Research On Fracture Characteristics Of Rock With High Energy Accumulation Under Dynamic Disturbance

With the development of social economy, the depth of underground constructions is increasing. The excavation of engineering rocks at high depth is subjected to the state of complicated circumferential stress, for example, the high in-situ stress, the high ground temperature, the high hydraulic pressure, and the dynamic disturbance caused by blasting and mechanical excavation. In fact, rock mass during deep excavation is already in the high stress field, and the high elastic strain energy is stored before it is applyed dynamic loads, such as blasting vibration. Therefore, rock mass is subjected to the interaction of static loads, dynamic loads and the stored elastic strain energy. The phenomena of rockburst and zonal disintegration induced by the process of rock excavation at high depth show that the release of stored elastic strain energy may lead to the failure of surrounding rock. Consequently, the characteristics of rock mass under high stress state, with unloading and dynamic disturbance during excavation, are becoming urgent research topics.In view of the aforementioned problems, a modified split-Hopkinson pressure bar (SHPB) testing system is applied to carry out static-dynamic coupling loading tests. The mechanical response and the characteristics of dynamic failure of sandstones with stored strain energy are investigated under the unloading of confined pressure. The thesis includes the following work.1) Experimental study on damage performance of high stress rock mass under unloading of confining pressure is performed. The measurement method of damage variables of rock is proposed on the basis of SHPB testing system and acoustic emission. By using the method the effect of unloading rates of confining pressure on the characteristics of stored elastic strain energy and damage variable of sandstone are obtained.2) Experimental study on fracture characteristics of damaged rock with different unloading rates is conducted. The effect of damage variable on dynamic strength and the law of energy dissipation and the distribution of fractal dimension are obtained.3) Static-dynamic combining experiments with different amplitudes of stress wave are carried out. The mechanical properties and failure patterns of sandstone are obtained. The failure of high stress rock is attributed to the interaction of the dynamic disturbance and the stored elastic strain energy, which is based on the analysis of the relationship between impact energy and fractal dimension.4) A series of dynamic experiments of rock with different stored elastic strain energy is conducted. The fracture characteristics of rock with different accumulated stress energy under dynamic loads are obtained. Then a index system evaluating the tendence of rockburst for rock with stress energy accumulation is proposed. This index shows that the influencing factors of the impellent rockburst are not only related to the characteristics of rock, but also closely related to static and dynamic loads.5) Synchronous control system can make SHPB and high-speed camera was established. It would be able to obtain the failure process and matching results between the history of stress-time and images captured by high speed camera. Based on digital speckle correlation method, a new optical non-contact method for measuring the surface displacement of cylindrical samples is proposed. The fracture characteristics of samples and the characteristics of surface displacement under different loading conditions are obtained.