Is it Dirt or Soil or Earth?

I have a big pile of dirt in my yard.  It's for my Compressed Earth Block (CEB) chicken house.  Only, CEBs are made of "earth."  That begs the question, do I have the right kind of earth?  As it turns out, I do.  But what is meant by earth, anyhow?

Dirt gets such a bad rap.  When you look at the components that makes up dirt, you can easily see that the clay bit is what *ahem* soils the good name of dirt!  The sand and organic fractions don't get nearly the negative press that clay does, especially when it comes to mud!  Still, dirt is highly variable, and those three components, sand, clay, and organic matter, are the basic components of dirt.  A soil engineer could expound ad nauseam on the myriad aggregates and clays and their properties in various soils.  For the CEB enthusiast, it boils down to a few simple rules.  70ish% sand, 30ish% clay and as little organic matter as can be achieved.  So while there are many many many types of earth, when it comes down to it, CEBs require a rather narrow definition of earth.

My soil, as I pointed out, fits the bill for CEBs.  As a matter of fact, it's nearly ideal.  This soil was excavated for a building foundation so it's subsoil rather than topsoil. All subsoils have differing ratios of base components, so I did the basic "jar test" to get a quick assessment of the fractions.

left: top soil, right: subsoil

For comparison, the jar on the left is a sample of top soil from a local garden center.  The organic fraction, in contrast to my soil, is much higher. It's great for top soil, bad for CEBs.  It's worth noting that adobe requires a fair bit of organic matter, as does wall renders (a fancy way of saying plaster). Given the nature of my project, and that I'm going to be stabilizing with lime, my soil will not need any further adjustments. Below is a filtered look to highlight the fractions.  The sand/gravel layer is nearly all fine sand.  I'm not sure about the relative sharpness of the sand yet.  Sharper is better. As a side note, my CEB soil sample settled clear enough that you can't quite tell that there is still water in that jar.

highlighted layers

Of course, when making CEBs for human dwellings, there are several more aspects of soil engineering to address.  To wit, clay plasticity, silt content, sand type (sharp or round) and aggregate size, to name a few.  As I get more into the project, I'll address these metrics little by little.