Bay Division Pipeline 2, Hayward Fault Crossing
San Francisco Public Utilities Commission
Evaluation completed 1998
Scope of work:
- Performed three-dimensional nonlinear inelastic finite element modeling and analysis
- State of the art nonlinear finite element analyses.
- Seismic analysis of a thin walled buried pipeline under fault offset.
The Bay Division Pipeline No. 2 is a 66" diameter, 3/8" thick pipeline delivering water from Hetch Hetchy Reservoir to the Bay Area. It is one of the original pipelines supplying Sierra Nevada water to the Bay Area. As built, this pipeline is buried where it crosses the Hayward Fault in the East Bay.
As subconsultant to Geomatrix, OPAC performed three-dimensional nonlinear inelastic finite element modeling and analysis of the pipeline and surrounding soil under a 5 foot fault offset. Analyses were made of varying pipe thicknesses in order to determine a proper range for pipe replacement retrofit. The main focus of these three-dimensional analyses was to predict the pipe's behavior and strain due to pipe ovalling, which is neglected in standard "beam theory" engineering theory. Results showed that the existing 3/8" pipe was subject to localized "snap through" buckling during the fault offset, with probable failure. Analyses on thicker 3/4" and 1" pipes showed less tendency to "snap through", more benign behavior and reasonable strain levels.