Abstract: The rock collapse from cliff generally follows the regularity of chain.The rock cavity formed due to different weathering is the starter of rock collapse.The perilous rock on cliff is mostly group of rocks and therefore, the interaction between them must be considered.The turning angle of rock block is used to measure the interaction between rock blocks.That is, we first calculate the turning angles of perilous rock blocks without considering their interaction and then calculate the real turning angles with consideration of their interaction by law of energy conservation.Based on this, a formula of equivalent bending moment by angle for each perilous rock is established.A formula for the collapse time of each perilous rock is also obtained based on the fracture mechanics and damage mechanics, verifying the law of chain perilous rock and providing a theoretical basis for the study of the formation of rock cliff and nearby landscape.

Key words: Rock mechanics, Perilous rock, Collapse mechanism, Damage mechanics, Fracture mechanics