DAYLIGHT BASEMENT ELEVATED FLOOR REACTIONS

[jnichol]

Just wondering what other do here.

Working on a project with a 13' tall daylight basement. the building is rectaugular, 140'X60'. Really I have (4) shearwalls for earth loading on the 140 foot side, each wall is roughly 15' long.

The at service at rest pressure is really high at 65pcf. I started by designing the wall as a foundation wall (pinned at top) but that service reaction is 2700#/ft. to transfer that force I need a deck attachment of 2500#/ft (possible on an elevated composite slab but stretching the limit of the system). Also I would need drags to transfer the force into the 15' walls, and that connection for drag force into the wall would be messy.

Next option is to simply design the wall as a cantilevered retaining wall and not worry about transfering force into the slab, but my footing get to be large to stop sliding.

I know the obvious answer is to use soil nails or something, but I am wondering what others do in this situation, Thanks

 

[civilperson]

Build a key under the cantilever retaining wall or thicken the footing for pressure on the non-retained face of the footing. Analyze the shear walls as sharing the load with the cantilever footing (similar to a concrete buried tank with the edges and bottom fixed, top hinged or free).

 

[scottiesei]

I have used keys before and they help quite a bit for sliding. If you do design the wall as a cantilever, make sure that load does not get transfered floor/roof system as it will not be designed for that force. Depending on your shear wall orientation, maybe consider designing the walls horizontally, not vertically.

 

[skier1578]

In this case we typically (residential applications), design the wall as cantilevered with a key as necessary and ask that the backfill be compacted to 90% BEFORE the floor diaphragm is connected to the wall, if it is attached at all. Also, your slab may be able to help you in the sliding problem.

 

[tdsull]

Can you analyze the wall as a rectangular plate fixed on three sides and free at the top? I just did that with a 15' tall fondation wall with soil pressures of 55 pcf.