Protecting Pipelines From Catastrophic Effects of Earthquakes

By Terry Meier | July 2013, Vol. 240 No. 7

Seismicity of the United States from 1900-2002 [1]

On Dec. 26 a gas pipeline blast followed by a mild earthquake struck Russia's Black Sea resort of Sochi, which will host the 2014 Winter Olympics. No one was hurt and there was no apparent damage to the city's infrastructure after a 5.2 magnitude earthquake was reported at 0242 local time. According to the U.S. Geological Survey, there are 14,000 earthquakes worldwide each year that have a magnitude of 4 or greater—700 of which occur in the U.S. and Alaska.

There are several methods for mitigating the effects of seismic activity on infrastructure, among the most notable being the use of EPS geofoam as a seismic buffer for buried structures and rigid retaining walls. Six years ago, Canadian engineers Richard Bathurst, Saman Zarnani and Andrew Gaskin showed, with shaking table testing and numerical modeling [2], that geofoam could reduce the seismic forces on rigid retaining walls. The lightweight EPS blocks that have become ubiquitous in highway embankments, green roofs, and landscape fill are growing in popularity for seismic and other buried applications.
Today the spotlight is shining on geofoam as a material with great potential for protecting pipelines. “If an earthquake occurs, high-pressure gas lines are one of the most important items to protect,” said Steven Bartlett. “If they rupture and ignite, you essentially have a large blowtorch, which can be catastrophic.” Bartlett is associate professor of civil engineering at the University of Utah. He and his team have been examining geofoam’s mitigating effects on pipeline damage due to seismic faulting since 2007.

Geofoam weighs roughly 1/100th of the weight of soil. “During summer 2007, Questar Gas Co. requested that the University of Utah evaluate a conceptual EPS geofoam cover system for a steel, natural gas pipeline crossing the Wasatch fault in the Salt Lake City valley,” explained Bartlett. “The fault rupture is expected to produce an earthquake with a potential magnitude of 7.5 and several feet of potential fault offset at the pipeline crossing.”
If a major earthquake were to strike the Wasatch fault zone in the Salt Lake Valley, the fault displacement and the subsequent weight of shifting and compacted soil on buried pipelines is likely to cause them to rupture. Many buried pipelines lie beneath six to eight feet of soil. Bartlett and his students at the University of Utah showed that a pipeline protected with a lightweight geofoam cover could withstand the fault offset and reduce the force on the pipe by up to four times the amount of force as a pipeline covered with conventional soil backfill [3].

When the 37-mile-long section of natural gas pipeline had to be replaced between Coleville and Ogden, UT, 20,000 cubic feet of EPS geofoam was specified to reduce movement, shears, axial forces and strains imposed on the pipeline. EPS types 22 and 15 were shipped from ACH Foam Technologies’ local plant in Murray, UT.

Pipeline Displacement Vectors During Failure
The goal of a geofoam cover system on top of a buried pipeline is to reduce the lateral, longitudinal and vertical forces induced on the pipe as the surrounding ground undergoes deformation. The properties of geofoam have distinct advantages that lead to improved pipeline performance during large ground deformation.