settlement_of_shallow_foundations_on_granular_soils (Lutenegger ang DeGroot)

Table 5.5 Influence Factors for Berardi et al. (1991)
HIB L/B=1 2 3 4 10 Circle
0.5 0.35 0.39 0.40 0.41 0.42 0.34
1.0 0.56 0.65 0.67 0.68 0.71 0.52
1.5 0.63 0.76 0.81 0.84 0.89 0.59
2.0 0.69 0.88 0.96 0.99 1.06 0.63
5.3.7 Robertson (1991)
Robertson (1991) suggested a method based on cone tip resistance to evaluate soil elastic
modulus which is similar to the method presented by Stroud (1989) for SPT blowcounts. The
operative soil modulus is related to the degree ofloading of the foundation, relative to the ultimate
calculated bearing capacity. Based on the theory of elasticity, settlement may be calculated as:
where:
[5.103]
s = settlement
B = foundation width
q"" = net applied footing stress
ll =Poisson's ratio
I, =influence factor which depends on footing geometry and rigidity and type of elasticitymodel
E' =drained Young's modulus
While Robertson (1991) does not give details for evaluating I, or j.l, it may be assumed that
appropriate I, values may be obtained from the charts presented by Christian and Carrier (1978) and
that Poisson's ratio equals 0.25.
In order to obtain the drained Young's modulus, E', the normalized cone tip resistance, q"
must be evaluated as:
where:
P, = atmospheric pressure
cr'vo =vertical effective stress where q, is measured
[5.104]
Since the correlation between q, and E' is a function of the degree of loading it is necessary to
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