SOIL MECHANICS

Chapter 35

TABLES FOR LATERAL EARTH PRESSURE

The computation of lateral earth pressure against retaining walls is such an important problem of soil mechanics that tables have been produced

for its solution, all on the basis of Coulomb’s method. These tables can be found in many handbooks, such as the German “Grundbau

Taschenbuch”. Following Coulomb these tables apply to soils without cohesion (c = 0), that is for sand or gravel. In this chapter some tables are

given for the active and the passive earth pressure against a retaining wall, with a surface that is practically vertical, and a sloping soil surface.

35.1 The problem

The general problem considered in this chapter concerns a retaining wall, having a surface inclined at an angle α with the horizontal direction. The

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Figure 35.1: Horizontal earth pressure.

soil surface is horizontal, or it may be sloping at an angle β with the horizontal direction, see Figure 35.1. The wall may be perfectly smooth, or it

may have a certain friction, so that the direction of the force Q is at an angle

δ with the direction normal to the wall. The friction angle δ is supposed to

be given. Because the wall often is rather smooth, its value is often taken

somewhat smaller than the friction angle of the soil itself, say δ =

φ. The

angle δ is considered positive in the active case, illustrated in Figure 35.1,

in which the sliding soil wedge is expected to slide in downward direction,

along the surface of the wall. In the case of passive earth pressure it can

be expected that the soil will move in upward direction along the surface

of the wall. The angle δ then should be given a negative value.

The tables record the values of the coefficient K in the formula

Q =

2Kγh2

. (35.1)

This coefficient would be equal to 1 in the case of a fluid against a vertical wall.

It should be noted that Q is the total force. The angle of this force with the vertical direction is α − δ. The horizontal component of this

force is

Qh = Q sin(α − δ). (35.2)

If the tables are used to determine the horizontal force, the multiplication by the factor sin(α − δ) should be performed by the user.

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