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Basement Slab Repour & Excavating Near Footing

Basement Slab Repour & Excavating Near Footing

Basement Slab Repour & Excavating Near Footing

(OP)
Hi all.  I'm an EE who's working on renovating my house.  I appreciate all input.

FACTS:

- House was built in 1950. 1-1/2 story.  600 sq ft footprint.  Original basement slab was in horrible shape.  Opted to remove existing slab and repour.  The base is clay.  Very high water table but waterproofing / weeping tile is in place.

- Height was under 7' so we wanted to lower the new slab to be level with the footing.  I had a structural engineer take a look and provide a stamped drawing.

- The drawing shows the cross section of the foundation, and calls for a new footing to be poured next to the old one, and for the new slab to be tied into the existing footing with rebar.

- The drawing calls for the bottom of the trench for the new footing will be a full 4" below the bottom of the footing.


QUESTIONS

- Is it safe to excavate the trench for the new footing along the perimeter of the house?  Everything I've read says no and excavating should be done at a 45 degree angle at the footing.

- Is it safe to drill into the existing footing to install a 24" rebar grid for the new slab?

- Is the additional 8"x8" footing absolutely necessary?

- I've read online that basement slabs are typically poured on top of the footing to provide lateral structural support to the foundation.  Is this true?


THANKS

I am getting a lot of varying opinions from other engineers (civil) and contractors.  I appreciate any input I could get here!  I have attached photos and a portion of the drawing.

 

RE: Basement Slab Repour & Excavating Near Footing

I'm sure you'll get many replies for this one....many of them different.
I'm not exactly sure what the engineer hoped to accomplish with the new 8"x8" "footing".  I personally have never seen that done.
His drawing is assuming that the wall is keyed into the existing footing, which it very well may be, but it also may not be.
Yes, We count on basement slabs to take shear force at the base of the wall. In simple terms, the slab keeps the wall from being pushed in by the exterior soil pressure.
Being that the wall is reinforced concrete, it may have rebars extending into the footing. If done properly, one would not need to count on the slab to take shear from the base of thee wall.
I also can see no reason to dowel the slab into the existing footing.

The only pitfalls I can think of to just re-pouring the slab lower are:
1). no slab to count on for shear at the wall base
2). It may be be easier for water to make its way in.

Suggestions:
Now that you have the slab torn out, NOW would be a great time to put in a new INTERIOR footing drain complete with gravel and a sump well. The hard work is done. Even if you just put the drains and sump well in and don't put in an actual pump and discharge. If you ever have a water problem, you'll really wish you had done it.  

RE: Basement Slab Repour & Excavating Near Footing

by the way, Jimi rocks.  

RE: Basement Slab Repour & Excavating Near Footing

(OP)
Thanks for the advice.  I am actually planning on doing an interior weeping tile system while I've got access.  Will also seal the joints to prevent water intrusion.

The engineer indicated that the new 8"x8" footing is required to support the slab.

I am not sure that the foundation is reinforced, keyed, or tied to the footing with rebar.  I have no way of knowing this.

Can't wait to get this done so I can get my Jimi posters up on the wall! :)

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