UndergroundQ We would like to place 4 in. (100 mm) thick shotcrete reinforced with welded wire reinforcement and anchoring bolts in a water pressure tunnel. The water velocity would be between 10 and 16.4 ft/s (3 and 5 m/s). We would like to know if there is a possibility of erosion or cavitation of the shotcrete at this range of velocity. It is mentioned in our concrete manual that cavitation and destructive erosion begin when water velocities reach about 40 ft/s (12 m/s). Because the roughness of the shotcrete surface is higher than the concrete surface, is erosion more likely to occur? Do you know what may be the maximum water velocity acceptable for reinforced shotcrete?
Shotcrete is a method of placing concrete and the surface finish can be as smooth as that of cast concrete. Even with a nozzle finish, shotcrete erosion or cavitation should not be an issue at the stated velocities. Examples of smooth shotcrete surfaces can be found in many Shotcrete magazine articles and in particular (“Restoring the Century-Old Wachusett Aqueduct”).
