settlement_of_shallow_foundations_on_granular_soils (Lutenegger ang DeGroot)

and circular foundation; 4B for strip footings (LIB> I 0) and intermediate values for intermediate
cases.
Settlement is determined from:
where:
q = applied footing stress
I = influence fator to account for footing rigidity
( o.'ooJav = [(1 + 2K,)/3]o.'vo + o:q
K. =at-rest coefficient of earth pressure
cr'vo =effective vertical overburden stress
o: =ratio between Acr' 001
induced by qat depth z; and q (determined from linear elastic theory)
Ki & Cr =constants determined from the plate test
Hi = zone of influence for the foundation
[5.126]
The constants Ki and Cr are determined from a plot of normalized load-settlement results from the
plate load test as shown in Figure 5.32. These transformed hyperbolic data give a linear curve with
slope of l!Cr and intercept of 1/Ki.
Numerous authors (e.g., Oweiss 1979; Ismael 1991; Ortigosa et a!. 1989 Papadopoulos 1992)
have compared the observed settlement of footing tests with the nondimensional width ratio vs.
settlement ratio curves ofBjerrum and Eggestad (1963) and others, and have found wide variations
in results.
5.6.6 Burland et a!. (1977)
Another interesting method for comparing the results of plate load and footing load tests was
presented by Burland eta!. (1977) and is shown in Figure 5.33. As indicated, the settlement per unit
applied pressure is seen to increase with footing size and is a function ofthe relative density. This
figure may be used to make preliminary estimates of settlement.
5.7 Drive Cone Test
The use of an impact driven point in the form of a cone penetrometer has frequently been
suggested as an expedient substitute for the Standard Penetration Test (e.g; Mohan et al., 1971).
Farren! (1963) had suggested that the test could be used to predict the settlement of footings on
granular soils. In this case, a cone tip of 50mm (2in.) diameter with an apex angle of 60° was used.
Comparisons made at two sites indicated that the blowcount values obtained by the drive cone (over
a distance of0.3m (1ft.)) were equivalent to SPT blowcount values over the same zone. The obvious
advantages of the drive cone are increased frequency of test data and expedience in deployment and
execution ofthe test.
130