settlement_of_shallow_foundations_on_granular_soils (Lutenegger ang DeGroot)

of~ to calculate I. (The tables provided in Bowles (1988)
which are also shown in Figure 4.4 may be used.)
7- Estimate the Fox (1948) embedment correction factor using
Figure 4.8.
8 - Obtain the weighted average E, in the depth z = H. The
weighted average can be calculated as:
[4.26]
The settlement calculation proceeds using Equation 4.1 and applying the Fox embedment correction
factor as presented by Bowles (1982, 1988) shown in Figure 4.9.
Bowles (1987) suggested that based on Boussinesq stress distribution profiles and
Schmertmann's (1970) strain profiles, for all practical purposes the soil mass below a depth of 4B
to 5B has little influence on the settlement. The value of H = 5B was taken to be slightly
conservative over using H = 4B and thus has a "substantial significance" on the Steinbrenner
influence factor over taking H = "'·
Additionally, it was reasoned that the soil modulus E, generally increases with depth in
homogenous sand deposits and therefore could be much larger at 5B than at the base of the
foundation. It was suggested then that the average E, over the depth H should be used and not the
value in the zone ofB to 2B beneath the foundation, as has been suggested by others. Reasonable
values of E, may be obtained from CPT or SPT results as indicated by Bowles from:
E, = 2.5 to 3 q,
E, = 10 (N + 15)
(in units of q,)
(in ksf)
[4.27]
[4.28]
Bowles (1987) summarized a number of case histories from the literature and found good
comparisons between observed and calculated settlements using this method. It was suggested that
the reason that earlier estimates of settlement were poor were because E, just below the base was
used and that a semi-infinite half space was used which produced an error in the influence factors
used.
4. 7 Papadopoulos (1992)
Papadopoulos (1992) suggested a method of estimating the settlement of footings resting on
granular soils of the elastic solution type as:
s = [(qB)/E,]f [4.29]
where:
33