Many parameters are used to calculate the stability of slopes in an open pit mine. An important parameter is Factor D, which is used to represent the disturbance zone of a slope as a result of the stress relaxation and blasting resulting from the excavation. This parameter can be a decisive variable in the calculation of stability. Currently, there is no consensus on how to incorporate the disturbance zone into a slope stability model though different authors have proposed different geometries for this purpose. This work proposes a method to incorporate the disturbance zone to stress relaxation by means of Factor D, proposing a geometry in which the strength properties of the rock mass are seen to be affected, which could determine a stable or unstable condition of slope. A finite element model was created to represent the stress relaxation effect for different qualities of rock mass − good, regular and poor − excavating the open pit in stages to reproduce the natural deformations by reducing the rock mas modulus. Then an iterative process was carried out to obtain the resistance properties, Hoek & Brown envelope and geometry of the disturbance zone for different qualities of rock mass evaluated. The results showed a triangular disturbance zone with respect to the surface for good and regular quality rock masses; however, for poor rock mass quality the disturbance zone was observed to be rectangular. The behavior of the strength properties and the Hoek & Brown envelope variable in the disturbance zone were also obtained for each quality of rock mass evaluated. In the disturbance zone, it is observed that the plastic deformations of the rock mass decrease with respect to the surface, presenting the greatest plastic deformations in the first meters of the surface, together with the lowest cohesion values, which leads to considerable disturbance in the rock mass, favoring unstable conditions. The most considerable disturbance zone varies from close to 25% to 15% and 3% of the overall height of the slope, for rock mass of poor, regular and good geomechanical quality, respectively.