$$ \sigma ‘ = \sigma – u$$
Total stress, \(\sigma\), is the total amount of stress due to the soil at the depth you are considering:
$$ \sigma = \rho_s g z $$
\(\rho_s\) is the soil density (e.g. 80 lb/ft^3).
\(g\) is the acceleration of gravity (e.g. 32.2 ft/s^2).
\(z\) is the distance of the surface, or beginning of the soil section, to the point you are considering(e.g. 10 ft).