Global was selected as a subcontractor to provide diving and marine construction services for the Willow Creek Dam rehabilitation in 2017. The rehabilitation of the dam involves lining the existing intake tunnel with steel liner sections and installing three new hydraulic control gates. The majority of work was designed to take place in a dewatered tunnel in 90 ffw, which could only begin after Global installed and grouted two offshore steel liner sections with a blind flange; the installation and timing of this component was critical in that the entire repair design relied on its installation.

Global designed a steel template that was inserted into the tunnel, confirming spacing for the flange. The team also designed a special handling system and rigging plan, allowing the two heavy steel liners to be welded together on the surface and inserted into the tunnel, then adjusted to a precise alignment. With the offshore steel liners installed, crews installed an 18” diameter HDPE ventilation pipe and the tunnel was dewatered ahead of schedule, allowing the GC crews to complete most of their work before winter shutdown.

Before the winter shutdown, Global crews removed the vent pipe and replaced the blind flange with a hydraulic control gate, giving the owner the ability to control water through the intake structure throughout the winter.