The study of plasticity in geomechanics is essential for understanding how soils and rocks behave under extreme stress, particularly in predicting failure and permanent deformation in civil and petroleum engineering. Unlike linear elasticity, which models reversible deformation, plasticity focuses on the irreversible "flow" of geomaterials once they reach a critical state. Core Concepts of Plasticity in Geomechanics
: These rules describe how the yield surface evolves as the material deforms.
: Used when a material's volume change (dilatancy) does not follow the yield surface, which is a hallmark of many granular soils. fundamentals of plasticity in geomechanics pdf
: This describes the direction and relative magnitude of plastic strain increments once yielding occurs.
: Assumes the plastic strain increment is normal to the yield surface (Normality Rule), common in metal plasticity but often less accurate for frictional materials like soil. The study of plasticity in geomechanics is essential
: This is a mathematical boundary—often represented as a surface in stress space—that defines the threshold where elastic behavior ends and plastic deformation begins. Common criteria include:
Plasticity theory replaces real, particulate materials (like sand or clay) with an idealised continuum that behaves elastically until a specific stress limit is reached. Key elements of this theory include: : Used when a material's volume change (dilatancy)
: The yield surface expands uniformly, representing an increase in strength.
: The yield surface shifts its position in stress space, often used to model the Bauschinger effect in cyclic loading.
: Widely used for soils and rocks, based on shear stress, cohesion, and internal friction.