You may think drilling into a dam embankment is an odd way to check its health. To Kristen Smith, TVA senior program manager, core drilling is sometimes necessary to provide her with soil data to ensure that TVA dams will be healthy for decades to come.
Just like people, dams need regular checkups. At TVA dam safety is especially important because the company’s Safety, River Management and Environment team manages a network of 49 river dams in a system that circumvents millions—if not billions—of dollars in flooding damage in the Tennessee Valley each year.
“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,” said Kristen Smith, P.E., senior program manager, River System Dam Safety.
Geotechnical core drilling is a safe, approved method to determine the quality of the soil layers beneath the dams. The data gathered allows TVA engineers to build and track each dam’s structural profile to better model how the dam would respond to floods and other events.
Program manager Kristen Smith, P.E., right, updates project manager Karen Officer-Bell on the progress of drilling at Chickamauga Dam.
In 2013, TVA completed an overall dam assessment at the Chickamauga Dam. Although the field investigation that year produced a lot of useful information, the TVA 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 analyze the soil types and thickness at the dam,” Smith remembers. “This data allows us to refine our computer modeling. With a few key strokes I can test different events to see how the dam will respond.”
To get the data, TVA crews drill into the earth at exact points around the dam’s north embankment. Then a special tool called a “split-spoon” is 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 on March 4, 2016. Smith noted that we should have results of the analysis by the end of the month.
“The Tennessee River is the life blood of the Valley—generating electricity, transporting commerce and enjoyed for recreation,” she says. “The river is also one of the most bio-diverse ecosystems in the world. Our work at TVA will ensure the reliability and safety of our dams for decades to come.
TVA is performing health checks on all 49 dams. Health checks at 28 dams are completed. The remaining 21 dams are scheduled to be completed by the end of 2017.
“Safety is TVA’s core mission. We have dams that are 50- to 100-years-old,” Smith explains. “So we have specific programs in place for each dam to ensure 100% reliability.