Soil Types for Building

Rock

• Solid rock, such as crystalline bedrock, bears the most weight of any type of soil, making it one building option. According to the Concrete Network, crystalline bedrock can handle up to 12,000 lbs. per square foot of load-bearing pressure keeping the structure stable. Other types of rock, including sedimentary, can bear up to 6,000 lbs. of pressure per square foot. However, some types of sedimentary rock, such as shale, are not always a safe option on which to build. In time, sedimentary rock can break apart, causing the ground to shift beneath your structure.

Gravel

• Although gravel soils can only bear up to about 5,000 lbs. of pressure, according to the Concrete Network, gravel soils, which typically feature a mixture of earth and bits of rocks or larger pieces, are often a solid, soil type for building. Unlike pure rock soils that may shift as the rock breaks,, gravel soils are created from a mixture of soil and rock that has already broken down. Gravel soils tend to stay in place and react well under pressure. They also are typically well drained.

Coarse Soils

• Coarse soils, like sand, are often stable building spots. Sand doesn't expand when wet. It's also difficult to move, making it one of the most stable soil choices on which to build. Due to the nature of the soil, sand can only bear about 3,000 to 5,000 lbs. of pressure per square foot. When evaluating sand for building, look at what's mixed in with the sand. Gravelly sand or basic sand is stable, but sand mixed with more unstable soils, like peat or clay, usually is not a good building option.

Other Soils

• Fine-grained soils, such as clay and silt, are typically not stable soils on which to build. Silt shifts easily, and clay expands when wet, often creating cracks in any foundation built upon it. Organic soils, such as peat in the process of decomposing, are also not stable for building, as the organic materials are often not fully compacted or settled. In some cases, organic soils are mixed with other soil types, such as sand, making them more stable.