Water Uplift on mat Foundation

[fadyachkar]

Greetings:

We have a project composed of three basement floors and three upper floors. The basement footprint is larger than the superstructure, which leaves a part of the building with only three basement floors...

Water table level is at Ground Floor Level; i.e. all three basement floors are submerged.

Starting ACI 318-11, H is now specifically stated as being "lateral soil pressure" including water pressure, so we assumed that H accounts for the lateral water pressure and placed thw water uplift on the mat foundation as being F, fluid pressure.

If the water uplift pressure was placed in the combinations as H, then the stability of the whole building is not ensured and piles would be needed even under the footprint of the superstructure, which is not logocal...

Any thoughts

thank you

 

[chekre]

why it is not logical ? 3 floors as superstructure is not that much load and watertable at ground floor is too high.
Whenever u run ur analysis, u check whether uplift is ok. If it is not, either pile Either u increase the mass of ur building.
u must also pay attention to the construction sequence of your structure to see when to stop water pumping.

 

[fadyachkar]

thank you for your reply,

we found it illogical since the weight of the 6 floors + mat foundation - ALL concrete - provides a safety factor exceeding 1.2. the issue is when using 0.6D + H, if H should include the hydrostatic pressure

I think this was the reason behind adding a clear definition in ACI 318-11 for H as being the lateral pressure

 

[manstrom]

IMO, part of the 0.6D factor is becasue of an overestimation of dead loads. It is conservative in most situations, except uplift. Maybe the LRFD factor would help?

If you need more uplift resistance, consider the soil-wall friction or the amount of soil over the footings (if you have some).

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[chekre]

i have used 0.6dl in one of the projects and included the waterpressure. However, i had above the podium around 15 floors. So the above combination dictated when pumping should stop. At working conditions, i didnt have any problem with the watertable.
i would say include it since the code dosnt make any exception.