How do cohesive soils differ from non-cohesive soils?

Cohesive soils are characterized by their fine particles, such as clay and silt, which have the ability to stick together due to their small size and the molecular attractions between them. This stickiness is primarily due to the plasticity and water retention capabilities of the fine particles. When moisture is present, cohesive soils can easily maintain their shape and structure, exhibiting behaviors like plasticity and swelling when wet. This is in contrast to non-cohesive soils, such as sand and gravel, which consist of larger particles that do not possess this adhesive quality.

The ability of cohesive soils to retain water and their capacity for cohesion makes them distinct in terms of behavior under loading conditions and during moisture variation, impacting their suitability for construction and other civil engineering applications. This characteristic of fine particles binding together is fundamental to understanding soil mechanics and is a key concept in construction materials testing.