settlement_of_shallow_foundations_on_granular_soils (Lutenegger ang DeGroot)

5.2.12 Parry (1971)
A method was proposed by Parry (1971) which is similar in form to the method of
D'Appolonia et a!. (1970) and not unlike the general elastic methods described in Section 4.
Settlement is calculated from:
where:
[5.44]
s = settlement (in inches)
a. =a constant= 0.25
q = footing stress (in tsf)
B = footing width (in ft.)
Nm =weighted average of uncorrected N values betweenD and D = 2B
Cd = embedment correction factor
= [1.3 (0.75 + D/B)]/[1 + 0.25 (D/B)]
Cw =water table correction factor
= 1 + (Dw)/(D + 3B/4) for O<Dw <D
= 1 + [Dw(2B + D-Dw)]/[2B(D+O. 75B)] for 0< (Dw -D) < 2B
[5.45]
[5.46]
[5.47]
C, =thickness of compressible sand stratum correction factor as shown in Figure 5.8.
This method assumes that in a uniform soil half of the settlement occurs within a depth of 3B/4
below the foundation level and the remaining half within a depth between 3B/4 and 2B below the
foundation.
The value of a. in Equation 5.44 was obtained by Parry (1971) by comparing predicted
settlements with a number of plate bearing tests and several published field records of settlements
from small and large footings, tanks, and rafts. With the exception of one reported case history of
a chimney settlement, the range in ratio of calculated to measured settlement was from 0.8 to 2.6
averaging 1.2. In twenty of twenty-four cases the range was 0.8 to 1.5, averaging 1.1.
The value of the "representative" blowcount, N,., for use in Eq. 5.44 was recommended as
follows:
1- Where N varies consistently Nm should be taken as the "observed"
value at a depth of 3B/4 below the foundation.
2 - Where N values do not vary consistently use the following procedure
to obtain Nm:
a- take the average value ofN between the foundation
level and a depth of3B/4 and multiply by 3, giving 3N,
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