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RE: Rammed earth construction

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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

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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