Design of pillars size in under ground mines by ground reaction curve method

Mining methods are mainly depending on physical and geometrical structure of ore bodies.Room & pillar mining is very important in underground mining methods. Because of it issimplicity, high production and low cost of operations. Room & pillar method includes someintersecting tunnels in ore body, for stability of these tunnels, some parts of ore body must remain in the form of columns or so called pillar. Designing of the pillars is very important for increasing of the performance and decreasing of ore loss. Hence many empirical formulae are presented for designing of the pillars, but based on limited data. In fact, the particular restriction of each formula limits its application in various conditions and ore bodies. In this paper a new method is suggested for determination of optimum pillars design in various conditions by numerical modeling and ground reaction curve. By this method all of rock mass geomechanical and geometrical characteristics can be considered for designing of the pillars. This new method is based on ground reaction curve by making 18 models in 30, 40 and 50 meters depth with different width to height ratio (W/h) of the pillar. Each of the resulted curves in linear part which states the elastic behavior of rock mass determines the desirable width to height ratio (W/h). An Underground salt rock mine (Soltan abad’s mine) was selected for validating of the suggested method. The W/h for stable pillars in the mine is between 1.3 and 1.6. The result obtained of ground reaction curves is 1.375 for W/h which showing the accuracy of suggested method.