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Inspection Of Fully-Submerged Water Intake Tunnel
Interactive Pipe Inspection (IPI) is building an impressive record of complex inspections of pipe submerged under water. Last year, Underground Construction magazine reported on projects for King County, WA, in which IPI inspected more than 50,000 feet of sanitary sewer lines beneath two lakes.
Following that project, IPI inspected 8,700 linear feet of the fully submerged, active, Lake Whatcom raw water intake tunnel of 78-inch diameter concrete and wood stave pipe in service since the 1940s. The tunnel carries raw water from Lake Whatcom to a screen and treatment facility operated by the city of Bellingham, WA.
The inspection was made to identify needed repairs and determine whether the useful life of the tunnel segments could be extended beyond original manufacturing specifications. IPI made the inspection without dewatering the tunnel.
Although earlier inspections had been performed by man entry with the tunnel dewatered, the city did not want to dewater for this inspection due to the tunnel’s age and other factors, said Randy Wilkinson, IPI laser manager and project coordinator.
“With limited access to the mile-and-a-half-long tunnel, active water flow, 100 percent volume and water extending seven-feet upwards from the top of the tunnel and into the small access points at the intermediate access shaft and the gate house at the lake, we were presented with logistical underwater challenges,” Wilkinson said.
Cutting edge tech
Live pipe inspection was accomplished using the latest unmanned inspection technology.
“This inspection could not have been accomplished using a conventional CCTV system,” Wilkinson emphasized. “IPI contracted with Leviathan Underwater Construction International to place robotic crawler and high-definition CCTV units fitted with underwater laser equipment at the bottom of the submersed tunnel. Without damaging components, the equipment was placed in the correct position, elevation of the sensors set, all connections were checked and the tether line protection device affixed at the top edge of the tunnel. The diver’s line also assisted with additional audio, video feed and recording.”
Equipment used was an Inuktun Versatrax 300 Crawler, Inuktun Pan and Tilt Spectrum 120 camera and 2G Robotics ULS-200 underwater Laser scanner. The Inuktun Versatrax 300 is designed to complete long-range pipe inspection.