Study On Stability Of Rock Mass And Rule Of Strata Movement For Transition From Open-Pit To Underground Mining

Most of the deep open-pits mines have been turned to underground mines because of the limited resource conditions. Many domestic open-pits mines are being or will be transferred to underground mines. At present, the study on the mechanical response by the secondary stress field, and the movement rules, the stability of rock masses under composite disturbance are inadequate. Technical research of open-pit to underground mining is lagging behind production requirements. Therefore, it is important to carry out comprehensive and systematic studies to identify reasonable methods for open-pit to underground mining.Open-pit to underground mining of Yongping Copper Mine was selected as the engineering background for in-depth studies in this paper. These studies mainly included from a new perspective on engineering rock mass quality classification, blasting damage control in tunnels, rock movement angle prediction, realm stope roof pillar thickness and structural parameters optimization as well as the combined mining system, stress field, displacement field variation, etc.6 parameters, uniaxial compressive strength (Re), rock acoustic wave velocity (Vp), number of joints volume (Jv), joint roughness coefficient (Jr), joint surface weathering of the coefficient of variation (Ja), permeable coefficient (Wk) were selected as the classification discriminant criterion for rock mass quality by applying Fisher discriminant theory. In-site monitoring data were used to establish FDA (Fisher Discriminant Analysis) analysis model of rock mass quality classification, and this model was applied to the Yongping Copper Mine open-pit for slope rock mass quality classification. It shows that, the FDA discriminant analysis model is comprehensive and reasonable; and it has low false rate for estimation of regressing sentence, high distinguishing precision, good classification performance. The established FDA discriminant analysis model can effectively reduce the influence of human factors; it is an effective rock mass classification method which can be widely applied in practical engineering.Based on the combined interaction theory of stress wave and detonation explosive gas, a good theoretical calculation formula which is comprehensive, and has wide applicability, good blasting effect for smooth blasting parameters was proposed by considering the explosive properties, rock conditions, original rock stress and optical burst layer damage effect. An application example affirms that this method can effectively improve the blast effect, reduce and control the tunnel rock blasting damage, provide a positive, active and effective measure for roadway stability, and can be widely applied in rock engineering.The combined rough set and neural network prediction model was established by analyzing the characteristics and basic principles of rough sets and neural network.According to measured 34 groups of strata movement data, the established prediction model was used to construct a stable and reliable rough set-BP neural network strata movement angle prediction model which was applied in Yongping Copper Mine open pit to underground mining for strata movement angle forecasting. The establishment of rough sets-artificial neural network prediction model provides a new and reliable way for strata movement angle prediction.Based on selected parameters according to rock mass quality classification, a numerical model to reflect the real model was established through MIDAS, SURPAC, and CAD. Yongping Copper Mine,an open pit to underground mines,the realm of the top columns and structural parameters of stopes are studied by using FALC3D. Rock stress field, displacement field, shear strain increment and the plastic zone changes were simulated according to the 12 parameters scheme. It shows that the best top column thickness is 50 meters, and the best stope width is 18 meters. This provides good reference for safe and efficient production.It focused on the optimal parameter scheme for rock mass movement and stability simulation based on 12 parameters scheme analyzing. The numerically simulated strata movement angles were compared with experimental and rough set-neural network calculated ones. It shows that the open-pit to underground mines is a complex dynamic system. The stress field superimposed with each other within a certain range, and it has obvious interaction. It was proposed that the slope rock could be divided into three sections according to the stress distribution. Displacements are all moving mined-out area, and the maximum displacement of top column locates in the middle; maximum displacement of rock slope locates in the bottom as the advancing of surface excavation. The optimal scheme has the advantage of good production safety and high resource recovery rate.The results of this paper can also be well applied to other open-pit to underground mining projects, and it may provide an important reference for other rock engineering.