Upside Down Retaining Wall 1

[RM87]

Hello folks,

I've been dealing with a challenge that I could definitely use some help on.

My client is looking to build a home on a relatively steep slope, going downhill from the face of the structure. The garage, which is at the face, is at the highest point at grade, and the grade continues to dip such that the worst case scenario is that the back of the wall of the garage is 12'-6" above grade.

I was thinking that an upside-down retaining wall, where the stem walls would serve in retaining the soil from below the garage, and the toe, which would serve as a mat slab, would be an alternative. Would this work? Any special considerations I should make note of?

Does anyone have any better ideas? A conventional retaining wall is not an option because of the proposed structures proximity to the neighbor.

Thank you,
R

 

[GeoPaveTraffic]

I would have to see a sketch to understand what you are trying to accomplish. Would also be helpful in understanding the site constraints.

On the surface, it sounds like someone is trying to jam too big a structure onto to small of a lot.

Mike Lambert

 

[BUGGAR]

Not totally sure what you mean but we have used drilled piers with a retaining wall spanning horizontally between them at the toe of a slope to retain the soils.
If your retaining wall is tied back into the house, analyze the block of soil beneath and make sure the whole thing won't move. You may find yourself saying to your neighbor, "Mi casa es su casa".

 

[RM87]

Forgive the poor drawing, but this is an 'artistic' section of what I'm proposing.

Any thoughts?

 

[BUGGAR]

Where's the grade outside the retaining walls? How will you construct this? Do you have a soils engineer to help you?

 

[RM87]

The grade outside the retaining wall would be at the bottom of the stems. I would probably design temporary shoring confining the soil within, and pouring or shotcreting the face of the concrete walls. No input from the soils engineer yet.

 

[msquared48]

You would need probably three levels intermediate concrete encased tie beams, the first at the bottom, intermediate and top, depending on the height of earth retained, all to keep the walls from spreading without external shoring. This can be done, but you are looking at hand tamping the fill. the two walls 90 degrees to this would be interesting...

Mike McCann, PE, SE (WA)

 

[GeoPaveTraffic]

Wouldn't it be easier to just put a structural floor in for the garage?

Mike Lambert

 

[hokie66]

GeoPaveTraffic's solution would be mine. You can use the void under the garage for storage, and you don't have to bring in all that fill material.

 

[BUGGAR]

Maybe construct it like a marine pier: set sheet pile (or equiv.) walls with tie backs between them, backfill and add more levels of tie rods. You could backfill with soil cement or lean concrete to keep lateral loads low. Angle the tie rods at the corners like at cofferdams.
Marine dolphins are built like this all the time.

 

[RM87]

@Geo and Hokie - I suggested the very same thing as well. The issue is that the planning department in this particular area is militant about uninhabitable space being converted illegally into habitable space, from what I've been told.

@Buggar - I think I'm understanding what you're saying, but do you have any samples I can look at?

 

[BUGGAR]

A lot of the piers in San Diego are constructed using sheet pile walls with cross ties. The Edmonds Ferry Terminal up in Washington, too. The sheets are driven to depth to restrain the toe but your design would allow low level cross ties to hold the toes.
I've also seen MSE walls (mechanically stabilized earth?) similar to what you are doing and refer you to the manufacturers of these systems.