Research On The Mining Effect From Mining Deep-Level Orebody In Jinchuan No.2 Mine

It is well-known that Jinchuan No.2 Mine is one of underground mines with the most difficult geological and mining conditions all over the world as its rockmass is extremely poor and it is subjected to complicated strata pressure. Nowadays, its mining operation has been descending to 850m level, the mining depth is about 1000 meters, and it might be regarded as a deep-level mine. As yet, it has been a controversial key topic whether continuous mining method or room and pillar mining method should be selected to extract NO.l orebody in the mine. Under the deep-level mining, the redistribution of ground pressure in surrounding rock and filling, induced by mining operation, inevitably became more complicated. Based on its mining engineering background and aiming at its concern about the main technical problems to be solved, the response of surrounding rock and filling to mining operation in deep level, and the relevant potential techniques for controlling dangerous response to mining, were studied systematically by means of field surveying, numerical modelling, model test, and theoretical analyse. The main research contents and conclusions in the dissertation are as follows:First of all, using three-dimensional finite difference code (FLAC3D), surface deformation, induced by underground mining operation in the mine, was simulated and studied. The space-time developing process and trend of distribution of subsidence and rise areas in the surface were found. The obtained conclusions were the basic of predicting the surface deformation from underground mining, and the main monitoring areas, reflecting the surface deformation, were circled.On the basis of finding the surface subsidence and rise phenomena, the surface deformation was further studied according to creep theory of rockmass with higher tectonic stress, the mechanism on the developing process of surface deformation, which experienced the evolution from one subsidence area at the beginning of mining to both of one subsidence area and a rise area as the mined-out range was expanded steadily, was pointed out qualitatively. The failure model of rock post in the mined-out range's substructure was put forward. According to the analysis of cause that higher tectonic strata pressure made surface movement's angle flat and made movement's range wide, the inclined failure cause of ventilation shaft, located in NO.14 prospecting section, was explained.The effect of the recovery of temporary horizontal pillar at 1000m level and other sublevel ore remains in deep level on the surface deformation was demonstrated. It was found that the distribution pattern of surface deformation from different mining methods (continuous mining and room-and-pillar mining) was similar; but the magnitude of deformation was different.All of these conclusions above-mentioned could be used as guidance for determining the location of surface facilities and buildings in the mine.Secondly, by means of investigating into the effect of temporary horizontal pillar support on the structure deformation of mined-out range, during its full period from the pillar's formation, thinning and disappearing finally as mining in sublevel downwards, the mechanism, on which temporary pillar support controlled redistribution of the ground pressure and convergence displacement in mined-out structure, was found, and the change in distribution of the pillar's stress and deformation was obtained as the horizontal pillar was thinned and disappeared due mining in sublevel downwards.The results showed that at the beginning of pillar formation, it played important role in controlling the convergence between the hanging wall and footwall surrounding rock of mined-out range, but obvious stress concentration occurred in the conjunction of the pillar and surrounding rock. After recovering the pillar, the convergence deformation of the footwall increased obviously in comparison with the hang wall's deformation, but it could not caused catastrophic ground pressure movement.By means of comparison analysis of change in stress and displacement of the pillar, respectively induced from room-and-pillar mining and continuous mining, it was found that in comparison with those of continuous mining, the integrality and smooth deformation trend of the temporary horizontal pillar were adversely influenced by the existence of panel vertical pillars (ribs) due to room-and-pillar mining, and the recovery of horizontal pillar would be more difficult in the future.Further, based on the stress state of temporary horizontal pillar under simultaneously mining in more than one levels, the cusp catastrophic model for predicting failure of the horizontal pillar was set up, the failure criterion of the pillar was deduced, and the little probability of the pillar failure was concluded as well. The engineering measures to be taken, aiming at safe recovery of the pillar, were given.Thirdly, the comparison investigation on the response of surrounding rock and filling to continuous mining and room-and-pillar mining, respectively, was made. The important conclusion that continuous mining was more suitable to be used to extract the deep-level orebody in the mine was obtained, and it was very helpful for the mine to make productive and technical decisions.Using FLAC3D modelling and theoretical analysis, the effect of different mining methods (continuous mining and room-and-pillar mining) on the stress, displacement and plastic zone in the bottom ore to be mine, on the stress and convergence displacement of hang wall and footwall surrounding rock, and on the stress and deformation state in upper mined-out range's surrounding rock and filling, was systematically investigated.For the panel vertical pillars due to room-and-pillar mining, their stability were studied, and aiming at the second-step mining panel pillars their recovery techniques were discussed. Further, the effect of recovery of panel pillars on development of response of surrounding rock and filling was probed.Fourthly, the distribution of critical sections and points in underhand cut and cemented filling stoping structure (artificial roof) was calculated according to structural mechanics model, the intrinsic factors causing deficiency in bearing capacity of plain filling structure were found, and the technical measures against the deficiency in structure strength and stability were pointed out.The physical model experiments on the effect of the mortar types (high density tailings + cement, classified tailings + paste) and reinforcement or not on the flexural performance of filling structure were carried out. The results showed that the flexural performance of filling structure, made of classified tailings-and-paste mortar, was obviously better than that of high density tailings-and-cement mortar, and the flexural capacity of reinforced filling structure with low reinforcement ratio was enhanced obviously.Fifthly, a new integrated continuous mining model with central panel of sequentially delayed mining was put forward. The new continuous mining model absorbed the technical merits of both continuous mining and room-and-pillar mining in controlling response of surrounding rock and filling to mining operation. The preliminary results of numerical modelling showed that as the new continuous mining model was used to extracting deep-level ore in the mine, it had obviously technical advantages in controlling the adverse response of surrounding rock and filling to mining in deep level, and in preventing catastrophic ground pressure movement from happening. With the new continuous mining model, some new research interests in controlling ground pressure movement from deep-level mining were provided.The key of new continuous mining model mainly was that a central panel was firstly selected as sequentially delayed mining panel, the boundary cut-off mining and sequentially delayed mining were carried out in the central delayed panel as other panels of its two wings were continuously mined downwards, and thus the convergence deformation and stress state of surrounding rock and filling structure were smoothly improved. The results of numerical modelling showed that, in comparison with room-and-pillar mining and continuous mining, the new continuous mining model had comprehensive technical advantages in improvements in smooth trend of convergence deformation and redistribution of stress state of surrounding rock and filling, and in controlling the magnitude of convergence displacement. All of these improvements in the response of surrounding rock and filling to mining were good for the mine to prevent the catastrophic ground pressure movement in deep-level mining engineering.