Applicability of excavatability classification systems in underground excavations: A case study

In this study, applicability of the excavatability classification systems in underground excavations is investigated. For this purpose, the entrance portal of the Konakönü (Arakli{dotless}-Trabzon) tunnel, excavated in volcanic rocks within the scope of Black Sea coastal highway project, is chosen as pilot study area. The entrance portal of tunnel is excavated through the rocks of Eocene-aged Kabaköy formation of basaltic-andesitic tuffs, aglomerate and basalt. In excavation, basaltic and andesitic tuffs were ripped by using hydraulic breaker; aglomerate and basalt were excavated by using explosives. Based on the results obtained from field and laboratory studies, rock masses are classified in terms of excavatability. According to Pettifer and Fookes (1994), basaltic and andesitic tuffs are included in "hard ripping", aglomerate and basalt in "blasting required" categories. With reference to Tsiambaos and Saroglou (2009), basaltic and andesitic tuffs fall in "ripping", agglomerate and basalt in "hammer and blasting" categories. It was found out that the classifications made according to these two methods are completely compatible with in-situ excavation works. Also, it is determined that the parameters give the best results for determining excavation class in underground excavations are GSI (Geological Strength Index), I s (50) (Point load strength index) and I f (Discontinuity spacing index).