The
earths surface can be categorized in one of four basic structural
compositions or soil classifications. They are gravel, sand, silt and clay and are classified
as such based on texture or grain size.
The soil at most sites are made up of a combination of soil types and are commonly referred to as "loams". A loam is further distinguished by its density or compression factor and compression and shear are two of the physical properties that we want to control.
Our caveman ancestors quickly realized that building a home in a seasonal river bed just didn't cut it. So... quickly he found out that caves on high grounds worked best. (Providing the cave didn't already have other inhabitants with very-sharp teeth.)
So let's look at the soil types that our caveman had to consider as he ventured to build homes.
First is coarse-grained soils which consist of gravel and sand and have a high shear strength and compacted rating.
Next is the fine-grained soils which consist of silts and clays and are more sensitive to moisture content. Fine-grained soils must have a good moisture control plan to be stable for building.
The last is clay or super-fine-grained soil (like sludge). Clay reacts to climatic conditions and is constantly moving and reacting (expanding and contracting) to moisture variations in the ground. Clay can cause differential movement, which can destroy a home and clay can expand as much as 60 percent in volume depending on its moisture content.
To learn more about soils, log on to the National Geological Society's website.