16' or 8' or 4' Retaining Wall?

[Apache1]

Hi everyone, I'm designing a foundation wall (see picture below). Curious how you all would design a wall like this. Is it an 8' tall retaining wall? Is it a 4' tall retaining wall? Depending how I design this I will get wildly different results for the rebar in the wall and the footing size.

This is an approximately 25' long by 13' wide structure with full height concrete walls with wood-framed trusses bearing on the top. What I'd like to do is make sure the front and back of the wall are backfilled at the same time and then consider this a 4' tall retained height to get a 2' wide footing at the bottom.

What do you think?

 

[jhnblgr]

Bring the footing up to slab height, insulation under slab to protect from frost if unheated. Backfill will 3/4” clean stone at a 45 degree slope back and install drainage. Slab needs to be installed prior to backfill and don’t drive equipment around the building prior to roof install. Roof will provide later restrain and will have significant leverage. Check footing design and throw a jog into the wall to provide additional strength. All likely overkill.

 

[jayrod12]

He may need the depth for frost. Where I practice the frost is routinely over 6 feet. 8 foot basements are the norm.

This wall has the loads on it that are there. The roof diaphragm would provide support for the top of the wall.

 

[sdz]

[B]jhnblgr[/B] has a good suggestion to bring the footing up to slab level.
Can the roof provide lateral restraint? What if roof need to be removed? I would tend to not rely on the roof providing restraint and allow some movement at the top of the wall.
What about drainage, exterior loads, property boundary?
One possible arrangement is shown below. ​

 

[BridgeSmith]

Is it an 8' tall retaining wall? Is it a 4' tall retaining wall?

Neither. It's a 12' tall non-gravity cantilever retaining wall with 4' of embedment. It would typically be anaylzed as such, similar to how a sheet pile wall is designed/analyzed. The 4' of soil inside the foundation and the friction between the soil and the footing provide the resisting forces. The 8' of soil on the outside and the wind load on the 8' of wall above are the driving forces.

However, if the top of the wall is restrained by the roof system, then you have the equivalent of a tie-back anchor, which can be included as a restraint or ignored.

 

[JAE]

I wouldn't even call it a cantilever retaining wall - the roof is there to laterally take out any horizontal loading from the soils, assuming you can design the diaphragm to transfer the loads properly and also to be stiff enough.

 

[jayrod12]

Not counting on the roof, assuming it has plywood, is being overly conservative in my mind.

What if roof need to be removed

What if? You can't plan for future removal of structure in every project, or else you must be panicking all the time. What if someone busted out the slab adjacent the wall to put in a new sump pit? I've seen that all the time but don't plan for it at the original design stage.

 

[brucesilver]

Hi everyone, I'm designing a foundation wall (see picture below). Curious how you all would design a wall like this. Is it an 8' tall retaining wall? Is it a 4' tall retaining wall? Depending how I design this I will get wildly different results for the rebar in the wall and the footing size.

This is an approximately 25' long by 13' wide structure with full height concrete walls with wood-framed trusses bearing on the top. What I'd like to do is make sure the front and back of the wall are backfilled at the same time and then consider this a 4' tall retained height to get a 2' wide footing at the bottom.

What do you think?

If you're backfilling both sides at the same time and keeping the grade level even, then yeah, I'd treat it as a 4' retained height since there's no real lateral load differential above that. Just make sure the backfill stays balanced during construction. I've done similar setups and used 2' footings with vertical bars spaced for 4' retain height without issues. If there's any chance of unbalanced fill though, I'd be more conservative.