Tennessee Valley Authority
Bear Creek Dam Rehabilitation
August 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
The Safety and Environmental Performance at Bear Creek has been perfect, with no reportable events.
Excavation and Soldier Pile Walls
Excavation has finished over the sluice tunnel to allow drilling and grouting of this area to begin. A large feature that extends over the existing sluice tunnel has been exposed. This feature has been cleaned and some dental grout has been placed. A plan is being developed to grout along the sluice tunnel alignment to insure any leakage paths are cut off.
Work is progressing for the vertical soldier pile walls at the sluice outlet structure and along the spillway wall. Lagging is being placed at the sluice wall and drilling of the supporting tendons has begun. Excavation of the soil adjacent to the wall will commence as soon as the anchors are setup.
There have not been any significant rainfall events, so the dewatering system is removing a minimal amount of water at this time.
Grouting
Verification of the grout curtain in the spillway was completed and there were some small areas that will need to be re-grouted. Drilling and grout operations are nearing completion in Phases 1, 2 and 3, with ongoing work being completed expeditiously. The problem areas found in Phases 1 and 3 will require installation of a concrete cutoff wall to the shale layer under the dam. A two-foot-wide slot will be excavated in the rock.
Current Activities
- Final excavation of phase 4 over the sluice tunnel is complete. Dental work of large feature is being performed.
- Installation of soldier pile walls near the sluice and spillway structures is proceeding as scheduled.
- Lagging and tendon anchors are being installed on the sluice soldier pile wall.
- Some additional grouting is required to complete the spillway and left embankment grouting operation.
- Drilling and grouting in Phases 1, 2 and 3 are nearing the completion.
- Plans are being finalized for the size and location of a cutoff wall in areas of large features.
- Concrete grade beams are being constructed for the sluice outlet is nearing completion.
A large feature was exposed over the sluice tunnel upstream of the outlet structure. Dental concrete was placed in lower sections of this feature.
Installation of lagging boards between the H piles on the sluice soldier pile wall along the sluice outlet structure.
