Building Construction Handbook, Eighth Edition

A graphical design solution, to determine the earth thrust (P)

behind a retaining wall. Data from previous page:

h = 3„300 m

 =30°

w = 1500 kg/m^3

Wall height is drawn to scale and plane of repose plotted. The

wedge section is obtained by drawing the plane of rupture through

an angle bisecting the plane of repose and vertical back of the

wall. Dimension `y' can be scaled or calculated:

Tangent x =

y

3„3 x=30

;and tan 30= 0„5774

therefore, y = 3„3 ¾ 0„5774 = 1„905 m

Area of wedge section =3„3 2 ¾1„905 m = 3„143 m^2

Volume of wedge per metre run of wall = 3„143 x 1 = 3„143 m^3

Weight .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. = 3„143 ¾ 1500 = 4715 kg

Vector line A † B is drawn to a scale through centre of gravity of

wedge section, line of thrust and plane of rupture to represent

4715 kg.

Vector line B † C is drawn at the angle of earth friction (usually

same as angle of repose, i.e. 30°in this case), to the normal to the

plane of rupture until it meets the horizontal line C † A.

Triangle ABC represents the triangle of forces for the wedge

section of earth, so C † A can be scaled at 2723 kg to represent

(P), the earth thrust behind the retaining wall.

Retaining Walls---Coulomb’s Wedge Theory