In November 2020, Underwater Construction Corporation (UCC) was contracted by a hydroelectric utility to conduct repairs to a dam’s stilling basin.  Previous inspections had identified areas of spalling and exposed concrete reinforcement.  Additionally, a section of baffle blocks had become dislodged and swept downstream during a high-water event.  

To access the areas needing repair, several challenges had to be overcome.

Seven barge sections were assembled to create a work platform, which carried a tracked crane.  In order to dewater the large work area, a temporary bulk-bag cofferdam reinforced with 28 pallets of sandbags was constructed. UCC assembled extensive scaffolding for safe access.  A 6” dry-prime pump kept water clear of the area enclosed by the cofferdam. 

The repair procedure began with pressure washing, hydraulic saw cutting and removal of material to sound concrete.  New reinforcement (#10 rebar) was installed using HILTI RE-500® epoxy. Custom formwork was fabricated on-site to construct a new north and south block, and a middle slot between the two.  Once completed, the formwork measured 14’ x 4’ x 9.’ Concrete was pumped a distance of 360’ to the work area. 

Smaller areas of spalling were repaired by removing material until sound concrete was identified, then patched using SIKA 212 and Metalcrete VertiPave. The photos above show an example of spalling (left), and the final repairs.

The project was completed safely per the client’s specifications and schedule.