Moisture adsorption in the coal seams affects the gas adsorption capacity and can alter the coal deformation and permeability criteria of the coal seam. The effect of dynamic loss of moisture content, both on moisture and gas sorption-induced coal swelling/shrinkage strains, during the coalbed methane (CBM) production, is crucial. This study investigates the interactions among coal matrix, absorbed gas, and moisture content, based on the coal swelling/shrinkage strains and gas adsorption decay criteria. Consequently, a mathematical model of the coal deformation is developed for the proper evaluation of the moisture effect. For developing the model, this paper considers the standard gas flow and moisture loss equations to assess the volumetric content, equilibrium pressure, and density of the moisture. Finally, it comprehensively analyzes the sensitive factors and effects of elemental parameters of moisture content on coal deformation and coal permeability. The results show that moisture content at adsorbed state significantly changes the coal swelling/shrinkage strain and that distorted swelling and shrinkage characteristics can promote the permeability alternation in wet coal reservoirs. Moreover, the intermolecular attraction between the coal structure and the moisture content has a significant effect on methane adsorption/desorptioninduced deformation in coal structure. This study also designs the coal deformation strains as a function of moisture content by the Langmuir type model and evaluates the hysteresis rate between the swelling and shrinkage characteristics. The findings of this paper can characterize a wet coal reserve for CBM production and anticipate future production under different operating conditions.

The study represents an analysis for the selection of backfill materials and backfill process for Barapukuria coal mine which is the only mining industry in the country under production state. Recently, this industry faced massive people protest due to mine-induced subsidence around the mining area. The backfill is the most emerging and developing technology in recent times in mining sectors which can be considered as a prospective option for Barapukuria coal mine in the purposes of increasing the ore recovery and mine stability, consequently reducing the subsidence. For the first time to have a backfill assessment in this underground mine, initially this study searched out the available resources to fill the mined out void as are alluvial sands, power plant fly ash, mine tailing, and Portland cement. In the subsequent steps, these samples were characterized for both cemented and uncemented option under particle size, compressive strength, shear strength, proctor test, and permeability analysis. The particle size analysis evaluates the sands and mine tailing as medium to fine grain uniform and well-graded sample, respectively. In the case of cemented backfill, the compressive strength test on different proportion mixtures of sand, cement, and ash shows compressive strength that is increased with time and cement content. The important finding is the significant influence of ash content, used as Portland cement replacement, in long-term strength. The determined permeability of sand sample is 3.60 9 10 -5 m/ s, which is higher than mine tailing valued at 1.11 9 10 -5 m/s. Shear strength of mine tailing with friction angle of 43.19°and cohesion of 5.33 kPa is greater than cohesion less sand sample with friction angle of 37°. Standard proctor test denoted the highest dry density of sand and mine tailing as 1.74 9 10 3 and 2.23 9 10 3 kg/m 3 at 18 and 11 wt% of water content, respectively. After taking into account the findings hydraulic backfill is preferred where the recommended backfill mixture for the mine is sand fill with 5-7 % cement and 8-10 % ash through the consideration of requires volume, materials characterization along with cost consideration.

Through the distinguish software application along with formal calculation method the study represents a volumetric estimation of require backfill Materials of Barapukuria coal mine in north western Bangladesh, the only coal mine of the country under production, which capable of a low recovery with sustaining mining method. The only productive coal seam of the mine, Seam VI is our main focus during the assessment. Different estimation method is applied to investigate the accuracy of calculation and find out the reasons beyond the deflections. Surfer 8.4 exploits two method of interpolation, inverse distance to power, a weighted average interpolator and Kriging, more flexible gridding method, those yields the volume of 169221180.5 cubic meters and 165323770.4 cubic meters respectively. On the contrary Rockworks is estimated the volume through Delaunay Triangulation method as 115,959,398.4 cubic meters whether another estimation which is made by inverse power weighting interpolation on saved stratigraphic model, gives 174,281,203 cubic meters volume, following 185,760,000 cubic meters through geological reserve calculation. After considering the interpolation approach, available data and previous study agreement, the result of inverse distance to power, at both of software's is consider for backfill materials volume estimation. The required volume of backfill materials is 101532708.3 m 3 and for 9% and 10% recovery that's are 9137943.747 m 3 and 10153270.83 m 3 respectively. The daily requirement of backfill is 562-636 m 3 and the system need to have a daily capacity of 702-795 m 3 .

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