basement slab thickness
basement slab thickness
(OP)
hi,
I'm noy familiar with basement construction to begin with; however, I'm asked to do a quick costing on basement carpark slab. What is the minimum thickness if the ground water table is above the slab? I'm using grade 30 concrete.
Any site I can browse for such information?
What sort of hydrostatic load from the bottom of the slab is expected under this circumstance?
Is subsoil pipe necessary under the slab to relieve the upheaving pressure?
thanks
I'm noy familiar with basement construction to begin with; however, I'm asked to do a quick costing on basement carpark slab. What is the minimum thickness if the ground water table is above the slab? I'm using grade 30 concrete.
Any site I can browse for such information?
What sort of hydrostatic load from the bottom of the slab is expected under this circumstance?
Is subsoil pipe necessary under the slab to relieve the upheaving pressure?
thanks






RE: basement slab thickness
In any case use the stricter measures for crack control (max mechanically caused crack width 0.1 mm) is recommendable, and also to get the more impermeable concrete available, what may mean using special concretes with mass impermeabilllizers, or important quantities of cementitious materials, significant part of them fly ash to help pore oclusion.
Rubber stops may be required, or alternative sealing of joints with special damp-proofing mortars.
RE: basement slab thickness
RE: basement slab thickness
thanks for the response.
More questions, supposed the ground water is 10 ft above the basement slab, does that mean the ground water pressure act on the bottom of the slab is 10ft by water density by factor of safety?
f of s X water density x elevationtion difference = pressure acted on the slab from the ground?
if so, what foundation system is appropriate?
I was thinking of the conventional one way joist-slab system with pile cap at column point; however, I found out that I need a beam of 5ft deep by a foot width main beam since the tributary area is about 640 sq ft between 2 columns(27ft c/c on main beams, floor joist of 27ft to the main beam, the grid is a 27 ft by 27 ft main beams with a 27 ft joists in the middle of the grid).
I thought of adding intermediate pilecaps to reduce the bending & shear of the main beams but that would mean tension to the intermediate the plie caps.
RE: basement slab thickness
Respect the safety factor if not enforced by code, can be minimum, since the flotation force from water is very exactly known. Then 1.2 may be enough, but ensure you count all the volume that can be submerged to generate flotation.
The tension piles need however be dimensioned with about the usual safety factors to give the allowable tension atop. I usually wouldn't consider a safety factor under 2 for the piles in tension except if an in situ pull out test has give me direct assessment of what to expect.
RE: basement slab thickness
You can also use the dead load of the superstructure to resist the uplift.