Cohesion

Cohesion, abbreviated as c, Is the internal molecular attraction or bonding force between soil particles.  It is one of the fundamental properties of soils and plays a significant role in determining their mechanical behavior, particularly in cohesive soils.

Cohesive soils, such as clays and silts, contain fine particles that have a tendency to stick together due to the cohesive forces between them.  These cohesive forces arise from electrostatic forces, surface tension, and other molecular interactions.  Cohesion gives cohesive soils their plasticity and allows them to retain their shape when unconfined.

Cohesion contributes significantly to the stability of slopes, retaining walls, and excavations in cohesive soils.  It also affects the behavior of foundations and the design of earthworks and geotechnical structures.  Engineers consider cohesion along with other soil properties, such as angle of internal friction and unit weight, in analyzing and designing geotechnical structures to ensure their safety and stability.

In cohesive soils, cohesion is particularly relevant because it can help prevent soil failure and sliding, even in the absence of external loads.  However, cohesive soils can also exhibit time-dependent behavior, such as consolidation and swelling, due to changes in moisture content and stress levels.  Therefore, understanding and accounting for cohesion is essential in geotechnical engineering to ensure the successful and safe execution of construction projects.