11:00 AM - 11:15 AM
[HGM02-01] Assessment of weathering grades for different chemical and geomechanical properties; A Sri Lankan case study
Keywords:Weathering grades, Rock weathering, Chemical weathering index
Fresh and weathered rocks of garnet-sillimanite gneiss were selected from the Samanalawewa Hydropower Project. Weathering grades were visually assessed initially, then confirmed with physical and strength properties using tests on dry density, water content, ignition loss, point load strength and slake durability. Whole rock geochemical data were used to calculate weathering indices.
Physical and strength properties show a marked difference with weathering grades. However, chemical indices are not very convincing. Silica-Titania, Product index and Ruxton ratio show a gradual variation with weathering grades. Mobiles index also shows an acceptable variation. However, the modified weathering potential index, which was formulated for metamorphic rocks, Parker index, which was formulated for all types of rocks, do not show a gradual variation with weathering grades. Chemical index of alteration and weathering (CIA and CIW) do not show a recognizable variation with weathering grades. Physical and strength properties show good correlation with most of chemical indices. In addition, most chemical weathering indices show good correlation with each other. The Lixiviation index is the one shows weak correlation with most of other chemical weathering indices. The failure of some indices in showing a good correlation can be accounted for the heterogeneity of garnet-sillimanite gneiss.