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<br />• analyze the results. A Mohr's envelope is then drawn as a best- <br />fitting line which is approximately tangent to the Mohr's circles <br />resulting from tests under differing confining stresses. The <br />intercept of the Mohr's envelope is defined as the cohesion, C, <br />and the slope of the envelope is defined as the angle of internal <br />friction, ~'. Ratios of shearing stress to normal stress which <br />lie above the Mohr's envelope result in rock breakage or failure. <br />Another procedure may be employed which eliminates any guessing <br />in drawing a best-fitting Mohr's envelope. This second procedure <br />involves plotting failure stress versus confining stress. <br />Theoretically, this relationship yields a straight line of the <br />form: <br />al ~ U + Tan B a3 [6] <br />where al ~ failure stress <br />U ~ uniaxial compressive strength <br />Tan 8 ~ elope of line - k <br />a3 ~ confining stress <br />• <br />The value of k or Tan 6 is related to the angle of internal <br />friction as follows: <br />1 + Sin ~' [~~ <br />k ~ 1 - Sin Q' <br />From this relationship the angle of internal friction may be <br />computed as follows: <br />~' ~ Sin 1(k+1) [8[ <br />The cohesion is related to the uniaxial compressive stength <br />and the angle of internal friction and may be computed as <br />follows: <br /> <br />SEEGMILLEN INTENM1ATIOI~AL <br />