Slide does not allow the explicit modeling of joint planes. You can model joints as a thin material layer in Slide, but if you have many joints, this becomes impractical. If your rock is highly jointed, you may consider using the Generalized Hoek-Brown rock mass failure criterion, and modeling the jointed area as a material region.
RS2, our finite element analysis program for excavations and slopes, allows you to model joints and joint networks explicitly. Note that the Generalized Hoek-Brown criterion can also be used in RS2 to model jointed rock as a material region.
Swedge and RocPlane are used for modeling the stability of rock wedges in jointed rock slopes.