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What is the best practice for backfilling over a basement foundation drain system?

I have a walk-in basement, with retaining walls that are about 3' above the footing. I've dug out a ton of dirt to remove the old foundation drain tile, while was (stupidly) installed on top of the foundation footing by our fly-by-night concrete crew, instead of beside it. Not surprisingly, we're getting water seeping into the basement all around from the top of the footing, which isn't getting drained away by this system. So now that I've dug it all out again, I'm going to install a new drain tile beside the footing, and I will do a good burrito wrap with geotextile fabric around 1 1/2" round rock. I will also use a really good waterproofing system on the foundation retaining walls, with a dimple mat to protect the waterproofing and relieve water pressure against the walls. I'm going to put in a new sump basin and pump, with the pump float level that is well below the footing. The original concrete crew did everything wrong, and I want to do everything right.

The specific question I have is how much gravel I can safely backfill on top of the foundation footing and drain tile, and the burrito-wrapped gravel. The soil here is clay. I know that with a french drain, you want to remove all of the top soil, just get it off the jobsite, so it doesn't clog up the filter fabric and the gravel. You never want to backfill over french drains with any of the soil that you excavate. But is that still true with a basement foundation drain? Do I need gravel, all the way up to grade level? That would be a crap ton of gravel to order ($$), and a crap ton of wet clay soil to remove from my yard ($$$). So, what is the best practice for basement foundations? Keeping costs in mind, for a walk-in basement, how much gravel do I put in, and how much of the dug-out clay can be used to backfill? Any of it?

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  • I hear "clay soil" and I think "expansive" and "frost heave susceptible." Clay soil beside basement walls is a common cause for problems. You should check out IRC R405.1 and its table if you're not already good friends. I might want to bring in a Group I soil for back filling depending on the exact soil properties.
    – popham
    Commented Jan 5 at 0:41
  • We don't get frost here. I'm mainly concerned if it will affect the foundation drainage system. Commented Jan 5 at 2:18
  • Expansive soils don't need frost to damage a foundation. Ask anybody from Texas.
    – popham
    Commented Jan 5 at 2:19

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