Imagine if you firmly held a straw at each end, and you slowly moved one hand away from you. The straw would slowly curve, twist and become oval until it bent.

That's what pipes do in earthquakes.

On April 6 Cornell University researchers simulated an earthquake's effects on gas and water pipes by exerting a 120,000-pound force on a 16-inch diameter, 35-foot-long high-density polyethylene pipe buried in 102 tons of sand in Thurston Hall.

"This is the largest test of ground rupture effects on underground structures that has ever been performed in a lab," said co-principal investigator Thomas O'Rourke, an engineering professor at Cornell who is affiliated with Cornell's National Science Foundation (NSF)-funded Network for Earthquake Engineering Simulation (NEES) in the School of Civil and Environmental Engineering. "You can't wait for an earthquake or a landslide, so tests like this give us a good idea of how a pipe will behave under ground displacement."

During such catastrophes as earthquakes, floods and landslides that cause earth to shift, gas- and water-carrying pipes of steel or polyethylene can break, causing fires and water damage.

In the simulation, sensors recorded the pipe movement and how the pipe curved, twisted and became oval. The data will be used to create numerical models that will allow researchers to improve their understanding of pipes and soil under duress.

Michael Palmer, a research associate in civil and environmental engineering and NEES project manager, added that the tests could lead to better design practices for lessening impacts and reducing recovery times in the case of catastrophic events.

"If a gas pipe breaks during an earthquake it can cause a fire," said Palmer. "If the nearby water pipe also breaks, the ability to control the fire is greatly reduced."

In the test, the researchers placed the pipe in two large test basins and secured the pipe at each end. The two basins, resembling large waste bins at construction sites, were filled with sand. One basin was held in place while the other was moved four feet in four minutes to simulate a sideways-sliding fault, called a strike-slip.

The pipe, buried three feet below the surface, did not break during the test, but the sand, which had a white grid painted on it, shifted, bulged and cracked and created webbed lines on the surface as the pipe bent.

The test was one of 10 in a four-year, multimillion-dollar project. In the first test with the polyethylene pipe, no sand was used; the second test had the same conditions as the April 6 test, except that a laser-mounted robot traveled inside the pipe before and after the test and measured how the pipe ovaled under stress. The next set of tests will duplicate these experiments with a steel pipe.

High-density polyethylene is thick plastic that bends and reforms. Low-density polyethylene is the material that goes into plastic lawn bags, for example. The commonly used pipes can withstand five to 10 feet of displacement without breaking.

Harry Stewart, associate professor of civil and environmental engineering and director of the Civil Infrastructure Laboratories, is co-principal investigator for Cornell's NEES project.

Cornell's facility is one among 15 George E. Brown Jr. NEES research laboratories funded by the NSF for construction, expansion and modernization of the nation's earthquake engineering experimental research. The data from these tests will be archived into NEES for public access.