Key questions in rock mechanics

This brief address repeats and reinforces what others have said in the past. Rock Mechanics is a mature and well developed branch of learning and engineering practice. It rests upon secure theoretical foundations, but presents unusual problems in continuum mechanics because of scale effects, particularly those relevant to yield and failure. The special characteristics making applications of theory difficult are the extreme problems of inhomogeneity and uncertainty in material properties and pre-existing stress states, which exhibit themselves at all scales. Interpretation of both experiments and field observations is thus a major problem.These special features lend a special significance to finite element methods. It is suggested that sedimentary rocks (and especially shales), with properties spanning those of soils and hard rocks, are worthy of more intense study, and that the circular cylindrical borehole is a geometry worthy of special attention.