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31-04-1994 11~35RM FROM 6LJhIMITT OFFICE TO 13034285469 P.04 • To use this expression one must assume that the bloc}: OAB :Ls rigid and the stress is uniformly distributed over the sur:'ace OB. So this expression is apoli ble to the west wall of the Spec-Agg pit; since the 60 degree angf the prominate joint plane is parallel, Or less than, the © pA, and the safety factor F is so high that it is indetermin. A better mathematical model would be from the geometry; SVfI 0 •~/ B ~V 5' A ~ C S vihere: OB is the bench OA is the slope wall BC is the joint Wf is the wieght of the fil'1 wr is the wieght of the rock S' = shear stress 5 = resistence to shear or shear strength and the factor of safety would be the ratio of S/S'; we know that the strength S has to have high cohesion and high angle ~f friCtiOri (coulomb or Griffith failure criteria) so one could assume a high: value and be correct and result in a determineate safety factor of above 2 to 10! Since the wieght of the fill Wf is about 60P of the wieght of the wall rock Wr, vre can conservatively say that the safe- t1 factor of the bench with fill is greater than 1.5! Barton, in 1976 (The Shear Strength of Rocks and Rock ,joints) r=viewed the literature (58 refezenccs) and performed an elaborate series of laboratozy experiments and measurements and concluded that "any stage of sliding of the frictional area contact is very small" (once again confirming the Bureau-Rennecott results); of importance in the laboratory was a confirmation of the Byerlee transformation ~` ~ 1/2 (d"1 - dz) sin 2B O^ = lJ2(61+ 63) - 1/2(61 - 63)cos B, wheze B is the angle that the defect makes with the major principal stress 61. Again, if we apply this expression to the geometry of the Spec-Agg pit we get a very high safety factor (ratio of the wiegIIt tV:_ + Wr to the strength ~)! C (3)