Gas Pipeline Earthquake - Simulations
8/18/2000 - Cornell University - ITHACA, N.Y. -- In many recent
large earthquakes -- such as in Northridge, Calif., in 1994 and in
Kobe, Japan, in 1995 -- some of the most alarming damage was to
buried natural gas pipelines, most of them curving along
rights-of-way using vulnerable elbow joints.
The danger from a ruptured
high-pressure gas pipeline can be an explosion or even a fireball.
To test the effects of earthquakes on gas pipelines, Cornell
University and Tokyo Gas Co. have teamed up in the largest
experimental facility of its kind ever constructed to see exactly
what happens when the earth moves violently against an underground
Over the coming weeks in Cornell's Winter Laboratory, scientists
from the two organizations, joined by earthquake expert Professor
Masanori Hamada from Waseda University in Japan, will be simulating
earthquake loads on four 30-foot-long steel, L-shaped gas pipelines
-- made in Japan for use under Tokyo streets -- by pitting them
against 60 tons of moving sand.
The results of the experiments will be used to draw up an
earthquake-resistance design code for gas pipelines in Japan.
However, says Thomas O'Rourke, professor of civil and environmental
engineering at Cornell and the principal researcher on the
experiment, "this test and simulation is a very significant step
forward for the design of all underground piping.
As we move piping into frontier
situations, such as gas or oil transmission across the seafloor or
mountain passes or earthquake-prone areas, we must gain a greater
understanding of the extreme deformation behavior of these critical
Koji Yoshizaki of Tokyo Gas, who has been a visiting scientist
at Cornell for the past two years and who led the design of the
"Because we have never been able to conduct this kind of
test in the ground, we have not been able to calibrate our computer
model on how buried pipeline behaves when it is subjected to the
massive forces of a landslide."
Tokyo Gas has contributed more
than $100,000 toward the cost of the experiment.
The device is truly earthquake-size. A massive L-shaped,
steel-reinforced wood box, 14 feet wide and 30 feet long, has been
filled with sand from a three-story hopper.
The box is built in two
sections, one fixed and the other -- the L-shaped part -- movable.
The pipeline, which has one elbow joint, passes through the box
structure at a right angle, under 3 feet of sand, and is bolted to
the floor at both ends.
Then in just 70 seconds the L-shaped box section is moved 4 feet
against the other, using a 10-ton crane hauling an eight-pulley
block and tackle.
The force of 60 tons of shearing sand on 4-inch-diameter steel
piping -- simulating the movement of the earth in a typical
magnitude 7 or greater earthquake -- is not expected actually to
rupture the metal but to deform it considerably.
In fact, the engineers on the
project estimate that maximum pressures of 50 pounds per square inch
will be mounted against the pipeline by the moving sand.
That makes the stress roughly
equal to the uniform pressure beneath a 250-ton stack of automobiles
or a 40- to 50-story building.
"The experiment has been designed quite cleverly with respect to the
worst conditions that pipelines could experience," says James Mason,
a Cornell graduate research assistant -- as well as a licensed civil
engineer -- on the project.
"Our aim is to benchmark that
condition and analyze it to a degree that conforms with real
The data are recorded through 120 strain gauges attached to each
pipe. In addition, other specialized sensors record such information
as the force between the pipe and the soil and the displacement of
the pipe relative to the size of the box.
This data will be fed to
analysts at the University of Cambridge in England, who are working
with Tokyo Gas to develop the next generation of soil-structure
The four tests will simulate different conditions in moving soil --
such as direct shear and lateral spread -- by changing the sand
density (through compaction) and moisture content.
The ground ruptures being
simulated, says O'Rourke, are generic to fault ruptures,
liquefaction and landslides.
Fault ruptures occur at plate
boundaries in the Earth's crust when the sudden release of energy
causes an earthquake. Liquefaction occurs when the tremors of an
earthquake create a fast-moving viscous mass of particles below the
water table that drags the solid ground above, creating enormous
forces on buried pipelines.
Large though the lab experiment is, Tokyo Gas's Yoshizaki originally
suggested a sand box twice the current size.
But, says Tim Bond, manager of
the Winter Lab, being able to move 60 tons of sand and place it
according to exacting standards is in itself "a major exercise in
industrial process control."
The experiment also is supported by the National Science
Foundation's program for U.S.-Japan Cooperative Research in Urban
Earthquake Disaster Mitigation and the Multi-Disciplinary Center for
Earthquake Engineering Research at the State University of New York
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Tokyo Gas Co.