Stability analysis of raise bored shaft in Balya Mine, Turkey

Raise boring machines are used for excavation of shafts and other vertical structures in mining and civil engineering fields for material and human transportation and ventilation purposes. In the classical raise bore method, machine from the top of the shaft begin to drill a pilot hole down to the required depth. Then, the pilot drill bits are removed and replaced with a large diameter reaming head. However, ground conditions need to be favorable to allow the use of raise bore method. The circular smooth walls characteristic of bored raises tend, in many cases, to make them self-supporting. Although, during reaming operation over-break could be occurred and lead to instability of shaft. In addition, there may be some concern about wedge type block failures from the excavation walls. Due to these concerns the stability of raise bored shaft should be analyzed to minimize the risk of using this method. This study aim to investigate the stability of raise bored shaft which recently was finished in Balya PB-ZN underground mine. The ventilation shaft was excavated between the 1200 and 1000 m levels. The depth and diameter of the shaft are 200 m and 2.44 m, respectively. In addition, in this paper, the simple numerical modeling will be presented due to analyze the stability of excavated shaft.