settlement_of_shallow_foundations_on_granular_soils (Lutenegger ang DeGroot)

N = uncorrected blowcount
C, = embeddment correction
= I - 0.25 (D/B)
[5.56]
5.2.16 Arnold (1980)
Arnold (1980) presented a method for estimating the settlement of shallow foundations on
sands which is based on establishing the relative density of a sand deposit, using empirical stressstrain
relationships for sands of various densities, predicting the strains below a footing and
integrating to give to total settlement. The relative density is obtained using the results of the SPT.
The settlement equation presented by Arnold (1980) may be stated as:
2B
S = 43.06B L& [aln(l/(1-Iq/Q))]/[1+(3.281B)m] 2
z=O
[5.57]
where:
s = settlement (in mm)
B = footing width (in meters)
a = an exponent
I = vertical strain influence factor
q = applied footing stress (kN/m 2 )
Q =hypothetical ultimate pressure (kN/m 2 )
m = an exponent
ll.z =individual layer thickness (in meters)
The influence factor I is related to the depth below the footing and is taken at the mid depth for each
soil layer within the compressible zone, assumed to be equal to 2B, as:
I= 1-0.5 (z/B) [5.58]
Values of Q, a, and m are related to the relative density of the sand, D, which is obtained from the
field blowcounts as:
D, = 25.6 + 20.37 [(1.26(N-2.4))/(0.0203yH + 1.36) -1] 05 [5.59]
where:
D, =relative density (in %)
N =field SPT blowcount at mid-depth of layer
yH = effective overburden stress where N is determined (in kN/m 2 )
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