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Soil Mechanics - Effective and Total Stress

Effective Stress, \sigma ' is in units of pressure (Pa, \dfrac{kg*m}{s^2}, \dfrac{F}{A}, etc) and is given by this equation:

 \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).

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