Characterization of weathered volcanic rocks in Hong Kong

Abstract

The mineralogical and fabric characteristics of weathered volcanic rocks, which are widespread in Hong Kong, are poorly documented. Consequently, the significant variations commonly observed, even at the same locality, in engineering properties and in situ behaviour of these rocks and the resulting soils cannot be adequately related to their basic mineralogical and fabric characteristics. A model for weathering of volcanic rocks, particularly those of pyroclastic origin, is presented in this paper. Modifications, similar to those recently proposed for granites by Irfan, are proposed to the material and mass weathering schemes commonly adopted in Hong Kong for the characterization of weathered volcanic rocks in engineering use. The appropriateness of various proposed petrographic and chemical weathering indices to generally fine-grained volcanic rocks is examined. A number of modifications are proposed to the standard soil preparation and testing methods for the soils formed from tropical weathering of volcanic rocks in order to obtain meaningful and more repeatable results.

Quantification of weathering depths in slightly weathered tuffs

“…Although the effects of weathering in the tuffs can followed by decomposition and disintegration of the feldspar phenocrysts, the matrix minerals forming the majority of tuff are fine-grained, so that individual minerals and the weathering products in the matrix can hardly be identified under an optical microscope. This observation is also in good agreement with other researchers (Irfan 1994(Irfan , 1999Ng and others 2001) who worked on tuffs. XRD analyses were performed on both white and pink tuff samples to assess the abundance of all minerals and the types of clay minerals within the tuffs.…”

“…The use of weathering grade classification, in practice, has its own shortcomings. Visual determinations of the weathered grade is subjective and does not provide a quantitative measurements of the rock properties (Irfan 1996(Irfan , 1999. The changes in mineralogical, chemical and engineering properties of the rocks as a result of weathering can be studied by means of a number of chemical and petrographical techniques.…”

“…Quantification of weathering effects also leads to consistent and objective material descriptions (Irfan 1996). A number of methods have been used to quantify the changes in mineralogical, chemical and engineering properties of rocks (Ramana and Gogte 1982;Hodder 1984;Martin 1986;Guolin and Yushan 1990;Hodder and Hetherington 1991;Esaki and Jiang 1999;Irfan 1999;Ng and others 2001). The methods include chemical analysis, X-ray diffraction (XRD) analysis, optical microscopy, scanning and transmission electron microscopy (SEM, TEM), electron diffraction (ED), infra-red spectroscopy (IS), differential scanning calorimetry (DSC) and tests for assessing the index properties of rocks.…”

Influence of Weathering on the Engineering Properties of Dacites in Northeastern Turkey

“…In addition, several researchers have explored the effects of weathering on sedimentary rocks [14][15][16][17][18]. Although some researchers [19][20][21][22][23][24][25] have focused on the influence of weathering on the engineering properties of volcanic rocks, only brief references have been made to the weathering characteristics of dacites.…”

Comparative study of weathering signatures in felsic igneous rocks of Hong Kong

“…In Hong Kong, the significance of weathering and its mineralogical, petrographical and chemical characterization in relation to physical and engineering properties of rocks and to slope stability in weathered profiles have been increasingly recognized in recent years (Irfan, 1996;1999;Kirk et al, 1997;Duzgoren-Aydin et al, 2000b;Guan et al, 2000;Parry et al, 2000;Malpas et al, 2001). However, there are only a few studies integrating the type and abundance of clay minerals to other weathering signatures (DuzgorenAydin et al, 2001).…”