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999 <br /> JOHN F.ABEL.JR. v p <br /> MINING ENGINEER -1 7 7_ 70 <br /> 310 LOOKOUT VIEW COURT <br /> GOLDEN.CO 80401 <br /> 303-279-4901 <br /> // FAX 278$163 <br /> yApril 27, 1993 <br /> Larry R. Perino <br /> /6unnyside Gold Corp. <br /> P. O. Box 177 <br /> Silverton, CO 81433 <br /> Dear Larry: <br /> This letter report was prepared in response to the list of <br /> rock mechanics concerns raised by the Apri , 993 letter from <br /> Allen R. Sorenson, Reclamation Specialist, of the Division off <br /> Minerals and Geology with respect to Technical Revision TR-14. <br /> Specifically item 8 (pages 6 and 7) , item 9 (page 7) and item 11 <br /> (pages 7 and 8) are addressed. <br /> 8. Potential for Failure from Thrust <br /> Near the bottom of page 6 is the statement, "There is little <br /> or no information included regarding the shear strength of the rock <br /> as a mass, or the resistance to shear of the rock-concrete <br /> interface." <br /> This statement is only partially correct. Measurement and <br /> analysis of the shear strength of the rock part of the interface <br /> was not performed for several reasons. The most important reason <br /> was given near the center of page 13 of the base report, "Bulkhead <br /> design for the Sunnyside Mine" dated March 10, 1993. The <br /> unconfined compression strength of the volcanic latite present at <br /> the Sunnyside Mine is consistently much stronger than the concrete <br /> design compression strength (Abel, 1993, Appendix B, page 54) . <br /> Additionally, 1) there is no direct method for measuring the shear <br /> strength (cohesion) of intact rock and only indirect methods of <br /> calculating the shear strength of rock are possible, 2) there is no <br /> mathematical possibility that the calculated intact shear strength <br /> of the latite could be as low as the concrete design shear <br /> strength, 3) the post-failure fragments from nine of the eleven <br /> unconfined compression tests performed indicated that the failure <br /> was structurally controlled and, therefore, the blast induced and <br /> natural structural weaknesses present in the latite adjacent to the <br /> proposed bulkhead locations were included in the measured rock <br /> unconfined compression strength, and 4) the shear (bond) strength <br /> of the rock-concrete interface was ignored because the lower, more <br /> conservative concrete shear strength was utilized for bulkhead <br /> design. These reasons for not treating the shear strength of the <br /> latite are discussed in detail below. <br />