Bearing resistance capacity of large slab fundation?

[drile007]

Hello all,

I'm not soil mechanics expert but I know something...
I have a large slab fundation which one part is "supported" by basement concrete walls. I don't know how to calculate bearing resistance (with well known equations Terzaghi, Mayerhov, Brinch Hansen equations):
1) As one large rectengular footing with eccentric loading of the whole structure or.
2) As one small 1m2 rectengular footing with loading on that m2?
Which depth should I take for the embedment depth?

Thank you for your comments

 

[jdonville]

drile007,

Without a more complete description of your situation, it is not possible to answer your question. However, I will start by asking some clarifying questions:

1) What are the overall dimensions of the slab/mat (H, W, D)?
2) Where is the "basement" wall located? Is it structurally attached to the mat/slab?
3) What are the dimensions of the basement wall?
4) What is the basement wall founded on?
5) What is the nature of the load on the slab (how large, and how is it applied)?
6) What kind of soils are located below the slab?

Jeff

 

[drile007]

Hi Jeff, thank you for your interest. Here are the answers on your questions:

1) Overall dimensions are 60x40x0.5m. Superstructure (it's shape is in L letter with width of 12m) follows left and lower side of rectengular foundation slab. Superstructure have 5 storeys (obove the ground) and the basement with one storey under the ground.
2) Basement walls are located under superstructure and are attached to the foundation. Remaining area (outside L) is covered with grid of columns (7.5x7.5m).
3) Basement walls are arranged in grid of aprox. 5.0x7.0m. Walls are made of reinforced concrete since the structure is located in seismic area.
4) Basement wall is founded on foundation slab.
5) The major part of load come from the superstructure slabs (dead and live loads) into the walls which are extended from top storeys to the foundation slab. This walls are then supported with foundation slab.
6) Below the slab are the layers 0-0.3m humus, 0.3-1m GM, 1-2.9m GW-GM, 2.9-3.4m GC, 3.4-3.6m CL, 3.6-4.1 GC

I hope that I've clarify all the question since my native language is not English (I'm not sure in meaning
of the word superstructure->Part of the structure above the ground?)

Drile

 

[jdonville]

drile,

Your situation is complicated by the size of the slab and the wide variety of loads supported on it, as well as the variation in supporting soils (for which you did not provide any data beyond the classification and thickness). The slab will, depending on the magnitude of the applied loads, have a very large zone of influence within the foundation soils.

I recommend that you get a local geotechnical engineer involved immediately.

Jeff