What does the term 'effective stress' refer to in soil mechanics?

The term "effective stress" in soil mechanics fundamentally refers to the intergranular stress within the soil skeleton. This concept is central to understanding how soils behave under load, particularly in relation to the presence of pore water pressure.

Effective stress is defined as the stress that contributes to the strength and stability of soil. It is the portion of the total stress that is carried by the soil skeleton, as opposed to the stresses carried by pore water. When external loads are applied to soil, they create both total stress and pore water pressure. The effective stress is calculated by subtracting the pore water pressure from the total stress acting on the soil, thereby highlighting how soil particles interact under loading conditions.

This intergranular stress plays a crucial role in determining the soil's shear strength and how it deforms under various conditions. As the effective stress changes (due to changes in total stress or pore water pressure), it significantly influences the behavior of the soil, including its consolidation, strength, and stability.

Understanding effective stress is essential for engineers in geotechnical applications, as it helps predict how soil will respond to loads, groundwater changes, and other environmental factors.