ORIGINAL PAPER Combined instability assessment and rockfall hazard in volcanic rocks (Keçiören, Ankara) Koray Ulamış 1 & Recep Kılıç 1 Received: 10 January 2019 /Accepted: 18 April 2020 # Saudi Society for Geosciences 2020 Abstract Discontinuity bearing rock masses might be subjected to various mass movements due to the steep slopes, alteration, and manmade operational activities. Rockfall will take place in case several discontinuities form prismatic blocks. Special care must be taken in order to determine the rockfall potential and offer precautions. This study deals with the instabilities and rockfall hazard in an abandoned quarry, located in the residential area of Keçiören town, Ankara. This region has been declared as “Rockfall Hazardous,” threatening nearby structures. Several rockfall events have been reported, and a huge wedge-shaped block has been released from the slope in the early 2000s. The whole slope has 660 m length and with an average height of 35 m. Eocene-aged dacite is the main rock unit. The whole slope was divided into sections, concerning slope instabilities and discon- tinuity characterization in order to delineate the Slope Mass Rating (SMR) classes. The rockfall hazard assessment along the slope was performed including the SMR classes, topography, and 2D rockfall analyses. Based on the evaluations, a combined mapping of the slope was conducted to offer mitigation methods. The methods included the removal of blocks from the slope face, covering the slope with anchored steel wire mesh and construction of an earth wall to prevent the possible rockfall damage to residents. Keywords SMR . ERHA . Instability . Rockfall . Hazard . Earth wall . Ankara Introduction Instabilities in rock masses form a significant level of geolog- ical hazards. Rockfall is the most critical one due to its occur- rence frequency and intensity. Thus, rockfall events might be assessed by qualitative and quantitative methods. Previous investigations about rockfall mechanism, determination of the coefficient of restitution, remedial measures, and laborato- ry modeling have been published (Wieczorek et al. 1999; Crosta and Agliardi 2003; Budetta 2004; Vandewater et al. 2005; Petje et al. 2005; Ulusay et al. 2006; Topal et al. 2007; Sturzenegger et al. 2007; Bolin et al. 2010; Corominas and Mavrouli 2011; Pedrazzini et al. 2010; Saroglou et al. 2012; Fityus et al. 2013; Ansari et al. 2013; Keskin 2013; Gratchev et al. 2013; Zimmer and Sitar 2015; Matteo Di et al. 2017; Mavrouli and Corominas 2017; Geniş et al. 2017; Asteriou and Tsiambos 2018; Laimer 2019; Verma et al. 2019). Several qualitative methods about the rockfall hazard included Rockfall Hazard Rating System (RHRS) (Pierson et al. 1990), UDOT Rockfall Hazard Rating System (Pack et al. 2006), CDOT system (Russell et al. 2008), Swiss code (Lateltin et al. 2005), and Evolving Rockfall Hazard Assessment (ERHA), developed particularly for coal pit mines (Ferrari et al. 2017). Mitigation against rockfall hazards based on site-specific geologic setting mostly includes cover- ing the slope and construction of barriers. Such methods con- sider the trajectories and energy of the falling blocks with their rolling distance and bounce heights (Chau et al. 2002; Hoek 2006; Wang et al. 2007; Asteriou et al. 2012; Giacomini et al. 2012; Spadari et al. 2012; Xu et al. 2018; Toe et al. 2018). Rock mass classification systems have become universal tools to identify the rock mass quality. Such classifications provide practical data for all types of projects. Slope Mass Rating (SMR) has been developed by Romana (1985) and has experienced modifications (Robertson 1988; Chen et al. 1994; Tomás et al. 2007, 2012). The system is mainly based Responsible Editor: Zeynal Abiddin Erguler * Koray Ulamış ulamis@ankara.edu.tr 1 Department of Geological Engineering, Ankara University, Ankara, Turkey Arabian Journal of Geosciences (2020) 13:349 https://doi.org/10.1007/s12517-020-05338-2