ORIGINAL PAPER The relationships between the rock material properties and weathering grades of andesitic rocks around I ˙ zmir, Turkey Mehmet Yalc ¸ ın Koca 1 • Cem Kıncal 1 Received: 27 January 2015 / Accepted: 7 October 2015 Ó Springer-Verlag Berlin Heidelberg 2015 Abstract I ˙ zmir 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 ande- sitic agglomerates in and nearby the city centre of I ˙ zmir. 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 I ˙ zmir 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 weath- ering index, based on major element analyses, was pro- posed to be used for the determination of weathering grade of andesitic rock. Keywords Andesite Á Weathering Á Weathering index Á Uniaxial compressive strength Á Point load strength index Introduction Weathering effects are important for the engineering assessment of rock. For site investigation and design assessments, variability in engineering properties due to weathering is a key factor; therefore, it is essential that the degree of weathering is clearly described and classified (U ¨ ndu ¨l and Tug ˘rul 2011; Fell et al. 2013; Hencher 2013). Weathering grade determination of rocks is also important to separate the similarity zones in rock masses located along the subway route. On the other hand, the rate of advance of tunnels opened in weathered rocks and the penetration rate, which is used to predict drilling perfor- mance, are much higher than in fresh and slightly weath- ered rocks, depending on rock softening. The geological description of each drill-hole log already includes the weathering grade of rock, as well as rock type, discontinuities, core recovery, RQD-rating, and field test results. Boreholes were drilled along the subway route to penetrate weak zones, weathered zones, and to determine their dimensions at depth at the stage of feasibility (ITU ¨ and DEU ¨ 1993; Bu ¨ku ¨len 2013). For the reasons given above, determination of the weathering grades of the vol- canic rocks, and the relationships between the rock mate- rial and weathering grades of these rocks, are very important in terms of the logging cores for engineering purposes, as well as classification of the rock masses existing along the subway route. Chemical, physical and mechanical properties of vol- canic rocks (andesite, autobreccia, basaltic andesites) in I ˙ zmir were determined by means of chemical tests, & Cem Kıncal cem.kincal@deu.edu.tr; cemkincal@gmail.com 1 Geological Engineering Department, Engineering Faculty, Dokuz Eylu ¨l University, Buca, Izmir, Turkey 123 Bull Eng Geol Environ DOI 10.1007/s10064-015-0813-y