inert landfill foundation

[msucog]

anyone ever built on an inert landfill? the landfill consists of 40-100' of trees, wood chips, strippings, concrete, cured asphalt, etc all mixed/capped with a few feet of soil per say 10' layer. other than the obvious issues of getting piles through the debris, venting, downdrag, etc, does anyone have stories or critical points for something similar to what i describe? we're recommending to not build on it (maybe make it a park or something green) but i'm open to suggestions. thanks.

 

[CarlB]

The situation I was involved in was more like 30' to 40' of landfill, maybe 2' to 6' of cap. It had the issues you mentioned. A vehicle maintenance building was supported on piles. A membrane was placed under the building, and a gravel layer with perf pipes to intercept gases. I believe it was just passive venting. Another issue was the local DEC was concerned that the piles would allow contamination to pass to a lower aquifer.

 

[Stego1]

If there are trees and wood chippings in it, it isn't inert!
As CarlB says Environmental Regulators may be concerned about creating a pathway for contaminants down to virgin ground, although there are methods you can use to minimise this. See UK Environment Agency publication NC/99/73 "Piling and penetrative ground improvement methods on land affected by contamination:guidance on pollution prevention". available here

http://www.environment-agency.gov.uk/commondata/acrobat/nc_99_73_piling_.pdf?lang=_e

One problem we encountered when advising a client who wanted to build over a landfill was (passive) vent spacing which pretty much got in the way of his proposed operations (large wagons etc). Maybe active venting would not require such close spacing but our scheme didn't progress much further.
Hope this helps!

 

[msucog]

http://www.gaepd.org/Files_PDF/techguide/lpb/swinertlfg.pdf

inert landfill by georgia definition

i hope my client makes it a community park or something. they've got it in their head to put in driven h-piles...they apparently have more money than i would know what to do with.

 

[Stego1]

UK landfill regs definition of inert waste is...

(4) Waste is inert waste if—
(a) it does not undergo any significant physical, chemical or biological transformations;
(b) it does not dissolve, burn or otherwise physically or chemically react, biodegrade or
adversely affect other matter with which it comes into contact in a way likely to give rise
to environmental pollution or harm to human health; and
(c) its total leachability and pollutant content and the ecotoxicity of its leachate are
insignificant and, in particular, do not endanger the quality of any surface water or
groundwater.

I would have thought vegetation cannot be inert as it can potentially produce gas as well as creating voids?!

They seem to like building schools over old landfills and gasworks over here!!

 

[oldestguy]

I've run into situations of similar nature, such as 100 feet of zero blow count orgainc silt, old landfills discovered durin the job, etc.

For light buildings, such as houses or a few stories of apartments built of wood, the foundation is built as a raft, heavily reinforced. Some are upside down waffle grids, others are a single thickness slab. The recommendation to the structural engineer is design any part of the slab to span at least 10 feet, maybe 15 feet square of nothing below. Expect some differential settlement, use control joints at all wall openings, etc. To date have never had a subsequent problem come up for these jobs

One job was a long 2 story apartment building, with the basement designed as a floating box, with side walls doing the beam action. Over a period of 20 years, plus, one end settled about a foot, yet no one in the building complains of sloping floors. Doors and windows work fine. Outside appearance shows no distress.

Add venting if methane production is expected.

 

[msucog]

thanks for the responses. we completed the drilling and the landfill portion is definitely 100' deep over a larger portion of the area. it contains large trees and massive stumps "fields", 20-30' thick layers of chippings/strippings with a few feet of soil scattered in layers throughout. i double checked a few of our borings with refraction microtremor and it indicated a similar depth to a velocity shift. all that added to the land owner's description of what's out there and we've got a good idea of what's there. the potential owner is considering deep foundation support...we reminded them of significant costs associated with doing such and suggested making it a greenspace area/park. we also noted that methane vents would be needed if they put buildings on this area.
i suppose they could also surcharge the area since they'll have soil coming from the other 1000+ acres but then again it might not be economical if they still get organic decay over time. the "good news" is that there is no water currently present in the fill layer (best we can tell from borings and based on the 100' slope adjacent to this area). they'll have plenty of blast rock that maybe they could fill another 20' or so with it then surcharge with an additional 30-50+ feet if they want to put very light buildings on it that can withstand erratic settlement over the long haul. i'm not sure how surcharging will effect the railroad adjacent to the area...the mine cut is probably 80' down in the area closest to the railroad so it's possible that it wouldn't be messed up but i wouldn't count on it. as it turns out though, the railroad may be shifted and rebuilt to allow for a roadway under it so it might not be an issue anyway.
anyway, thanks again for the input.