Study On Mechanism Of Induced Caving Roof And Control Of Its Secondary Catastrophe Chain Effect

Technology of continuous mining-induced caving roof is the organic combination of continuous mining technology and induced caving roof technology. Induced caving roof is a technological innovation, which is different from traditional block caving and forced caving substantively. It is based on the principle of rock mechanics system instability induced by artificial disturbance. The thinking formulary of underground mining disaster initiated by stress in rock mass is changed. So the stress and its time-space evolution can be induced to favorable factors used for broken rocks. While ensuring continuous advancing of the mine face, it can realize safe disposal of the mined-out area and chain breaking control. On traditional view, complex stress and strain environment of underground rock engineering is the main factor of development of disaster. However, under the condition of stress concentration or high stress condition, hard rock can be easily drilled and blasted. This phenomenon tells us how to make full use of stress concentration, energy release of stoping disturbance and unloading failure effect to induce rupture of ore rock, which has important significance for safe and efficient mining. Therefore, induced caving roof technology has extensive value in mining and gob handling.Based on the Tenth Five-year and the Eleventh Five-year National Key Project of Scientific and Technical Supporting Programs Funded by Ministry of Science & Technology of China, the mechanism of induced fracture of roof and its secondary disaster control have been deeply studied. The main contents of the study are as follows:Operation background of induced caving roof and the feasibility of coupling continuous mining with mined stope processing in area of induced caving are analyzed. Based on classic elastoplastic theory, instability principle is studied on the basis of plane model, which is simplified mechanical system of roof. The yielding and failure conditions of roof are explained by Griffith's Theory of twin Shear strength.Cusp catastrophe mathematical model of roof failure induced by disturbance is built based on catastrophe theory to analyze instability mechanism of rock mechanics system of roof induced by effect of micro-disturbance under critical condition and macro-disturbance under near critical condition. The nonlinear character of failure disturbed by inducement dilapidation is reinforced by description using bifurcation and chaotic theory. Basic principle of induced caving roof explained from angle of rock mechanical system motion.By using numerical simulation and similar material simulation, the process of continuous mining-induced caving roof is studied. The results show that advance caving roof in special stoping time and space is important to safety control of gap.The experiment of characters of unloaded rock mass under disturbing condition of caving induced roof is to be mainly studied. By using MTS815 electro-hydraulic servo testing machine, true triaxial, pre-peak and post-peak unloading experiments of roof limestone in Tongkeng No.92 ore-body are conducted, strength character and failure characteristics of rock with different confining pressures unloaded condition are analyzed, and reflect property weakening and deformation failure mechanism of rock with caving induced roof. It reveals that mechanical properties is different between disturbing unloaded and general loaded stress path, and then discussed mechanism of pre-split blasting and mechanical mechanism of crack initiation, extension and transfixion.The digital optical prospects borehole television and digital panoramic borehole camera system (DPBCS) were used to detect rock joint and crack at the different disturbance time after engineering implementation. The effect of induced caving was evaluated objectively. Based on the analysis of crack statistics, by introducing fractal theory to analyze the fractal characteristics of crack distribution inner rock, and obtained the relativity between cracks evolution and macro-aging of rock crack.Using disaster chain theory to indicate the broken chain of disaster reduction mode that leading induced caving of gap roof to prevent the unpredictable secondary disasters, and proposed the concept of mining disturbance hazard chain effect, then built a chain effect of mining disasters mathematical model. Using the broken chain of disaster reduction method used on the research of induced caving and controlling the mine disaster, which provided a certain reference for the engineering practice.