Civil Engineering Reference
In-Depth Information
Figure 4.49
Variation of deduced soil modulus with pile deflection (Barton, 1982).
sand, reported by Barton (1982), show that the deduced stiffness of the soil decreases
sharply as the head deflection of the pile increases. Taking a shear modulus for the
sand which increases proportionally with depth,
z
, according to
G
=
mz
, the variation
of the deduced value of
m
∗
=
m
(1
+
3
v
/
4) with head deflection was as shown in
Figure 4.49.
In practice, the critical design criterion will usually be the maximum bending
moment down the pile rather than the head deflection. Equation (4.80) shows that
this maximum moment will be relatively insensitive to the value of soil modulus
adopted. Indeed, Barton's centrifuge tests showed that the elastic solution gave a
reasonably good estimate of the position and magnitude of the maximum bending
moment.
4.4.2.1 Short piles
For piles that are shorter than their critical length, the head deformation will be
larger than given by equations (4.79). The increase in deflection is small until the
