Rock Engineering

[PY2-78] Evaluation of Water Vapour Diffusion in Mchenga Sandstone

○Umali Muhammad YASIDU¹, Yoshiaki FUJII¹, Jun-ichi KODAMA¹, Daisuke FUKUDA¹, Johnson DANDADZI² (1. Hokkaido University, 2. Mchenga Coal Mine)

Keywords:Coal Mines in Malawi, Roof falls, Vapour diffusion, Tensile strength

There are seven coalfields spread across Malawi, with four coalfields of bituminous coal located in the Northern Region where underground mining is done. One of the major challenges facing these coal mines is occurrence of hanging roof falls after the rainy season. It was clarified that the humidity was highest in April and May underground and that tensile strength of roof rocks decreased with environment humidity. To evaluate the extent of weakened zone around the roadways with time, water vapour diffusion in coal bearing rocks; arkose sandstone and fine-grained sandstone from Mchenga and Kaziwiziwi underground coal mines in the Livingstonia coalfield; was studied aiming to clarify the influencing factor of roof falls and to propose countermeasures against the roof falls. Rock samples from the mine were oven dried at 80°C for seven days, jacketed using heat shrinkable tubing and oven dried again for three days. The specimens were then treated in high humidity achieved by pure water in isothermal condition (22°C) in accordance with ASTM E96/E96M-16 water method. For comparison, Japanese Neogene tuffaceous Kimachi sandstone was also tested following the same procedure. The results of diffusion coefficient evaluations and numerical simulation will be shown.