Short-term stability in cohesive soils is defined by their undrained shear strength. However, after some time the stability decreases and experience shows that on the long run only those slopes are stable where the inclination is smaller than the soil's angle of internal friction. The short-term stability is due to the pore pressure change (“suction”) that emerges on soil removal. This negative excess pore pressure degrades over time due to a consolidation process, which results in a behaviour similar to granular soil. Numerical experiments were made to study the problem via the change of cohesion over time.