Aug. 8, 2022

Plinth Crews Work at 29-Degree Angle on the Right Abutment

Crews are currently working on a very technical, difficult section of the reinforced concrete plinth at Chimney Hollow Reservoir on the right (east) abutment at a 29-degree slope. As they move up the ridge, the angle increases to 43 degrees.  

The plinth provides a solid base along the entirety of the almost three-quarter mile long main dam. The plinth is fixed to the bedrock using  rock anchors and steel pipes that are placed through the rebar to provide  conduits for grouting. With holes drilled as deep as 230-feet below the foundation of the dam, grouting involves pumping Portland cement grout into the holes to seal any voids, such as cracks and fissures, in the bedrock to reduce seepage. Blanket grouting also helps reduce seepage in the upper rock zones and helps to prevent consolidation of the foundation under the weight of the main dam. Concrete is then placed on top in 20-foot sections, at a minimum thickness of 18 inches. 

Each 20-foot section takes about a week to complete. To put that in perspective, while working on a flat section of the plinth at the base of the dam, crews were able to complete four to six 20-foot sections per week. 

To help construct this steep section of the plinth, a 300-ton crane was brought to reach 280 feet of radius and lift approximately 12,400 pounds. Carpenter and concrete placement crews are using the crane to move equipment, reinforcement, and formwork up and down.