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Performing Pressuremeter Testing Under Pressure
Over the last few years, Terracon has become known for our ability to help clients who need specialized services to characterize subsurface conditions. In fact, we have worked for several of our U.S. clients on international assignments. One example is with Paul C. Rizzo Associates, a long-term client of Terracon. We often perform pressuremeter testing for nuclear power plant sites throughout the U.S for Rizzo. Last year, they asked Terracon to perform testing on a nuclear power plant site located thousands of miles away near the city of Visaginas, Lithuania. Jason Mapes, P.E., a geotechnical engineer with Terracon, loves an adventure. So, last March, when he was asked to take on a pressuremeter project in foreign land, Jason said yes.
Design work for nuclear power facilities is subject to intense regulatory scrutiny. The International Atomic Energy Agency (IAEA) works with its Member States and multiple partners worldwide to promote safe, secure, and peaceful nuclear technologies. The agency requires rigorous testing on sites that are proposed for a nuclear power plant, and their requirements for design on the Lithuania site were extraordinarily strict and required huge amounts of data.
The Pressuremeter test is a procedure used to determine the stiffness of underlying soil and rock, so the method was an essential part of designing the foundations. But it is not a simple test to perform. This in-situ test requires a special combination of skills and capabilities essential to address the many variables that are inherent to drilling equipment, drilling methods, and soil and rock conditions. To perform the test, an engineer must possess a combination of mechanical skill, engineering expertise, endless patience, and common sense.
Why would an English-speaking engineer and 500 pounds of equipment fly thousands of miles to perform this one service? Why not just hire an engineer from Lithuania or a nearby European country? “The fact is, few companies perform this specialized pressuremeter testing,” said Mapes. “Even if they found someone in Europe who could do it, there was still a high probability of a language barrier. But most importantly, there was no room for error and no second chances. Rizzo trusted Terracon to get the job done.”
The Pressure is ON
When Jason boarded the plane in mid-July 2012 he knew that he would have to push the limits of pressuremeter testing for this assignment. An excessively thick layer of soft soils would require his testing program to extend to a depth of 60 meters. Anything over 50 meters is considered very deep, which creates technical challenges. Equipment for depths exceeding 50 meters is not readily available. For example, high pressure coaxial tubing had to be custom-manufactured to reach depths of 60 meters. Spare parts for equipment were purchased in huge volumes, and arrangements were made to ship delicate equipment to Lithuania, a “high risk destination,” as defined by the shipping company.
Seven drill rigs were on site for approximately three months performing the standard geotechnical investigation for Rizzo, and Mapes worked with the individual drillers to obtain the right drilling equipment and tools and to develop the special drilling techniques needed to get his pressuremeter work done. Over the next few weeks, Mapes performed 29 pressuremeter tests, usually in the rain and always in the mud.
“I was testing at depths deeper than I had ever tested, in unfamiliar soil conditions, with only a handful of people who spoke my language,” said Mapes. “I had to solve every problem based on what I knew and what I had with me onsite. I could not pick up a phone and ask for assistance, recommendations, or spare parts.”
Responsive, Resourceful, and Reliable
Terracon approaches every project with a sincere commitment to provide the best in responsive, resourceful, and reliable service — our “3Rs”. The Lithuania pressuremeter testing project, despite the challenges inherent to performing services in a foreign nation, was no different.