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RE: Rammed earth construction

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I agree with Yi's reply too.  We have found that, like Bruce King and Peter
Walker, judicious choice of particle size distribution can help get
strengths up to 800 psi.

Thor A. Tandy P.Eng, C.Eng, Struct.Eng, MIStructE
Victoria, BC

  -----Original Message-----
  From: Yi Yang [mailto:YI(--nospam--at)]
  Sent: Friday, October 31, 2008 9:37 AM
  To: seaint(--nospam--at)
  Subject: RE: Rammed earth construction

  We are designing a rammed earth residence right now in California.

  There is a book by Bruce King, "Building of Earth and Straw".  It has good
information in it.

  I'm not sure what kind of building code is used in Rwanda, but there
currently isn't any code for rammed earth wall in CA.  The closest code I
found was the New Mexico building code, which has some design requirement in
it.  We are going to get the contractor to build a mock-up, and take core
samples from the mock-up for testing.  A cylinder made just for testing may
not be accurate because of the compaction process.  Compacting a wall
section then take a core sample is more realistic.  According to the
contractor, there is a particular soil, Nun's Canyon Fine, that's been used
around here, and proved to be good in the past projects, when it's done
right, a breaking compressive strength as high as 2000 psi can be achieved.
A 300 psi allowable compressive strength would be a good start for
preliminary design.  I don't think a geotechnical engineer is going to help
much for the wall design.


  Do you really need to print this e-mail?

  From: Michael Hemstad [mailto:mhemstad(--nospam--at)]
  Sent: Friday, October 31, 2008 10:17 AM
  To: seaint(--nospam--at)
  Subject: Rammed earth construction

  I have a project in Rwanda on which my client wants to try some
alternative means of construction.  Rammed earth and straw bale construction
have come up.

  (For those who haven't heard of these, rammed earth is made by building
wall forms, placing soil in them, and pounding it until it rings.  It makes
a durable, fireproof wall with local materials and labor.  Straw-bale
construction involves stacking straw bales, often dowelling them together
with wood dowels, then applying thick parging to each side.   This
apparently results in a strong, fireproof, relatively durable wall too,
although I know less about it than rammed earth.)

  Does anyone have information on either of these?  I am specifically
looking for information on what soil properties are needed for a successful
rammed-earth installation (e.g. clay content, sand content, moisture
content).  I don't yet know whether a geotechnical engineer is available to
the project; so information of the "holds together as a ball when dropped"
type is also appreciated.

  I appreciate any help, or alternate suggestions.

  Mike Hemstad, P.E., S.E.
  Minneapolis, Minnesota