One of the major issues in room and pillar mining is to design of optimum pillar dimensions. The aim of this research is to design the optimum pillar dimensions for layer C1 in Parvadeh coal mine, resulting in significant improvement on pillar recovery and productivity for the mine. There are several methods for pillar design including numerical and empirical methods. With this regard, FLAC software was utilized for numerical analysis and Bieniawski's method was chosen from among the empirical methods due to its generality and reliability. Using Bieniawski's method, the pillar length, width and extraction ratio were found to be 35 ft, 25 ft and 63%, respectively. After verifying these results using FLAC software, the optimum pillar length, width and extraction ratio were modified and found to be 25 ft, 25 ft and 68.2%, respectively. Consequently, these new pillar dimensions can successfully be considered for future mining operation instead of the previous design.
Room and pillar mining method is one of the underground mining methods that is commonly used for the extraction of coal seams. In this method, coal extracted from rectangular shaped rooms with leaving part of the coal that are used for supporting the hanging wall of the deposit. Generally, in the room and pillar mining method, pillars are left for many purposes such as stability, control, safety and support. Excessive leaving of coal, as a pillar, may overshadow the mine planning from economical point of view, on the other hands, low leaving of it can lead to supporting problems, hence, design of precise pillar dimensions is significant in two aspects; firstly, it keeps the stop safe and stable and to maximizing the extraction ratio, its dimensions must be minimum. Therefore, applying the room and pillar method is reasonable, if the pillar dimensions would be optimum. Nowadays, numerical methods are widely used in mining engineering while some researchers believe that numerical methods, solely, cannot be suitable for engineering assessment, although the combination of empirical and numerical methods can be led to more precise analysis. The main purpose of this study is to design the optimum pillar dimensions. Basically; there are three major parameters to design the pillars including safety factor, pillar strength and in situ stresses. As a part of study, Tributary Area Theory was utilized to determine the stresses acting on the pillars and in order to evaluate the pillars strength, bieniawesky's method was employed due to its simplicity and popularity.
Tabas coal mine, the largest and unique fully mechanized coal mine in Iran, located in central part of Iran near the city of Tabas in Yazd province and situated 75 km far from southern Tabas. The mine area is a part of Tabas-Kerman coal field. The coal field is divided into 3 parts in which Parvadeh region with the extent of 1200 Km2 and 1.1 billion tones of estimated coal reserve is the biggest and main part to continue excavation and fulfillment for future years.
