We don't have a particular tutorial that discusses disturbed zones, but in general the idea is to define a zone around your excavation with a disturbed state.
You add the disturbed zone in the stage in which the material is excavated, turn on the Stage Properties option, and turn off the checkbox for resetting the stresses. You can reset the yield flag as well. This is like putting in a brand new material but with a lower strength. The material will start off with the stress state from the stronger original material. See the image below.
You do not apply the disturbance factor to the entire rock mass. The disturbance factor, D, should only apply to a limited zone of damaged rock around an excavation or behind a slope face.
For guidance of choosing an appropriate D factor, see Chapter 11: Rock Mass Properties from Hoek's Practical Rock Engineering.
Define Material Properties dialog