Study On Stability Of Complex Cavity And Safety In Near-Cavity Excavation

Large amount of Mining cavities in Dabaoshan Mine with big volum and complex shapes have posed serious threaten for the production safety and personnel safety. In order to fulfil production safety for near-cavity excavation, some key problems should be studied: the cavity detecting method, the stability of hanging wall and pillar among cavities, back-filling and strength analyse of fill in cavities, how to realize near-cavity excavation, how to establish the corresponding early warning system. The main contents are as follows.In view of the characteristics of the mining cavities of Dabaoshan Mine, Induced polarization electrical method and laser scan technique were used for large-scale localization at surface and detailed 3D imaging in cavity. More than 1800,000 m~3 minig cavities have been detected, which offer essential data for the stability analyse and back-filling of cavities.Reasonal thichness of cavity roof has been analyzed with structure mechanics law, Lou's method, load transmission line, ratio between height and span, beam and plate method and numical simulation. The comprehensive method was proposed for safety evaluation and thickness determination for cavity roof.Numerical method was used to investigate the dynamic response of pillar among cavity, which suffers high static load and dynamic loading from blasting simultaneously. The results provide references to understanding the failure mechanism and choosing prevention approach for pillars among cavities. With wedge model, the stability of collapse body of waste rock was analyzed by carrying out coupling analyse bteween collapse body and wall rock.The damage and failure rules were obtained through laboratory tests of tailings with different blending ratio with cement. The optimal blending ratio was investigated with catastrophe theory. The results showed that the minimum strength of back fill for cavities filling should be 0.5MPa.With mechanical model of near-cavity excavation, reliability theory was applied to investigate the reasonable pillar size. The theoretical analyse and in-situ practices showed that, for the excavation of ore body at north of mining cavity 576#, if the middle section is 70m, then the width of pillar should be 12m.With numerical model of back fill, the mechanical rules of fill under different excavating conditions were studied with Limiting equilibrium analytic method. The results showed that, the back fill with blending ratio of 1:10 can satisfiy the technical requirement of near-cavity excavation in Dabaoshan Mine, and the explosure area of back fill should be controlled within 3500m~2.Acoustic emission tests were conducted for specimens from mining cavaties. The AE signals were recorded during the process of loading and failure of specimens. The chaos theory was used to analyze the AE characteristics of rock mass in Dabaoshan Mine. The results showed that, before the failure of rockmass, AE tended to be abnormal with AE energy ratio and AE event ratio decreasing rapidly. The decreasing of chaos attractor D is the premonitor of rockmass failure. Finally, the intellective warning system of rockmass stability for near-cavity excavity in Dabaoshan Mine was established combing chaos method and neural network.