Ground penetrating radar for the evaluation of rockfall potentials in the vertical rock slope of Sumela Monastery (NE Türkiye)

The aim of this study is to investigate the rockfall potential of the steep rock slope above the Sumela Monastery (Trabzon, Türkiye) by using Ground Penetrating Radar (GPR) and surface fracture analysis on discontinuity. In this context, studies were carried out on 10 risky blocks determined after the investigations made by a team of industrial mountaineering and observations on the orthophotos. The discontinuity analysis data on the rock masses containing of mainly andesites and basalts were combined with discontinuities observed in the ground penetrating radar sections (radargrams) and the risk status of the blocks was revealed by using the location and characteristics of the dominant discontinuities. By using GPR data, discontinuities with 4 main sets were detected in 3 blocks at a depth of 2.0–2.5 m from the surface and the loose rocks were removed from the slopes using a combination of manual and mechanical techniques, including the use of lifting jacks and jackhammers, as well as explosives. In another block where GPR measurements were taken, a main fracture was detected from the surface to a depth of 2 m, but the continuity of the fracture to a deeper depth was not observed. Thus, this block was reinforced together by wrapping them with steel nets. Ground penetrating radar measurements could not be taken from the other six blocks because they did not have smooth surfaces. The stability of these blocks, which are smaller than the others, was assessed using observational data collected in situ by industrial climbers. In addition, the monastery was opened to visitors after the other small blocks on the slope that were at risk of falling were dropped. It has been demonstrated that fracture-crack systems of rocks on steep and weathered rock slopes, which are difficult to apply in rock engineering studies, can be successfully visualized using GPR measurement.