Zone of moisture changes

[nagatalluri]

Guys:

We are working on a project in Pan Handle Texas. I am wondering if there is a generalized active zone map (zone of moisture changes) for Texas. I am concerned about moisture changes in the Fat/Lean clay soils in the area that could lead to potential swell in the foundation backfill or below the foundation.

Your help in appreciated

Thanks
NT

 

[oldestguy]

Chances are there is none. However, you might contact a city building inspection department to see if they have any recollection of jobs where work has to be done to correct problems due to those changing moisture conditions. Up here in Wisconsin the drying effects go very deep, on the order of 20 feet or so resulting in lots of settlement due to shrinkage of clays. I'd bet Texas is even worse. Trees have a significant effect.

 

[msucog]

USACE has some rough maps

 

[nagatalluri]

msucog

Can you please point me to the right document from USACE?

Thanks

 

[msucog]

TM 5-818-7 has useful info. There is a very generalized map stuck in one of the USACE (or UFC) manuals in a rather oddball place, as I recall. Most of the USACE manuals are not yet word searchable so I cannot dig for it. Google "depth of seasonal moisture variation" to see what you find. I do not have all my references in front of me but when I run across it, I will let you know. Keep in mind the reason it is difficult to find maps is because the actual depth is not set in stone depending on the subsurface conditions...also, remember when discussing "seasonal active zone", surface conditions (cuts/fills/granular backfill), drainage and other things like dumping a roof drain next to the foundation or planting a little OAK sapling next to the foundation will influence the actual movement that may occur and cannot accurately be calculated on the front end. It would be best to consult a (or several) local geotechnical engineer(s) for their thoughts but answers will vary depending on what information you do/don't give them. Should probably also inquire regarding degree of compaction for clayey fill...we typically go with a slightly lower compaction at a higher moisture content than other areas to hedge the swelling of fill...but all depends on the site, the structure, the geotech, the mechanism built into the recommendations to offset the shrink/swell and what level of confidence the geo has to be heavily involved in the construction.

Depending on groundwater depth, sand/gravels present, rock depth, etc etc etc, 5' to 15' (usually closer to 15') is fairly common for the lower half of TX. If you ask the USACE in certain areas, they may suggest 50'. Oldestguy, I'm surprised it goes that deep up there...there again, I've never worked that region, plus we don't have 'real' trees down here in south TX (it's too dang hot!).

 

[Ron]

Try the soil conservation service soil maps for Texas. Lots of info, though generalized. Here's a link:

Texas Soil Maps

 

[charlesreed]

I think turning to a local engineer can help you further a geotechnical site investigation. It all depends on the mechanism, structure and geotech to measure the moisture changes that accumulates over the site.

 

[fattdad]

consider the work of Steven Wright. He attributes moisture changes in strength reduction to fully-softened state to depths up to 20 ft.


at least that's what I think he said. . .


f-d

ípapß gordo ainÆt no madre flaca!

 

[Terratek]

Any map you find will be of only limited use. The depth of active moisture varies depending on soil properties as much as location, so location alone will not be enough. As a general guideline, if you have relatively sandy soils and/or lean clays within the upper 20 ft in Amarillo, you might expect your depth of active moisture change to be about 8 ft. For the most part, the concern with shrink-swell is fairly limited in the pan handle of Texas. If your findings reveal that you'll need more than 2 or 3 ft of non-expansive fill below the floor slab to reduce movements, you will raise some eyebrows with local engineers and contractors in the area.

Fattdad, Dr. Wright was one of my college professors. Really nice guy - landed me an awesome summer internship. My guess is the studies of his that you are referencing are related to slope stability.

 

[fattdad]

Terratek,

I'm aware of the practical aspects of Dr. Wright's work. How would his research in slope stability negate the OP in addressing zone of moisture change, which he attributes to the development of fully-softened soil strength. Maybe I don't get your ultimate point?

f-d

ípapß gordo ainÆt no madre flaca!

 

[Terratek]

I think its relevant to at least provide some insight to the OP that the studies you are referencing are in no way making an attempt to investigate potential heaving of foundations on horizontal ground surfaces. Were the studies done in the presence of active clays? What kind of permeability did the soils have? Did slope movements or surficial sloughing create any fracturing or ponding that could have increased the depth of moisture penetration compared to a static, flat site?

I guess my "ultimate" point is that while spending tedious time reading slope stability papers could give you some insight to the depth of active moisture change, its not a practical way to get a usable answer, in my opinion. To suggest that OP should read a slope stability study and possibly determine that the active depth in Amarillo could be up to 20 ft deep almost laughable.

Also, should OP want to research the work, it would probably make the document search a little easier if it was know that "Slope Stability" would be the predominate topic.

 

[fattdad]

o.k. then. Laugh away!

f-d

ípapß gordo ainÆt no madre flaca!

 

[Terratek]

That's the problem with these type of forums. I was simply adding more value to your post, fattdad, by pointing out that your info probably came from slope stability research. That's it. Nothing more was implied. It is completely valid that someone point that out since you didn't. I was polite about it, too. Instead of just letting the information lie there to be seen, you took umbrage at what you conceived as a challenge and attempted to challenge me, irrespective of the fact that I laid out practical advice to the OP based on direct experience in the area. So if my reply to your challenge revealed my true thoughts about overly deep assumptions of active depth based on research papers and not direct experience, well, you did ask for it.

Shame too-because I've read many of your posts and you appear to be more technically competent than me in geotech, overall, if not in the active soils arena.

 

[killswitchengage]

Also i want to add that CPTu test can help detect horizons effected by seasonal changes , same thing for DCPT you will notice small N of blows in the uppers portion of the soil followed by increase in N blows in soils of less sensitivity to seasonal changes

 

[fattdad]

my comment was based on a conversation I had with Dr. Wright at a CGPR workshop at Virginia Tech. I haven't studied under Dr. Wright and read few of his papers. I did not suggest that the OP read Dr. Wright's slope stability papers. I just suggested that he see whether Dr. Wright had any publication that spoke to that matter as he has some background in both Texas and on the subject matter.

Meant no harm to you or the OP. I didn't try to make a statement beyond my familiarity. I did not think my point, "Laughable," as you suggested. You have reacted to my point and I to yours. I'm sure we'd have a fine time in life if/when we meet.

f-d

ípapß gordo ainÆt no madre flaca!