In mining of an ore body, the study of effective parameters and selection of the best condition could be affected in reduction of mining costs. The long wall mining method is one of the most common methods in coal mines. Tabas coal mine is located in 75 km from Tabas twon. The Parvadeh mine is part of Tabas coal mine that its thickness of mining seam (C1) is about 2m and its extraction method is by backward longwall mining. Main gates of mine is supported by rock bolts and IPB160 steel sets. The aim of this research is to determine suitable width of ribs, convergence of tail gates and optimum length of panel in l. in order to obtain this object the required ribs width with variation of seams depth and workface length was investigated by using the software FLAC3D. For this approach, considering the gof distance, workface length, depth and position of the bedding layer the convergence of the main gate was modeled and analyzed. The amount of damage distance as for the layer bedding and depth was be modeled and analyzed. And the optimal length of workface as for gof distance, seam depth and bedding was investigated by using the software FLAC3D. The results show that the width of ribs increases due to increasing the workface length, But for lengths up to 220 m rib width did not change. Considering this fact that near the workface the pressure is high, Convergence of the main gate was increased, And far from the workface, the convergence was decreased. At a distance of 70-80 meters from the workface it reached to the initial value. Main gate converge is high and increases by increasing gof distance, bedding, layer depth and length of workface. But for lengths up to 220 m stress induced in ribs is almost constant. Convergence of the main gate remains unchanged. One of the important parameters in longwall mining method is gof distance that decreases by increasing of depth and increases due to increasing of bedding and strength properties. By changing the properties of roof coal, the optimum workface length was changed. and the optimum workface length was decreased by increasing of bedding and layer depth .
