Page 324 - Numerical Analysis and Modelling in Geomechanics

F.BASILE 305
For clays, a correlation between initial E and SPT N-value (blows/300 mm,
s
corrected to a rod energy of 60%) has been proposed by Poulos (1993), based on
the work by Wroth et al. (1979):

(10.11)

For convenience, a linear correlation may also be adopted, as suggested by
Hirayama (1991, 1994) and Poulos (1993, 1994):

(10.12)

However, it is probably more reliable to correlate the initial soil modulus with
the undrained shear strength (C ), and the following correlation is suggested by
u
Hirayama (1991, 1994) and Poulos (1993, 1994):
(10.13)

Several other correlations have been proposed, i.e. E =1500–3000C (Jardine et
s
u
al., 1986), E =1200–2700C u (Kuwabara, 1991), E =1900C u (Kagawa, 1992).
s
s
Thus, Equation (10.13) may give average values which are expected to be on the
safe side.
For silica sands, the following correlation between initial E and SPT N-value
s
may be used (Ohsaki and Iwasaki, 1973; Poulos, 1994):
(10.14)
Alternatively, the initial soil modulus may be correlated with the Cone
Penetration Test (CPT) results, as proposed by Imai and Tonouchi (1982) and
Poulos (1989, 1994):

(10.15)

where q is the cone resistance (in MPa).
c
It must be stated that the empirical correlations presented above (Equations
(10.11)−(10.15)) can only be expected to provide an approximate estimate of
initial soil modulus and may be rather inaccurate if applied to cases outside the
scope of previous experience. Thus, as discussed by Gazetas (1991), their use
may only be recommended in practice in some cases as follows: (a) in feasibility
studies and preliminary design calculations; (b) for final design calculations in
big projects as supplementary data or in small projects as main data; (c) for
initial data in back analyses; (d) to provide an order-of-magnitude check against
the experimentally determined values.
It should be emphasised that such correlations refer to the axial response of
pile foundations. For piles under lateral loading, the effects of pile installation