This report describes laboratory experiments to determine the strength, and the stress-strain characteristics up to fracture, of cylinders of coal subjected to triaxial stresses, with lateral confining pressures of up to 4,000 lb/in2. Two coals were studied:Brantley (Top Herds) from Rossington Colliery, a strong compact bituminous coal, and Grew from Cwmtillery Colliery, a friable coking coal.nThe strength increased, though at a decreasing rate, as the confining pressure was increased, the strengths of the two coals tending to similar values in the range 15,000 to 20,000 lb/in2 at a confining pressure of 4,000 lb/in2, although their uniaxial compressive strengths were in the ratio of 5:1. The mode of failure was in each case by fracture along one or more surfaces inclined to the specimen axis.
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