15th Oil Shale Symposium, Colorado School of Mines, Golden, Colorado, 28–30 April 1982
Authors: J. F. T. Agapito and M. P. Hardy (AAI)

Pillar design in oil shale by the induced horizontal stress method is based on in situ stress determinations of pillars before and during failure, on computer analysis incorporating site-specific rock properties, and on the pre-mining stress field. An empirical strength equation which relates vertical and horizontal stresses at failure was developed from stress determinations through the center of 60-ft cube pillars. Induced horizontal stresses within the pillars are then evaluated for different width-to-height ratios by simple finite element analysis. Design curves are developed relating pillar stresses and strength with pillar widths and extraction ratios. The induced horizontal stress method, which is based on the in situ strength of large pillars, has been used for planning and resource recovery evaluations throughout the Piceance Creek Basin.

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