The population of Southern California relies on an extensive system of canals and tunnels to deliver water. Construction of these structures is an intricate undertaking that requires a considerable amount of engineering expertise and attention to detail.

Because of the terrain and site conditions, it also means that custom solutions to unique situations must often be devised. When Shank/Balfour Beatty was contracted to build the West Tunnel-Inland Feeder in Highland, California, they determined that site conditions at the tunnel entrance required a portal structure not specifed in the original plans. The contracting/engineering firm designed an arched structure with 18" thick concrete walls to protect workers from possible rock slides at the opening during tunneling operations. Project Engineer Stuart Lipofsky asked Symons® by Dayton Superior to propose a forming system for this important element.

The 7'-9" walls were typical straight walls, but the 10'-10" inside radius arch between the walls presented some form design challenges. Flex-Form was an obvious choice to form the arch. However, because the inside forms would be inaccessible to a crane after concrete placement, a means to strip and move these forms had to be devised.

To provide the support and mobility required, a framework of Symons Soldier and rolling components was proposed. This system allowed the inside forms to be pulled in slightly, lowered with screw jacks and then rolled to the next concrete pour position.

While moving the outside forms was not an issue, the relatively tight curve of the arch created some other challenges that required modifications because standard pour doors are not designed to accommodate the specified radius. Symons proposed inserting Flex-Form void panels at intervals instead. They provided the necessary openings for concrete placement and vibration, and were closed as the concrete level was raised in the form.

Load calculations and engineering drawings were provided to Project Manager John MacDonald for his review. They detailed how Anchor Clamps attached in sleeves cast into the straight walls transferred loads from the forms and concrete and other important details. Based on this information and a job site inspection before the first pour, he approved the plan.

Shank/Balfour Beatty report that the system performed exactly as planned. They were impressed with the speed of this design and happy to cycle the Flex-Form system through all four concrete pours in just 10 working days, safely beginning their tunneling operations.

Symons® Soldier Beam System


Flex-Form® All Steel Flexible Forming System

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