Trans-Alaska Pipeline Seismic Engineering Legacy

• Main Authors: Nyman, Douglas, Hall, William, Szymkowiak, Vincent
• Format: Conference Object
• Language: unknown
• Published: Network for Earthquake Engineering Simulation (NEES) 2014
• Subjects: Arctic; San Fernando; north slope; Prudhoe Bay; Alaska
• Online Access: https://dx.doi.org/10.4231/d3j09w50h; https://nees.org/resources/12125

The Trans-Alaska Pipeline System (TAPS) transports crude oil from the Prudhoe Bay on Alaska’s North Slope to a marine tanker terminal in Valdez. The TAPS project was conceived almost concurrently with the 1971 San Fernando earthquake, a magnitude 7.1 event that called attention to the vulnerability of the nation’s infrastructure to earthquakes and the potential for environmental damage. Since TAPS was located in a fragile arctic environment and passed through areas with high potential for significant seismic activity, serious concerns were raised about the feasibility of constructing a 48-inch diameter oil pipeline across Alaska with assurance that seismic hazards could be effectively mitigated. Consequently, major seismic design requirements were imposed on TAPS, namely that the entire pipeline system should be capable of withstanding all reasonably anticipated effects of earthquakes without impairing the structural integrity of the oil pipeline or the associated pressure containing system components. For many aspects of TAPS design, just as in the case of nuclear power plants, no seismic criteria, standards or codes existed at the time of design (1970s). Alyeska's adoption of seismic criteria for pipeline design was the first major action of this kind in the pipeline industry. Even so, during that time period, TAPS design and construction was benefited immensely by the research and development conducted for seismic design of nuclear power plant facilities. Consequently, the design of TAPS was state-of-the-art for its time and has remained remarkably consistent with current practice in earthquake engineering. The philosophy underlying the original design of TAPS was that modest inelastic behavior and limited damage would be permitted for design level events, but without structural collapse, loss of function of essential facilities, or release of crude oil. The amount of permissible damage varied according to the type of structure or component and its function, similar to the use of reduction factors in today’s seismic codes. The functionality of essential control, communications and emergency systems was specified to be maintained without interruption. In support on ongoing operations, an earthquake monitoring system with near real-time computational and reporting capability, has been in use on TAPS since project start-up and has progressed through three generations of configuration over the past 36 years. The attention given to seismic design paid off on November 3, 2002, with the occurrence of the magnitude 7.9 Denali Fault earthquake. Ground motions approached the seismic design criteria for the section of the Trans-Alaska Pipeline passing through the Alaska Mountain Range in the vicinity of the Denali fault. The surface rupture passed across the Trans-Alaska pipeline right-of-way, producing approximately 5.5 m of right-lateral offset and 0.6 m of vertical displacement. There was no damage to the pipeline or release of crude oil; but there was incidental damage to the above-ground pipeline support hardware where violent pipe shaking and ground motion apparently took place. Limited displacement of the below-ground pipeline occurred in liquefaction areas, but there was no damage to the line pipe.