Eighty years ago Tennessee Valley Authority (TVA) in the US was tasked with the mission to provide flood control, improve navigation and generate affordable electricity for the people of the Tennessee Valley. With many of its 49 dam facilities approaching 50 to 100 years of age, TVA is now on an important maintenance and safety mission.
TVA’s Safety, River Management and Environment team manages a network of 49 dams in the Tennessee Valley. Engineers are constantly working hard to gather data to build and track each dam’s structural profile, and model how it would respond to floods and other events. One method which has recently been employed is geotechnical core drilling – a safe and approved procedure used to determine the quality of soil layers beneath the dams.
“We are always trying to better understand our dams, and one way to do that is to explore what we can’t see, which means we drill into the foundation to gather data,” says Kristen Smith, Senior Programme Manager for River System Dam Safety at TVA.
An extra step
Built in 1940 the 39m high Chickamauga dam is used for hydropower, flood control and recreational purposes. In 2013, TVA completed an overall assessment at the dam and, although field investigations produced a lot of useful information, the dam safety team wanted to take an extra step to include material sampling of the foundational structure in the engineering analysis. To do this TVA needed to conduct geotechnical core drilling along the north embankment.
“We needed to analyse the soil types and thickness at the dam,” Smith said. “This data allows us to refine our computer modelling. With a few key strokes I can test different events to see how the dam will respond.”
To get the data, TVA crews drilled into the earth at exact points around the dam’s north embankment. Then a special tool called a “split-spoon” was inserted into the hole to take out a core sample. Samples are carefully documented, placed into a specimen jar and sent off to a lab for analysis. After the samples are removed, the hole is sealed with special grout.
Core drilling at Chickamauga Dam was completed in March 2016. TVA is performing health checks on all 49 dams. To date 28 dams are completed and those remaining are scheduled for completion by the end of 2017.
“Safety is TVA’s core mission. We have dams that are 50 to 100-years-old and we have specific programmes in place for each dam to ensure 100% reliability,” Smith explains. “Our work at TVA will ensure the reliability and safety of our dams for decades to come.”