Numerical investigation on gate-entry stability of trial panel in indonesia longwall coal mine

Indonesia is known for its abundant coal reserve. However, weak geological condition is one of the most common challenges in Indonesian coal mine. The study area of this research is PT Gerbang Daya Mandiri (GDM) mine which is situated in East Kalimantan. Stratigraphy of this area comprises of claystone as dominant rock and multiple coal seams with the thickness ranging from 0.15 m to 9.8 m. In this mine, the longwall mining method attempts to be applied for coal seam extraction. Recently, GDM begun their development of trial panel for depth around 100 m to 150 m to understand the behavior of the rock for the real longwall operation. Based on rock mechanical analysis of core sample from drill holes, the competence of claystone is increasing according to the depth. This analysis also shows that for the depth up to 100 m, claystone is generally weaker than coal. Thus, by leaving part of coal seam on top and bottom of the excavated entry-gate would help to retain its stability. For 150 m depth on the other hand, the competence of claystone is increased to somewhat similar to those of coal. This paper uses numerical simulation by FLAC3D to investigate the optimum remain coal thickness (RCT) for stability of the entry-gate of trial panel for 100 m depth. This work also seeks to identify appropriate roof support for both 100 m and 150 m depths. The outcome results show that the optimum RCT is 1 m on roof and on the floor for 100 m depth. SS540 with 1 m spacing is appropriated for adopting for this trial panel except the case of high stress ratio, which required stronger support capacity by narrowing the support spacing or incorporating rock bolt.