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Evolving Thermal Grouts Aid Growth of Underground Power Transmission Lines
“Indeed, there are stories of project failures attributed to ‘bad’ grouting,” Dickes said. “In my experience, few contractors like to grout and unfortunately, grouting is left to the end of the job and given to the low man on the totem pole with little oversight. Untrained personnel pumping the wrong mix design into an expensive underground casing can be a very expensive mistake. A correct grouting operation starts at the planning stages of a project, should be fully developed prior to construction and properly executed by skilled personnel.
“Thermal grouting should be treated like any other technical part of the project -- properly designed from thermal performance and constructability standpoints. In all its forms, grouting is a sophisticated technology that requires a specialist to perform. It is an operation that needs to be properly planned and executed. The mix design needs to be correct for the application.”
There is no one thermal mix design. Each grouting project has its own unique characteristics and must be planned accordingly.
“Thermal grouting is an engineered solution,” Dickes emphasizes. “There are no ‘cookie cutter’ specifications or mix designs. Often, we try to use locally available materials in order to minimize costs. Manufactured materials are available, suitable for long distance thermal grouting, but their thermal properties may not be as good as quarried aggregates and the cost is higher. Grout costs using these manufactured materials can run as high as $300 or more per cubic yard. The advantage of the manufactured materials is the ability to design grouts for pumping over greater distances.”
Dickes said his experience and role on thermal grouting projects is as a consultant and job-site manager. He considers Deepak Parmar, president of Geothermal Inc., the foremost scientist on thermal grouting.
“Deepak has been designing thermal grouts for underground power transmission projects for more than 30 years,” said Dickes.
Parmar said no product should be marketed or promoted as 'thermal grout' unless its thermal characteristics are defined and acceptable for the intended use.
“Each mix design of thermal grout is different and is based on several requirements: thermal conductivity, flow (time of efflux), strength, rate of hardening and heat of hydration,” said Parmar.
Two essential characteristics of thermal grout for underground power projects are flowability and pumpability, terms that are not interchangeable. A mix may “flow,” but not be easily pumped.