The stone roofs of coal mine roadways typically comprise low strength, thinly bedded and closely jointed mudstones, siltstones and sandstones. A practical strength criterion for use in currently available numerical codes should include consideration of the pronounced transverse isotropy introduced by the bedding and the tensile strength should be set to zero. The compressive strength is then the greater of either the damage/brittle criterion implemented as cohesion = UCS/6 and a friction angle of 0° or a purely frictional component with a friction angle of 33°. This criterion can be used to estimate the maximum height of a roof fall in bedded sedimentary rocks similar to coal measures.
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