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Doweling into SOG

Doweling into SOG

Doweling into SOG

(OP)
Hi,

I am working on a basement remodel and have recently trenched approximately 120' lf (1' wide) of the existing basement slab for plumbing. Since most of the flooring under the trenched areas will be tile, I had planned on doweling into the existing slab on either side before I pour back.

My question is regarding the type of dowel and spacing I should be using.

- Should be I be using actual dowels, or will rebar suffice? I had hoped to use #3 rebar (partly for the next bullet point)
- I'm worried about spalling the concrete if I drill (4" sog), and with the trench being 12" wide I'm reduced to drilling at a slight angle. Will this be an issue?
- Is #3 bar enough? What should my spacing be?

Thank you for any help!!!!

RE: Doweling into SOG

We typically have not doweled in trenches like that. We have used a detail where the trench is cut and you leave 4" of undisturbed soil exposed along the edges for the repour to sit on. If there is a vapor barrier, it also allows enough room to splice in a new piece. then we place WWF within the trench strip. I would think this would work alright, but you probably want a decoupler membrane or something just in case.

RE: Doweling into SOG

You need *something* to keep differential settlement down, but not a lot. My goto detail would be #3 rebar @ 24" o.c. Embed about 4".

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

RE: Doweling into SOG

Dowels will function only to maintain continuity across the trench, between old and new concrete. In this situation, they may actually bridge the trench, supporting the new concrete. Over a 12" wide trench, you could probably cut grooves down from the surface about 2 inches deep and 3/4" wide. Place #4 bar across the gap, using a repair mortar where the dowels are in old concrete (high strength, low shrink.) Make the concrete in the repair area thicker, so it will not flex. If there is a chance of soil heaving/expanding below the repair, undercut the old concrete by a couple of inches so the repair in held up by the bars and held down by the existing slab. This will help assure continuity across the repair.

RE: Doweling into SOG

Ditto Manstrom #3 @ 24" o.c. and drill at a horizontal angle if needed for tool clearance.
Find the shortest bit you can

RE: Doweling into SOG

(OP)
If I do #3 bars 24" OC do I need to epoxy/grout them in?

RE: Doweling into SOG

yes.

RE: Doweling into SOG

I personally haven't done it, but I have seen partially installed tapcons being used in a similar fashion to the #3 dowels. Obviously, the spacing was much closer.

RE: Doweling into SOG

your chance of differential settlement is slim to begin with and greatly reduced by using good quality sand or gravel backfill and adequate compaction. hopefully your subgrade is not clay and you kept it as dry as possible.

unless you saw cut the existing concrete, you will have a rough surface that will provide interlock. you should not need dowels and drilling and doweling into 4 inch thick un-reinforced slab is questionable at best. that may create more problems than it solves. leaving a bench of undisturbed material so you have a T-top trench repair as mentioned above is another good method to support your new concrete but might require a wider slab cut.

RE: Doweling into SOG

(OP)
Unfortunately keeping the area dry was not an option as the trench was wet-saw cut. Existing subgrade doesn't appear to have any fines, so either a 3/8 or 1/2" clean gravel.

In addition, the new drain line we install we be near the bottoman of slab in areas, so proper compaction will be difficult for much of the area. Likely the same 3/8th to 1/2" clean gravel will be used for backfill in other area.

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