Overview

Ballard Marine Construction led the design-build process to construct a specially designed in-line bulkhead to accommodate the dewatering / bypass of wastewater for the maintenance of the tunnel system. The plug was designed for 300ft. of head pressure. Ballard mobilized a specially trained and experienced confined space and dive team to clean the host tunnel and then install the custom designed and fabricated aluminum bulkhead.

Scope of Work

The extreme cold weather and high current emergency response project included:

• Lowering divers 300ft. in a 10ft. diameter vertical shaft to access the tunnel.
• Divers penetrated 250ft. to the 10ft. tunnel work site.
• Divers used jetting and specialized pumping equipment to break up 4ft.of consolidated material that was then removed by the treatment plants pumps.
• Crews installed the 5,000lb aluminum bulkhead in the tunnel. To accommodate the ease of installation, the plug was designed to be neutrally buoyant underwater.
• Divers installed the plug in the tunnel at a pre-designated location allowing the client to isolate the system and replace their pumps as needed.
• All work was done in zero visibility HAZMAT conditions.

Innovative Solutions

A challenge presented during the project included removing consolidated material (sediment and debris) to facilitate placement of the bulkhead plug. Ballard mobilized an industrial jetting package to assist in the breakup of material to be removed. Due to the extreme distance from the surface pumping sediment back to the surface posed technical problems. Ballard worked with the owner to cycle their main sewer plant conveyance pumps to draw the loose materials out of the tunnel. This innovative idea used existing systems to accomplish the work safety and on time.