settlement_of_shallow_foundations_on_granular_soils (Lutenegger ang DeGroot)

6.16 van der Vlugt and Rosenthal (1989)
Using the settlement procedure proposed by Schmertmann (1970) and Schmertmann eta!.
(1978) van der Vlugt and Rosenthal (1989) presented a design chart for allowable soil pressure for
surface loaded footings to produce a settlement of 25 mm (I in.), Figure 6.26 which is similar to the
technique used by Spangler and Handy (1982). The form of the settlement curves for different values
of cone resistance, q" are different than proposed by Terzaghi and Peck (1948) and Peck eta!. (1974)
but are similar to that shown by Taylor (1948). These curves simply indicate higher allowable
pressures for smaller footings and lower pressures for larger footings than do previous curves which
is consistent with previous observations made by others. Approximate equivalent SPT values are
also shown in Figure 6.26 assuming qjN equals 4.
6.17 Comparison of Design Charts
In order to illustrate the difference between the different proposed charts, a comparison can
be made of the observed and predicted footing pressure producing a settlement of25 mm (I in.). To
do this, the results of the FHWA footing load test performed at the Texas A&M NGES are used.
These tests represent footing widths of I, 1.5, 2.5, and 3 m as indicated in Table 6.2. The values of
footing pressures were obtained from footing settlement curves presented by Briand and Gibbens
(1994).
Table 6.2 Observed and Predicted Footing Pressure at 25mm (lin.) Settlement
Method 1 x1m l.Sxl.Sm 2x2m 3x3m 3x3m
A B c D E
Observed 850 670 560 580 480
Terzaghi & Peck 193 180 !58 !56 !56
(1948)
Peck, Hanson &
-
192 !52 !51 !51
Thornburn (1953,
1974) 172 172 172 172 172
Meyerhof (1956)
(1965) 201 194 169 163 163
Sowers (1962) 235 235 235 235 235
Bowles (1968) 322 306 257 245 245
(1982) 336 307 264 256 256
171