Do ramp interiors need backfill?

[StrEng007]

I have a 6 foot wide pedestrian ramp that climbs up to a 7'-0" elevation (1:12 pitch). This is an exterior ramp that will be used as primary egress. The ramp walls are reinforced CMU and there will be a concrete slab at the top to create the walking surface (handrails and guards post-installed). Is it necessary to backfill the inside of the ramp walls if the walking surface can span the 6ft wide ramp as a structural slab? Or is it best practice to backfill the inside of the ramp walls and treat the slab as a slab on grade?

If backfilling is required can the slab act as a tension tie (I would provide adequate reinforcing and not allow slab joints parallel to the path of travel). This would allow me to keep the top of wall restrained (using the at rest pressure coefficient Kp). Or must the wall be designed as a pure cantilever during the backfill process, before the 'tie-slab' is placed? I'm not sure what means and methods are available for bracing the wall during backfill, if any.

 

[Enable]

Tad drunk on Yeni Raki at the moment (Armenian wife and all) but why would you think it has to be one way or the other? Design it how you want! The only thing you need to consider is that there must be a form surface for the base of the slab. Obviously earth fills this role quite well, but if you want a suspended slab you could also use a combination of earth + void form or else angles bolted to the CMU and metal deck between (could use plywood but some dont like that for fire reasons).

Usually walls would be designed as cantilevered. If they couldn't be for some reason, there can absolutely be bracing placed on the exterior but that would be unusual and you should call that up on a note.

 

[StrEng007]

bracing placed on the exterior but that would be unusual

OK, that's the bit I was looking for. To use the most conventional approach, I will assume cantilever walls.

 

[XR250]

If you use fill, def. design as a structural slab as the fill will likely settle.
Sometimes, I will give the contractor the option of building the walls pinned - pinned and throw it in their court to provide the external temp. bracing or just cross his fingers. Depends on his budget and if the footings are already poured.

 

[StrEng007]

Thanks. This is a tight budget and I can already hear complaints about having to increase the block size.

However, due to logistics I know they won't be spending the time to figure out how to temp. brace this.

 

[Celt83]

Take a peak at this thread may be able to reduce the soil pressure a little bit, Link
Could also provide a layer of geofoam to reduce the amount of soil.

We usually fill with soil which accomplishes giving them a form for the slab and limits the void space which in some of our jurisdictions is required to attempt to mitigate rodents.

 

[bones206]

If the wall is designed as a cantilevered retaining wall and the top of the wall extends past the slab, then I let the slab float like a typical sidewalk with compacted fill.