Pile Design and Construction Practice, Fifth edition

(Joyce) #1

where ycis the deflection corresponding to the strain ‡cat a stress equal to the maximum
stress resulting from the laboratory stress/strain curve. The strain ‡ccan also be obtained
from the established relationship between cuand the deformation modulus Eu(see
Section 5.2.2). Matlock(6.17)quotes values of ‡cof 0.005 for ‘brittle and sensitive clays’and
0.020 for ‘disturbed or remoulded clays or unconsolidated sediments’. These values of ‡c
have been based on the established range of Eu/cuof 50 to 200 for most clays, and they can
be applied to stiff over-consolidated clays, for example the value of Eu/cufor stiff London
Clay is 400. Matlock(6.17)recommends an average value of 0.010 for normally consolidated
clays for use in the equation:


(6.39)

The effect of cyclic loading at depths equal to or greater than xrcan be allowed for by cutting
off the p–ycurve by a horizontal line representing the ultimate resistance pbof the clay under
cyclically applied loads. From the experimental work of Matlock(6.17), the point of intersection
of this line with the p–ycurve (shown in Figure 6.32 as point b) is given by


(6.40)

The p–ycurves for cyclic loading with values of y/ycfrom 3 to 15 and for depths of less than
xr, at x 0 are shown in Figure 6.32.
There are little published data on values of pbfor various types of clay. The application of
a static horizontal load after a period of cyclic loading, say in a deep-sea structure where a
berthing ship strikes a dolphin after a period of wave loading, produces a more complex
shape in the p–ycurve and a method of establishing the curve for this loading condition has
been described by Matlock(6.17).
The shape of a p–ycurve for a pile in sand as established by Reese et al.is shown in
Figure 6.33. It is in the form of a three-part curve up to the stage of the ultimate failure pu.


pbpu 0.72

yc 2.5εcB

344 Piles to resist uplift and lateral loading


p

Y

pu 5 Apc

pm 5 Bpc

x 5 x 1

k

m
m

3 B

Curve defined by

8 O

l

yu (^5)
u
ym 5 B 60
yk (^5) ncx n
h
n– 1
p 5 Cy^1 n
Figure 6.33Determining shape of p–ycurve in sand (after Reese et al.(6.10)).

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