Building on Organic Soils
Building on Organic Soils
(OP)
We will be building a lightly loaded commercial warehouse (1 storey). Organic layer about 15 ft thick is present below 20 ft from proposed floor level. Building loads will not structurally affect the organics. We are concerned about settlement due to secondary effects such as volume change to decomposition. The organics are below water table and we think that they will not oxidize( aerobic) as it happens in most swamps settling. However we are concerned with the anerobic reduction of volume causing settlement.
Need Help in estimating settlements. Then we can decide on foundation options.
Any help?
Need Help in estimating settlements. Then we can decide on foundation options.
Any help?





RE: Building on Organic Soils
how far below the water table are these organics? you currently experiencing a drought or in a wet area?
without knowing any real details, it sounds like i'd be more concerned about the consolidation of the materials themselves even before the results of organics...but that's just me.
RE: Building on Organic Soils
RE: Building on Organic Soils
Secondary compression can be a concern on organic soils, but again, I'm not quite sure these are truely organic soils. Do the liquid limits using both the wet-prep and the oven-dry-prep methods and see if the oven-dry prep liquid limits are 25 percent lower then the wet-prep LL. If not you are not dealing with an ASTM "organic soil" and unlikely to expect "organic soil" behavoir (i.e., high coefficient of secondary compression. Additionally, if there is no additional load from the proposed construction (and no appreciable fill) this is a moot point.
Hope this helps (or at least doesn't further confuse - ha).
f-d
¡papá gordo ain’t no madre flaca!
RE: Building on Organic Soils
Sounds real strange to me.
Mike McCann
McCann Engineering
RE: Building on Organic Soils
Just an aside. . . . .
f-d
¡papá gordo ain’t no madre flaca!
RE: Building on Organic Soils
that msucog referred to is quite interesting. My take on the cause of settlement: It would be the effect of moisture on wood chips. Wood is affected by fluctuating water conditions. In the site, since water drained into during rain, the wood chips are subjected to on and off water conditions. This causes the wood to rot and sometimes causes sinkhole-like features visible on surface. Such conditions have been observed over abandoned mine areas where wooden supports rot after sometime. To make a log storey short, If possible, a test pit or two may be dug near the buildings to observe the conditions. Also look for any sinkhole features on surface especially after heavy rains.
RE: Building on Organic Soils
RE: Building on Organic Soils
The lack of cracking in the foundation still puzzles me no end. I can't believe that the framer was that drunk when he built the building, and, for some unthinkable reason, I can't percieve concrete to be rubber. I'm missing something here. Maybe the sinkhole idea is the answer, but why no cracking in the foundation?
I'm going to look at this one real hard.
Mike McCann
McCann Engineering
RE: Building on Organic Soils
I have seen from reports on projects constructed during 1977 that geotextiles were used then. I think that at that time, geotextiles were in the initial stages of evolution. Now they have come a long way.
Regarding cracking of footings: Without knowing the details and looking at the site, it would be difficult to even speculate the cause. Let me guess anyway.Subsurface directly under the footing may not contain enough wood chipa. So there may not be enough magnitude of settlement and/or differential settlement directly under footing to cause cracking.
RE: Building on Organic Soils
not to get too far off the initial question of the thread but msquared48, when you say there's no cracking in the foundation, are you able to actually see all the foundation? if the footings aren't all tied together in to one "rigid" foundation, the individual pieces might be moving. maybe there's only 2 or 3 locations that the thing is cracked and/or rotating. maybe look at the exterior cont footing as one thing and the others as others. if you find the trend in the perimeter cont. footing, that might give you more clues since the interior footings may be moving more or less from the perimeter footings.
it's always hard to figure out what's going on with houses built that far back...you never know if it was built out of whack or if something is moving/decaying/settling or all of them. heck, even today, residential construction is so shotty that coming to a resolution can be tough. thank goodness we (my firm) stays away from residential work...not that commercial is much better but at least we've got some backup from the permit requirements standpoint. i'd say the forensic work on residential work is pretty interesting since you do have to fit all the many unknown pieces together to come to a logical "solution" (maybe the word "logical" should've had the parenthesis). anyway, enough of my ramblings...good luck with both of your situations.
RE: Building on Organic Soils
So far we are just having fun in the absence of data. . . .
f-d
¡papá gordo ain’t no madre flaca!
RE: Building on Organic Soils
The crawlspaceis 4 to 5 feet deep and all the exterior stem wall is visible. The interior strip footings are fully visible too from the inside of the crawl. The client took some pretty good pictures for me to get an initial idea of the problem.
I will let you know how the inspection goes today.
Mike McCann
McCann Engineering
RE: Building on Organic Soils
Thanks to all the responders.
DocDirt
RE: Building on Organic Soils
Thanks for all the comments
Mike McCann
McCann Engineering
RE: Building on Organic Soils
DocDirt
RE: Building on Organic Soils
f-d
¡papá gordo ain’t no madre flaca!
RE: Building on Organic Soils
We have just started testing. As soon as classification data becomes available, I will let you know
RE: Building on Organic Soils
Might the organic soil generate methane? If so, methane barriers, collection systems and vents may be needed to keep the interior safe.
RE: Building on Organic Soils
Thanks, we already considered that due to a last minute suggestion by a friend of mine. We tested for gas during boring by using portable gas meter and also installed gas wells and tested for gas. While we noted concentrations of upto 5% in volume by air for methane in a couple of pockets in the peat during drilling, we did not detect any gas in the fill and in the monitoring wells. Our conclusion is that while there are some isolated areas in which methane is present, there is not enough volume of methane to come up to fill or in the well in concentrations high enough to be detected.
Consol testing is in progress to determine the settlement parameters. This is long term
RE: Building on Organic Soils
f-d
¡papá gordo ain’t no madre flaca!
RE: Building on Organic Soils
I am on vacation and the testing is in still in progress. I have the following information which I am providing of the top of my head
Tube from Boring A - Natural Water Content = 270% LL= about 200 Pl could not be determined as it was too fibrous peat. Dry Density = 27 pcf.( Material found in borings from 23 to 33 ft)
Tube from Boring B- Natural Water Content = 60% LL= 90 PL= 50 Dry Density = 70 pcf Material is Organic. ( Material found in borings from 18 to 30 ft)
Tube from Boring C -Natural Water Content = 70% LL= 90 PL= 50 Dry Density = 55 pcf Material is organic. ( Material found in borings from 15 to 30 ft)
Boring D - ( Material found in borings from 13 to 30 ft)
Boring E- No organic/peat Encountered
Tube from Boring F-Natural Water Content = 65% LL= 80 PL= 40 Dry Density = 70 pcf Material is organic.( Material found in borings from 28 to 40 ft)
Boring G - ( Material found in borings from 18 to 35 ft)
Organic contents seem to vary from 2 to 5% in Organics and from 5 to 10% in peat.
LL, Pl are air dried.
I will be back on 1/22.
Study is a feasibility study.
DocDirt