Numerical Simulation Method Of The Evolution Of Caving Zone During Underground Mining

Top coal caving mining technology is widely utilized for thick seam mining. However, overburden rock can be severely damaged when using ACM(All Caving Method) to manage the coal mining roof since ACM’s mining influence is dramatic. Roof collapse above the goaf during mining causes that the air in goaf is sharply compressed. A high speed airflow then generated in goaf and tunnel, the staff and device in which would be under threat. Therefore, the prediction for caving position is necessary when mining with top coal caving.This paper propose an approach to simulate the dynamic development of caving zone based on finite difference software FLAC3 D. Our approach suppose that the caving begins if tensile strain reach a threshold and the caving ends while caving zone reach theoretically computed height. Comparing with previous prediction method on ground surface settlement, the simulations with this approach indicate that: 1) the simulations are effective since the deviation of computed caving zone and fractured zone is acceptable comparing with theoretical result. 2) This approach is more practicable on predicting ground surface settlement than previous prediction method which obtains the connection between maximum ground settlement and mechanics parameters by adding interface unit in the separatrix of rock-face roof and coal layer.Using the proposed simulation approach, we predict the caving evolution, fractured zone distribution and ground settlement of Anjialing Mine No. 1, working surface No. 4107. The prediction shows that 1) The caving phenomenon firstly appears when working surface move 60 meters forward, while it ends until move 100 meters further when the goaf is filled up by caving rocks. After that, caving appears if working surface move 40 to 60 meters forward, until 20 to40 meters further moved that the caving ends. 2) The fractured zone height is between 70 and 100 meters, which slightly deviate from theoretical height. 3) There shows up a bowl-shaped collapse basin which is parallel to the mining boundary. The maximum settlement and settlement ratio are 10.5 meters and 0.875, which is very close to the actual monitoring values. Through comparison and analysis we conclude that the proposed simulation approach on caving zone evolution is effective since the simulation correspond with the theoretical result and actual monitoring values.