ABSTRACT: 670 pillar is a geological barrier that will trap the rock block falling and rolling from the deformation zone of the Eynez fault as well as to prevent the materials belonging to the landslides to be formed along the fault zone from reaching the coal production area It forms the foot wall of Soma-Eynez  and consists of Neogene aged marls The toppling failures observed in the 670-pillar´s slopes threatened the safety of excavation works for coal production in the open pit t. The maximum runout distances of  rock fragments that had toppled, fallen and rolled at different slope heights as a result of the mentioned mass movements were determined using computer softwares. Theproject excavation limit for  the open pit coal mine was determined by considering the runout distances calculated for different slope heights n this work, toppling failures observed in  the 670-pillar´s slopes were investigated both kinematically and numerically, using stereographic projection and different computer softwares, respectively. Safety factors obtained from different softwares for  the same slope geometries were compared and the effect of frictionangle (ɸ) and cohesion (c) values of the joint surfaces on safety factor that cause toppling failures were investigated. In addition, the time-dependent changes of joint aperture increase rate obtained from 20-deformation measurement points installed on the cracks causing toppling failures were investigated. The areas where the joint aperture increaserate is highest and the areas where the toppling failure is observed in  the pillar´s slope were associated.