Cob: Re: Foundation Strength Relative to Soil Type

[Myra Bonhage-Hale]

Hi Kim, you can usually get your County Extension Agent or the Univ. of Arkansas Extension Service (you also have ATTRA there in Fayetteville) to give you a soil test - you can get the bags they supply at the county Extension Office and send them in - the analysis is usually free, unless you want to also know organic content.    The Extension Service also knows the prevailing soil type in your county.  Just take a sample at the proposed site of your house and send it in.  If the clay content is not enough, at least you will know what will grow there!!!!! - and they will also tell you what amendments need to be added for specific crops....Namaste.  Happy Holidays.  Myra
  ----- Original Message ----- 
  From: Kim West 
  To: Cob List 
  Sent: Friday, December 20, 2002 9:59 PM
  Subject: Cob: Foundation Strength Relative to Soil Type


  A while back I made a post relating the clay content of our soil here. A nice fella, I do not remember who it was, wrote to me that there is no way I can know the make-up of our soil without lab tests. Yesterday I found a book that I knew we had, yet did not know where it was. It is entitled "Soil Survey, Ouachita County Arkansas". After a bit of time studying the maps and information in the book, I now have a generic lab test result for our soil. Granted, it was not taken directly from this property, but it was a sample of this soil type.

  I found that our land is classified as Kirvin fine sandy loam. When this book was published, the classes of soil were standard country-wide. That was in 1973 so things may have changed somewhat, although the description would not change with the class name if indeed the class name has changed.

  =======================================================================================
  What follows are some of the properties of Kirvin soil:

  Depth to seasonal high water table: 30-60 in.
  Depth from surface of typical profile:
      0-9 in......fine sandy loam........AASHO A-2 or A-4.........30-40% passing #200 sieve...shrink/swell low
      9-55 in....red clay, plastic.......AASHO A-7...................75-95% passing #200 sieve...shrink/swell moderate
      55-73.....silty clay loam..........AASHO A-4 or A-6..........60-75% passing #200 sieve...shrink/swell low

  Kirvin soil limitations relative to foundations of dwellings: Moderate if slopes are less than 15%; moderate bearing strength; moderate shrink/swell potential; severe if slope greater than 15%.

  As relates to septic systems: severe-slow percolation.

  ========================================================================================

  Firstly, let me say that the depth to seasonal high water is no problem. We have lived here for nearly 13 years, through near-drought and through high precip years. Where I plan to build is atop a hill, the highest point on the property, and water has never been a problem, even during floods and/or high precip years.

  Secondly, The clay content given above pretty much agrees with the jar tests that I did. I had said that 6-12 inches down is pure red clay. The lab tests say that 9 inches down is 75-95% non-sand soil. This hypothetically could contain silt, but there are not three layers in my clay samples, only two. After the gentleman drew my attention to the need for a lab test, I did get a magnifying glass and do another examination using it. I found that under magnification the fine sand content that wasn't visible to my naked eye was indeed there. I owe him, whoever he was, a thank you for influencing me to back up and re-examine my samples. Had I not come across this soil survey I may have continued erroneously thinking the clay was pure. Thank you!

  Anyway, the reason I posted this is because of the previous discussions we have had on rubble trench foundations, and the fact that they have been around a while and work very well. I'm wondering if part of the success of those foundations was because they were set on stable, weight bearing soils. Above, it says the foundation limitations here are only moderate, meaning they can be overcome with good planning, so long as the slope is less than 15%. There is no problem here with that. Where I planned to build does indeed have a slope of less than 15%. My concerns, though, is the A-7 AASHO rating of the soil at 9-55 inches deep. A-1 is gravelly soil with a high bearing strength, and the scale goes down to A-7 which is clay with little strength if wet. If I built on top of the ground I would be working with an A-2 rating which is not bad, but once I dig down for the foundation I will be in A-7 soil which is the worst for weight bearing. I know I've been told "tamp, tamp, tamp...and good drainage is a must", and I know that is a very important part of building, but I am not *completely* comfortable that would be sufficient for the near-pure clay soil that is under the shallow topsoil. Somewhere I read that lime can be used to stabilize clay soils, and I am wondering if anyone here knows how I can use lime to stabilize this soil. I really would HATE to put out alot of work to have my home fall down due to a lack of bearing strength under the foundation! LOL! If anyone here has any info on how I can stabilize my soil with lime, please, please let me know.   :D

  Kim
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<DIV><FONT face=Arial size=2>Hi Kim, you can usually get your County Extension 
Agent or the Univ. of Arkansas Extension Service (you also have ATTRA there in 
Fayetteville) to give you a soil test - you can get the bags they supply at the 
county Extension Office and send them in - the analysis is usually free, unless 
you want to also know organic content.    The Extension Service 
also knows the prevailing soil type in your county.  Just take a sample at 
the proposed site of your house and send it in.  If the clay content is not 
enough, at least you will know what will grow there!!!!! - and they will also 
tell you what amendments need to be added for specific crops....Namaste.  
Happy Holidays.  Myra</FONT></DIV>
<BLOCKQUOTE dir=ltr 
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
  <DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
  <DIV 
  style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B> 
  <A title=kwest at arkansas.net href="mailto:kwest at arkansas.net">Kim West</A> 
  </DIV>
  <DIV style="FONT: 10pt arial"><B>To:</B> <A title=coblist at deatech.com 
  href="mailto:coblist at deatech.com">Cob List</A> </DIV>
  <DIV style="FONT: 10pt arial"><B>Sent:</B> Friday, December 20, 2002 9:59 
  PM</DIV>
  <DIV style="FONT: 10pt arial"><B>Subject:</B> Cob: Foundation Strength 
  Relative to Soil Type</DIV>
  <DIV><BR></DIV>
  <DIV><FONT face=Arial size=2>A while back I made a post relating the clay 
  content of our soil here. A nice fella, I do not remember who it was, wrote to 
  me that there is no way I can know the make-up of our soil without lab tests. 
  Yesterday I found a book that I knew we had, yet did not know where it was. It 
  is entitled "Soil Survey, Ouachita County Arkansas". After a bit of time 
  studying the maps and information in the book, I now have a generic lab test 
  result for our soil. Granted, it was not taken directly from this property, 
  but it was a sample of this soil type.</FONT></DIV>
  <DIV><FONT face=Arial size=2></FONT> </DIV>
  <DIV><FONT face=Arial size=2>I found that our land is classified as Kirvin 
  fine sandy loam. When this book was published, the classes of soil were 
  standard country-wide. That was in 1973 so things may have changed somewhat, 
  although the description would not change with the class name if indeed the 
  class name has changed.</FONT></DIV>
  <DIV><FONT face=Arial size=2></FONT> </DIV>
  <DIV><FONT face=Arial 
  size=2>=======================================================================================</FONT></DIV>
  <DIV><FONT face=Arial size=2>What follows are some of the properties of Kirvin 
  soil:</FONT></DIV>
  <DIV><FONT face=Arial size=2></FONT> </DIV>
  <DIV><FONT face=Arial size=2>Depth to seasonal high water table: 30-60 
  in.</FONT></DIV>
  <DIV><FONT face=Arial size=2>Depth from surface of typical 
  profile:</FONT></DIV>
  <DIV><FONT face=Arial size=2>    0-9 in......fine sandy 
  loam........AASHO A-2 or A-4.........30-40% passing #200 sieve...shrink/swell 
  low</FONT></DIV>
  <DIV><FONT face=Arial size=2>    9-55 in....red clay, 
  plastic.......AASHO A-7...................75-95% passing #200 
  sieve...shrink/swell moderate</FONT></DIV>
  <DIV><FONT face=Arial size=2>    55-73.....silty clay 
  loam..........AASHO A-4 or A-6..........60-75% passing #200 
  sieve...shrink/swell low</FONT></DIV>
  <DIV><FONT face=Arial size=2></FONT> </DIV>
  <DIV><FONT face=Arial size=2>Kirvin soil limitations relative to foundations 
  of dwellings: Moderate if slopes are less than 15%; moderate bearing strength; 
  moderate shrink/swell potential; severe if slope greater than 
15%.</FONT></DIV>
  <DIV><FONT face=Arial size=2></FONT> </DIV>
  <DIV><FONT face=Arial size=2>As relates to septic systems: severe-slow 
  percolation.</FONT></DIV>
  <DIV><FONT face=Arial size=2></FONT> </DIV>
  <DIV><FONT face=Arial 
  size=2>========================================================================================</FONT></DIV>
  <DIV><FONT face=Arial size=2></FONT> </DIV>
  <DIV><FONT face=Arial size=2>Firstly, let me say that the depth to seasonal 
  high water is no problem. We have lived here for nearly 13 years, through 
  near-drought and through high precip years. Where I plan to build is atop a 
  hill, the highest point on the property, and water has never been a 
  problem, even during floods and/or high precip years.</FONT></DIV>
  <DIV><FONT face=Arial size=2></FONT> </DIV>
  <DIV><FONT face=Arial size=2>Secondly, The clay content given above pretty 
  much agrees with the jar tests that I did. I had said that 6-12 inches 
  down is pure red clay. The lab tests say that 9 inches down is 75-95% non-sand 
  soil. This hypothetically could contain silt, but there are not three layers 
  in my clay samples, only two. After the gentleman drew my attention to the 
  need for a lab test, I did get a magnifying glass and do another examination 
  using it. I found that under magnification the fine sand content that wasn't 
  visible to my naked eye was indeed there. I owe him, whoever he was, a thank 
  you for influencing me to back up and re-examine my samples. Had I not come 
  across this soil survey I may have continued erroneously thinking the clay was 
  pure. Thank you!</FONT></DIV>
  <DIV><FONT face=Arial size=2></FONT> </DIV>
  <DIV><FONT face=Arial size=2>Anyway, the reason I posted this is because of 
  the previous discussions we have had on rubble trench foundations, and the 
  fact that they have been around a while and work very well. I'm wondering if 
  part of the success of those foundations was because they were set on stable, 
  weight bearing soils. Above, it says the foundation limitations here are only 
  moderate, meaning they can be overcome with good planning, so long as the 
  slope is less than 15%. There is no problem here with that. Where I planned to 
  build does indeed have a slope of less than 15%. My concerns, though, is the 
  A-7 AASHO rating of the soil at 9-55 inches deep. A-1 is gravelly soil 
  with a high bearing strength, and the scale goes down to A-7 which is clay 
  with little strength if wet. If I built on top of the ground I would be 
  working with an A-2 rating which is not bad, but once I dig down for the 
  foundation I will be in A-7 soil which is the worst for weight bearing. I know 
  I've been told "tamp, tamp, tamp...and good drainage is a must", and I know 
  that is a very important part of building, but I am not *completely* 
  comfortable that would be sufficient for the near-pure clay soil 
  that is under the shallow topsoil. Somewhere I read that lime can be used to 
  stabilize clay soils, and I am wondering if anyone here knows how I can use 
  lime to stabilize this soil. I really would HATE to put out alot of work to 
  have my home fall down due to a lack of bearing strength under the foundation! 
  LOL! If anyone here has any info on how I can stabilize my soil with 
  lime, please, please let me know.   :D</FONT></DIV>
  <DIV><FONT face=Arial size=2></FONT> </DIV>
  <DIV><FONT face=Arial size=2>Kim</FONT></DIV></BLOCKQUOTE></BODY></HTML>