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c~ <br />REFEREFlCES CITED <br />(1} Allen, A. S., and Paone, J., Surface Subsidence Control, U. S. <br />~. Bureau of 14ines Report. <br />(2) Obert, O~vall, and 1.lerrill, Design of Underground Openings in <br />Competent Rock, U. S. Bureau of dines, Bulletin 587, 1960. <br />(3) 1Jilson, A. H., Research into the Determination of Pillar Size: <br />Part I an Hypothesis Concerning Pillar Stability, t4ining <br />Engineering, June 1972, Vol. 131, No. 111. <br />(4) Dunrud, C. R., Some Engineering Geologic Factors Controlling Coal <br />Hine Subsidence in Utah anal Colorado, U. S.G. S. Prof. Paper 969, <br /> <br /> <br />(19) <br />