Stability of Underground Coal Mine Roadway Excavated in Soft Rock Mass

This paper studies the stability and ground behavior of the main roadway excavated in a soft rock mass at PT Gerbang Daya Mandiri (GDM) underground coal mine in Indonesia. The stability and ground behavior of the main roadway under various geological and excavation conditions was analyzed and discussed through numerical simulations and field measurement data. Based on the results, it is found that the mechanical conditions of claystone and the geological conditions of the roof have an obvious impact on the stability of the main roadway. The large roof displacement of the roadway occurs when the roadway is excavated in the deteriorated claystone, whereas the small roof displacement occurs when the roadway excavation is made in the undeteriorated claystone and when the coal layer is present in the roof. Under undeteriorated conditions of claystone, the small failure zone and displacement of the roadway occur. The current support system using the steel arch SS400 is effective to control the roadway stability. As the claystone has deteriorated due to groundwater, the failure zone and displacement expand considerably, and the roadway stability decreases significantly. The use of the current support system (steel arch SS400) is difficult to control the stability of the main roadway. Under this situation, a stronger steel arch SS540 is recommended to apply. Furthermore, the presence of a coal layer during the excavation considerably improves the stability of the main roadway. Compared with the roadway excavated in claystone only, the displacement decreases significantly. In addition, by leaving a thicker coal layer in the roof, a better stability condition of the roadway can be achieved.