Rock Mechanics, 7:101–120, Springer-Verlag, 1975
Authors: B. T. Brady, V. E. Hooker and J. F. T. Agapito
Preliminary results are reported of a cooperative research agreement between the U.S. Bureau of Mines and the Colony Development Operation of the Atlantic Richfield Corporation. The overall objective of this program is to correlate laboratory and in situ behavior of fractured oil shale pillars and to use this information to develop design criteria for underground room-and-pillar mining of oil shale. In situ stress measurements in the Colony mine have been made in pillars of oil shale containing joints of which the planes of weakness are oriented at low angles (<45°) to the pillar axis. Four findings of importance have resulted from these measurements. (1) Some pillars are in a post-failure condition, that is, an increase in deformation in the pillars results in a decrease in the load the pillars can sustain; (2) Pillar failure begins when the maximum and minimum stresses within the pillar become approximately 5,000 psi and 800 psi, respectively; (3) In situ measurements suggest that 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, that is, further fracturing can be prevented by the addition of small radical confinement such as provided by rock bolting normal to the major joint pattern in the pillar. The latter three observations are predicted from laboratory studies on model pillars of oil shale containing joints oriented with respect to the applied stress field as its in situ counterpart. The application of these results and problems associated with applying them to design room-and-pillar mining in oil shale is discussed.