settlement_of_shallow_foundations_on_granular_soils (Lutenegger ang DeGroot)

The influence factor, i~ as presented in the CFM, is taken from Kany (1959) and is shown in Figure
4.14 for different values of ziB and LIB and therefore, like other influence factors, takes into
account the layer thickness and foundation geometry.
4.4. Oweiss (1979)
A method known as the "Equivalent Linear Model" was presented by Oweiss ( 1979) which
is essentially an elastic solution model in which the elastic deformation modulus of the soil is
obtained from the standard penetration test (SPT) blowcounts. Settlements from individual soil
layers beneath the foundation are calculated and the total settlement is obtained by su=ing all
individual settlements. In this method, the settlement is calculated from the expression:
n
s = qB~ (\lf/EJ
i=1
[4.12]
where:
s =settlement (ft.)
q = applied footing stress (kst)
B = footing width (ft.)
I = individual layer
n = total number of layers
\If; = settlement factor of layer i
E; = elastic modulus of layer i
Initially, the compressible zone beneath the foundation to a depth of at least D + 2B, where D =
depth of the foundation, is divided into sub layers. The sub layers may be of any thickness and it may
be convenient to define layer boundaries at obvious changes in soil properties, such as blowcount,
grain-size, water table, etc. Ifthere are no obvious distinct property variations, i.e., the compressible
zone is more or less uniform, it is suggested that the zone between D and D + 2B be divided up into
at least four or five sublayers to improve the accuracy of the settlement estimate.
For each soil layer, Oweiss (1979) suggested that the SPT blowcount should be corrected
for overburden stress using the correction factor suggested by Peck and Bazaraa (1969) as:
N, = 4N/(1 +2 p')
N, = 4N/(3.25 + 0.5 p')
where:
(for p',: 1.5 kst)
(for p' > 1.5 kst)
[4.13]
[4.14]
N, = corrected blowcount
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