Hydrostatic pressure under SOG?

[Blue1997]

I'm trying to understand a situation that occurred in my office. This is not my area of expertise, but I'd still like to know why the decision was made. In a nutshell: someone specified water proofing, the contractor pulled it in VE and replaced it with a vapor barrier. From the geotechnical report, there's no issue with the water table. However, there a small 3' depressed area, SOG, and the decision was to fight for waterproofing in that area. Why? I was told rain water or sprinklers would produce water that would exert hydrostatic pressure on the slab. I get the walls, but how can water flow down and then push up on the slab? Like the elevator, there a perforated pipe lining the 3' wall. If the pipe wasn't there, would that be an issue? I'm having trouble grasping the physics behind this hydrostatic pressure under the slab. How can there be a head pushing up? Im totally missing something here. I appreciate your thoughts.

 

[fattdad]

Water won't make a right or left hand turn just to bother your slab. If the sprinklers go off and the water moves through the upper slab, the water will percolate vertically downward to the water table. The water table will mound and such mounding (if it's prominent enough) could come in contact with the sump/lower slab grade. Then again, what's the chance or that happening?

f-d

¡papá gordo ain’t no madre flaca!

 

[cvg]

waterproofing does not protect against hydrostatic pressure, i don't think that is the real issue. water could seep through the cracks in the slab though, the vapor barrier might not be able to prevent it.