1993-04-27_REVISION - M1977378 ‎(2)‎

• Permit No: M1977378
• IBM Index Class Name: REVISION
• Doc Date: 4/27/1993
• Doc Name: Response
• From: John F. Abel, Jr.
• To: Sunnyside Gold Corp
• Type & Sequence: TR14
• Media Type: D
• Archive: No

L.R. Perino Page 2 27, 1993
As stated by Obert, et al in U. S. Bureau of Mines Bulletin
587 (1960, p 6) , titled, Design of Underground Openings in
Competent Rock stated that "A criterion of failure based on the
shear strength is not used, because no satisfactory means has been
found to measure the shear strength of rock. " Direct shear testing
of rock by the same method employed for soils produces irrationally
high shear strength values for rock. Obert and Duvall in their
book Rock Mechanics and the Design of Structures in Rock (1967, p
334-338) discuss the indirect method of calculating the angle of
internal friction (�) and intact rock cohesion (c) by uniaxial and
triaxial compression testing of core samples. The cohesion value,
i.e. shear strength under no normal load, derived by this method is
calculated from the compression test results, as follows:
Sin _ (Tan R - 1)/(Tan 0 + 1)
Tan - Passive pressure coefficient, increase in failure
strength per psi increase in confining pressure,
c = UC/(2 VTan R )
UC - Unconfined compression strength
The minimum unconfined compressive strength measured for the
eleven Sunnyside Mine latite bulkhead location samples was 10260
psi. This lowest of eleven uniaxial compression test samples was
measured on a core sample which indicated structural control of the
failure. Structurally controlled failure means natural failure
planes present in the rock mass have weakened the sample, as
evidenced by the presence of planar surfaces in the failed sample
fragments. These natural weaknesses in the core were frequently
coated by the white mineral described in Appendix D of the March
12, 1993 Simon Hydro-Search report. The decrease in strength
resulting from natural and blast induced weaknesses in the stronger
rock substance was, therefore, accounted for by the testing
performed.
Cohesion of the latite can be calculated after performing
triaxial compression tests on rock core samples collected at the
proposed bulkhead locations. Triaxial compression testing was not
recommended and performed because the uniaxial strength of the core
was so much higher than the 3000 psi design strength of the
concrete (Abel, 1993, p 13) . Obert & Duvall (1967, p 289)
presented typical values for cohesion (c) , unconfined compression
strength (UC) , Tan 0 and Tan � for similar volcanic rocks, andesite
and basalt. For andesite, Obert and Duvall reported c = 4060 psi,
UC = 18900 psi, Tan R = 5.7 and Tan � = 1.0 and for basalt c = 4500
psi, UC = 24600 psi, Tan 0 = 7.4 and Tan � = 1.0. The passive
pressure coefficient for rocks ranges from about 2.5, rock salt, to
20, shale. Calculated cohesion for the latite in the Sunnyside
Mine is probably about 1870 psi to 2150 psi. Given an unlikely