Protecting Gas Pipelines From Earthquakes
10/1/2012 - University of Utah - SALT LAKE CITY, Oct. 2, 2012 –
Lightweight and stiff as a board, a plastic foam material is being
used to protect Utah’s natural gas pipelines from rupturing during
an earthquake occurs, high-pressure gas lines are one of the most
important items to protect,” says Steven Bartlett, associate
professor of civil engineering at the University of Utah. "If they
rupture and ignite, you essentially have a large blowtorch, which is
Bartlett has partnered with natural-gas company Questar to use large
expanded polystyrene blocks called “geofoam” as a compressible,
protective cover for natural gas pipelines buried underground.
“This low-impact technology has an advantage in urban environments,
particularly if you need to realign already buried structures such
as gas lines or utilities without affecting adjacent buildings or
other facilities,” says Bartlett.
Geofoam has been used for decades in Europe, North America and Asia
to lighten loads under roads and reduce settlement. One-hundredth
the weight of soil with similar strength, geofoam blocks reduce
construction time and don’t erode or deteriorate.
Bartlett previously researched the design and use of geofoam as a
lightweight road embankment in the Interstate-15 reconstruction
project through the Salt Lake Valley a decade ago, and more recently
in the TRAX light rail line that opened last year to serve West
Valley City, Utah. Geofoam currently is being used in the TRAX
extension to the airport.
Questar – which provides natural gas to almost 900,000 customers in
Utah, southwestern Wyoming and southeastern Idaho – is using geofoam
in lightweight covers for minimizing damage to natural gas pipelines
caused by severe earthquakes.
“Most pipelines are designed to withstand some ground shaking, but
not several feet of sudden fault offset that may occur in a major
earthquake,” says Bartlett.
“When a fault breaks, it occurs in milliseconds. It is an extreme
event. The problem Questar faced was, how could a buried pipeline
survive that offset?”
Geologists expect that when a major earthquake strikes the Wasatch
fault zone in the Salt Lake Valley, a fault rupture likely will make
the valley drop down relative to the mountains.
As the valley drops down, a buried pipeline would start to lift up.
However, most buried pipelines lie under six to eight feet of
compacted soil. This weight becomes too much for a pipe to bear,
causing it to rupture, Bartlett says.
Numerical simulations of earthquake fault ruptures performed by
Bartlett and his students show a geofoam-protected pipeline on the
valley side of the Salt Lake City segment of the Wasatch fault could
withstand up to four times more vertical force than traditional soil
Based on Bartlett’s experience with geofoam, Questar asked him to
develop a strategy for protecting buried pipelines crossing
earthquake faults in urban areas, such as 3300 South, an arterial
street in the Salt Lake Valley.
“In this situation, we had to put the pipeline right down the center
of the roadway. When we looked at what other countries did, they
built a trapezoidal geometry above the pipe—basically just a wedge,”
Such a wedge would require many blocks of foam and would disrupt a
large section of road, Bartlett says.
“This would be a major problem
in an urban area, as you might have to tear up 20 feet of lateral
roadway. Try to do that for 3300 South – you’d have to shut the
whole road down.”
Rather than gut a major thoroughfare, Bartlett proposed a “slot
trench” design in which a block of geofoam is placed in a narrow
trench between a pipeline and the pavement above.
In this design, if
the pipeline begins to lift up, it will displace the geofoam block
and compress it.
Although geofoam is solid, it contains tiny air pockets that can
compress without sacrificing the material’s overall integrity.
the geofoam is compressed further, it will slide upward along the
trench sidewalls and could eventually damage the pavement above.
However, says Bartlett, the pipeline will remain intact and
Since the 3300 South project, Questar has been installing geofoam to
protect other natural gas pipelines in the valley.
In addition, Bartlett and colleagues at the University of Memphis
and University of Illinois at Urbana-Champaign are investigating
geofoam to help new buildings withstand earthquakes.
When a building shakes during an earthquake, says Bartlett, soil
adjacent to the building puts additional pressures on its walls as
it tries to move back and forth.
By placing a geofoam buffer between a building’s walls and
neighboring soil, it can sway without experiencing additional
The geofoam, which deforms in a controlled manner when placed
against a structure, can reduce earthquake pressures by 30 to 50
percent, according to Bartlett’s calculations.
This also reduces the
amount of steel and reinforcing concrete needed to protect the
building from earthquake damage.
Compared with compacted soil, geofoam is competitive when total
construction costs are considered, Bartlett says.
What’s more, geofoam requires typical road embankment construction times of one
month, compared with 12 to 15 months using traditional methods.
“When there are sensitive utilities involved, seismic stresses or
time is a factor, this technology wins hands down,” says Bartlett.
University of Utah College of Engineering
72 S. Central Campus Dr., Room 1650 WEB
Salt Lake City, UT 84112