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.
YI YANG, S.E.
From: Michael Hemstad [mailto:mhemstad@mbjeng.com]
Sent: Friday, October 31, 2008 10:17 AM
To: seaint@seaint.org
Subject: Rammed earth construction
All,
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.
Thanks,
Mike Hemstad, P.E., S.E.
MBJ
Minneapolis, Minnesota