settlement_of_shallow_foundations_on_granular_soils (Lutenegger ang DeGroot)

For different soils Menard suggested different values of a as: (1) sand & gravel, 1/3; (2) silt, 1/2;
(3) clay. 2/3; (4) peat, 1. Based on the correlation exhibited between measured and predicted
settlements, Martin (1977) found that the PMT modulus, Em, closely approximates the soil modulus,
E,, i.e., o:: = 1, for the soils investigated when using Schmertmann's 2B-0.6 strain influence factors.
5.4.3 Baguelin et a!. (1978)
Baguelin et a!. (1978) present a simplified approach to estimating foundation settlements for
preliminary design as:
where:
s = settlement
qnet = net footing pressure = q -yD = q'
y = soil total unit weight
D = foundation depth
f = an empirical coefficient which is a function of soil type and footing
geometry
Em= PMT modulus within a depth of2B below the footing
[5.110]
The value of Em should be adjusted to give the weighted average of values obtained in the
zone 2B below the footing if the soil is not uniform. Values off may be obtained from Figure 5.28
and will have units of length as shown. Both Em and qnet must have the same units.
5.4.4 Briaud (1992)
An alternative approach which is presented by Baguelin eta!. (1978) and Briaud (1992) is
to use a simple elastic solution to calculate settlement as:
s = 1,1 1 (1 - u 2 ) q(B/E)
[5.111]
where:
s = settlement
I,I 1 = influence factors
u =Poisson's ratio
q = bearing pressure
B = footing width
E = PMT modulus within the zone of influence
This approach is essentially the same as other elastic methods presented, with the exception that the
soil modulus is obtained directly from the PMT.
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