2312002 - Soil-Foundation-Structure Interaction of Deep Foundations in Liquefied Ground

Project Title/ID Number	Soil-Foundation-Structure Interaction of Deep Foundations in Liquefied Ground—2312002
Start/End Dates	10/1/02—9/30/03
Project Leader	Ross Boulanger (UCD/Faculty)
Team Members	Scott Brandenberg (UCD/Grad Student), Dongdong Chang (UCD/Grad Student)

Project goals and objectives
The objectives of this project are to develop and validate nonlinear p-y, t-z, and q-z material models for OpenSees-based simulations of the seismic response of deep foundations in liquefied and laterally spreading ground.
Role of this project in supporting PEER’s vision
These material models and their validation against centrifuge experiments provide the basis for developing performance based design methods for deep foundation in liquefied and laterally spreading ground. This project provides an essential integrated test of the OpenSees platform for liquefaction/foundation modeling and provides necessary tools for the Humboldt Bay Bridge demonstration project.
Methodology employed
The project involves material model development and coding in OpenSees, along with comparisons with the p-y/t-z behavior back calculated (“imaged”) from prior centrifuge studies. The implemented models are then used in nonlinear time-history analyses of centrifuge tests, from which the limitations of the soil models and p-y/t-z models are evaluated. Sensitivity studies aid in identifying the main sources of uncertainty in these FEM models.
Brief description of past year’s accomplishments and more detail on expected Year 6 accomplishments
The first set of p-y/t-z/q-z material models for non-liquefaction and liquefaction conditions were implemented in OpenSees. These models communicate with the multiple yield surface soil models of Elgamal and Yang, as implemented in OpenSees. Single element examples illustrate the ability of the models to capture key aspects of observed p-y behavior, including inverted s-shaped loops, dependence on soil relative density, dependence on level of shaking in the free-field, and dependence on pile foundation stiffness. This figure shows results for a cyclically-loaded single soil element connected to a “pile” with a single p-y spring; responses are shown for the soil element and for the p-y spring without liquefaction (includes gapping) and with liquefaction. The implemented models have been used in analyses of pile foundation models in liquefying soil profiles, as tested in the centrifuge at UCD. For example, the three pile-supported structures shown in this photo includes one single-pile supported structure (circled). Tests were performed with the upper sand being loose (Dr about 35%) and medium dense (Dr about 55%). Comparisons of predicted and recorded responses are shown in these two plots (upper one for Dr about 35%, lower one for 55%). The effects of liquefaction and the importance of the sand’s Dr on both the site response and the lateral response of the structure were captured well by the analyses. Work is currently progressing on the numerical modeling of the pile groups in these and other centrifuge tests. We have coded some macro programs for automatically generating the p-y/t-z/q-z parameters and element input files for OpenSees models.		Figure 1. Larger View Figure 2. Larger View
Other similar work being conducted within and outside PEER and how this project differs
Boulanger and Kutter have been performing dynamic centrifuge model tests of piles in liquefied and laterally spreading ground with Caltrans funding. That project provides imaged (back-calculated) soil-pile interaction behavior and evaluations of simplified design methodologies. The project proposed herein benefits from those centrifuge studies.		Figure 3. Larger View
Plans for Year 7 if this project is expected to be continued
The validated models will be used to address two pressing design issues: the ability of pile foundations to restrain lateral spreading of bridge abutments, which reduces the loads compared to those predicted by uncoupled analyses of the lateral spreading and foundation responses; and parametric studies to evaluate suitable kinematic and inertial load combinations for simplified design practice.
Describe any instances where you are aware that your results have been used in industry
Results from the centrifuge testing work have been used by Caltrans and others to guide selection of p-y parameters for liquefied soils. The material models being developed for OpenSees have not yet been used in practice.
Expected milestones
Next generation of material models to be implemented, May 2003 PEER report on validation studies, December 2003
Deliverables
Validated p-y, t-z, & q-z material models for simulating soil-pile interaction in liquefied soil that are implemented in OpenSees with technical and user documentation. A report documenting the evaluation of OpenSees-based numerical models against existing dynamic centrifuge data, including the relative effects of uncertainties in the parameters that describe the soil continuum, structure, and p-y/t-z/q-z springs.