All 10 tunnels on this part of the railway are between Marko Nikolov and Dolene. In April 1928 as a result of the Chirpan earthquake (M6.8), a huge amount of rocks collapses over the track at km 11.7. A new tunnel Nr 2 is constructed to avoid the small radius curves of the temporary track around the collapse. The abandoned old tunnel is still existing next to the new one. It is visible from the road, but not from the train. The open track between tunnels Nr 3, 4, 5, 6, 7, 8 is now covered to prevent another rock collapses on the route.