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01-04-1994 11:35RM FROM SUI'R11TT OFFICE • "measured" stress was 1.5, or greater. TO 13034285469 P.03 '' The test had two small failures (both predicted by the design eng- ineer), one of which was in a highly faulted zone on the south side of the pit and in a "nose" that was in the north side of the wall. Aleasurements and a finite element computer analyses (first of its Y.ind for slope walls) both confirmed that the slope wall want out and up in reaction to the removal of the weight of the rock mass. In a later test the rock mass was blasted with a large detc>nation and the slope wall.stood, even with the daylighting of the defects! The conclusions reached by the researchers was that the be:;t infor- mation regarding a slope wall stability is from full scalp observat- ions because the stresses are so low that they defy measurement and the rock cests have questionable impact on the final results. The test generated a new interest in slope stability analyses t>y re- searchers over the world and some of the better known, or other wise applicable, studies are reviewed as follows: SLOPE I•IALL STUDIES: One of the first classic studies caas by Jaeger (Frictions of Rocks and Stability of Rock Slopes, 1971). He concluded that "the criter- ia o£ failure of rocY. are empirical" and."numerical values for frict- ion and other parameters of jointed systems are uncertain" and, in effect, the design engineer can, at best, use simple mechanical formulas for estimates that are subject to broad assumptions; he reviewed the four basic criteria of failure for rock, namely, Cou- lomb, Poncelet, Griffith and the power law, and suggested that the Griffith failure was perhaps best for low values of stress; he also reviewed laboratory and field test methods, such as confined compr- essive strength, shear boxes and artificially filled joints, and concludes that "none of these is applicable to brittle materials such as rock". So Jaeger finally concluded that for rock si~~pes there are three simple situations which can be used to appraise rock slopes: 1) a definite plane of weakness by the orientation of i:.he joint to the sliding plane (the case at Spec-llgq) 2) .in highly anisotropic rocks there is a definite plaice of weaknessbht there may also be little change in sheaf' str- ength for angles up to 20 degrees from the plane 3) The rock is 5o broken that it can be treated as a soil He concurred with the conclusions of the Bureau-Kennecott study ahd stated "the fundamental difficulty for rock slopes is tY„at the law of friction for low values of normal stress is not clearly ]cnown and attempts to measure the parameters by laboratory exper- iments are liable to considerable scatter". fIowever questionable the results - he continued to show that the safety factor could be suggested by the total shear strength gnu on the Failure surface must be F-times that to maitain equilibrium or the factor of safety A B where; -- F= .(fT 2) u^ _ ( w/L sin a) ii I W a n ~ L (2)