Report No. : GEO Report No. 66

Report Title : Mineralogical and Fabric Characterization and Classification of Weathered Volcanic Rocks in Hong Kong (1998), 113 p.

Author : T.Y. Irfan

Abstract

As part of its research and development programme, the Geotechnical Engineering Office has been looking into ways of determining and characterising the mineralogical and fabric properties of weathered rocks, in particular the soil grades, with the objective of understanding their behaviour in the laboratory and in the field.

The results of the research on weathered granitic rocks have already been described by lrfan (1996a). This document summarizes the study results on the weathered volcanic rocks, in particular, the tuffs. It documents the typical chemical, mineralogical and fabric changes that occur in these rocks due to weathering and other alteration effects.

Based on the results of the study, a model for weathering of volcanic rocks is established. The effects of hydrothermal alteration which are a major influence in profile development and soil formation in Hong Kong are also considered. Modification, similar to those recently proposed for granites (lrfan, 1996a), are proposed to the material and mass weathering schemes commonly adopted in Hong Kong for the characterization of volcanic works in engineering uses.

The results of the studies on weathered granitic and volcanic rocks have already been used by the GEO in drafting local standards for soil classification and index tests.

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