settlement_of_shallow_foundations_on_granular_soils (Lutenegger ang DeGroot)

The use of the drive cone test is well documented for sand deposits (e.g., Palmer and Stuart
1957, Mohan et al. 1970, and Muromachi and Kobayashi 1982) as well as in gravelly materials (e.g.,
Rao et al. 1982 and Hanna et al. 1986). Charts have been presented providing a comparison between
SPT's and DCT's and in some cases allowable bearing capacity charts for shallow foundations on
granular soils have been developed based on the results ofDCT's (e.g., Mohan et al. 1971).
Parrent (1963) suggested the following approach could be used to calculate settlements based
on the elastic approach presented by Terzaghi (1943):
s = KqB[(l - !J. 2 )/E]
[5.127]
where:
s = settlement
K = a constant depending on the position where settlement is desired
q = applied footing stress
2B =width of the footing
Jl = Poisson's ratio
E =Young's Modulus
It was further suggested that Jl and E could be assumed constant provided that the applied stress did
not exceed about 1/3 to 1/2 of the ultimate bearing capacity (with FS = 2 to 3). Based on back
calculation of load-settlement curves presented by Terzaghi and Peck (1948) for different values of
SPT penetration resistance, Parrent suggested:
E/(l-Jl 2 ) = 15,000N (psf) [5.128]
where:
N = SPT or DCT blowcount.
5.8 Comparison of Methods
To illustrate results that can be obtained using various methods, settlement calculations were
performed using the SPT and CPT results obtained at the site of the FHW A footing load tests at
Texas A & M University and reported by Briaud and Gibbens (1994). Settlement estimates were
made for a 3m x 3m footing (Test Footing #1) using the applied pressure corresponding to a
settlement of25mm (lin.) obtained from the actual load vs. settlement curve. The results of these
estimates are presented in Tables 5.9 and 5.10. The resulls presented in both of these tables indicate
a wide range of estimated settlement, from about 18 to 124=, however, there are a number of
methods that show very close agreement with the observed value.
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