A jointed rock slope cut in a road construction is chosen as the project background.Firstly

the numerical model of slope is established by using FLAC3D.The computation results show that the safety factors of slope in five steps of excavation are 2.62

2.39

1.61

1.06 and 0.67

respectively

and the failure mode is of the type of bi-block slide collapse.Secondly

based on the failure mode

theoretical models are established for slope stability analysis.By changing dip angle and mechanical parameters（c and ） of joint planes

the influences of these parameters on the stability of slope are obtained

which show that:（1） the safety factor decreases firstly

then increases with the increase of the dip angle of the joint plane of the bottom slip block;（2） the safety factor increases gradually with the increase of dip angle of the joint plane of the upper slip block;（3） when the values of c1 and c2 are small

their influences on the stability of slope are approximately the same;but when they increase

the effect of c2 is larger than that of c1.