The relationships between the rock material properties and weathering grades of andesitic rocks around İzmir, Turkey

Izmir is the third largest city in Western Turkey founded on sedimentary and volcanic rocks. Pyroxene andesitic rocks with the age of Late Miocene are found as andesitic lavas, autobreccias, basaltic andesites, and andesitic agglomerates in and nearby the city centre of Izmir. There are a number of major engineering structures under construction in andesitic rocks involving large slope cuts, tunnels and shafts in the city. Thus, the short-term and long-term engineering behaviours of these rocks are very important in terms of the excavation and the stability of these structures. For these reasons, rock material properties of andesitic rocks were investigated in this study. The relationships between the rock material and weathering grades of the volcanic rocks were determined. Initially, the weathering grades of andesitic rocks were established on core samples recovered from boreholes drilled for site investigations of the Izmir subway route and the abandoned andesite quarries in the region. The samples were also subject to petrographic modal analysis, chemical analysis, and laboratory tests to determine the physical and mechanical properties of andesitic rocks. The relationships between the index and engineering properties for different weathering grades of andesitic rocks are also established for engineering use in practice. In addition, a new weathering index, based on major element analyses, was proposed to be used for the determination of weathering grade of andesitic rock.