| Rockmass movement due to mining steep metallic orebody in high stress area is a considerable question in the mining subsidence issue induced by underground mining. As of now the home and abroad research to this theory is only at an early stage, and there isn’t mature theory or practical prediction method, which made a great impact on safety production.In this paper, the study object—Shizishan copper mine, which is typical caving mining steep metal deposit in high stress area, characterized by high geostress, complex geological conditions, cracked rockmass, developed faults, and prominent engineering stability problems. In this study, the regularity of rockmass movement, deformation and failure mechanism, and its forecast were studied based on the data acquisition, engineering geology survey, detailed rockmass movement monitoring, theoretical analysis, numerical simulation and nonlinear prediction.(1)The distribution law of geostress field in this mining area was analyzed through in site three-dimensional geostress measurement. Results show that the in-situ stress in Shizishan copper mine is dominated by horizontal tectonic stress field rather than the gravity stress field. The maximum horizontal principal stress is oriented in NNW-SSE direction. The numerical inversion method of high horizontal tectonic stress was analyzed by using FLAC3D and 3DEC, which shows that the initial ground stress field inversion method based on the initial strain energy theory, the simulation results accords with actual best, should be preferred method to simulate high tectonic stress field. The initial ground stress field inversion method based on the initial strain energy theory is that all unit body setting initial value using trapezoidal stress distribution in computational domain, which set the initial state of elastic strain energy, to make the meet or fitting the measured values of stress changing with depth. Then this method is used to back analyze the high geostress field of Shizishan mining area, the inversion results were in good agreement with the actual, which provided theory basis to calculate analysis in mining induced strata movement under high geostress condition.(2)Analyzed the barrier effect and mechanism of fault plane and fault zone on rockmass movement, this paper expounded the sliding rule of mining induced fault activation, and analyzed the influence factors of fault activation and fault barrier effects. Results show that with the decrease distance between goaf to fault, the increase buried depth of fault upper boundary, the increase size of mining area, the easier that fault activation, the more intensity of the barrier action to the spread of the displacement field and stress field. When the fault intersects with goaf, the greater dip angle of fault is, the easier fault activation is, the greater displacement difference on both sides of the fault. With the increase thickness of fault zone, the barrier effect enhanced accordingly. On the basis, studied on the fault activation regularity and mechanism induced by deep continuous mining. The nature of fault activation is that the additional tensile stress appeared in fault planes due to excavation unloading. First proposed the activation of echelon and steep angle faults caused by mining of this mining area have a domino effect.(3)The comprehensive monitoring of rockmass in fault activation slip and surface movement and deformation were carried out. In view of actual situation of fault activation, fault activation slip monitoring system is designed, based on the monitoring achievement analyzed the activation sliding rule of fault F2, F3 and F4. Results show that fault F2 and F3 are in a state of stable sliding, and fault F4 has not been activated, which proves the domino effect of fault activation. The ground surface movement and deformation law of this mining area were studied through GPS monitoring. The study found that surface movement deformation are developing to the hanging side at present, and the rate of surface subsidence and horizontal movement of each measuring points are increasing dramatically, the surface subsidence is in an active development stage.(4) Analyzed the effect of gravity stress field and tectonic stress field on the rockmass movement law caused by caving mining steeply inclined orebody. The influence of orebody dip angle and thickness on rockmass movement law was studied under different stress conditions. On this basis, studied on surface subsidence and stratum inbreak regularity of this mining area induced by deep continuous caving mining, and proposed six stages for this type mining, such as: ① The initial mining stage; ②The overlying rock initial inbreak stage; ③The overlying rock inbreak largely stage; ④Surface collapse stage; ⑤The collapse pit develops slowly down in deep continuous mining; ⑥Surface subsidence decays after end of the mining. According to the actual mining situation, the rockmass movement monitoring results and the characteristics of the surface movement, it can be drawed that the ground surface movement is in the third stage. It will gradually turn to the surface collapse stage in the deep 17th and 18th level.(5)Analyzed the causes and harmfulness of surface movement disasters, the surface movement disasters were evaluated through surface deformation monitoring results and the ground fissures development evolution. According to the field measured data of fault slip, established grey system forecasting model based on GM (1,1) model, which has higher accuracy for prediction of fault slip. In the state of stable sliding, it can be used in fault slip prediction for good results. By using neural network established knowledge repository model of strata movement angle of metal ore caving mining, by predicting the displacement angle of the docimastic mine, which indicates that the neural network knowledge repository model has higher precision. And using this model to predict the displacement angle of Shizishan copper mine and rockmass movement range, which provides the basis for mine production and design. |
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