The effect of petrographical and petrochemical features of the Evciler (Gölbaşı/Ankara) basalt on its usability as railway ballast and sub-ballast

Based on the field observation, petrographic, chemical and physico-mechanical tests, we investigated the usability of the Evciler Basalt and subballast (Elmadağ Volcanic Complex-EVC, Ankara) as railway ballast, and test results variation according to the required test standards and sample sizes in accordance with the ballast and sub-ballast material specifications were also investigated in this study. The EVC is one of the most important Miocene volcanic field, comprising mafic mildly alkaline and intermediate to felsic calc-alkaline lavas. The mafic lavas are called as the Evciler basalts, and represented by alkali basalts. They display porphyritic texture with olivine and clinopyroxene phenocrysts in an intergranular groundmass including mainly plagioclase, clinopyroxene, lesser opaque and rare anorthoclase. The field characteristics of the basalts resemble those of "aa lavas". Based on the field observations, we identified three zones from top to bottom in a few meter cooling unit of the basalts: (A) a vesiculated flow top, (B) a massive interior, and (C) a basal breccia. Following the physico-mechanical tests, we observed that water absorption, Los Angeles abrasion and magnesium sulphate soundness of the zone B are the lowest, but particle density of the zone B ranges between those of the zone A and C. Based on the obtained data, we found that the zone B is appropriate for ballast material in just conventional railway rather than the zone A and C. Accordingly, our findings show that small-scale vertical physical heterogeneity is so high in a basaltic flow, and it is advised to be careful for selection of ballast material from basaltic volcanic rocks.