URI engineer conducts seismic tests of Scituate Reservoir dam to assess its integrity against earthquakes

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KINGSTON, R.I. – October 2, 2014 – A University of Rhode Island engineering professor has conducted seismic tests on the Gainer Memorial Dam at the Scituate Reservoir to determine its vulnerability to earthquakes. His analysis thus far suggests that the 88-year-old dam could withstand, with minimal damage, the region’s most likely earthquake scenarios, which include a magnitude 5 earthquake nearby the dam and a magnitude 6.8 earthquake 125 kilometers away.

According to Aaron Bradshaw, URI assistant professor of civil engineering, the dam retains 39 billion gallons of water. If it were to fail, 60 percent of the state’s population would lack drinking water, and flooding could stretch 20 miles southeast to T.F. Green Airport in Warwick.

With funding from the URI Water Resources Center, Bradshaw and his students conducted a series of tests at the 3,000-foot-long, 109-foot-high dam, which parallels Scituate Avenue (Route 12) in Scituate and is operated and maintained by the Providence Water Supply Board.

“Back when it was built, engineers may not have had the technology we have now, but they certainly had the knowledge and the quality of workmanship, and we’re seeing their impressive structures,” Bradshaw said.

The URI professor’s study was the first time the Gainer Dam had been evaluated for its resilience to earthquakes. When Bradshaw and graduate students Christopher Norton of West Haven, Conn., and Bivian Reyes of the Dominican Republic approached the agency about conducting the study, officials saw it as a rare opportunity.

“Looking at what’s downstream and the significance of this dam, we thought it would be prudent for Dr. Bradshaw and his students to conduct their analysis,” said Peter LePage, senior manager of engineering at the Providence Water Supply Board.

Agency officials and Bradshaw’s team were especially concerned about the potential for liquefaction in the soils comprising the dam. The shaking from an earthquake can cause loose saturated sands to lose their strength. This scenario could cause the dam to breach.

Bradshaw and his students could not easily bore into the dam to check the density of the soil. Instead, they turned to Gopu Potty, URI associate research professor of ocean engineering, who had perfected a system of using ground sensors called geophones and a heavy weight to eliminate the need for soil samples. By setting up the geophones and striking the ground with a 100-pound weight, they could monitor the vibrations traveling through the earth to analyze the soil conditions.

Bradshaw said the method holds promise for dam owners to screen for possible problems and learn if further soil testing and analyses are needed. The geophones and computer analysis are less intrusive and disruptive to the dam.

“You can think of it as a good first step,” Bradshaw said. “If the results look good, we may not need to do more.”

The research will serve as a blueprint for future studies at the Gainer Memorial Dam, as well as at least one doctoral thesis at URI.

Pictured above: URI graduate student Chris Norton prepares to conduct a seismic test at the Gainer Dam at the Scituate Reservoir. (Photo courtesy of Aaron Bradshaw)