settlement_of_shallow_foundations_on_granular_soils (Lutenegger ang DeGroot)

q, = allowable bearing pressure (tsf)
N =uncorrected SPT blowcount
B = footing width (ft.)
In saturated very fine or silty sands, Meyerhof suggested using the equivalent N values ifN > 15
as:
N, = 15 + 0.5 (N- 15) [5.12]
which is the same as Equation 5.8.
The settlement for any footing loaded to some stress level other than q, (presumably less) could then
be obtained by proportioning the settlement from 25mm (1 in.) as a proportion of the q/q, ratio.
Since submergence increases the settlement, the allowable bearing capacity Equations 5.9, 5.10 and
5.11 should be reduced to account for position of the water table as 112 for fully submerged.
Meyerhof (1965) suggested a slight modification to his earlier (Meyerhof, 1956) expression
to increase the allowable bearing capacity giving a settlement of 25 mm (1 in.) by 50% to account
for the fact that the earlier method tended to be conservative. The expressions for settlement then
become:
s = 4q/N
(forB ,;; 4ft.)
s = [6q/N][B/(B+ I)]' (forB> 4ft.)
s = 6q/N
(for rafts)
[5.13]
[5.14]
[5.15]
where:
s = settlement (in inches)
q = footing stress (in tsf)
N = uncorrected blowcounts
B = footing width (in ft.)
C, = embedment correction factor
No correction is applied to blowcount values for overburden stress and since it is assumed that the
presence of ground water is reflected in the blowcount values, no additional correction is applied
for the ground water table.
5.2.3 Hough (1959, 1969)
Hough (1959) presented an approach for calculating settlements of foundations on sands
which is similar in form to calculating the one-dimensional consolidation settlement of structures
on clay. The subsurface is divided into a number of appropriate layers, the change in vertical
59