Where,

is the vertical pressure on the top of the element,
( +d ) is the vertical reaction on the bottom of the element,
is the horizontal reaction on the retaining wall,
is shear between the back fill and the back of retaining wall,
is shear between the sliding backfill and the remaining backfill at rest,

dw is the weight of the element.

The shearing forces on the top and bottom of the element are neglected, considering that the wedge slides as a whole. Considering the equilibrium condition of the vertical forces on the element, the basic equation for the unit earth pressure on the retaining wall is given by,

where,

is the friction angle between the back of retaining wall and the backfill,

is the internal friction angle of the backfill,

H is the height of the retaining wall,

is density of the backfill material.