On the basis of the YAI(yield approach index) concept and its phase complementary parameter ω called danger coefficient

which were proposed in the previous paper by the authors

the new concept

FAI

is introduced. It is the sum of danger coefficient ω and FD(failure degree) which describes the damage degree of rockmass in the plastic zone. Two cases are presented to analyze the validity and utility of FAI. The results proved that this parameter can line out the position and extent of failure zones

damage zones and disturbed zones

and characterize the stability rules of rockmass. In the stability assessment of slope engineering

the sliding surface denoted by this parameter perfectly agrees with that measured in situ. So

FAI is of very importance in the stability assessment

the election of excavating and supporting schemes.