Publication Abstract

Proceedings of the 39th Annual Conference on Deep Foundations, 2014, Atlanta, GA, USA, (DFI)

Cofferdam Solution for Steeply Sloping Rock Using Flat-Sheet Piles
Robert Bittner, P.E., Bittner-Shen Consulting Engineers, Inc., Norm Kirk, P.E., Independent Consultant

The addition of a new powerhouse at the existing Tulloch Hydroelectric site on the Stanislaus River in the western foothills of the Sierras Nevada Mountains of central California required a deep excavation in rock on the downstream face of the dam. A cofferdam (water exclusion device) was necessary to isolate the powerhouse construction site excavation from the existing Goodwin Reservoir and the turbulent discharge from the existing powerhouse. The cofferdam was positioned on a steeply sloping fractured rock surface exceeding 50 degrees. This paper describes the challenges encountered during design and construction of the cofferdam and describes the unique design features used to address these challenges including: The use of flat-sheet-piles to form cellular walls on the steeply sloping rock surface. The use of 5-ft deep tremie concrete plugs in the bottom of the sheet pocket cells to create the bottom seal of the cellular cofferdam walls against the sloping rock surface. The use of vertical post-tensioned rock anchors to provide shear resistance at the contact point between the base of the cellular-wall and the sloping rock surface.

 article #2007; publication #1011 (AM-2014)