settlement_of_shallow_foundations_on_granular_soils (Lutenegger ang DeGroot)

Sutherland (1963) compared the results of this procedure with a number of reported case
histories in which the results of plate bearing tests were available and found that this procedure
provided an improvement over the original Terzaghi and Peck procedure, however, it still tended
to overestimate settlement since it appeared that the allowable bearing pressure was underestimated
by almost 40%.
5.2.6 AI pan (1964)
Another settlement method based primarily on the Terzaghi and Peck (1948) method was
presented by Alpan (1964). This method indirectly uses a corrected blowcount to evaluate a modulus
of sub grade reaction from a plate loading test.
The method assumes that the settlement response of a shallow footing resting on sands will
be linear in the range of allowable bearing pressures (i.e., qu 1 /2.5) and is given as:
s = S 0
[2B/(B+ I )] 2 mCw
[5.23]
where:
s =settlement (in inches)
S 0 =settlement of a 1 ff plate (in inches)
B =footing width (in ft.)
m = shape correction factor
Cw = water table correction factor
= 2.0 = 0.5 (D/B) ,; 2.0 for water located immediately
below the footing
[5.24]
The settlement of the 1 ff plate is given as:
S 0
= aqB
[5.25]
where:
q = footing stress (in tst)
0'. = a constant (dependent upon the corrected blowcount N,)
The blowcount value at the foundation level is first used to estimate the relative density of
the sand, Dn using the suggestions of Gibbs and Holtz (1957) which was put into a more convenient
form by Coffman (1960) as shown in Figure 5.5. The correction factor, a, is shown in graphical
form in Figure 5.6. Note that two charts are suggested by Alp an (1964); one for corrected blowcount
values between 5 and 50; and another for corrected blowcount values between 25 and 80.
65