= o'a+ u = Ka\\ydz + q-u -2c'jK~a + u fThis equation is missing from Eurocode 7 (which only gives an equation for dry soil), but a version of it appears in the UK National Annex.

where o'a = the horizontal effective earth pressure and u = the pore water pressure in the ground at z; Ka = the ground's active earth pressure coefficient, y = its weight density, and c' = its effective cohesion; and q = the surcharge at ground surface behind the virtual plane. (This equation ignores the beneficial effect of any adhesion along the virtual plane.)

The pore water pressure is given by: u = yw x(z - dw)

where yw = the weight density of water and dw = the depth of the water table below the top of the wall.

For the special case where the pore pressure is zero (i.e. above the water table), the equation for oa reduces to:

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