settlement_of_shallow_foundations_on_granular_soils (Lutenegger ang DeGroot)

s = settlement
q = foundation stress
B = width of a rectangular foundation
E, = constrained modulus of the soil for the appropriate stress range
f = a dimensionless factor which depends on soil stress history,
geometry, loading and the relation between constrained modulus and effective stress.
According to Papadopoulos (1992) the settlement factor, f, is related to the stress history of
the soil, the geometry of the foundation (depth and dimensions), the foundation loading, and the
relation between the constrained modulus and the effective stress, cr', as shown in Figure 4.18. The
influence of stress history and other factors, expressed in terms of the dimensionless factor, a, where
a= the ratio of applied footing stress to the footing width times the effective soil unit weight, i.e.,
a= q/(y'B) [4.30]
is indicated in Figure 4.18.
The constrained modulus, E, is related to the effective stress for stresses cr' ,; 600 kPa by a linear
expression:
E, = E, + A.cr'
[4.31]
where:
E 50 = constrained modulus for zero effective stress
"-=the rate of E, increase with stress.
In practice, since it is difficult to evaluate '}.._from undisturbed samples, the alternative is to use an
average E, in settlement calculations evaluated from in situ tests and "- = 0. The following
expressions for estimating soil modulus were suggested by Papadopoulos:
E,=2.5 q,
E, = 7.5 + 0.8N (MPa)
(for CPT results)
(for SPT results)
[4.32]
[4.33]
A comparison between the settlements predicted using this method and settlement
observations using cases reported primarily by D'Appolonia eta!. (1968), Schmertmann (1970), and
Schultze and Sherif (1973) showed that in more than 90% of the cases the deviation of the estimated
settlement from the measured settlement was ± 50%.
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