Abstract:The cantilever beam type is a common form of the upside-down dangerous rock-mass,and it is easily to collapse under earthquake action.Thus,the study on the evaluation method of earthquake-induced bending collapse of the upside-down dangerous rock-mass have great significance on evaluating its security degree.On basis of the calculation theory of the cantilever beam,firstly,the calculating formula for the maximum tensile stress of the cantilever beam type dangerous rock-mass with arbitrary shape under the action of seismic loading and its own gravity has been proposed,and the time-history curve of the maximum tensile stress has been established.At the same time,the tensile failure criterion is considered as the criterion of crack propagation,combined with the relationship between the elastic strain energy and fracture propagation energy,and an approach for calculating the depth of crack has been established to study the crack depth along with the earthquake time.Secondly,according to the shapes of dangerous rocks in real engineering,they are simplified into two special forms:rectangular parallelepiped and cylinder,and has proposed a calculation formula for the critical depth of crack to define the safety factor of dangerous rock under the action of earthquake.At last,a dangerous rock-mass located at the entrance of a tunnel is taken as an example to illustrate the application of the proposed method in this paper.The results show that,under the action of 8.0 magnitude earthquake,the total depth of crack induced by earthquake of this dangerous rock-mass at 14 s is 0.1759 m,which is greater than the critical depth of crack (0.167 m),implying that this dangerous rock-mass would collapse at 14 s.