settlement_of_shallow_foundations_on_granular_soils (Lutenegger ang DeGroot)

The reliability of settlement estimates for shallow foundations on granular soils has also
received considerable attention and has been discussed by Schultze and Sievering (1977); Tan and
Duncan (1991); Nova and Montrasio (1991a, 1991b); Cherubini and Greco (1991); and Berardi and
Lancellotta (1994).
Investigations of the settlement behavior of bridge abutments and piers resting on granular
soils, which is the primary focus of this project, have also been performed by a number of
researchers. Table 2.1 summarizes previous reported studies involving settlement of bridges, piers
and abutments on granular soils.
Most of the available methods for predicting the settlement of shallow foundations on
granular soils rely on the results of in situ tests. The results of the tests are either used: (1) to
estimate an elastic modulus of the soil which is used in an elastic analysis; (2) directly to estimate
settlement using an empirical correlation; or (3) to estimate some other soil property, such as relative
density, and then an estimate of settlement is made.
A review of previous comparisons made between predicted and observed settlement of
shallow footings in sands or sands and gravels reveals that no single method works better than any
other method in all cases. Some methods appear to work better than others and it appears that more
recent methods are promising. This may be in part related to the fact that our understanding of soil
behavior has increased but may also be the result of careful consideration of all of the factors that
may influence performance of an individual foundation.
The majority of available methods for estimating settlement assume a linear response
between load and deformation of granular material (i.e. a constant modulus). Additionally, there
has been little effort to relate the settlement or relative displacement to the kYla of a load; i.e. -
relative to an ultimate or failure load. This appears to be the primary deficiency in existing
methods.
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