A parametric analysis comparing the influence of different factors on predicted induced principal stress around the cavity roof was performed. A finite difference method (Flac2D) was applied to study a cavity under internal pressure. The influence of internal pressure, cavity geometry (size and shape), horizontal stress, depth of was studied. The maximum normal stress criterion also known as Coulomb’s criterion is based on the Maximum normal stress theory. According to this theory failure occurs when the maximum principal stress reaches the ultimate strength of the material for simple tension. Based on this theory, the largest principal stress will initiate cracks in the rock and lead to the failure of rock mass. The results show the high impact of internal pressure, cavity geometry (size and shape), and horizontal stress, depth of cover. A suggested algorithm is presented for applying two dimensional finite difference method in order to predict the maximum cavity size that can be obtained without stability concerns.


The economic extraction of thin-seam coal deposits with thicknesses of less than 1 meter are often problematic due to several significant limitations associated with conventional mining methods, operating practices, and equipment. Mines with low-seam heights are endemic of operations that possess low labor productivities, high operating costs, and relatively small production capacities. Furthermore, the ability to implement new equipment and automation in order to efficiently exploit these thin-seams is hampered by the limited cash-flow positions of most of these operations and the inability to amortize their high costs over a sufficiently large resource base. Consequently, these mines are usually small, labor intensive, and rely extensively on used and rebuilt equipment modified to operate in these challenging work environments.

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