Study On Cumulative Damage Effects And Stability Of Rock Mass Under Blasting Loading

The dynamic loadings generated by recurrent blasting operations will inevitably bring cumulative damage to surrounding rock mass and even induce rock mass of underground engineering to instability, when the drilling and blasting methods are used in the underground rock mass construction engineering and the excavating production in mines. The blasting damage is embodied in two aspects, which are weakness of rock mass mechanical properties and degression of rock mass integrality. So it is certain that the mechanical parameters of rock mass will be weaken and stability of rock mass engineering will be affected accordingly. At present, researches on cumulative damage effects and stability of rock mass under blasting loadings lack systemic study. It is awaited for more researches in theory and experiment further. The weaken effects induced by excavation and blasting can not be considered sufficiently in existing methods to confirm mechanical parameters of rock mass, so there are obvious shortages. Aiming at above questions, the author studied deeply and systematically on the cumulative damage effects and its stability of rock mass under blasting loadings, combining with the two projects: the special performance of the 10th five-year national key technologies R&D subject 'Study on integrated mining technology of large-scale ore avalanche with coupling of force and abduction under complicated mined-out areas' (No. 2003BA612A-10-2), and the innovated project of PHD candidate supported by Central South University 'Study on dynamic instability mechanism and forecast models of complicated correlative mined-out areas' (No.040109). The main research contents and results in the dissertation are as follows:First of all, the growth laws of rock mass cumulative damage under blasting for many times have been studied systemically, taken the lead in using sonic measurement technology. The experiments were carried out in situ for blasting cumulative damage effects of surrounding rock at some laneway in Changba Lead-zinc Mine with RSM-SY5 intelligent sonic measuring system, through simulating blasting for ten times with little charge. The statistic laws between blasting times and cumulative damage degree, sonic velocity of rock mass under blasting loadings have been obtained based on a lot of measuring data in situ. The influences on rock mass blasting cumulative damage effects brought by some factors, such as the distance from the blasting center, have been analyzed and the nonlinear degression relationship between blasting cumulative damage and the distance from the blasting center has been set up.Secondly, the internal relationship between the blasting cumulative damage degree of rock mass and the change laws of frequency spectral parameters of sonic measuring signals, such as waveform, key frequency and energy, with increasing of blasting times under repetitious blasting have been discovered for the first time. The increasing laws of blasting damage cumulative and instability mechanism of rock mass have been uncovered further. The variation laws of key frequency, energy and its distribution of bands of sonic signals with increasing of blasting times have been found out creatively, with the Fourier transform and the wavelet (wavelet packet) analytical methods.Thirdly, the nonlinear fatigue forecast models and the extension models of rock mass blasting cumulative damage have been established for the first time, based on the abundant sonic measurement data. The damage and fracture mechanism of rock mass subjected to blasting stress wave for many times at moderate or far distance has been studied systemically by damage mechanics and fracture dynamics theory; The nonlinear damage cumulative characters of rock mass and the laws of fatigue cracks propagation under blasting for many times have been searched for, based on the cumulative fatigue damage theory.Fourthly, Hoek-Brown expressions were amended and improved further and research methods of rock mass mechanical parameters damaged by blasting 'BDRMP (Blasting Damaged Rock Mechanical Parameters)' were taken forward, based on the weaken effects of rock mass quality caused by blasting damage. The method of BDRMP can take disturbed and weaken degree of rock mass caused by blasting into account well, and set up the quantitative relationship among blasting cumulative damage, rock mass integrity degree and weaken degree of rock mass mechanical parameters. It can make certain the mechanical parameters of rock mass between disturbed and undisturbed better. The mechanical, parameters of rock mass at Changba Lead-zinc Mine were obtained by BDRMP method, which laid solid foundation for further numerical simulation in three dimensuions of stability and analysis with catastrophe theory of instability mechanism of underground engineering rock mass under blasting loading.Fifthly, the micro-disturbance mechanisms under critical condition of the instability of rock mass in underground engineering induced by blasting for many times have been analyzed systemically for the first time. The catastrophe models of instability of the roof of underground chambers and rectangle pillars under the blasting disturbance have been set up. The nonlinear evolvement laws of instability process have been analyzed and the necessary and sufficient mechanical conditions of instability have been derived. What's more, critical safe thickness of the roof of underground chambers has been confirmed and the key influence factors of dynamic instability of critical safe thickness and rectangle pillars have been analyzed.Finally, taken the influence of excavtion (or mining) and blasting vibration on the stability of mined-out areas into account at the same time, numerical simulation in three dimensions was carried out for the stability of complicated mined-out areas with FLAC^3D under group mined-out areas. The instability mechanism of mined-out areas and influenced characters of blasting cumulative damage effects on the stability of mined-out areas were uncovered, through contrasting the influenced degree on the stability of mined-out areas of three different conditions, which were excavation process, individual action of once blasting vibration and combined action of twice blasting vibration.In short, the research in this dissertation is based on the frontal of the subject and combined with engineering practice close. The theories and methods of mathematical and mechanical, numerical simulation software tools and advanced experiment means, are used in studying on rock mass cumulative damage effects and its stability under blasting loading. It founded a theoretical and technological basis for studying on the stability of rock mass, such as mined-out areas, underground power chambers, tunnels and slopes, under the frequent blasting operations systemically. The research in the dissertation is of important theoretical significance and engineering application values.