Principles for Description and Classification of Weathered Rock for Engineering Purposes

There is a clear need for separate descriptive schemes for the degree of weathering at a small scale (material grades) and at a large scale (mass zones). Such weathering classifications should be established according to clear principles using well defined terminology. The schemes recommended in BS 5930 for this purpose are considered inadequate due to confusing terminology, loosely defined material grades and unjustified mass zonal boundaries. In this paper, published schemes both at the material grade scale and the mass zonal scale are reviewed and proposals made for standardised terminology. Examples of three schemes for classifying materials, and which meet many of the criteria advocated here, are presented. An idealised zonal scheme for heterogeneous weathered rocks is presented and the engineering significance of each proposed zone boundary is discussed.