Abstract

The description and classification of weathered rocks for engineering purposes has been a subject of debate since engineering geologists first produced standards and codes. Several previous working parties from the Engineering Group of the Geological Society have addressed the problem as part of other, fuller tasks and yet there still remains a lack of agreement and considerable confusion.

This Working Party was establishing in 1989 to review the way in which weathered rocks are described and classified in engineering practice and to make recommendations. It was decided, as a first step, to circulate a questionnaire internationally. Correspondents were asked what weathering processes are significant in their region and how these processes are described and classified in practice. A response of 15% was received from approximately 200 questionnaires distributed. The Working Party is deeply indebted to those that responded, as their replies were both informative and encouraging. The respondents are acknowledged in Appendix 2 to this report. The Working Party Membership and correspondents are listed in Appendix 3.

It was particularly interesting to note the degree of consensus in replies received on certain key points:

• different lithologies weather in very different ways in the same climatic regime

• lithological heterogeneity or penetrative ‘master’ joints and faults can give rise to complex weathering fronts or profiles

• weathered rocks are difficult to classify unless the fresh end member is seen, particularly in weak rocks

• attempts are often made to apply the same weathering classification in all situations, even when clearly

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