Evaluation on the instability of stope mining influenced by the risks of slope surface and previous mined-out activities

Open stope mining is the most common mining method adopted in underground metal mines in Myanmar. However, the assessments on the stability of stope still remain quite limited for this method. Even though mining objective is to recover ore as much as possible from the vein, safety of workers and machinery in the advancing stopes must be ensured. The main reasons for the occurrence of underground mine’s instability come from the stress redistribution of previous mined-out activities, the existence of discontinuities and void space, and the influence of on-going mining activities, etc. In addition to these problems, if the underground mining is conducted near the slope surface, the influence of slope surface should be taken into account to that mining activities. Therefore, considering the importance of rock stability, the investigations on the strength of rock mass near the slope surface are carried out and stability of advancing stope with previous mined-out activities are conducted at Modi Taung gold mine, one of the largest underground gold mines in Myanmar. From the preliminary outcome of this research, the rock mass near the slope surface can be more subjected by differential stress than inside of the rock mass. This result indicates that the condition of rock mass near slope surface is more unstable than that of the places far from slope surface. Moreover, the results highlight that the potential buckling failures from hanging wall and foot wall are more severe than the roof falls from the stope in this mine site.