Liquefaction Hazard Analysis for Design of the Kern River Pipeline at the Muddy River Crossing, Southern Nevada

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by Jeffrey R. Keaton, Sergent Hauskins & Beckwith, Geotechnical, Salt Lake City, United States,
Jon E. Bischoff, Sergent Hauskins & Beckwith, Geotechnical, Salt Lake City, United States,
T. Leslie Youd, Sergent Hauskins & Beckwith, Geotechnical, Salt Lake City, United States,
Matthew A. Mabey, Sergent Hauskins & Beckwith, Geotechnical, Salt Lake City, United States,

Document Type: Proceeding Paper

Part of: Lifeline Earthquake Engineering:

Abstract: The 91.4-cm (36-in.) diameter Kern River natural gas transmission pipeline will cross the Muddy River in Moapa Valley, about 5 km west of Glendale, Nevada, in an area of relatively low seismic activity. The river drains about 2,330 km2 of southern Nevada and has cut down into late Tertiary fine-grained sedimentary rocks. Aggradation of the river, probably in Holocene time, has resulted in floodplain deposition. The modern floodplain is approximately 500 m wide at the pipeline crossing and slopes about 0.1° toward the channel which is approximately 4 m deep. Hollow-stem auger drilling and Standard Penetration Test (SPT) sampling revealed a consistent subsurface profile of approximately 7 m of stiff to medium stiff silt and clay overlying about 5 m of loose to very loose sand and silt with the water table at 4.3 to 5.5 m. N-values ranging from 2 to 8 correspond to critical accelerations of 0.10g to 0.16g as the threshold of liquefaction; the 100-yr, 10 percent exceedance probability acceleration, selected for design, is 0.20g. An acceleration exceeding 0.3g is considered necessary to cause ground failure on the floodplain because of the thickness of the non-liquefiable surface layer. However, since the channel has cut to a depth of 4 m, ground failure could occur at the design acceleration. A conservative displacement analysis using the Newmark procedure suggests that about 15 cm of displacement could occur if the design acceleration were produced by a magnitude 6 earthquake, while about 46 cm could occur in a magnitude 7 earthquake. Maximum liquefaction-induced ground settlement resulting from anticipated 4 percent volumetric strain is not expected to exceed 20 cm. Interbedded liquefiable and non-liquefiable sediments at floodplain margins are expected to limit abrupt differential settlement. The pipeline ditch will be backfilled with medium dense sand to control soil-pipe interface friction. Stresses and strains developed in the pipe by possible liquefaction-induced ground failure at the design acceleration are expected to remain in the anelastic range.

Subject Headings: Soil liquefaction | Geohazards | River crossing | Pipeline crossing | Penetration tests | Mud | Gas pipelines | Light rail transit | Hydraulic design | Pipeline design | Soil water | Failure analysis | Floods | Seismic design | Nevada | North America | United States

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