What is the term for soil that has some particle sizes missing?

The term that describes soil with some particle sizes missing is referred to as gap graded. This classification indicates that certain sizes of soil particles are absent from the distribution, resulting in voids within the particle size range. This characteristic can significantly affect the soil's physical properties, such as its density, permeability, and shear strength.

In gap graded soils, there is a noticeable lack of intermediary sizes, which can lead to issues in compaction and stability during construction activities. Understanding this classification is crucial for engineers and geologists when evaluating soil behavior and making decisions regarding foundation design, earthworks, and other civil engineering projects.

In contrast, well-graded soils have a complete range of particle sizes, providing better compaction and stability. Uniform graded soils contain particles that are similar in size, leading to less efficient packing. Fine-grained soils consist of very small particles, typically clay and silt, which do not specifically indicate any missing sizes. Therefore, recognizing the distinction of gap graded helps professionals assess soil behavior effectively.