Examination of Shotcrete Liner at Devil’s Slide Tunnel Utilizing ASTM 1550 Field Test Results and Back Analysis

Synopsis:

The Devil’s Slide Tunnel project, located south of San Francisco along Highway 1, consists of twin bore tunnels approximately 1250 meters long. The tunnels are currently being excavated and supported utilizing the “New Austrian Tunneling Method” (NATM). In NATM design a flexible initial lining is used to allow some deformation to occur to mobilize the strength of the rock. The initial lining support utilizes fiber reinforced shotcrete (FRS). The ASTM 1550 Round Determinate Panel Test “Pizza Test” is being conducted on site to ensure the flexural properties or post-crack performance of the FRS. However, the ASTM 1550 does not analyze shear failure due to ground loads imposed on the liner. Therefore, it must be coupled with typical compressive strength testing. Furthermore, measured convergence during excavation presents the opportunity to back calculate and analyze the in situ loading of the FRS liner for a better understanding of its actual performance. In this paper, the to date results of the ASTM 1550 field test program along with a back analysis based on measured convergence to determine the loading of the FRS initial lining will be presented. A brief discussion of the ASTM 1550 testing and the back calculated in situ loading of the liner and how these demonstrate the overall performance of the FRS liner at the Devil’s Slide Tunnel will be given.

44th US Rock Mechanics Symposium and 5th U.S.
Canada Rock Mechanics Symposium Proceedings
Examination of Shotcrete Liner at Devil’s Slide Tunnel Utilizing ASTM 1550 Field Test Results and Back Analysis
June 27-30, 2010
Salt Lake City, Utah

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