where si = immediate settlement of the footing (ft or m)
q = vertical footing pressure (psf or kPa)
B = footing width (ft or m)
I = shape and rigidity factor (dimensionless). This factor is derived from the theory of elasticity
to account for the thickness of the soil layer, shape of the foundation, and flexibility
of the foundation. Theoretical values of I can be obtained for various situations as
shown in Fig. 7.10.
m = Poisson’s ratio (dimensionless), which is usually assumed to be 0.5 for saturated plastic
soil subjected to undrained loading
Eu = modulus of elasticity of the soil (psf or kPa). This is often obtained from an undrained
triaxial compression test performed on an undisturbed specimen where the stress-strain
curve is plotted (i.e., see Fig. 3.32). The initial tangent modulus to the stress-strain
curve is often assumed to be the value of Eu.