What is Effective stress

The concept of effective stress is one of Carl Terzaghi’s most important contributions to soil mechanics. It is a measure of the stress on the soil skeleton (the collection of particles in contact with each other), and determines the ability of the soil to resist shear stress. It cannot be measured in itself, but must be calculated from the difference between two parameters that can be measured or estimated with reasonable accuracy. The effective stress on the soil mass plane (σ’) is the difference between the total stress (σ) and the pore water pressure (u).