Tennessee Valley Authority
Bear Creek Dam Rehabilitation
September 2008
Since its completion in 1969, the earthen Bear Creek Dam has experienced foundation leaks. Previous efforts to control leaks have been ineffective over the long term.
Following periods of heavy rainfall, the reservoir level can rise, and increase the risk of dam failure. To reduce this risk, TVA prepared an Environmental Impact statement to evaluate alternatives for a long-term solution. After thorough study, public involvement, and several opportunities to provide comment, TVA signed a Record of Decision on September 10, 2007 stating it would build a roller compacted concrete structure at the downstream toe of the existing dam along with a water cutoff "wall" under the new structure to block water passage under the dam. Site preparation began in September 2007.
Construction Report Update
Safety and Environmental Issues
Continued emphasis is being placed on Safety and Environmental Performance at Bear Creek. To date, contractors have experienced two minor incidents resulting in one lost time event.
Excavation and Soldier Pile Walls
Drilling and grouting over the sluice tunnel is ongoing due to a large feature that extends under the existing sluice tunnel to ensure cutoff of any leakage paths. This feature had been cleaned and filled with dental grout.
Work is nearing completion on the vertical soldier pile walls at the sluice outlet structure and along the spillway wall. Lagging is being placed at the sluice wall. The soil is excavated as the lagging is placed between the H piles.
There have been no significant rainfall events, so the dewatering system is removing a minimal amount of water at this time.
Grouting
Verification of the grout curtain was completed in the left embankment, spillway and Phase 2 area and along the right abutment. Work is nearing completion on all other phases of the foundation. Problem areas found in Phases 1 and 3 will require a concrete cutoff wall installed to the shale layer under the dam and which is scheduled to commence in the near future.
Current Activities
- Final excavation and dental concrete placement in Phase 4 over the sluice tunnel is complete.
- Installation of soldier pile walls near the sluice and spillway structures is proceeding as scheduled and will be completed in mid September.
- Drilling and grouting of the foundation is nearing completion.
- Plans are finalized for the size and location of a cutoff wall in areas of large features with work in these areas commencing in mid September.
- The foundation for the concrete grade beams over the sluice outlet structure is being installed.
- The RCC contract will be awarded and contractor mobilization is to begin this month.
View of the sluice tunnel soldier pile wall. Lagging is being placed between the vertical H piles.
