Adaptive Prediction For Pit Slope Failure Due To Transformation From Open-pit To Underground Mining Based On FDM

High and steep slope will be formed on the ground surface when steep iron ore bodies are mined continuously. The stability, economic and the environment of the project should be considered. Thus it is needed to change the mining method by mining from open-pit to underground. The conventional practice of underground mining is pillarless sublevel caving. In this method, ore bodies are mined by layers starting from the bottom of the pit, and the order of mining is from the top to the bottom. With the increase of excavation depth, the free surface of the slope will gradually expand, and slope rock mass will collapse with large non-continuous deformation and displacement. In order to ensure the project proceed safely, it is necessary to predict the stability of the slope. This paper describes the shortcomings of the software FLAC3 D in predicting the slope failure due to the transformation from open pit to underground, then an adaptive remeshing method for predicting slope failure based on Finite Difference Method(FDM) is also proposed. The main work and results are as follows:(1) Analyses on the slope failures when ore bodies are excavated from the open pit to underground. Based on the characteristics of mining from open pit to underground, the deformation and destruction mode of slopes are analyzed, and then the shortage of the software FLAC3 D in predicting the stability of slopes caused by mining from open pit to underground is presented.(2) An adaptive remeshing method for predicting slope failure by utilizing the software FLAC3 D. When stability of slopes is calculated by using the software of FLAC3 D, an illegal geometry error may occur if the deformation of models is too large, and then the numerical calculation does not converge. The maximum shear strain increment zone becomes run-through which indicating the slope failure. Algorithms and codes are designed to search, obtain the elements with illegal geometry in the model. The elements with illegal geometry are optimized to meet the requirements of numerical calculation by remeshing. Physical field variables are transformed from the old mesh into the new mesh by utilizing of shape functions to guarantee the continuity of numerical calculations.(3) The application of this adaptive remeshing method for slope failure forecast. According to the geological exploration data of Yanqianshan iron mine in Anshan, the 3D geological model is built by taking use of the software ANSYS. The model is imported into the software FLAC3 D to analyse the stability of the slope. When calculations are not convergent, the adaptive remeshing method for slope failure forecast is adopted to realize the simulation of the slope landslide. This method represents the process from stability to instability of slopes. This method has reference value for the project which has the possibility of multiple landslides.