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 line.
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 facilities."
Adds 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 experiment, "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 circumstances."
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 computer models.
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 at Buffalo.
Related World Wide Web site:
Tokyo Gas Co.: http://www.tokyo-gas.com.jp/techno/index_e.html
The above story is based on materials provided by Cornell University. Note: Materials may be edited for content and length.
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