residental building on foundation slab with or without edge beam?

[greznik91]

Hi,

A new residental buidling will be build on the ground that is lower than the surrounding terrain (for aprox. 0,50 m).
I'd like to elevate the foundation slab for 0,40 m so the new structure will be around the same level as surrounding terrain.
Should I design an edge beam around the perimeter of RC foundation slab (edge beam is bellow existing terrain and bellow frost zone) or
is there an option to make the foundation slab with no edge beam - to put compacted gravel on existing ground/terrain and then make a foundation slab on top.
I'm going back and forth about this with some client and a contractor which are certain it can be done without an edge beam.

 

[phamENG]

Probably a bad idea. Not sure what country "SI" refers to (Singapore?), but if it's even an option I'm assuming you're in a tropical zone where 70 degree weather brings out the winter parkas. In other words, frost heave must not be a concern. Even so, US building codes require at least some amount of embedment into the underlying soil even if frost depth is essentially non-existent.

Erosion is going to be a big issue if you don't. A little bit of surface runoff will get under the slab and wash out the foundation. Using gravel under the slab may help, but probably won't prevent it forever.

 

[BSVBD]

I don't see the plan view for your site plan, but, in order for you to provide enough gravel/soil to taper the grade enough to prevent detrimental erosion, I would think that the material cost for gravel and other "finished" earth/soil along with the labor cost for necessary compaction would exceed the cost for the concrete edge/grade beam.

 

[greznik91]

Thank you for replies. Frost is an issue. Just that alone should be the reason for the edge beam in my opinion. But contractors are never fond of it. How about seismic forces? If structure is build on compressed gravel alone (without any foundation embedment in the terrain) everything depends on friction beween compressed ground and foundation slab.

 

[phamENG]

If you're in a seismic zone, then this would certainly be a no-go. Tell the contractor to do it, or move on to the next job and the owner can find a new contractor.

Same contractor? thread507-469685