Behavior of a Single Gasket System for a Precast Concrete Segmental Liner Subject to High External Hydrostatic Pressure

Abstract
High external hydrostatic pressure is anticipated during the construction of the Inland Feeder Arrowhead Tunnels in Southern California. A bolted and gasketed precast concrete segmental liner will be used as the primary support for the tunnels. The performance of the gasket is critical for the ability of the segmental liner to meet stringent water inflow criteria under the maximum design groundwater head of 275 meters during construction. Since limited data is available for the performance of gaskets at pressures anticipated for this project, testing at the University of Illinois at Urbana-Champaign and Metropolitan Water District of Southern California (MWD) was conducted to study the performance and compatibility of various gaskets designs.

The testing focuses upon the following issues: ability of proposed gaskets to seal effectively under the maximum hydrostatic conditions; failure mode of the gasket; correlation of contact pressure to sealing pressure and joint gap; compatibility of the gasket line loads with the segment joint design; and stress relaxation of the gasket after initial compression. Design recommendations and testing procedures specific for gaskets subject to high hydrostatic head will be presented, as well as how these findings were implemented for the Inland Feeder project.

2002
Howard Lum, David Crouthamel & David Hopkins
Jacobs Associates, San Francisco, California

Ed Cording
University of Illinois, Urbana-Champaign, Illinois

John Shamma
Metropolitan Water District of Southern California, California