I have to take down a large pecan tree and I believe a portion of one of the main roots extends below my garage foundation. Pecan tree roots decay fully and rapidly, so I'm trying to figure out the best way to fill the void with some sort of stable material. Everything I've seen online is to use a mix of sharp sand and topsoil, but that's going to be virtually impossible to move into the full length of the void. Is there a way to pump some sort of sand slurry or other material into the void?

If your garage has concrete beams in it, you probably don't need to worry about it. But if it were bad enough, and there were a huge voyages, you'd have to pump a cementitious grout into it. I don't think you're going to have to do this though.

jt2hunt said:

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If your garage has concrete beams in it, you probably don't need to worry about it. But if it were bad enough, and there were a huge voyages, you'd have to pump a cementitious grout into it. I don't think you're going to have to do this though.

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I have at least 12" deep beams.

YES indeed, SOP

Friend's in-the-day plumbing backup problems ala spec.house.builder, no license, no education BUT struct.eng.foundation slab.on.grade on bad soils. Poop don't run up hill, plumber w/license. WTH?

Dig dig dig ... awful & stinky ... replace pipe so it goes downhill.
Eng.formula slurry pumped into place.

That said, that was old school and a struct.eng these days could spec/supervise a foamed solution if docile enough a problem.

Know that I'm thinking back, I seem to recall when the garage was being built, there was concern they would have to mess with the tree roots to lay the foundation and my builder was worried it would kill the tree. Maybe they did cut some roots and the tree finally died after 10 years.

Tree is off to the right about about 6 feet from the corner.

I would talk to a plumber that does under slab sewers. They could probably refer you to a company that pumps that concrete slurry mix into the voids.

That said, we did redo under slab plumbing on our house where they pumped that in. When remodeling the bathroom later, there was still a massive void where they didn't fill successfully. Very empty under the old tub location. I think a good foundation on your garage won't be troubled by the root. Never hurts to ask though.

Better hope that sewer line never breaks. If you have to bust out all that concrete to get to it.

After seeing your slab before the concrete I would say you are good. A few voids is not going to hurt that foundation.

We have used these foam companies that fill voids or help lift sections of driveway that has sunk. But it is not cheap.

jt2hunt said:

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Better hope that sewer line never breaks. If you have to bust out all that concrete to get to it.

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There is no plumbing under the slab.

Sorry I wasn't referring to your project. I was referring to the other gentleman that had his plumbing redone and then filled it with slurry.

jt2hunt said:

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Sorry I wasn't referring to your project. I was referring to the other gentleman that had his plumbing redone and then filled it with slurry.

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Had I been paying attention, I would have seen that.

Yeah it's been fixed now with the remodel. Really difficult to fill all voids without cutting slab (at least what I could tell) - just seems like there would be settling regardless, but no engineer here.

On another note, I have a rental that I went to inspect a few years back. Toilet was rocking and when I flushed, I noticed water leaking slightly underneath it. Tenant (sweet older lady) never informed me. Had the plumber come out and flange had broken away from the sewer pipe. The amount of erosion underneath compliments of many flushes was crazy. If something looks suspicious, don't ignore it.