The meeting was opened by Dr. R. K. Taylor, Chairman of the Engineering Group.

J. A. Hudson (Imperial College, London) pointed out in a paper on ‘Discontinuities and excavation design in rock engineering’ that early studies of rock behaviour had centred on intact rock. He went on to outline the information about discontinuities in terms of orientation, frequency and persistence which are required for the design of excavations and associated rock support systems.

The reaction of rock mass to applied stress and the transmission of stress and water through rock masses are modified by the presence of discontinuities. For a particular rock mass, provided sufficient is known about the properties of both the rock itself and the discontinuities, the deformability, permeability, joint frequency and orientation, in situ stress and strength can all be estimated theoretically. However, since deriving solutions for real rock masses is a very complex operation, rock engineering tends to be a mixture of theory and empiricism. This may be adequate for situations for which there are accepted practices, but when dealing with new applications, for example radioactive waste disposal or geothermal energy exploitation, design must be based on a clear understanding of fundamental rock mass principles.

It is important to appreciate that engineering work may have the effect of changing the behaviour of the rock mass and although some aspects have received a great deal of attention there has been little work done on others, for instance the relationship between water flow and weathering; an important factor

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