Lateral Pressrues In Soils

LATERAL PRESSURES IN SOILS, FORCES ON RETAINING WALLS

The Rankine theory of lateral earth pressures, used for estimating approximate values for lateral pressures on retaining walls, assumes that the pressure on the back of a vertical wall is the same as the pressure that would exist on a vertical plane in an infinite soil mass. Friction between the wall and the soil is neglected. The pressure on a wall consists of (1) the lateral pressure of the soil held by the wall, (2) the pressure of the water (if any) behind the wall,
and (3) the lateral pressure from any surcharge on the soil behind the wall.

Symbols used in this section are as follows:

g=unit weight of soil, lb / ft³ (kg/m³) (saturated unit weight, dry unit weight, or buoyant unit weight, depending on conditions)

P=total thrust of soil, lb / linear ft (kg / linear m) ofwall

H= total height of wall, ft (m)

f= angle of internal friction of soil, degree

i= angle of inclination of ground surface behind wall with horizontal; also angle of inclination of line of action of total thrust P and pressures on
wall with horizontal

K_A= coefficient of active pressure

K_P= coefficient of passive pressure

c= cohesion, lb/ft² (kPa)