According to the increase of environmental concern and legal regulation, most open-pit mines in Korea consider to change their excavation method to underground method. A silicate mine in Kyung-gi province plans to establish the vertical shaft which will be used for ore-pass channel in their new glory hole mining method. The dimension of this vertical shaft will be 3 meter in diameter and 200 meters in length and the amount of ore blocks through the ore-pass will be 140kg/sec. A dropped ore blocks to the bottom of ore-pass shaft will be crushed in underground concentration plant. In this system, the design of proper discharge amount from ore-pass shaft, the gate for controlling the discharge of ore blocks, and the dog-leg for minimizing shocks at the gate will be essential. The PFC-2D which is one of the discrete element numerical methods has been applied to simulate this phenomenon. From the results of numerical analysis, the optimum system to minimize the shock of the dropped ore blocks has been proposed.
PFC-2D (Particle Flow Code 2-Dimension) analysis has been made for identifying the flow mechanism of ore blocks as well as their shock energy to the ore-pass shaft. Considering the capacity of ore block production through the conveyor belt, the discharge rate from the gate, the optimum stacking height, the installation of dogleg have been studied for minimizing the shock of ore block drop. Also the wall element simulated by a straight line and the ball element simulated by a circular ball were arranged for the whole model. Fig. 1 shows the example of the PFC simulation model to analyze the flow phenomena of the real ore block in the ore-pass channel. In this simulation, a single ore block has been considered to simulate the free fall of ore blocks. Its size has been considered to be random in the range of 150~250mm in diameter, which has been proposed to be a real ore block size by the mining company. Fig. 2 shows the example of PFC model. Also the diameter of ore-pass channel is 3m and its height is 180m. The arrow in this figure denotes the velocity of free fall of ore block 250mm diameter in every second.
Flow mechanism of ore blocks according to the discharge rate The damaged zone in ore-pass channel and the shock amount in the bottom of the gangway with a free fall of ore block have been analyzed according to the constant discharge rate of ore blocks. The discharge rate has been selected to be 140 kg/sec on the basis of working capacity of crusher, which is 500 ton/hrs. As shown in Fig.2, each ore block has been discharge in constant time interval, but the distance between each group has been shown to be increased. This can be explained with acceleration of gravity acting on each ore block. Fig. 3 shows an example of discharge pattern of an ore block group at the top of the ore-pass.
