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The increasing demand for tin-tungsten (W-Sn) due to its versatile applications in various industries and its attractive high market price has created a motivation for mining companies to extract deep-seated tin-tungsten deposits in Myanmar at a fast pace to meet the world demands. At Hermyingyi (W-Sn) Deposit Mine, the feasibility of exploiting ore in multiple inclined veins simultaneously is being explored as a pilot project aimed at increasing W-Sn production. Thus, this study is aimed at the development of optimal design and guidelines for excavating multiple veins with stability certitude in weak rock mass based on the evaluations undertaken. The analyses were carried out using FLAC3Dver. 5.0 and Phase2 V 7.0 software. The results demonstrate that excavation of large stope dimensions with ≥ 5 m width in parallel multiple veins simultaneously is not recommendable as the stopes experience high potential stope failure, thus the development of stopes with width dimensions of ≤ 3 m in all the parallel multiple veins simultaneously in weak rock mass conditions is ideal. In terms of space intervals between parallel inclined veins, it is recommendable to undertake multiple vein excavations for gentle inclined veins in weak rock mass conditions only if the interval of the veins is emplaced at ≥ 14 and 10 m for steep dipping inclined veins with good rock mass conditions. The study also shows that the cut and fill method is a more favorable mining method for multiple veins excavation than the open stoping method.

This paper attempts to predict the surface subsidence induced by multi-seam longwall mining in the PT Gerbang Daya Mandiri (GDM) underground coal mine in Indonesia. Several numerical models of multi-seam longwall mining under various depths were built in the finite difference code software “FLAC3D” which was used as a tool for numerical simulations. Effect of mining sequence and influence of lower seam mining were firstly investigated. The angle of draw (AoD) and maximum surface subsidence (Smax) were used to describe characteristics of the surface subsidence. Based on simulated results, it is indicated that the undermining provides a better mining sequence in multi-seam longwall mining compared to the overmining. Mining the coal seam in an undermining order will not cause any difficult mining conditions in a lower seam, whereas some ground control problems in an upper seam are expected when the coal seam is mined in an overmining order. Under all mining depths in the undermining, extracting the lower seam panels significantly influences the magnitude of surface subsidence. The AoD and Smax increase significantly after all panels in the lower seam is mined. This indicates that very large surface subsidence is expected when multi-seam mining is applied at GDM underground coal mine. An application of some countermeasures such as adopting a large pillar width and a small panel width is suggested in this underground coal mine in order to minimize the surface subsidence caused by multi-seam longwall mining. Minimizing the surface subsidence by adopting a large pillar width and a small panel width is therefore numerically investigated in this paper. Based on simulated results, it is found that the AoD and Smax decrease significantly when larger pillar width and narrower panel width are adopted. The use of larger pillar width and narrower panel width result in smaller AoD and Smax.