What type of materials, primarily consisting of organic matter, are known for making poor bases for foundations?

The choice of organic materials as poor bases for foundations stems from their inherent properties and behavior under load. Organics, such as decomposed plant matter or peat, contain a significant amount of moisture and air spaces, leading to high compressibility and low bearing capacity. These materials can undergo substantial changes in volume with moisture fluctuations, which can disrupt the stability of any structures built on them.

In the context of site selection and foundation design, it's crucial to assess the soil composition to ensure proper support for building loads. When organic materials are present, they can lead to issues such as settling, shifting, or even complete failure of the foundation over time. Therefore, when constructing foundations, it is essential to either remove organic matter or replace it with more suitable materials that provide necessary support and stability.