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along the concrete-rock interface under the applied hydraulic <br /> thrust, or <br /> (b) provide test data that gives a value for the shear <br /> strength at the concrete-rock interface and calculations to <br /> show that the resistance to shear failure is sufficient to <br /> prevent failure under the applied hydraulic thrust, even in <br /> the case of regular or smooth tunnel walls, or <br /> (c) additional design details should be submitted to provide <br /> additional resistance to shear failure, such as tapering the <br /> bulkhead from water-side to air-side or installing rebar into <br /> specially drilled holes in the bulkhead location ribsides as <br /> mentioned in the report. <br /> The Division is also somewhat concerned about the absense of any <br /> data regarding the shear strength of the rock mass at the proposed <br /> bulkhead locations. The Division believes that direct shear tests <br /> should be performed on sawed and surface ground samples of the <br /> tunnel wall rock and on samples that contain the "healed" fractures <br /> with the associated white mineral described in Appendix D of the <br /> March 12, 1993 Simon Hydro-Search report, and that failure in shear <br /> along these partings, caused by the applied hydraulic thrust, <br /> should be the controlling design criterion if the measured shear <br /> strengths are less than that of the concrete. The shear strength <br /> analysis of the wall rock should further consider the likelihood <br /> that water will be flowing through the fracture system once a <br /> hydraulic head builds up behind the bulkheads. Alternatively, data <br /> can be provided, perhaps through additional coring of the tunnel <br /> walls, that the fractures caused by blast damage, as well as the <br /> natural fractures, are oriented and spaced in such a way, or have <br /> short enough trace lengths, that the material strength of the <br /> concrete would control any failure in shear. Either way, the <br /> potential for failure through the rock mass needs to be quantified. <br /> 9. Diversion Pipe Flow Data <br /> The flow from the American Tunnel by-pass pipe must be measured <br /> daily from the time that by-pass is initiated. This data must be <br /> provided to the Division prior to the concrete pour for the <br /> American Tunnel bulkhead, and again after the curing period, prior <br /> to closing of the valve. Obviously, if the flow from the pipe <br /> approaches the maximum design flow, the stability of the bulkhead <br /> could be compromised. <br /> 10. Water Rights Issues <br /> The American and Terry Tunnels have been discharging significant <br /> flows into the Animas River Basin for many years. It is <br /> conceivable that by shutting off a portion of this flow, the water <br /> rights of downstream users could be- damaged. Sunnyside Gold should <br /> contact the Office of the State Engineer regarding water rights <br /> issues related to bulkhead installation, and copy the Division with <br /> correspondence related to the State Engineer's determination. <br /> 11. Ultimate Life of the Bulkheads <br /> The bulkhead seals proposed in this technical revision are intended <br />