Soil is made up of different sized particles, air, and water. The four main types of soil are: gravel, sand, silt, and clay. The type of soil used can make or break the overall quality of the foundation so it’s important to understand a few basics of soil science to ensure a long-lasting foundation.
Poor drainage results in moisture in the base, sub-base, or subgrade materials and creates water pressure that alters the soil’s bearing capacity.
Coarse grained soils such as gravel and sand have excellent drainage characteristics. Fine grained and platty soils such as silt, clay and highly organic soils have poor drainage characteristics.
The strength and stability of soil will depend on its physical properties. Sand and/or clay mixed with gravel is typically more stable than clay alone because it drains well. It’s important that soil is stable through wetting and drying cycles and temperature changes, so expanding soil does not impact the foundation.
The shape and size of the particles in a soil determine its shear strength and how well it performs as a foundation. Shear strength is the most important factor in determining load bearing capacity and the ability of a soil to support the structure. Soil that contains particles of many different shapes and sizes, such as clay mixed with gravel and sand, will have greater shear strength and will ensure a more sturdy foundation that will last.
