Pile Design and Construction Practice, Fifth edition

and the mean horizontal pressure pmare shown in Figure 9.17. Methods of calculating pm
and the height huare described by Springman and Bolton.
When calculating lateral forces on the piles for a range of values of cuthe higher values
should be used to obtain the bending moments and pile deflections, and the lower values for
assessing the stability of the embankment. It is also important to ensure that the side slopes
of the embankment have an adequate safety factor against rotational shear failure.
De Beer and Wallays (9.29)have established an empirical method of calculating the lateral
pressure on vertical piles due to unsymmetrical surcharge loading. The surcharge is represented
by a fictitious fill of height Hfwith a sloping front face, as shown for three arrangements of
piles and embankment loading in Figure 9.20a to c. The height Hfis given by

(9.2)

where is the density of the fill in tonne/m^3.
The fictitious fill is assumed to slope at an angle which is drawn by one of the methods
shown in Figure 9.20a to c, depending on the location of the surcharge loading in relation
to the piles. The lateral pressure on the piles is then given by

pz fp (9.3)

where fis a reduction factor given by

f (9.4)

0.5

90 0.5

Hf H



1.8

Miscellaneous piling problems 461

Figure 9.19Interaction diagram for horizontal soil pressure on vertical pile driven through soft clay
into an underlying stiff stratum (after Springman and Bolton(9.24)). Crown copyright 1995.
Reproduced by permission of HM Stationery Office.

Plastic flow around pile

Ultimate plastic failure

of soil mass and soil

around pile

Ultimate bearing

capacity

Elastic loading lines

p) (2 +p) (1 + 2d/s)(2 +

q/cu

pm

/cu

(2 +p)

1.5

Elasto-plastic

zone

Local onset of yield on pile

0

10.5

2 p

Pseudo-elastic

zone

h/d= 10

h/d= 4

Serviceable

bearing capacity