Posted on December 24, 2020
A big dam problem required a big dam solution. After seven years, the U.S. Army Corps of Engineers Pittsburgh District is wrapping up the East Branch Dam Cutoff Wall Rehabilitation project in Elk County, Pennsylvania.
The project was to install a cutoff wall – a 1,500-foot concrete barrier designed to seal the dam’s interior from the dam’s exterior – which concluded construction earlier this year. The cutoff wall prevents trace amounts of water from leaking through the dam, but fixing this issue was not easy.
“Building a cutoff wall is a complicated process,” said Denise Polizzano, Supervisory Civil Engineer. “We had to stabilize the existing soil in the dam, we did a lot of exploratory drilling to make sure we knew the existing parameters and that we wouldn’t compromise the structure’s integrity, and we had to make sure we wouldn’t cause any environmental damage. This was more than an engineering project.”
District personnel solved these issues by lowering lake levels and using a hydromill – a large excavation machine attached to a crane that digs downwards through the dam’s center. The hydromill dug spaces 10-feet wide and 3-feet thick, called panels, down through the soil and rock foundation to reach the 250-foot depth necessary for installing the cutoff wall.
After successfully removing the foundation, stabilizing liquid was poured into the panel to maintain the dam’s structural integrity until the panel could be filled with concrete. After the concrete was installed, the hydromill was moved to the next 10-foot area to excavate another panel. Rinse and repeat.
Construction crews had to dig 150 panels in order to build the full cutoff wall.
“It amazes me that the engineering and construction teams were able to complete this monumental effort to protect the citizens of the local community and preserve water quality,” said Steve Fritz, project manager at Pittsburgh District.
The project began in 2013 and wrapped construction earlier this year. As of December 2020, work at the dam is focused on restoration activities, such as removing construction equipment and installing guardrails.
While businesses across the nation shut down earlier this year due to the COVID-19 pandemic, the project did not encounter any issues or delays.
“COVID hit at just the right time – we buttoned up the wall just as COVID shutdowns began,” said Greg Hensley, lead project engineer. “We didn’t have any 14-day quarantines. Since we completed major work items before the pandemic, we could shrink the number of on-site staff, ensure everyone wore masks and reduce the chance of exposure.”
As progress continued, there was a noticeable reduction in the amount of seepage from the dam.
“It’s been a really interesting project because you could see, as they filled in concrete, the reaction in the weirs and areas that had been leaking downstream and the cutoff wall was reducing leakage,” said Autumn Rodden, supervisory natural resource specialist at East Branch. “This project is making it safer for downstream communities for years to come.”
While the new cutoff wall helps protect local communities from flooding, the project’s completion is a signal to residents near East Branch Dam that lake levels will be returning to normal.
“It’s been a long haul, but everyone at the club is looking forward to having our water back in the spring,” said John Dippold, president of the East Branch Boating Club. “East Branch Dam is a beautiful gem in Elk County, and we’re really happy to see the lake restored.”
The reservoir’s pool is expected to return to pre-construction levels by the beginning of the 2021 boating season.
Source: dvidshub
