Slab On Grade Foundation For G+3 Structure??

[TekEngr]

I am designing a slab on grade foundation for G+3 hospital building, loads are coming on slab foundation through LGS walls and steel columns (UDL loads and Point Loads).
Plot is 1.5m deep from adjacent road level so we have plan to fill that plot with special granular material up to road level so we are expecting bearing capacity of new surface is about 125KN/m^2 (existing SBC 75KN/m^2) .
Water table is 2.5m deep from new surface.
So my question is that, under these conditions slab on grade foundation is suitable choice for ground + 3 stories hospital structure??

 

[WARose]

I am designing a slab on grade foundation for G+3 hospital building, loads are coming on slab foundation through LGS walls and steel columns (UDL loads and Point Loads).
Plot is 1.5m deep from adjacent road level so we have plan to fill that plot with special granular material up to road level so we are expecting bearing capacity of new surface is about 125KN/m^2 (existing SBC 75KN/m^2) .
Water table is 2.5m deep from new surface.
So my question is that, under these conditions slab on grade foundation is suitable choice for ground + 3 stories hospital structure??

No. (At least not usually.) Slabs on grade are typically for moving vehicular loads and have light reinforcing. (And cracking doesn't have dire consequences. Especially since we are talking permanently placed loads.) What you probably want is a mat (especially since we are talking a hospital). But even that choice will depend on several factors....one of which is sub grade modulus.

You could ultimately wind up with spread footings and grade beams with a slab on grade in between. Just depends on how the numbers work out.

 

[TekEngr]

Actually my planing is to design this foundation as mat/raft foundation but now only question is that i can place this foundation on grade? So it will become raft/mat foundation on garade.
Is it possible?

 

[jayrod12]

That would be a good question for the project's geotechnical engineer.

 

[oldestguy]

I think it is a question that should not be posted here. It is likely not possible to provide sufficient information and thus do not expect the best answers can come via this medium.

 

[WARose]

Actually my planing is to design this foundation as mat/raft foundation but now only question is that i can place this foundation on grade? So it will become raft/mat foundation on garade.
Is it possible?

Depends on your loads and what the geotech tells you. You said you are "expecting" a bearing capacity of 125 KN/m^2. That sounds ok for 1-2 story commercial structure (i.e. with timber/light gauge framing).....but if you are pushing 3 stories and it's got a masonry veneer......not sure about that.

You need a geotech to verify your bearing pressures and to give you spring constants/settlement values. Your question is a bit too nebulous to give a definitive answer on at this point.