as rock, concrete, metal powders and biological tissues. It is crucial for understanding the mechanical behaviour of porous media, as effective stress governs both their strength and volume change (deformation).

More formally, effective stress is defined as the stress that, for any given pore pressure , produces the same strain or strength response in a porous material (such as soil or rock) as would be observed in a dry sample where . In other words, it is the stress that controls the mechanical behaviour of a porous body regardless