Question: A regular room and pillar method is used in a hard rock leadzinc mine. The ore horizon is at a depth of 300 m where

A regular room and pillar method is used in a hard rock lead–zinc mine. The ore horizon is at a depth of 300 m where the overburden averages 25kN/ms. Laboratory tests on core samples (L/D = 2) show that the ore has an unconfined compressive strength of 86 MPa and a tensile strength of 7 MPa. Find an algebraic expression for the maximum extraction ratio possible, if no size effect exists, then evaluate the expression for the given data.

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