Structural Modifications to Dam Turbine Draft Tube Ceiling with Overhead Wet-Mix Shotcrete

Shotcrete has been used widely for rehabilitation and retrofit of concrete structures. More and more large infrastructures, in particular, in the hydro power industry, is using shotcrete for major rehabilitation and retrofit. Recently, the US Army Corps of Engineers has been engaged in structural modifications to reinforced concrete draft tube exits from the turbines in the Ice Harbor Lock and Dam located on the Snake River, Washington. These structural modifications, along with installation of new advanced technology hydroelectric generating turbines, are intended to improve hydraulic conditions for fish passage, as well as provide improved electrical generating efficiency. As part of this re-shaping of the draft tubes, there was a need to apply an accelerated wet-mix steel fiber reinforced wet-mix shotcrete, up to 2 m thick overhead. Overhead application of shotcrete to such thickness is seldom done and posed a challenge for the designer and contractor. This presentation details the structural modification to the draft tube which was successfully completed using wet-mix shotcrete.

Learning Objectives:

1. Advancement of shotcrete technology
2. Hydro dam structural modifications
3. Overhead wet-mix shotcrete application
4. QC monitoring and inspection for shotcrete application