Geotechnical assessment of the rock massif in the area of the medieval cultural monument Asen’s Fortress, Bulgaria

The medieval fortress Asenova Krepost (Asen’s Fortress) is built on a rocky massif of metamorphic rocks in south-central Bulgaria. The rock hill, on which the fortress was built, stands about 100 m above the Chepelarska River and the road Asenovgrad–Bachkovo Monastery, which passes at the foot of the slope. The slopes of the hill are steep and overhanging the road, making them completely inaccessible. A characteriza tion of this area was made in order to assess the state of the rock massif in the area of the Asen’s Fortress. Rock samples (marbles and gneisses) were collected and examined. Laboratory tests and field studies were carried out to determine physical and strength parameters of the studied rocks. An assessment of the cracking of the rock massif was made. The results show that the cracking of the marbles and the direction and inclina tion of the schistosity in the gneisses are of essential importance for the stability of the massif.