Guidelines for the seismic design of oil and gas pipelines have not been updated in a single reference document since 1984, when the American Society of Civil Engineers released their publication, Guidelines for the Seismic Design of Oil and Gas Pipeline Systems. Since 1984, substantial progress has been made in identifying and quantifying seismic hazards, understanding pipeline response under large, displacement-controlled strain conditions, and analytical methods for assessing pipeline response to permanent ground displacement. In 1998, the Pipeline Research Council International, Inc. (PRCI) initiated a project to update seismic design guidelines for pipelines with the goal of incorporating advances in current engineering practice since the early 1980s and to create a document that can be regularly updated to take advantage of new research findings. The PRCI project to develop the guidelines was undertaken by two investigators heavily involved in the 1984 American Society of Civil Engineers guidelines. Two teams of independent expert reviewers were used during the project to assure the recommended practices were technically consistent with the current state of knowledge of seismic hazard assessment, pipeline behavior, and analysis methods.
The performance of pipeline systems during earthquakes is a critical consideration in seismically active areas. Unique approaches to quantitative estimation of regional seismic vulnerability were developed for a seismic vulnerability assessment and upgrading program of a 500-km-long natural gas pipeline system in British Columbia, Canada. Liquefaction-induced lateral spreading was characterized in a probabilistic manner and generic pipeline configurations were modeled using finite elements. These approaches, developed during the early part of this 10-year program, are more robust than typical approaches currently used to assess energy pipeline systems. The methodology deployed within a GIS environment provided rational means of distinguishing between seismically vulnerable sites, and facilitated the prioritization of remedial works. While ground improvement or pipeline retrofit measures were appropriate for upgrading most of the vulnerable sites, replacement of pipeline segments using horizontal directional drilling to avoid liquefiable zones were required for others.
The Trans-Alaska Pipeline System is one of the most significant engineering achievements of the 20thcentury and the first major pipeline system for which considerable attention was focused on the identification and quantification of potential seismic hazards and the implementation of design and operational features to address those hazards. One of these special design features included the concept for an above-ground supporting system for the pipeline crossing of the Denali fault. The 2002 M7.9 Denali fault earthquake represents the first successful test of a structure specifically designed for fault displacement. The earthquake also demonstrated the benefits of the multi-tiered earthquake preparedness and response strategy in place at the time of the earthquake.
The interaction between a buried pipeline and surrounding soil during large ground displacements is typically simulated using numerical nonlinear soil-restraint springs aligned with the longitudinal axis of the pipeline and in the two directions orthogonal to it. There are only very limited experimental data available to characterize the soil springs for simulating pipelines crossing reverse faults where large oblique soil displacements relative to the pipe could occur. Full-scale model testing was undertaken to evaluate this complex soil–pipe interaction problem. The tests simulated the performance of ∼400 mm diameter (nominal pipe size, NPS 16) pipe specimens buried in moist sand and crushed limestone trench backfill. The peak normalized oblique soil restraint (Nθ) values for oblique pipe movement angles (θ), when θ = 0° (horizontal movement) and θ = 90° (vertical movement), estimated based on state-of-practice approaches, were in agreement with those from full-scale testing. The value of Nθ was found to depend significantly on the peak friction angle of soil ([Formula: see text]) when θ was closer to 0°, whereas Nθ was less sensitive to [Formula: see text] when θ was beyond about 35°. The theoretical values of Nθ based on limit-equilibrium approaches compared well with the experimental findings.
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