Shallow foundations are extensively used to support structures of all
sizes and derive their support from near surface soils. Thus, they are typically
embedded up to a few meters into the soil profile. Designers of shallow
foundations are required to meet two limit states: overall failure of the soil
beneath the foundation (bearing capacity) and excessive settlement. Existing
bearing capacity design methods use an assumed shearing plane within the soil
and perfectly plastic soil behavior to estimate the ultimate resistance available.
The immediate settlement of a shallow foundation is typically approximated
using an elasticity-based method that does not account for actual, nonlinear
soil behavior. A load test database was developed from footing load tests
reported in the literature to assess the accuracy and uncertainty in existing
design methodologies for calculating bearing capacity and immediate
settlement. The assessment of uncertainty in bearing capacity and immediate
settlement was accomplished through the application of a hyperbolic bearing
pressure-displacement model, and the adaptation of the Duncan-Chang soil
constitutive model to footing displacements.
The prediction of bearing capacity using the general bearing capacity
formula was compared to the bearing capacity extrapolated from the load test
database using a hyperbolic bearing pressure-displacement model. On average
the general bearing capacity formula under-predicts the bearing capacity and
exhibits a significant amount of variability. The comparison was used to
develop resistance statistics that were implemented to produce resistance
factors for an LRFD based design approach using AASHTO load statistics.
The Duncan-Chang model was adapted to predict bearing pressure displacement
curves for footings in the load test database and used to estimate
governing soil parameters. Bearing pressure-displacement curves fitted to the
observed curves were used to back calculate soil stiffness. The soil stiffness
was used with an elasticity-based displacement prediction method to evaluate
the accuracy of the method. Finally, the back-calculated modulus from the
fitted Duncan-Chang model was used to assess the accuracy and uncertainty
associated with the elasticity-based K-factor, a correlation based stiffness
parameter. In general the comparisons indicate that the current design
procedures over-predict the bearing pressure associated with a given
displacement and exhibit a significant amount of uncertainty. / Graduation date: 2012
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28739 |
| Date | 14 March 2012 |
| Creators | Strahler, Andrew W. |
| Contributors | Stuedlein, Armin |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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