settlement_of_shallow_foundations_on_granular_soils (Lutenegger ang DeGroot)

6.6 Sowers (1962)
Sowers (1962) in Leonards (1962) presented a chart illustrating the relation between
allowable foundation pressure and standard penetration resistance for small structures with column
loads between 25,000 and 100,000 lb. The resulting chart for different soils is shown in Figure 6.8.
Sowers (1962) recommended using the average penetration resistance for a depth of 1.5B below
the footing.
6. 7 Bowles (1968, 1977, 1982, 1988)
Bowles (1968) suggested that the chart ofTerzaghi and Peck (1948) and the expressions
presented by Meyerhof (1956, 1965) were too conservative, stating that "There seems, at present,
to be considerable evidence ... that both of these proposals ... are too conservative. These data
indicate that the allowable soil pressure could be increased possibly as much as two or three times
without excessive settlements occurring, and further, that the location of the groundwater beneath
the footing is not as critical as presented ... ". Accordingly, Bowles (1968) recommended increasing
the allowable soil pressures to produce 24 mm (I in.) of settlement and presented charts for both the
Terzaghi and Peck Method and MeyerhofMethod. These charts are shown in Figure 6.9 and 6.10,
respectively.
In the 1982 edition of his text, Bowles (1982) had dropped the modified Terzaghi and Peck
(1948) chart and had only included a slightly different chart based on Meyerhofs Method than in
previous editions, Figure 6.11. This chart also appears in Bowles (1988).
6.8 Mohan, Aggarwal and Tolia (1971)
A chart incorporating the corrected SPT values and the use of dynamic cone penetration tests
(DCT) for determining allowable soil pressure was presented by Mohan et al. (1971) as shown in
Figure 6.12. The allowable soil pressure is written approximately as:
q, = (Ns,)/(7P+5)
q, = [(Ns,)/(14P + 10] [(B+ 1)/Bf
q, = (Ns,)/(IIP+8)
where:
(forB< 1.5 m)
(forB :>: 1.5 m)
(for rafts)
[6.15]
[6.16]
[6.17]
q, = allowable soil pressure (in kg/cm 2 )
B =footing width (in meters)
N = SPT blowcount
P = overburden pressure (in kg/cm 2 )
s, = allowable settlement (in em)
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