Originally posted by: MrDudeMan
ok, im sick of the crap being thrown around by googer about basements. ive designed 300+ foundations in areas that you would think were impossible to develop. a high water table means you need an engineer that isnt a retard; thats all. in Irving, Texas, the water table is 5-8 feet below surface, yet we still manage to build houses on steep hills with no retaining structures to hold the load. go figure!
high water tables are EASILY countered with piers. below water, there is always rock. soil has a safe loading pressure of 1500lbs/in^2, but you can go up to 4000 since 1500 has a large safety zone built in. all that matters when you are designing a house is the potential vertical rise (PVR) and plasticity (PI). if you have a PVR of > 4", that means the height in the soil can change 4 inches in the span of a year (or 4 seasons, including 1 wet and 1 dry season). in Irving, ive designed 150,000sq. ft. multi-level slabs on a PVR of 14-16". that takes a big crap on residential contruction criteria, even in a place like florida.
the second factor is PI. that is the soils ability to retain water without swelling. the higher the PI, the less water it can hold until it starts losing its ability to retain usable Qu (loading pressure). the worst it gets is high 70s or low 80s (found mostly on coast lines). again, once you hit that saturation, you rely on the engineering. how the hell do you think they build skyscrappers and massive hotels on coast lines? surely if that can be done, a house with less than 4000lb reactions (specific force at a point in metal structures) can have a basement.
as for new orleans, it is no different in terms of PVR, PI, or Qu than anywhere else that experiences unfavorable soil conditions for construction.
edit: i forgot the most important part of this...basement design! basements are sometimes less susceptible to movement than the actual house. a properly designed french drain and sump pump can keep any basement dry. if you guys dont think so, its just because wherever you have lived, the builders were using the "cheap" or "light" engineers. if the engineering is done properly, there is almost no obstacle which can not be overcome for residential use. dont forget that prestressed concrete can hold many thousands of pounds for long distances, and only the perimeter of a house is going to lift or sag, so once again, proper engineering will counter this water "problem".