Study On Characteristics And Time-dependent Deformation Mechanism Of Delayed Rockburst In Deep Tunnel In Rock Mass

Since the rapid development of society, more and more underground space are being used, of which the "big, long, deep, multitudinous" has become the characters. Thus, more deep rock mechanics problems come up, especially the rockburst problem. The outburst of it is always sudden and violent. Delayed rockburst usually happens a long time after rock mass being excavated, which makes it looked like a safe situation for staff to start working. So delayed rockburst is very dangerous. Although so many delayed rockbursts have happened all around the world, and many experts have paid a lot attention to it, an uniform recognized theory of formation mechanism has not come to existence.Focusing on the scientific problem of time-dependent deformation mechanism of the surrounding rock in deep tunnel with delayed rockburst, basing on microseismic monitoring program in Jinping Ⅱ hydropower station, characteristics of delayed rockburst in engineering practice are studied, and a microseismic monitoring technique is used to forecast rockburst in deep tunnels buried in rock mass. By analyzing the precursor of micro-fracture and its temporal and spatial change rules during the creep process of surrounding rock, probe a method of monitoring and forecasting delayed rockburst. Basing on damage mechanics, a finite element numerical analysis process called RFPA2D (Realistic Failure Process Analysis) is used to study the process of delayed rockburst caused by time-dependent deformation of surrounding rock, so that explore a new idea on theory research and monitoring and prediction of delayed rockburst. The main results can be summarized as bellow:1. Rockburst and delayed rockburst gathers where the tunnels are deep buried and get a high stress. And they also gathers on the tunnel face.2. Geologic structure has a control function to delayed rockburst, especially at areas where is alternatively distributed soft and hard rock mass and the center of syncline.3. The accumulation of creep damage, and micro-fracture production, development, and forming failure are the inoculation process and reason of delayed rockburst.4. Microseismic activities always occur ahead of rockburst, while the location of them coincide with rockburst, which are foundation and premise of monitoring and prediction of delayed rockburst.5. The time that rockburst delayed can be longer when the confining pressure is higher, but not in proportion to it; a higher confining pressure will also makes intensity and failure scale of delayed rockburst become higher and bigger.