new concrete retaining wall / abutting existing rubble wall

[Ben29]

We had a series of (6) rowhomes burn down. There is now a 90' wide lot between the remaining rowhomes. My job is to design a ~90 foot long concrete retaining wall to separate the existing sidewalk from the monstrous "pit". We are retaining about 6ft of soil. The retaining wall design is easy enough.

The problem is that the new concrete retaining wall wants to abut (be in the same plane as) the existing front basement wall of the remaining house (which is vacant and probably condemned). I think the bottom of the rubble wall is at grade, or maybe 8" below grade at best. So I will undermine the rubble wall when we dig the footing for the retaining wall.

Another issue is how do I make the joint between the new and old walls?

 

[JoelTXCive]

Could you do some thing like this for the transition.

I'm not sure about the temp shoring. Could you post a plan view sketch?

 

[Ben29]

Joel: What you are showing in your sketch is exactly right. I actually had that same idea regarding the small 2-3ft wall return.

 

[Ben29]

 

[TRAK.Structural]

I would probably be looking to shotcrete the exposed portion of that existing basement wall, maybe with a mesh of #4 bars, just so it doesn't crumble during construction. I wouldn't make any hard connection of the new wall to the old.

I think your idea could work, but I wonder if you will start to lose soil material out from the bottom of the wall where the footing depth transition occurs. It's a little hard to visualize.

 

[jhnblgr]

Should be noted keeping the existing wall is a bad idea and likely will collapse since it appears to have been a basement wall and was braced at the top.

 

[rlmengineer]

I recommend removing the rubble wall and extend the new retaining wall. Too many hidden issues with the existing house and foundation. I would recommend a construction joint between the new retaining wall and whatever your client wants to do with the existing house and foundation to allow future removal without damaging the new retaining wall. I would also disclaim any damage to the existing house due to its condition.

 

[Mark_J]

This looks like Philadelphia. The rubble wall is clearly at the same bottom of elevation as it's no longer neighbors. Do you mean the front porch area?
You can undermine walls within reason, similar to an underpinning operation. You can even underpin the location of house that is about to fall down if you feel that area is problematic for the digging of the new footings.
I've never seen a rowhome like that need to remove the 6' stone foundation wall and replace with a concrete retaining wall for temporary support. Those stone walls stand on their own for many years.

 

[Mark_J]

I would think the building department would make the owner(s) backfill the pit. They don't like open pits next to sidewalks for extended periods of time.