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2. Rock compressive strength;Hobbs;Colliery Engng,1964
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4. Meigh A. C. Greeenland S. W. (1965) Proc. 6th Int. Conf. Soil Mech. (Montreal), In situ testing of soft rocks, 1, pp 73–73.
5. The nature and physical properties of some Coal Measure strata;Phillips;Trans. Instn Min. Engrs,1930