix fly ash with the clay. Since then he's retired. Could anyone else please elaborate? Or is there anything better (like sand); and whats the best way to mix this? Any suggestions would greatly be appreciated - thanks.
Craig

 

[DaveAtkins]

I believe you water the soil around your basement walls during a drought not to relive pressure on the walls, but to prevent soil dessication, which will allow the walls to settle.

DaveAtkins

 

[techmaximus]

Desiccation is the formation of cracks in drying clayey sediments. Desiccation cracks indicate an alternately wet and very dry environment.

The idea is to wet the ground during the dry part of the cycle in order to maintain the moisture content of the soil thus preventing the cracks from forming. The cracks could potentially provide a pathway for water to reach both the wall and the foundation. If large cracks form and heavy rain occur the water tightness of the wall may be tested and the foundation, depending on the depth of fill, may be eroded resulting settlement.

Engineered fill is probably a reference to an imported soil not made up primarily of clayey sediments and thus not susceptible to desiccation.

Reducing pressure on the walls? I don’t see cracks causing pressure on the walls. Wouldn’t water filling the cracks cause some head, assuming the drain tile is not working?

Fly ash. This would require excavation, mixing,, and compaction. I can see the properly compacted mix being less susceptible to desiccation; however, the compaction process would probably blow out the walls as residential walls are not made to be compacted against.




Techmaximus

 

[cgroth]

Thank you both for answering. I understand about dissication, that's why I'm doing this. I was told that adding/mixing fly ash to my clay soil would stop the ground from drying out and forming cracks (which will later fill with rain runoff containing debris or soil thus causing pressure on the wall-like a wedge). I also know how messy fly ash can be and was wondering if there's an easier way of doing this procedure. Also-- I have to dig up my entire basement cause of pressure now on the wall, which is due to the cracks. I plan on pulling my wall back and adding concrete deadmans along the wall. Then I'm going to install a waterproof membrane, drain tile (which it currently does not have), and then a couple feet of gravel. I was wanting ideas on the backfill--I don't want to push the clay back in if there's a way I can "doctor" it up, such as mixing fly ash into the clay to keep it from dissication. Thanks.

 

[techmaximus]

When you say that you plan on "pulling the wall back", does this mean that the wall is already in distress or failure?

Also, maybe I’m missing something, but I don’t see how “cracks in the soil “cause pressure on the wall" or "allow the walls to settle". The fill material dries out causing vertical cracks. If the fill material is drier than it was before and thus weighs less per cubic foot than it previously did how does a having less weight against the wall cause this pressure or allow settlement?



Techmaximus

 

[cgroth]

Sorry it has taken awhile to respond, lifes been busy. Yes the wall is already in distress. It has moved about 3 to 4 inches in the middle top of the wall inward and tapers of as it gets to the corners (connecting to the other walls). When the soil becomes very dry, it shrinks and causes cracks in the soil. This doesn't seem so bad cause you figure when it rains again, the soil will expand back to its original size. The trouble is that when it rains, these cracks fill up with debris (other loose dirt, leaves, and so on). This debris fills in the cracks so that when the soil does expand, it can't. Well it can but it does by putting pressure on the wall - forcing it in. This is all I can write now, something just came up but I'll get back to this later or tomorrow (I hope). Thanks for your interest. Craig

 

[DrEvo]

Hope this isn't too late... the best backfill in your situation would be pea gravel. It allows movement without building up lateral pressure. You must grade the clay at 45 degrees from the footer up to grade. Backfill with pea gravel then landscape. The pressure created by the movement of the clay will be dissipated by the gravel.. I've done it before with excellent results...