Pipeline Fragility Assessment against Liquefaction-Induced Differential Settlement in the Cities of Alameda and Oakland, California

Abstract

The East Bay Municipal Utility District (EBMUD) is major water utility providing water to more than 1.3 million people on the eastern side of the San Francisco Bay Area. The EBMUD has approximately 4,200 mi of treated water distribution and transmission pipelines within a 331 square miles (sq mi) customer service area. Approximately 360 mi of this system are large-diameter pipelines consisting of 20 in. and larger welded steel pipe, 36-in. and larger reinforced concrete cylinder pipe, 16-in. and larger diameter cast-iron pipe, and 20-in and larger pretensioned concrete cylinder pipe. System data are managed using a comprehensive geographic information system (GIS) geodatabase of pipeline characteristics, location, and seismic hazard. Due to the proximity to active faults such as the Hayward Fault, Calaveras Fault, San Andreas Fault, and Concord Fault, the EBMUD service area is very susceptible to earthquakes. Previous studies have suggested that water pipelines are damaged during earthquakes when settlements impose high stresses on the pipeline and its components. Permanent ground deformation is estimated from seismic hazards such as a landslide, fault offset, or liquefaction-induced settlements. A service area that represents this scenario is the City of Alameda, where soil is highly liquefiable in the event of an earthquake. The geology of the city is compromised predominantly by artificial fill and Holocene alluvial fan deposits, with the artificial fill being the most vulnerable to liquefaction. Using 212 cone penetration tests (CPT) soundings located throughout the City of Alameda and geographic information systems (GIS), a pipeline fragility study is performed to determine pipeline segments that have the potential for failure or some level of damage during an earthquake event. In addition, a pipeline map similar to the United States Geologic Survey (USGS) ShakeMap will be created to identify damaged pipeline segments and their corresponding level of damage. After identifying pipeline segments with potential for failure, a repair program is outlined by the authors. The researchers generate the prediction model for the pipeline fragility study for the EBMUD service area, the City of Alameda, based on settlement values obtained by peak ground acceleration values (PGA) and a M7.0 earthquake magnitude. Estimated liquefaction-induced settlement values are verified using the program software SHAKE2000.