Floodproof by compaction
Floodproof by compaction
(OP)
I have a building that will be in the floodplain.... FF will be 8' below flood elevation!!
While we are dealing with 8' of water pressure on the walls we are also dealing with a large bouyancy pressure... or are we?
The geotechnical engineer came up with a theory that if we compact the soil underneath the building so that the flood water penetrates it so slowly that bouyancy never has a chance to develop. He theorizes it would take weeks of standing floodwater for the bouyancy force to develop which is much longer than a flood would last.
Has anyone used this rationale to "floodproof" a building?
Any help is appreciated.
While we are dealing with 8' of water pressure on the walls we are also dealing with a large bouyancy pressure... or are we?
The geotechnical engineer came up with a theory that if we compact the soil underneath the building so that the flood water penetrates it so slowly that bouyancy never has a chance to develop. He theorizes it would take weeks of standing floodwater for the bouyancy force to develop which is much longer than a flood would last.
Has anyone used this rationale to "floodproof" a building?
Any help is appreciated.





RE: Floodproof by compaction
Along comes the flood. Water is stacked up on the ground surface and adjacent to your building. Let's say there's 8 ft of water just sitting on the ground. How long does it take to fully saturate 5 ft of unsaturated ground?
Well, somewhere in this problem lies D'Arcy's law. We don't know the soil permeability, but we do know that 5 ft of soil only has about 1 or 1 1/2 ft of voids and we know that from time zero (i.e., if you could just wish the water in place) the hydraulic gradient is REALLY HIGH. I mean if you have 8 ft of water head in instant 1 that's 8 ft of head acting on a minescule "length."
I'd never buy into this concept; well unless I'm really missing something.
I would worry about your building "popping" off it's footings though. I could imagine you'd need at least 5 stories above flood stage (or tie-downs) to resist the bouyancy of the building.
f-d
¡papá gordo ain't no madre flaca!
RE: Floodproof by compaction
Will the interior of the building flood? Wouldn't that negate the bouyancy and wall pressure?
Could you build it like beach houses in storm surge areas, with ground floors designed to withstand flooding and breakaway walls that allow the floodwaters to pass through without overloading the support columns?
Maybe the tyranny of Murphy is the penalty for hubris. - http://xkcd.com/319/
RE: Floodproof by compaction
FEMA discourages dry floodproofing for flood depth of 3 feet or greater. 8 feet of flooding is not likely to be approved, regardless of what your geotech thinks. Either way, your local floodplain manager would need to approve this and you should ask them if they have ever approved such a thing.
RE: Floodproof by compaction
We have the lateral hydrostatic pressure on the walls covered... it's the bouyancy force we are wrestling with. The first design was to anchor down the interior slab with helical anchors to counteract the bouyancy.... this got real expensive.
Now the Geotechnical Engineer comes up with the theory of densifying the soil around and below the building such that hydrostatic pressure needed to cause bouyancy under the building would take so long that the flood would be gone before it could develop.
Obviously we aren't quite comfortable with this approach or I wouldn't be posting here. I'm wondering if anyone else has used this approach....
Thanks for your time.
RE: Floodproof by compaction
I'd concur that you need to account for buoyancy for slab support.
f-d
¡papá gordo ain't no madre flaca!
RE: Floodproof by compaction
RE: Floodproof by compaction
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Floodproof by compaction
RE: Floodproof by compaction
RE: Floodproof by compaction
RE: Floodproof by compaction