Philosophy for Treatment of High-Pressure Natural Gas Pipelines at Active Fault Crossings

by Jeffrey R. Keaton, Sergent, Hauskins & Beckwith, Geotechnical Engineers, Salt Lake City, United States,
Robert M. Robison, Sergent, Hauskins & Beckwith, Geotechnical Engineers, Salt Lake City, United States,
George H. Beckwith, Sergent, Hauskins & Beckwith, Geotechnical Engineers, Salt Lake City, United States,
David B. Slemmons, Sergent, Hauskins & Beckwith, Geotechnical Engineers, Salt Lake City, United States,



Document Type: Proceeding Paper

Part of: Lifeline Earthquake Engineering

Abstract: Natural gas from fields in the overthrust belt of southwest Wyoming will be collected and transported to Southern California. The proposed Kern River Pipeline will transport gas to Daggett, California, to connect with the proposed Mojave Pipeline which will transport Mid-Continent gas to Bakersfield, California. The Kern River Pipeline has a planned operating pressure of 8.274 MPa (1200 psi). The gas will be used to generate steam for secondary and tertiary oil recovery; burning gas to generate steam is environmentally and economically preferable to burning oil. The Kern River Pipeline crosses the Basin and Range Seismotectonic Province of North America and enters the Mojave Desert of California. The Basin and Range Province is characterized by isolated mountain ranges bounded by active normal faults. The Mojave Desert is characterized by active northwest-trending right-lateral and east-northeast-trending left-lateral strike-slip faults. Anticipated coseismic fault offset at the ground surface ranges from 1.5 to 3 m (5 to 10 ft). A philosophy for treatment was developed which was intended to provide public safety from possible hazards associated with fault rupture of the pipeline, to protect the owner from loss of pipeline function, and to comply with federal mitigation requirements. This philosophy was based on the (1) age of the most recent offset on the fault, (2) recurrence interval for fault offset, and (3) proximity to population. Proximity to population was determined by the U.S. Department of Transportation (DOT) classification system. Design treatments consisted of maintaining relatively straight, unanchored lengths of about 200 pipe diameters (180 m [600 ft] on each side of the fault traces, configuring the construction ditch to distribute stresses and strains, and specifying the ditch backfill to soften the p-y curve. Active normal faults were crossed in construction trenches deepened on the footwall block; active strike-slip faults were crossed in widened construction ditches. The dimensions of the ditch configurations were developed with the aid of a finite element stress analysis program.

Subject Headings: Geological faults | Gas pipelines | Natural gas | Public health and safety | Pressure pipes | Pipeline crossing | Rivers and streams | Basins | North America | California | United States | Mountain ranges | Wyoming

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