Combination of Heave and Water Pressure

[smonver]

I am designing a building with 6 basement and as it is low rise we have to go for raft.
As there is heave pressure along with a water head of 22.5m I am not sure that whether in floatation check I have to include both heave and water pressure or one at a time.
Similarly in Service and Ultimate load case I have to consider both together or sepratly. It would also be helpfull if anyone can define Load combination for both SLS and ULS.

 

[BAretired]

Heaving pressure does not cause flotation, so only the water pressure must be considered in a flotation check. Sounds like a nasty site.

The raft must be sized so that the dead weight of the building plus raft exceeds the weight of displaced water. Then, of course, the raft must be reinforced for uplift pressure of 22.5m of water...wow!

 

[DaveAtkins]

Are you off by a decimal place? Is the hydraulic head 2.25m instead of 22.5m? If not, are you telling us this mat is 73.8 feet below the water table? Something doesn't sound right.

DaveAtkins

 

[kslee1000]

Can you identify the cause for "heave"?

 

[hokie66]

Heaving is normally associated with gain in volume of moisture sensitive clay. But if the clay at the level of your mat is 22.5 metres below the water table, the water content will be stable, thus no heave.