Undergound Parking Garage Floor Question

[cvanoverbeke]

I just received an geotechnical report for an undergound parking garage which has some issues since it is below the water table. The geotechnical engineer states thtat the slab on grade floors should be independent of load bearing walls and columns. This is going to be the case.

However they state the floor slab should be design for a subgrade reaction (k) of 30 MPa/m. Can someone explain this reaction force?

Cvanoverbeke

 

[dik]

The modulus of subgrade reaction is a measure of the stiffness of the underlying soil and the value quoted is pretty competent stuff... You could use a 4" or 5" concrete slab; for commercial stuff, I don't generally use anything less than 5". Control joints, slope and sawcutting time is critical.

Also if below the watertable, then you might look into using 'pop-outs'. These are formed plugs that lift to reduce the uplift force. If the water flow is sufficient, you may have to size pumps that can handle a lake1! Else, subfloor drains and a good sump system can work OK and use the pop-outs for added protection.

Use rebar with 2" conc cover and provide the owner with a maintenance 'manual/schedule' Also make sure there are hose bibs to encourage flushing the slab if deicing salt is an issue and try for minimum 1-1/2% slopes to drain.

Dik

 

[cvanoverbeke]

Thank you for the explanation.

Regards,
Cvanoverbeke