Pouring the opening in existing slab 1

[trivedi123]

I need to fill the approximate 3'x3' opening in existing slab.
The slab is designed for 25 psi ultimate loading and is 9" thick with #6 rebar's T/B each way.
Any suggestion for designing the area? I can drill and use dowels in existing slab but area is small for matching existing reinforcement in the opening.

 

[SlideRuleEra]

Make sure the subgrade for the patch is thick, very good material that is well compacted. Don't just rely on whatever soil is present at this time.

I would drill and epoxy #6 rebar dowels, say 4 dowels on each of the four sides. Suggest a pattern such as my sketch, below, to avoid rebar congestion in the corners. This still allows one dowel be located reasonably close to each corner. Evenly space the dowels, without regard to the location of the existing rebar. Ideally the drilled holes will be near the center (vertically) of the existing slab. You may have to adjust to miss the existing rebar mat. Use #6 rebar (5 bars, each way) inside the patch, positioned to tie to the dowels.

This is one of those times when, IMHO, you do what can be reasonably done.

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[trivedi123]

Thanks, SlideRuleEra.
This opening on tunnel underneath so new slab portion will not be slab on grade but framed into existing slab. The existing opening is preplanned so I am suspecting additional rebars around the opening and opening has edge protective angles all around the opening that need to be removed also.

 

[JAE]

We've used a detail like this one - with variations depending on slab thickness, etc.

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[trivedi123]

Thank you guys