Pile Design and Construction Practice, Fifth edition

262 Pile groups under compressive loading

correlating the observed settlements of structures with the determinations of Evfrom plate
loading tests and laboratory tests on good undisturbed samples of clay. Butler(5.12)in his
review of the settlement of structures on over-consolidated clays has related Evto the
undrained cohesion cuand arrived at the relationship Ev 130 cfor London Clay.
Various correlations between the soil modulus and the undrained shear strength of clays
for piles with a length to diameter ratio equal to or greater than 15 are shown in Figure 5.24.
In commenting on these data Poulos(5.1)stated that they should be taken as representing
values of the undrained modulus. He commented on the wide spread of the data suggesting
that this could be due to differences in the method of measuring cuand the soil modulus,
differences in the level of loading at which the modulus was measured, and differences
between the type and over-consolidation ratio of the various clays. Where the undrained
shear strength increases linearly with depth, equation 5.21 can be used to obtain Ev
and hence the total settlements from Figure 5.19. From an extensive review of published and

Table 5.2Value of geological factor g

Type of clay gvalue

Very sensitive clays (soft alluvial, estuarine, and marine clays) 1.0–1.2
Normally consolidated clays 0.7–1.0
Over-consolidated clays (London Clay,Weald, Kimmeridge, Oxford, and Lias Clays) 0.5–0.7
Heavily over-consolidated clays (unweathered glacial till, Mercia Mudstone) 0.2–0.5

120

100

80

60

40

Young's modulus

Es

(MN/m

2 )

20

0

100

Undrained shear strength Cu (kN/m^2 )

Curve

1 Driven

2 Bored

3 Driven (Es 750 Cu)

4 Bored (lower bound) Es 200 Cu

Poulos (1972)

Poulos (1972)

Aschenbrenner and Disen (1984)

Callanan and kulhawy (1985)

200 300

3

2 4

1

Pile type Reference

Figure 5.24Correlations for soil modulus for piles in clay (after Callanan and Kulhawy, for references
see Poulos(5.1)).