Researchers have found that cured-in-place pipeline (CIPP) liners perform well in shake-table seismic tests, greatly strengthening the pipelines into which they are installed. © Amjad J. Aref/University at Buffalo
A research team tests cured in place pipeline liners on a shake table and finds they significantly enhance the seismic performance of a ductile iron pipeline.
July 22, 2014—Researchers at the University at Buffalo (UB) and Cornell University have tested the seismic performance of ductile iron pipes retrofitted with cured-in-place pipeline (CIPP) liners, finding that the system performs so well on shake tables they had to more than double the ground motions recorded in two strong California earthquakes to cause the liners to fail.
CIPP liner is an effective and common repair method for aging pipes. A tube with a polymeric resin-impregnated fibrous exterior—commonly glass fibers—and a smooth interior is pressed through the pipeline. Once in place, the tube is expanded and cured with a source of heat. The repair eliminates leaks and strengthens the pipe without the expense of digging up the line and replacing it. But although it has been around for years, the technology has never been validated for seismic performance improvement. Until now.
The research team was led by Andre Filiatrault, Ph.D., P.E., M.ASCE, Amjad Aref, Ph.D., M.ASCE, both professors in UB’s Department of Civil, Structural, and Environmental Engineering, and Thomas D. O’Rourke, Ph.D, Hon.D.GE, Dist.M.ASCE, who holds the Thomas R. Briggs Professorship in Engineering at Cornell. The research is detailed in the paper “Seismic Testing of Critical Lifelines Rehabilitated with Cured in Place Pipeline Lining Technology,” published recently in the Journal of Earthquake Engineering. The research work was conducted by Zilan Zhong, S.M.ASCE, a Ph.D. candidate in the Department of Civil, Structural, and Environmental Engineering at UB.
“[The liners] are used in many places, but their behavior under seismic events is not known,” Aref says. “Since they are used in nonseismic regions, we thought it might be a good solution to retrofit or rehabilitate water lines in seismic regions.”
The liners have the potential to prevent ruptures of key water pipelines during earthquakes, ensuring a continuous supply of water to not only service the public but also to aid firefighters in battling the fires that often result from strong temblors.
The team tested a push-on (bell and spigot) joint in a ductile iron pipe. This type of joint possesses low resistance to pullout, which simulates a weakened joint, and the natural gap between the bell and spigot portions simulates a small circumferential crack.
“The ductile iron pipes have been widely used for the last few decades,” Aref says. By selecting a weak joint—“basically it could move, you could push it back and forth,” Aref says—the team hoped to simulate a crack that extended completely around the circumference of the pipe, even though that scenario is more severe than what is typically seen in the field.
The pipelines tested were each approximately 150 mm in diameter and a total of nearly 9.14 m long, divided into three segments connected by two joints. The team chose two versions of CIPP liner, one initially more rigid than the other, but both featuring layers of resin with a core of glass fibers. The liner was approximately 3.81 mm thick.
After establishing the strength and shear properties of the liner material, the team tested the liner inside the pipeline using the twin shake tables at UB. The ends of the pipelines were secured to either shake table and the center was secured to a central stationary concrete podium mounted into the laboratory floor. The pipelines were tested under different conditions: sealed, filled with water, and under 345 kPa of water pressure; partially pressurized; and not pressurized. The pressure not only simulates a typical pipeline state, but also provides enhanced friction that increases performance in some measures.
The team performed eight tests, ranging in complexity from basic monotonic and cyclic tensile stresses that pulled the pipeline in opposite directions, to re-creations of two powerful California earthquakes, using the ground movements recorded at Joshua Tree National Park during the 7.3-magnitude temblor that struck Landers in 1992 and the ground motions recorded at Rinaldi during the 6.7-magnitude Northridge earthquake in 1994.
“They are unique, in a sense, for this testing,” Aref explains. “The Rinaldi ground motion ...has a large pulse followed by much smaller pulses. [This] represents a pipeline that is close to the source—that would be the kind of motion it will see. The Joshua Tree record ...has smaller pulses and many of them …with a [long] duration of excitation.
“We did the same thing for both,” he says. “We started at the base record and we started amplifying the input joint-displacement records based on simulations. We started at one level—100 percent—then we went up until we failed the joint or reached the displacement limits in some cases.”
The tests revealed that the liner enhanced the strength of the joints significantly, carrying most of the seismic loads during the simulated earthquakes. As the forces increased, portions of the liner became debonded from the pipeline, creating ductility that actually enhanced the pipeline’s performance during a seismic event.
“I would say [the liners] are extremely useful for seismic regions because we have seen that we have to magnify the records significantly before we fail some of these joints,” Aref says. “They represent a robust solution to rehabilitate pipelines in seismic regions.
Fortunately, the installation methods for the technology are already relatively mature. However, because there are a great number of material combinations that can be used to create the liners, ranging from highly flexible to rigid, the technology is not ready to appear as a single answer in design codes, he says.
“The design space from an engineering point of view is still vast. But it could be designed by an engineer based on the information from a manufacturer, based on the stiffness, strength and bond properties of the liner,” Aref says.
He notes that in future research will focus on the larger diameters typically found in water supply systems, as well as the performance of an entire pipeline system, including smaller distribution lines. And because this project essentially looked at new pipes, the team would like to examine the performance of the aged pipes likely to be encountered in a rehabilitation application.
“In reality, the parts may be rusted or there are contaminants inside [and that] may affect the bond. There are some technical challenges as to the versatility and application of that based on conditions in the field,” Aref notes.
The test facility at UB is part of the George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES). NEES is funded by the National Science Foundation to advance earthquake research via a collaborative network of researchers and facilities.