Abstract
The use of the effective stress principle led to a general theory for the
strength and volumetric behavior of saturated soils. Presently, all constitutive models
for saturated soils are based on this principle. In 1959, Bishop proposed an equation
for the effective stress of unsaturated soils. However, it was severely criticized
because it could not explain by itself the phenomenon of collapse upon wetting.
Moreover, an analytical expression for the determination of its main parameter was
not provided, and in addition, its value could not be easily determined in the
laboratory. Since then, several equations to determine the value of parameter have
been proposed. Sixty years later, it is acknowledged that Bishop’s effective stress
equation can be employed to simulate the behavior of unsaturated soils when it is
complemented with a proper elastoplastic framework.