Laboratory and in situ behavior of fractured oil shale pillars were correlated, and the information was used to develop design criteria for underground room-and-pillar mining of oil shale. In the colony oil shale mine, in situ stress measurements have been made in pillars of oil shale containing joints of which the planes of weakness are oriented at low angles (<45 deg) to the pillar axis. Four findings of interest have resulted from these measurements: (1) some pillars are in the post-failure condition; (2) pillar failure begins when the maximum and minimum stresses within the pillar become approximately 5,000 psi and 800 psi, respectively; (3) the stresses carried by the "solid" portion of a pillar become constant when the fractured pillar is in a post-failure condition; (4) severely fractured pillars in a post-failure condition can be stabilized by rock bolting normal to the major joint pattern in the pillar.
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