Effective stress

Effective stress is the stress transmitted through a porous material’s solid framework after accounting for pressure in its pores. It governs deformation and strength in saturated soils and rocks.

Terzaghi's effective stress principle: A principle stating that saturated soil behavior depends on total stress minus pore-water pressure. This principle gives the foundational relation between total stress, pore pressure, and effective stress.
Soil consolidation test: A laboratory test measuring how a soil specimen compresses under controlled vertical loading. The test tracks pore-pressure dissipation and the resulting increase in effective stress.
Stress (mechanics): A measure of internal force per unit area within a material. Effective stress is a specialized stress measure that separates the framework's load from pore-fluid pressure.
Total stress analysis: An analysis that uses total stresses without explicitly subtracting pore-water pressure. It contrasts with effective-stress analysis, especially for short-term undrained soil behavior.
Pore pressure: The pressure exerted by fluid within the pores of a soil or rock. Pore pressure reduces the portion of total stress carried by the solid framework.
Slope stability: The ability of a soil or rock slope to resist movement under gravity and other loads. Rising pore pressure lowers effective stress and can reduce resistance to sliding.
Porous medium: A material containing interconnected or isolated pores within a solid matrix. Effective stress describes load sharing inside porous materials.
Bishop's effective stress: A proposed effective-stress expression for unsaturated soil that includes the degree of saturation and suction. It extends the saturated-soil formulation to partially saturated conditions.
Total stress: The stress at a point from all applied forces, without subtracting pore-fluid pressure. Effective stress is calculated from total stress and pore pressure.
Liquefaction: A loss of soil strength and stiffness when cyclic loading raises pore pressure in saturated granular soil. In severe liquefaction, pore pressure approaches total stress and effective stress nearly vanishes.

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