Trans Alaska Pipeline System prepares for future earthquakes

The Trans Alaska Pipeline System (TAPS) survived the century's biggest slip-fault earthquake without spilling any oil. That was because engineers anticipated the risk and constructed the pipeline to withstand a magnitude 8.0 earthquake in the Denali Fault corridor.

A 2,000-foot section of pipeline was built on top of "shoes" that rest on long slider beams to allow ground movement without overstressing the pipeline. The system worked and the pipeline survived the 7.9 magnitude Denali Fault earthquake on Nov. 3, 2002 that shifted the ground beneath the pipeline 18 feet horizontally and 2.5 feet vertically.

However, many of the slider beams moved so much that they would not protect TAPS from another major Denali Fault earthquake. Scientists do not expect another similar event for 500 years. But Alyeska wanted to reset the pipeline to maintain its strict safety standards and commitment to protect the environment.

"Technology doesn't allow us to predict when the next big earthquake will hit," said Tom Coghill, an Alyeska line-wide civil project manager. "A hurricane can be seen on the horizon or by satellite, but not an earthquake. We can't let our guard down because we never know when the next big one will hit."

Studies show that future ground movement around the pipeline will be to the west. Consequently TAPS crews reset the fault crossing this summer by moving 16 of the beams westward and extending 9 of the 16 beams to accommodate possible ground movement. They also replaced a vertical support member that bent during the earthquake with an at-grade slider beam support.

"Since the pipeline performed so well we didn't want to make changes to the integrity of the original design," said Coghill.

This project cost approximately $6.5 million and should allow the pipeline to move another 18 feet horizontally and 5 feet vertically.