Evaluation of Land Subsidence Hazard on Steel Natural Gas Pipelines in California

Buried infrastructure like natural gas pipelines may be impacted by soil movement due to landslides, flood scours, fault ruptures, liquefaction, and subsidence. Subsidence induced settlement is an identified hazard for natural gas pipelines in Central California and has two components: vertical and horizontal. In the past, investigations have revealed that the horizontal displacement is more destructive than the vertical settlement since it may cause pipe ruptures. With the increase in droughts and groundwater pumping due to climate change, more land subsidence has been attributed to these factors. This study discusses the maximum impact of land subsidence on natural gas pipelines and provides design recommendations. The maximum subsidence induced settlement recorded in Central California has been applied to a buried pipeline using non-linear finite element analysis. To capture the most accurate results, 2-miles of steel pipe located in the subsidence zone is included in the finite element model and a simplified soil-pipe interaction modeling technique is used to determine the soil stiffness around the buried pipeline. Based on the results, buckling forces due to the horizontal movement of the soil on the underground pipe are more critical than the bending stress caused by the vertical soil settlement. Although the risk of failure ascribed to buckling is high, the buried steel natural gas pipeline is resilient enough to accommodate the internal forces due to subsidence.