Cracking Mechanism Along the North Batter of Maddingley Brown Coal Open Pit Mine, Victoria, Australia

Cracks manifested on the north batter at Maddingley Brown Coal Open Pit Mine, Victoria, Australia in November 2013. The crack opened varies from trace to approximately 150 mm wide was located at about 20 m back from the coal face and extended for approximately 50 m on the eastern side and terminated 10 m away from the access road. Site investigations and remedy measures were implemented immediately after the cracking. This study involves in a three dimensional modeling on the cracking mechanism using finite element method (FEM) encoded in Plaxis 3D software program. From the study, it was found that the initial model based on north batter being stable for many decades tended to lead a circular critical path while the model after overburden removal showed a trend of block sliding. The safety factor of initial north batter was 1.38 through safety analysis while it was decreased to 1.17 for the coal batter after overburden removal. But the simulated shear and tensile strains indicated that the coal batter after overburden removal in fact experienced block failure. Furthermore, the simulated location of cracking was in good agreement with the actual location, and the simulated heave of the coal seam was in good agreement with the experience in Victoria brown coal open pit mining The observed vertical crack would be a combined action of the overburden removal and the groundwater flow in the unconfined aquifer.